/*
 * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "server.h"
#include "atomicvar.h"
#include "cluster.h"
#include "script.h"
#include "fpconv_dtoa.h"
#include <sys/socket.h>
#include <sys/uio.h>
#include <math.h>
#include <ctype.h>

static void setProtocolError(const char *errstr, client *c);
int postponeClientRead(client *c);
int ProcessingEventsWhileBlocked = 0; /* See processEventsWhileBlocked(). */

/* Return the size consumed from the allocator, for the specified SDS string,
 * including internal fragmentation. This function is used in order to compute
 * the client output buffer size. */
size_t sdsZmallocSize(sds s) {
    void *sh = sdsAllocPtr(s);
    return zmalloc_size(sh);
}

/* Return the amount of memory used by the sds string at object->ptr
 * for a string object. This includes internal fragmentation. */
size_t getStringObjectSdsUsedMemory(robj *o) {
    serverAssertWithInfo(NULL,o,o->type == OBJ_STRING);
    switch(o->encoding) {
    case OBJ_ENCODING_RAW: return sdsZmallocSize(o->ptr);
    case OBJ_ENCODING_EMBSTR: return zmalloc_size(o)-sizeof(robj);
    default: return 0; /* Just integer encoding for now. */
    }
}

/* Return the length of a string object.
 * This does NOT includes internal fragmentation or sds unused space. */
size_t getStringObjectLen(robj *o) {
    serverAssertWithInfo(NULL,o,o->type == OBJ_STRING);
    switch(o->encoding) {
    case OBJ_ENCODING_RAW: return sdslen(o->ptr);
    case OBJ_ENCODING_EMBSTR: return sdslen(o->ptr);
    default: return 0; /* Just integer encoding for now. */
    }
}

/* Client.reply list dup and free methods. */
void *dupClientReplyValue(void *o) {
    clientReplyBlock *old = o;
    clientReplyBlock *buf = zmalloc(sizeof(clientReplyBlock) + old->size);
    memcpy(buf, o, sizeof(clientReplyBlock) + old->size);
    return buf;
}

void freeClientReplyValue(void *o) {
    zfree(o);
}

int listMatchObjects(void *a, void *b) {
    return equalStringObjects(a,b);
}

/* This function links the client to the global linked list of clients.
 * unlinkClient() does the opposite, among other things. */
void linkClient(client *c) {
    listAddNodeTail(server.clients,c);
    /* Note that we remember the linked list node where the client is stored,
     * this way removing the client in unlinkClient() will not require
     * a linear scan, but just a constant time operation. */
    c->client_list_node = listLast(server.clients);
    uint64_t id = htonu64(c->id);
    raxInsert(server.clients_index,(unsigned char*)&id,sizeof(id),c,NULL);
}

/* Initialize client authentication state.
 */
static void clientSetDefaultAuth(client *c) {
    /* If the default user does not require authentication, the user is
     * directly authenticated. */
    c->user = DefaultUser;
    c->authenticated = (c->user->flags & USER_FLAG_NOPASS) &&
                       !(c->user->flags & USER_FLAG_DISABLED);
}

int authRequired(client *c) {
    /* Check if the user is authenticated. This check is skipped in case
     * the default user is flagged as "nopass" and is active. */
    int auth_required = (!(DefaultUser->flags & USER_FLAG_NOPASS) ||
                          (DefaultUser->flags & USER_FLAG_DISABLED)) &&
                        !c->authenticated;
    return auth_required;
}

client *createClient(connection *conn) {
    client *c = zmalloc(sizeof(client));

    /* passing NULL as conn it is possible to create a non connected client.
     * This is useful since all the commands needs to be executed
     * in the context of a client. When commands are executed in other
     * contexts (for instance a Lua script) we need a non connected client. */
    if (conn) {
        connEnableTcpNoDelay(conn);
        if (server.tcpkeepalive)
            connKeepAlive(conn,server.tcpkeepalive);
        connSetReadHandler(conn, readQueryFromClient);
        connSetPrivateData(conn, c);
    }
    c->buf = zmalloc(PROTO_REPLY_CHUNK_BYTES);
    selectDb(c,0);
    uint64_t client_id;
    atomicGetIncr(server.next_client_id, client_id, 1);
    c->id = client_id;
    c->resp = 2;
    c->conn = conn;
    c->name = NULL;
    c->bufpos = 0;
    c->buf_usable_size = zmalloc_usable_size(c->buf);
    c->buf_peak = c->buf_usable_size;
    c->buf_peak_last_reset_time = server.unixtime;
    c->ref_repl_buf_node = NULL;
    c->ref_block_pos = 0;
    c->qb_pos = 0;
    c->querybuf = sdsempty();
    c->querybuf_peak = 0;
    c->reqtype = 0;
    c->argc = 0;
    c->argv = NULL;
    c->argv_len = 0;
    c->argv_len_sum = 0;
    c->original_argc = 0;
    c->original_argv = NULL;
    c->cmd = c->lastcmd = c->realcmd = NULL;
    c->multibulklen = 0;
    c->bulklen = -1;
    c->sentlen = 0;
    c->flags = 0;
    c->slot = -1;
    c->ctime = c->lastinteraction = server.unixtime;
    clientSetDefaultAuth(c);
    c->replstate = REPL_STATE_NONE;
    c->repl_start_cmd_stream_on_ack = 0;
    c->reploff = 0;
    c->read_reploff = 0;
    c->repl_applied = 0;
    c->repl_ack_off = 0;
    c->repl_ack_time = 0;
    c->repl_last_partial_write = 0;
    c->slave_listening_port = 0;
    c->slave_addr = NULL;
    c->slave_capa = SLAVE_CAPA_NONE;
    c->slave_req = SLAVE_REQ_NONE;
    c->reply = listCreate();
    c->deferred_reply_errors = NULL;
    c->reply_bytes = 0;
    c->obuf_soft_limit_reached_time = 0;
    listSetFreeMethod(c->reply,freeClientReplyValue);
    listSetDupMethod(c->reply,dupClientReplyValue);
    c->btype = BLOCKED_NONE;
    c->bpop.timeout = 0;
    c->bpop.keys = dictCreate(&objectKeyHeapPointerValueDictType);
    c->bpop.target = NULL;
    c->bpop.xread_group = NULL;
    c->bpop.xread_consumer = NULL;
    c->bpop.xread_group_noack = 0;
    c->bpop.numreplicas = 0;
    c->bpop.reploffset = 0;
    c->woff = 0;
    c->watched_keys = listCreate();
    c->pubsub_channels = dictCreate(&objectKeyPointerValueDictType);
    c->pubsub_patterns = listCreate();
    c->pubsubshard_channels = dictCreate(&objectKeyPointerValueDictType);
    c->peerid = NULL;
    c->sockname = NULL;
    c->client_list_node = NULL;
    c->postponed_list_node = NULL;
    c->pending_read_list_node = NULL;
    c->client_tracking_redirection = 0;
    c->client_tracking_prefixes = NULL;
    c->last_memory_usage = 0;
    c->last_memory_type = CLIENT_TYPE_NORMAL;
    c->auth_callback = NULL;
    c->auth_callback_privdata = NULL;
    c->auth_module = NULL;
    listInitNode(&c->clients_pending_write_node, c);
    listSetFreeMethod(c->pubsub_patterns,decrRefCountVoid);
    listSetMatchMethod(c->pubsub_patterns,listMatchObjects);
    c->mem_usage_bucket = NULL;
    c->mem_usage_bucket_node = NULL;
    if (conn) linkClient(c);
    initClientMultiState(c);
    return c;
}

void installClientWriteHandler(client *c) {
    int ae_barrier = 0;
    /* For the fsync=always policy, we want that a given FD is never
     * served for reading and writing in the same event loop iteration,
     * so that in the middle of receiving the query, and serving it
     * to the client, we'll call beforeSleep() that will do the
     * actual fsync of AOF to disk. the write barrier ensures that. */
    if (server.aof_state == AOF_ON &&
        server.aof_fsync == AOF_FSYNC_ALWAYS)
    {
        ae_barrier = 1;
    }
    if (connSetWriteHandlerWithBarrier(c->conn, sendReplyToClient, ae_barrier) == C_ERR) {
        freeClientAsync(c);
    }
}

/* This function puts the client in the queue of clients that should write
 * their output buffers to the socket. Note that it does not *yet* install
 * the write handler, to start clients are put in a queue of clients that need
 * to write, so we try to do that before returning in the event loop (see the
 * handleClientsWithPendingWrites() function).
 * If we fail and there is more data to write, compared to what the socket
 * buffers can hold, then we'll really install the handler. */
void putClientInPendingWriteQueue(client *c) {
    /* Schedule the client to write the output buffers to the socket only
     * if not already done and, for slaves, if the slave can actually receive
     * writes at this stage. */
    if (!(c->flags & CLIENT_PENDING_WRITE) &&
        (c->replstate == REPL_STATE_NONE ||
         (c->replstate == SLAVE_STATE_ONLINE && !c->repl_start_cmd_stream_on_ack)))
    {
        /* Here instead of installing the write handler, we just flag the
         * client and put it into a list of clients that have something
         * to write to the socket. This way before re-entering the event
         * loop, we can try to directly write to the client sockets avoiding
         * a system call. We'll only really install the write handler if
         * we'll not be able to write the whole reply at once. */
        c->flags |= CLIENT_PENDING_WRITE;
        listLinkNodeHead(server.clients_pending_write, &c->clients_pending_write_node);
    }
}

/* This function is called every time we are going to transmit new data
 * to the client. The behavior is the following:
 *
 * If the client should receive new data (normal clients will) the function
 * returns C_OK, and make sure to install the write handler in our event
 * loop so that when the socket is writable new data gets written.
 *
 * If the client should not receive new data, because it is a fake client
 * (used to load AOF in memory), a master or because the setup of the write
 * handler failed, the function returns C_ERR.
 *
 * The function may return C_OK without actually installing the write
 * event handler in the following cases:
 *
 * 1) The event handler should already be installed since the output buffer
 *    already contains something.
 * 2) The client is a slave but not yet online, so we want to just accumulate
 *    writes in the buffer but not actually sending them yet.
 *
 * Typically gets called every time a reply is built, before adding more
 * data to the clients output buffers. If the function returns C_ERR no
 * data should be appended to the output buffers. */
int prepareClientToWrite(client *c) {
    /* If it's the Lua client we always return ok without installing any
     * handler since there is no socket at all. */
    if (c->flags & (CLIENT_SCRIPT|CLIENT_MODULE)) return C_OK;

    /* If CLIENT_CLOSE_ASAP flag is set, we need not write anything. */
    if (c->flags & CLIENT_CLOSE_ASAP) return C_ERR;

    /* CLIENT REPLY OFF / SKIP handling: don't send replies. */
    if (c->flags & (CLIENT_REPLY_OFF|CLIENT_REPLY_SKIP)) return C_ERR;

    /* Masters don't receive replies, unless CLIENT_MASTER_FORCE_REPLY flag
     * is set. */
    if ((c->flags & CLIENT_MASTER) &&
        !(c->flags & CLIENT_MASTER_FORCE_REPLY)) return C_ERR;

    if (!c->conn) return C_ERR; /* Fake client for AOF loading. */

    /* Schedule the client to write the output buffers to the socket, unless
     * it should already be setup to do so (it has already pending data).
     *
     * If CLIENT_PENDING_READ is set, we're in an IO thread and should
     * not put the client in pending write queue. Instead, it will be
     * done by handleClientsWithPendingReadsUsingThreads() upon return.
     */
    if (!clientHasPendingReplies(c) && io_threads_op == IO_THREADS_OP_IDLE)
        putClientInPendingWriteQueue(c);

    /* Authorize the caller to queue in the output buffer of this client. */
    return C_OK;
}

/* -----------------------------------------------------------------------------
 * Low level functions to add more data to output buffers.
 * -------------------------------------------------------------------------- */

/* Attempts to add the reply to the static buffer in the client struct.
 * Returns the length of data that is added to the reply buffer.
 *
 * Sanitizer suppression: client->buf_usable_size determined by
 * zmalloc_usable_size() call. Writing beyond client->buf boundaries confuses
 * sanitizer and generates a false positive out-of-bounds error */
REDIS_NO_SANITIZE("bounds")
size_t _addReplyToBuffer(client *c, const char *s, size_t len) {
    size_t available = c->buf_usable_size - c->bufpos;

    /* If there already are entries in the reply list, we cannot
     * add anything more to the static buffer. */
    if (listLength(c->reply) > 0) return 0;

    size_t reply_len = len > available ? available : len;
    memcpy(c->buf+c->bufpos,s,reply_len);
    c->bufpos+=reply_len;
    /* We update the buffer peak after appending the reply to the buffer */
    if(c->buf_peak < (size_t)c->bufpos)
        c->buf_peak = (size_t)c->bufpos;
    return reply_len;
}

/* Adds the reply to the reply linked list.
 * Note: some edits to this function need to be relayed to AddReplyFromClient. */
void _addReplyProtoToList(client *c, const char *s, size_t len) {
    listNode *ln = listLast(c->reply);
    clientReplyBlock *tail = ln? listNodeValue(ln): NULL;

    /* Note that 'tail' may be NULL even if we have a tail node, because when
     * addReplyDeferredLen() is used, it sets a dummy node to NULL just
     * to fill it later, when the size of the bulk length is set. */

    /* Append to tail string when possible. */
    if (tail) {
        /* Copy the part we can fit into the tail, and leave the rest for a
         * new node */
        size_t avail = tail->size - tail->used;
        size_t copy = avail >= len? len: avail;
        memcpy(tail->buf + tail->used, s, copy);
        tail->used += copy;
        s += copy;
        len -= copy;
    }
    if (len) {
        /* Create a new node, make sure it is allocated to at
         * least PROTO_REPLY_CHUNK_BYTES */
        size_t usable_size;
        size_t size = len < PROTO_REPLY_CHUNK_BYTES? PROTO_REPLY_CHUNK_BYTES: len;
        tail = zmalloc_usable(size + sizeof(clientReplyBlock), &usable_size);
        /* take over the allocation's internal fragmentation */
        tail->size = usable_size - sizeof(clientReplyBlock);
        tail->used = len;
        memcpy(tail->buf, s, len);
        listAddNodeTail(c->reply, tail);
        c->reply_bytes += tail->size;

        closeClientOnOutputBufferLimitReached(c, 1);
    }
}

void _addReplyToBufferOrList(client *c, const char *s, size_t len) {
    if (c->flags & CLIENT_CLOSE_AFTER_REPLY) return;

    /* Replicas should normally not cause any writes to the reply buffer. In case a rogue replica sent a command on the
     * replication link that caused a reply to be generated we'll simply disconnect it.
     * Note this is the simplest way to check a command added a response. Replication links are used to write data but
     * not for responses, so we should normally never get here on a replica client. */
    if (getClientType(c) == CLIENT_TYPE_SLAVE) {
        sds cmdname = c->lastcmd ? c->lastcmd->fullname : NULL;
        logInvalidUseAndFreeClientAsync(c, "Replica generated a reply to command '%s'",
                                        cmdname ? cmdname : "<unknown>");
        return;
    }

    size_t reply_len = _addReplyToBuffer(c,s,len);
    if (len > reply_len) _addReplyProtoToList(c,s+reply_len,len-reply_len);
}

/* -----------------------------------------------------------------------------
 * Higher level functions to queue data on the client output buffer.
 * The following functions are the ones that commands implementations will call.
 * -------------------------------------------------------------------------- */

/* Add the object 'obj' string representation to the client output buffer. */
void addReply(client *c, robj *obj) {
    if (prepareClientToWrite(c) != C_OK) return;

    if (sdsEncodedObject(obj)) {
        _addReplyToBufferOrList(c,obj->ptr,sdslen(obj->ptr));
    } else if (obj->encoding == OBJ_ENCODING_INT) {
        /* For integer encoded strings we just convert it into a string
         * using our optimized function, and attach the resulting string
         * to the output buffer. */
        char buf[32];
        size_t len = ll2string(buf,sizeof(buf),(long)obj->ptr);
        _addReplyToBufferOrList(c,buf,len);
    } else {
        serverPanic("Wrong obj->encoding in addReply()");
    }
}

/* Add the SDS 's' string to the client output buffer, as a side effect
 * the SDS string is freed. */
void addReplySds(client *c, sds s) {
    if (prepareClientToWrite(c) != C_OK) {
        /* The caller expects the sds to be free'd. */
        sdsfree(s);
        return;
    }
    _addReplyToBufferOrList(c,s,sdslen(s));
    sdsfree(s);
}

/* This low level function just adds whatever protocol you send it to the
 * client buffer, trying the static buffer initially, and using the string
 * of objects if not possible.
 *
 * It is efficient because does not create an SDS object nor an Redis object
 * if not needed. The object will only be created by calling
 * _addReplyProtoToList() if we fail to extend the existing tail object
 * in the list of objects. */
void addReplyProto(client *c, const char *s, size_t len) {
    if (prepareClientToWrite(c) != C_OK) return;
    _addReplyToBufferOrList(c,s,len);
}

/* Low level function called by the addReplyError...() functions.
 * It emits the protocol for a Redis error, in the form:
 *
 * -ERRORCODE Error Message<CR><LF>
 *
 * If the error code is already passed in the string 's', the error
 * code provided is used, otherwise the string "-ERR " for the generic
 * error code is automatically added.
 * Note that 's' must NOT end with \r\n. */
void addReplyErrorLength(client *c, const char *s, size_t len) {
    /* If the string already starts with "-..." then the error code
     * is provided by the caller. Otherwise we use "-ERR". */
    if (!len || s[0] != '-') addReplyProto(c,"-ERR ",5);
    addReplyProto(c,s,len);
    addReplyProto(c,"\r\n",2);
}

/* Do some actions after an error reply was sent (Log if needed, updates stats, etc.)
 * Possible flags:
 * * ERR_REPLY_FLAG_NO_STATS_UPDATE - indicate not to update any error stats. */
void afterErrorReply(client *c, const char *s, size_t len, int flags) {
    /* Module clients fall into two categories:
     * Calls to RM_Call, in which case the error isn't being returned to a client, so should not be counted.
     * Module thread safe context calls to RM_ReplyWithError, which will be added to a real client by the main thread later. */
    if (c->flags & CLIENT_MODULE) {
        if (!c->deferred_reply_errors) {
            c->deferred_reply_errors = listCreate();
            listSetFreeMethod(c->deferred_reply_errors, (void (*)(void*))sdsfree);
        }
        listAddNodeTail(c->deferred_reply_errors, sdsnewlen(s, len));
        return;
    }

    if (!(flags & ERR_REPLY_FLAG_NO_STATS_UPDATE)) {
        /* Increment the global error counter */
        server.stat_total_error_replies++;
        /* Increment the error stats
         * If the string already starts with "-..." then the error prefix
         * is provided by the caller ( we limit the search to 32 chars). Otherwise we use "-ERR". */
        if (s[0] != '-') {
            incrementErrorCount("ERR", 3);
        } else {
            char *spaceloc = memchr(s, ' ', len < 32 ? len : 32);
            if (spaceloc) {
                const size_t errEndPos = (size_t)(spaceloc - s);
                incrementErrorCount(s+1, errEndPos-1);
            } else {
                /* Fallback to ERR if we can't retrieve the error prefix */
                incrementErrorCount("ERR", 3);
            }
        }
    } else {
        /* stat_total_error_replies will not be updated, which means that
         * the cmd stats will not be updated as well, we still want this command
         * to be counted as failed so we update it here. We update c->realcmd in
         * case c->cmd was changed (like in GEOADD). */
        c->realcmd->failed_calls++;
    }

    /* Sometimes it could be normal that a slave replies to a master with
     * an error and this function gets called. Actually the error will never
     * be sent because addReply*() against master clients has no effect...
     * A notable example is:
     *
     *    EVAL 'redis.call("incr",KEYS[1]); redis.call("nonexisting")' 1 x
     *
     * Where the master must propagate the first change even if the second
     * will produce an error. However it is useful to log such events since
     * they are rare and may hint at errors in a script or a bug in Redis. */
    int ctype = getClientType(c);
    if (ctype == CLIENT_TYPE_MASTER || ctype == CLIENT_TYPE_SLAVE || c->id == CLIENT_ID_AOF) {
        char *to, *from;

        if (c->id == CLIENT_ID_AOF) {
            to = "AOF-loading-client";
            from = "server";
        } else if (ctype == CLIENT_TYPE_MASTER) {
            to = "master";
            from = "replica";
        } else {
            to = "replica";
            from = "master";
        }

        if (len > 4096) len = 4096;
        sds cmdname = c->lastcmd ? c->lastcmd->fullname : NULL;
        serverLog(LL_WARNING,"== CRITICAL == This %s is sending an error "
                             "to its %s: '%.*s' after processing the command "
                             "'%s'", from, to, (int)len, s, cmdname ? cmdname : "<unknown>");
        if (ctype == CLIENT_TYPE_MASTER && server.repl_backlog &&
            server.repl_backlog->histlen > 0)
        {
            showLatestBacklog();
        }
        server.stat_unexpected_error_replies++;

        /* Based off the propagation error behavior, check if we need to panic here. There
         * are currently two checked cases:
         * * If this command was from our master and we are not a writable replica.
         * * We are reading from an AOF file. */
        int panic_in_replicas = (ctype == CLIENT_TYPE_MASTER && server.repl_slave_ro)
            && (server.propagation_error_behavior == PROPAGATION_ERR_BEHAVIOR_PANIC ||
            server.propagation_error_behavior == PROPAGATION_ERR_BEHAVIOR_PANIC_ON_REPLICAS);
        int panic_in_aof = c->id == CLIENT_ID_AOF 
            && server.propagation_error_behavior == PROPAGATION_ERR_BEHAVIOR_PANIC;
        if (panic_in_replicas || panic_in_aof) {
            serverPanic("This %s panicked sending an error to its %s"
                " after processing the command '%s'",
                from, to, cmdname ? cmdname : "<unknown>");
        }
    }
}

/* The 'err' object is expected to start with -ERRORCODE and end with \r\n.
 * Unlike addReplyErrorSds and others alike which rely on addReplyErrorLength. */
void addReplyErrorObject(client *c, robj *err) {
    addReply(c, err);
    afterErrorReply(c, err->ptr, sdslen(err->ptr)-2, 0); /* Ignore trailing \r\n */
}

/* Sends either a reply or an error reply by checking the first char.
 * If the first char is '-' the reply is considered an error.
 * In any case the given reply is sent, if the reply is also recognize
 * as an error we also perform some post reply operations such as
 * logging and stats update. */
void addReplyOrErrorObject(client *c, robj *reply) {
    serverAssert(sdsEncodedObject(reply));
    sds rep = reply->ptr;
    if (sdslen(rep) > 1 && rep[0] == '-') {
        addReplyErrorObject(c, reply);
    } else {
        addReply(c, reply);
    }
}

/* See addReplyErrorLength for expectations from the input string. */
void addReplyError(client *c, const char *err) {
    addReplyErrorLength(c,err,strlen(err));
    afterErrorReply(c,err,strlen(err),0);
}

/* Add error reply to the given client.
 * Supported flags:
 * * ERR_REPLY_FLAG_NO_STATS_UPDATE - indicate not to perform any error stats updates */
void addReplyErrorSdsEx(client *c, sds err, int flags) {
    addReplyErrorLength(c,err,sdslen(err));
    afterErrorReply(c,err,sdslen(err),flags);
    sdsfree(err);
}

/* See addReplyErrorLength for expectations from the input string. */
/* As a side effect the SDS string is freed. */
void addReplyErrorSds(client *c, sds err) {
    addReplyErrorSdsEx(c, err, 0);
}

/* See addReplyErrorLength for expectations from the input string. */
/* As a side effect the SDS string is freed. */
void addReplyErrorSdsSafe(client *c, sds err) {
    err = sdsmapchars(err, "\r\n", "  ",  2);
    addReplyErrorSdsEx(c, err, 0);
}

/* Internal function used by addReplyErrorFormat and addReplyErrorFormatEx.
 * Refer to afterErrorReply for more information about the flags. */
static void addReplyErrorFormatInternal(client *c, int flags, const char *fmt, va_list ap) {
    va_list cpy;
    va_copy(cpy,ap);
    sds s = sdscatvprintf(sdsempty(),fmt,cpy);
    va_end(cpy);
    /* Trim any newlines at the end (ones will be added by addReplyErrorLength) */
    s = sdstrim(s, "\r\n");
    /* Make sure there are no newlines in the middle of the string, otherwise
     * invalid protocol is emitted. */
    s = sdsmapchars(s, "\r\n", "  ",  2);
    addReplyErrorLength(c,s,sdslen(s));
    afterErrorReply(c,s,sdslen(s),flags);
    sdsfree(s);
}

void addReplyErrorFormatEx(client *c, int flags, const char *fmt, ...) {
    va_list ap;
    va_start(ap,fmt);
    addReplyErrorFormatInternal(c, flags, fmt, ap);
    va_end(ap);
}

/* See addReplyErrorLength for expectations from the formatted string.
 * The formatted string is safe to contain \r and \n anywhere. */
void addReplyErrorFormat(client *c, const char *fmt, ...) {
    va_list ap;
    va_start(ap,fmt);
    addReplyErrorFormatInternal(c, 0, fmt, ap);
    va_end(ap);
}

void addReplyErrorArity(client *c) {
    addReplyErrorFormat(c, "wrong number of arguments for '%s' command",
                        c->cmd->fullname);
}

void addReplyErrorExpireTime(client *c) {
    addReplyErrorFormat(c, "invalid expire time in '%s' command",
                        c->cmd->fullname);
}

void addReplyStatusLength(client *c, const char *s, size_t len) {
    addReplyProto(c,"+",1);
    addReplyProto(c,s,len);
    addReplyProto(c,"\r\n",2);
}

void addReplyStatus(client *c, const char *status) {
    addReplyStatusLength(c,status,strlen(status));
}

void addReplyStatusFormat(client *c, const char *fmt, ...) {
    va_list ap;
    va_start(ap,fmt);
    sds s = sdscatvprintf(sdsempty(),fmt,ap);
    va_end(ap);
    addReplyStatusLength(c,s,sdslen(s));
    sdsfree(s);
}

/* Sometimes we are forced to create a new reply node, and we can't append to
 * the previous one, when that happens, we wanna try to trim the unused space
 * at the end of the last reply node which we won't use anymore. */
void trimReplyUnusedTailSpace(client *c) {
    listNode *ln = listLast(c->reply);
    clientReplyBlock *tail = ln? listNodeValue(ln): NULL;

    /* Note that 'tail' may be NULL even if we have a tail node, because when
     * addReplyDeferredLen() is used */
    if (!tail) return;

    /* We only try to trim the space is relatively high (more than a 1/4 of the
     * allocation), otherwise there's a high chance realloc will NOP.
     * Also, to avoid large memmove which happens as part of realloc, we only do
     * that if the used part is small.  */
    if (tail->size - tail->used > tail->size / 4 &&
        tail->used < PROTO_REPLY_CHUNK_BYTES)
    {
        size_t old_size = tail->size;
        tail = zrealloc(tail, tail->used + sizeof(clientReplyBlock));
        /* take over the allocation's internal fragmentation (at least for
         * memory usage tracking) */
        tail->size = zmalloc_usable_size(tail) - sizeof(clientReplyBlock);
        c->reply_bytes = c->reply_bytes + tail->size - old_size;
        listNodeValue(ln) = tail;
    }
}

/* Adds an empty object to the reply list that will contain the multi bulk
 * length, which is not known when this function is called. */
void *addReplyDeferredLen(client *c) {
    /* Note that we install the write event here even if the object is not
     * ready to be sent, since we are sure that before returning to the
     * event loop setDeferredAggregateLen() will be called. */
    if (prepareClientToWrite(c) != C_OK) return NULL;

    /* Replicas should normally not cause any writes to the reply buffer. In case a rogue replica sent a command on the
     * replication link that caused a reply to be generated we'll simply disconnect it.
     * Note this is the simplest way to check a command added a response. Replication links are used to write data but
     * not for responses, so we should normally never get here on a replica client. */
    if (getClientType(c) == CLIENT_TYPE_SLAVE) {
        sds cmdname = c->lastcmd ? c->lastcmd->fullname : NULL;
        logInvalidUseAndFreeClientAsync(c, "Replica generated a reply to command '%s'",
                                        cmdname ? cmdname : "<unknown>");
        return NULL;
    }

    trimReplyUnusedTailSpace(c);
    listAddNodeTail(c->reply,NULL); /* NULL is our placeholder. */
    return listLast(c->reply);
}

void setDeferredReply(client *c, void *node, const char *s, size_t length) {
    listNode *ln = (listNode*)node;
    clientReplyBlock *next, *prev;

    /* Abort when *node is NULL: when the client should not accept writes
     * we return NULL in addReplyDeferredLen() */
    if (node == NULL) return;
    serverAssert(!listNodeValue(ln));

    /* Normally we fill this dummy NULL node, added by addReplyDeferredLen(),
     * with a new buffer structure containing the protocol needed to specify
     * the length of the array following. However sometimes there might be room
     * in the previous/next node so we can instead remove this NULL node, and
     * suffix/prefix our data in the node immediately before/after it, in order
     * to save a write(2) syscall later. Conditions needed to do it:
     *
     * - The prev node is non-NULL and has space in it or
     * - The next node is non-NULL,
     * - It has enough room already allocated
     * - And not too large (avoid large memmove) */
    if (ln->prev != NULL && (prev = listNodeValue(ln->prev)) &&
        prev->size - prev->used > 0)
    {
        size_t len_to_copy = prev->size - prev->used;
        if (len_to_copy > length)
            len_to_copy = length;
        memcpy(prev->buf + prev->used, s, len_to_copy);
        prev->used += len_to_copy;
        length -= len_to_copy;
        if (length == 0) {
            listDelNode(c->reply, ln);
            return;
        }
        s += len_to_copy;
    }

    if (ln->next != NULL && (next = listNodeValue(ln->next)) &&
        next->size - next->used >= length &&
        next->used < PROTO_REPLY_CHUNK_BYTES * 4)
    {
        memmove(next->buf + length, next->buf, next->used);
        memcpy(next->buf, s, length);
        next->used += length;
        listDelNode(c->reply,ln);
    } else {
        /* Create a new node */
        clientReplyBlock *buf = zmalloc(length + sizeof(clientReplyBlock));
        /* Take over the allocation's internal fragmentation */
        buf->size = zmalloc_usable_size(buf) - sizeof(clientReplyBlock);
        buf->used = length;
        memcpy(buf->buf, s, length);
        listNodeValue(ln) = buf;
        c->reply_bytes += buf->size;

        closeClientOnOutputBufferLimitReached(c, 1);
    }
}

/* Populate the length object and try gluing it to the next chunk. */
void setDeferredAggregateLen(client *c, void *node, long length, char prefix) {
    serverAssert(length >= 0);

    /* Abort when *node is NULL: when the client should not accept writes
     * we return NULL in addReplyDeferredLen() */
    if (node == NULL) return;

    /* Things like *2\r\n, %3\r\n or ~4\r\n are emitted very often by the protocol
     * so we have a few shared objects to use if the integer is small
     * like it is most of the times. */
    const size_t hdr_len = OBJ_SHARED_HDR_STRLEN(length);
    const int opt_hdr = length < OBJ_SHARED_BULKHDR_LEN;
    if (prefix == '*' && opt_hdr) {
        setDeferredReply(c, node, shared.mbulkhdr[length]->ptr, hdr_len);
        return;
    }
    if (prefix == '%' && opt_hdr) {
        setDeferredReply(c, node, shared.maphdr[length]->ptr, hdr_len);
        return;
    }
    if (prefix == '~' && opt_hdr) {
        setDeferredReply(c, node, shared.sethdr[length]->ptr, hdr_len);
        return;
    }

    char lenstr[128];
    size_t lenstr_len = snprintf(lenstr, sizeof(lenstr), "%c%ld\r\n", prefix, length);
    setDeferredReply(c, node, lenstr, lenstr_len);
}

void setDeferredArrayLen(client *c, void *node, long length) {
    setDeferredAggregateLen(c,node,length,'*');
}

void setDeferredMapLen(client *c, void *node, long length) {
    int prefix = c->resp == 2 ? '*' : '%';
    if (c->resp == 2) length *= 2;
    setDeferredAggregateLen(c,node,length,prefix);
}

void setDeferredSetLen(client *c, void *node, long length) {
    int prefix = c->resp == 2 ? '*' : '~';
    setDeferredAggregateLen(c,node,length,prefix);
}

void setDeferredAttributeLen(client *c, void *node, long length) {
    serverAssert(c->resp >= 3);
    setDeferredAggregateLen(c,node,length,'|');
}

void setDeferredPushLen(client *c, void *node, long length) {
    serverAssert(c->resp >= 3);
    setDeferredAggregateLen(c,node,length,'>');
}

/* Add a double as a bulk reply */
void addReplyDouble(client *c, double d) {
    if (isinf(d)) {
        /* Libc in odd systems (Hi Solaris!) will format infinite in a
         * different way, so better to handle it in an explicit way. */
        if (c->resp == 2) {
            addReplyBulkCString(c, d > 0 ? "inf" : "-inf");
        } else {
            addReplyProto(c, d > 0 ? ",inf\r\n" : ",-inf\r\n",
                              d > 0 ? 6 : 7);
        }
    } else {
        char dbuf[MAX_LONG_DOUBLE_CHARS+32];
        int dlen = 0;
        if (c->resp == 2) {
            /* In order to prepend the string length before the formatted number,
             * but still avoid an extra memcpy of the whole number, we reserve space
             * for maximum header `$0000\r\n`, print double, add the resp header in
             * front of it, and then send the buffer with the right `start` offset. */
            dlen = fpconv_dtoa(d, dbuf+7);
            int digits = digits10(dlen);
            int start = 4 - digits;
            dbuf[start] = '$';

            /* Convert `dlen` to string, putting it's digits after '$' and before the
	     * formatted double string. */
            for(int i = digits, val = dlen; val && i > 0 ; --i, val /= 10) {
                dbuf[start + i] = "0123456789"[val % 10];
            }

            dbuf[5] = '\r';
            dbuf[6] = '\n';
            dbuf[dlen+7] = '\r';
            dbuf[dlen+8] = '\n';
            dbuf[dlen+9] = '\0';
            addReplyProto(c,dbuf+start,dlen+9-start);
        } else {
            dbuf[0] = ',';
            dlen = fpconv_dtoa(d, dbuf+1);
            dbuf[dlen+1] = '\r';
            dbuf[dlen+2] = '\n';
            dbuf[dlen+3] = '\0';
            addReplyProto(c,dbuf,dlen+3);
        }
    }
}

void addReplyBigNum(client *c, const char* num, size_t len) {
    if (c->resp == 2) {
        addReplyBulkCBuffer(c, num, len);
    } else {
        addReplyProto(c,"(",1);
        addReplyProto(c,num,len);
        addReplyProto(c,"\r\n",2);
    }
}

/* Add a long double as a bulk reply, but uses a human readable formatting
 * of the double instead of exposing the crude behavior of doubles to the
 * dear user. */
void addReplyHumanLongDouble(client *c, long double d) {
    if (c->resp == 2) {
        robj *o = createStringObjectFromLongDouble(d,1);
        addReplyBulk(c,o);
        decrRefCount(o);
    } else {
        char buf[MAX_LONG_DOUBLE_CHARS];
        int len = ld2string(buf,sizeof(buf),d,LD_STR_HUMAN);
        addReplyProto(c,",",1);
        addReplyProto(c,buf,len);
        addReplyProto(c,"\r\n",2);
    }
}

/* Add a long long as integer reply or bulk len / multi bulk count.
 * Basically this is used to output <prefix><long long><crlf>. */
void addReplyLongLongWithPrefix(client *c, long long ll, char prefix) {
    char buf[128];
    int len;

    /* Things like $3\r\n or *2\r\n are emitted very often by the protocol
     * so we have a few shared objects to use if the integer is small
     * like it is most of the times. */
    const int opt_hdr = ll < OBJ_SHARED_BULKHDR_LEN && ll >= 0;
    const size_t hdr_len = OBJ_SHARED_HDR_STRLEN(ll);
    if (prefix == '*' && opt_hdr) {
        addReplyProto(c,shared.mbulkhdr[ll]->ptr,hdr_len);
        return;
    } else if (prefix == '$' && opt_hdr) {
        addReplyProto(c,shared.bulkhdr[ll]->ptr,hdr_len);
        return;
    } else if (prefix == '%' && opt_hdr) {
        addReplyProto(c,shared.maphdr[ll]->ptr,hdr_len);
        return;
    } else if (prefix == '~' && opt_hdr) {
        addReplyProto(c,shared.sethdr[ll]->ptr,hdr_len);
        return;
    }

    buf[0] = prefix;
    len = ll2string(buf+1,sizeof(buf)-1,ll);
    buf[len+1] = '\r';
    buf[len+2] = '\n';
    addReplyProto(c,buf,len+3);
}

void addReplyLongLong(client *c, long long ll) {
    if (ll == 0)
        addReply(c,shared.czero);
    else if (ll == 1)
        addReply(c,shared.cone);
    else
        addReplyLongLongWithPrefix(c,ll,':');
}

void addReplyAggregateLen(client *c, long length, int prefix) {
    serverAssert(length >= 0);
    addReplyLongLongWithPrefix(c,length,prefix);
}

void addReplyArrayLen(client *c, long length) {
    addReplyAggregateLen(c,length,'*');
}

void addReplyMapLen(client *c, long length) {
    int prefix = c->resp == 2 ? '*' : '%';
    if (c->resp == 2) length *= 2;
    addReplyAggregateLen(c,length,prefix);
}

void addReplySetLen(client *c, long length) {
    int prefix = c->resp == 2 ? '*' : '~';
    addReplyAggregateLen(c,length,prefix);
}

void addReplyAttributeLen(client *c, long length) {
    serverAssert(c->resp >= 3);
    addReplyAggregateLen(c,length,'|');
}

void addReplyPushLen(client *c, long length) {
    serverAssert(c->resp >= 3);
    addReplyAggregateLen(c,length,'>');
}

void addReplyNull(client *c) {
    if (c->resp == 2) {
        addReplyProto(c,"$-1\r\n",5);
    } else {
        addReplyProto(c,"_\r\n",3);
    }
}

void addReplyBool(client *c, int b) {
    if (c->resp == 2) {
        addReply(c, b ? shared.cone : shared.czero);
    } else {
        addReplyProto(c, b ? "#t\r\n" : "#f\r\n",4);
    }
}

/* A null array is a concept that no longer exists in RESP3. However
 * RESP2 had it, so API-wise we have this call, that will emit the correct
 * RESP2 protocol, however for RESP3 the reply will always be just the
 * Null type "_\r\n". */
void addReplyNullArray(client *c) {
    if (c->resp == 2) {
        addReplyProto(c,"*-1\r\n",5);
    } else {
        addReplyProto(c,"_\r\n",3);
    }
}

/* Create the length prefix of a bulk reply, example: $2234 */
void addReplyBulkLen(client *c, robj *obj) {
    size_t len = stringObjectLen(obj);

    addReplyLongLongWithPrefix(c,len,'$');
}

/* Add a Redis Object as a bulk reply */
void addReplyBulk(client *c, robj *obj) {
    addReplyBulkLen(c,obj);
    addReply(c,obj);
    addReplyProto(c,"\r\n",2);
}

/* Add a C buffer as bulk reply */
void addReplyBulkCBuffer(client *c, const void *p, size_t len) {
    addReplyLongLongWithPrefix(c,len,'$');
    addReplyProto(c,p,len);
    addReplyProto(c,"\r\n",2);
}

/* Add sds to reply (takes ownership of sds and frees it) */
void addReplyBulkSds(client *c, sds s)  {
    addReplyLongLongWithPrefix(c,sdslen(s),'$');
    addReplySds(c,s);
    addReplyProto(c,"\r\n",2);
}

/* Set sds to a deferred reply (for symmetry with addReplyBulkSds it also frees the sds) */
void setDeferredReplyBulkSds(client *c, void *node, sds s) {
    sds reply = sdscatprintf(sdsempty(), "$%d\r\n%s\r\n", (unsigned)sdslen(s), s);
    setDeferredReply(c, node, reply, sdslen(reply));
    sdsfree(reply);
    sdsfree(s);
}

/* Add a C null term string as bulk reply */
void addReplyBulkCString(client *c, const char *s) {
    if (s == NULL) {
        addReplyNull(c);
    } else {
        addReplyBulkCBuffer(c,s,strlen(s));
    }
}

/* Add a long long as a bulk reply */
void addReplyBulkLongLong(client *c, long long ll) {
    char buf[64];
    int len;

    len = ll2string(buf,64,ll);
    addReplyBulkCBuffer(c,buf,len);
}

/* Reply with a verbatim type having the specified extension.
 *
 * The 'ext' is the "extension" of the file, actually just a three
 * character type that describes the format of the verbatim string.
 * For instance "txt" means it should be interpreted as a text only
 * file by the receiver, "md " as markdown, and so forth. Only the
 * three first characters of the extension are used, and if the
 * provided one is shorter than that, the remaining is filled with
 * spaces. */
void addReplyVerbatim(client *c, const char *s, size_t len, const char *ext) {
    if (c->resp == 2) {
        addReplyBulkCBuffer(c,s,len);
    } else {
        char buf[32];
        size_t preflen = snprintf(buf,sizeof(buf),"=%zu\r\nxxx:",len+4);
        char *p = buf+preflen-4;
        for (int i = 0; i < 3; i++) {
            if (*ext == '\0') {
                p[i] = ' ';
            } else {
                p[i] = *ext++;
            }
        }
        addReplyProto(c,buf,preflen);
        addReplyProto(c,s,len);
        addReplyProto(c,"\r\n",2);
    }
}

/* Add an array of C strings as status replies with a heading.
 * This function is typically invoked by from commands that support
 * subcommands in response to the 'help' subcommand. The help array
 * is terminated by NULL sentinel. */
void addReplyHelp(client *c, const char **help) {
    sds cmd = sdsnew((char*) c->argv[0]->ptr);
    void *blenp = addReplyDeferredLen(c);
    int blen = 0;

    sdstoupper(cmd);
    addReplyStatusFormat(c,
        "%s <subcommand> [<arg> [value] [opt] ...]. Subcommands are:",cmd);
    sdsfree(cmd);

    while (help[blen]) addReplyStatus(c,help[blen++]);

    addReplyStatus(c,"HELP");
    addReplyStatus(c,"    Print this help.");

    blen += 1;  /* Account for the header. */
    blen += 2;  /* Account for the footer. */
    setDeferredArrayLen(c,blenp,blen);
}

/* Add a suggestive error reply.
 * This function is typically invoked by from commands that support
 * subcommands in response to an unknown subcommand or argument error. */
void addReplySubcommandSyntaxError(client *c) {
    sds cmd = sdsnew((char*) c->argv[0]->ptr);
    sdstoupper(cmd);
    addReplyErrorFormat(c,
        "unknown subcommand or wrong number of arguments for '%.128s'. Try %s HELP.",
        (char*)c->argv[1]->ptr,cmd);
    sdsfree(cmd);
}

/* Append 'src' client output buffers into 'dst' client output buffers.
 * This function clears the output buffers of 'src' */
void AddReplyFromClient(client *dst, client *src) {
    /* If the source client contains a partial response due to client output
     * buffer limits, propagate that to the dest rather than copy a partial
     * reply. We don't wanna run the risk of copying partial response in case
     * for some reason the output limits don't reach the same decision (maybe
     * they changed) */
    if (src->flags & CLIENT_CLOSE_ASAP) {
        sds client = catClientInfoString(sdsempty(),dst);
        freeClientAsync(dst);
        serverLog(LL_WARNING,"Client %s scheduled to be closed ASAP for overcoming of output buffer limits.", client);
        sdsfree(client);
        return;
    }

    /* First add the static buffer (either into the static buffer or reply list) */
    addReplyProto(dst,src->buf, src->bufpos);

    /* We need to check with prepareClientToWrite again (after addReplyProto)
     * since addReplyProto may have changed something (like CLIENT_CLOSE_ASAP) */
    if (prepareClientToWrite(dst) != C_OK)
        return;

    /* We're bypassing _addReplyProtoToList, so we need to add the pre/post
     * checks in it. */
    if (dst->flags & CLIENT_CLOSE_AFTER_REPLY) return;

    /* Concatenate the reply list into the dest */
    if (listLength(src->reply))
        listJoin(dst->reply,src->reply);
    dst->reply_bytes += src->reply_bytes;
    src->reply_bytes = 0;
    src->bufpos = 0;

    if (src->deferred_reply_errors) {
        deferredAfterErrorReply(dst, src->deferred_reply_errors);
        listRelease(src->deferred_reply_errors);
        src->deferred_reply_errors = NULL;
    }

    /* Check output buffer limits */
    closeClientOnOutputBufferLimitReached(dst, 1);
}

/* Append the listed errors to the server error statistics. the input
 * list is not modified and remains the responsibility of the caller. */
void deferredAfterErrorReply(client *c, list *errors) {
    listIter li;
    listNode *ln;
    listRewind(errors,&li);
    while((ln = listNext(&li))) {
        sds err = ln->value;
        afterErrorReply(c, err, sdslen(err), 0);
    }
}

/* Logically copy 'src' replica client buffers info to 'dst' replica.
 * Basically increase referenced buffer block node reference count. */
void copyReplicaOutputBuffer(client *dst, client *src) {
    serverAssert(src->bufpos == 0 && listLength(src->reply) == 0);

    if (src->ref_repl_buf_node == NULL) return;
    dst->ref_repl_buf_node = src->ref_repl_buf_node;
    dst->ref_block_pos = src->ref_block_pos;
    ((replBufBlock *)listNodeValue(dst->ref_repl_buf_node))->refcount++;
}

/* Return true if the specified client has pending reply buffers to write to
 * the socket. */
int clientHasPendingReplies(client *c) {
    if (getClientType(c) == CLIENT_TYPE_SLAVE) {
        /* Replicas use global shared replication buffer instead of
         * private output buffer. */
        serverAssert(c->bufpos == 0 && listLength(c->reply) == 0);
        if (c->ref_repl_buf_node == NULL) return 0;

        /* If the last replication buffer block content is totally sent,
         * we have nothing to send. */
        listNode *ln = listLast(server.repl_buffer_blocks);
        replBufBlock *tail = listNodeValue(ln);
        if (ln == c->ref_repl_buf_node &&
            c->ref_block_pos == tail->used) return 0;

        return 1;
    } else {
        return c->bufpos || listLength(c->reply);
    }
}

/* Return true if client connected from loopback interface */
int islocalClient(client *c) {
    /* unix-socket */
    if (c->flags & CLIENT_UNIX_SOCKET) return 1;

    /* tcp */
    char cip[NET_IP_STR_LEN+1] = { 0 };
    connAddrPeerName(c->conn, cip, sizeof(cip)-1, NULL);

    return !strcmp(cip,"127.0.0.1") || !strcmp(cip,"::1");
}

void clientAcceptHandler(connection *conn) {
    client *c = connGetPrivateData(conn);

    if (connGetState(conn) != CONN_STATE_CONNECTED) {
        serverLog(LL_WARNING,
                "Error accepting a client connection: %s",
                connGetLastError(conn));
        freeClientAsync(c);
        return;
    }

    /* If the server is running in protected mode (the default) and there
     * is no password set, nor a specific interface is bound, we don't accept
     * requests from non loopback interfaces. Instead we try to explain the
     * user what to do to fix it if needed. */
    if (server.protected_mode &&
        DefaultUser->flags & USER_FLAG_NOPASS)
    {
        if (!islocalClient(c)) {
            char *err =
                "-DENIED Redis is running in protected mode because protected "
                "mode is enabled and no password is set for the default user. "
                "In this mode connections are only accepted from the loopback interface. "
                "If you want to connect from external computers to Redis you "
                "may adopt one of the following solutions: "
                "1) Just disable protected mode sending the command "
                "'CONFIG SET protected-mode no' from the loopback interface "
                "by connecting to Redis from the same host the server is "
                "running, however MAKE SURE Redis is not publicly accessible "
                "from internet if you do so. Use CONFIG REWRITE to make this "
                "change permanent. "
                "2) Alternatively you can just disable the protected mode by "
                "editing the Redis configuration file, and setting the protected "
                "mode option to 'no', and then restarting the server. "
                "3) If you started the server manually just for testing, restart "
                "it with the '--protected-mode no' option. "
                "4) Set up an authentication password for the default user. "
                "NOTE: You only need to do one of the above things in order for "
                "the server to start accepting connections from the outside.\r\n";
            if (connWrite(c->conn,err,strlen(err)) == -1) {
                /* Nothing to do, Just to avoid the warning... */
            }
            server.stat_rejected_conn++;
            freeClientAsync(c);
            return;
        }
    }

    server.stat_numconnections++;
    moduleFireServerEvent(REDISMODULE_EVENT_CLIENT_CHANGE,
                          REDISMODULE_SUBEVENT_CLIENT_CHANGE_CONNECTED,
                          c);
}

void acceptCommonHandler(connection *conn, int flags, char *ip) {
    client *c;
    char conninfo[100];
    UNUSED(ip);

    if (connGetState(conn) != CONN_STATE_ACCEPTING) {
        serverLog(LL_VERBOSE,
            "Accepted client connection in error state: %s (conn: %s)",
            connGetLastError(conn),
            connGetInfo(conn, conninfo, sizeof(conninfo)));
        connClose(conn);
        return;
    }

    /* Limit the number of connections we take at the same time.
     *
     * Admission control will happen before a client is created and connAccept()
     * called, because we don't want to even start transport-level negotiation
     * if rejected. */
    if (listLength(server.clients) + getClusterConnectionsCount()
        >= server.maxclients)
    {
        char *err;
        if (server.cluster_enabled)
            err = "-ERR max number of clients + cluster "
                  "connections reached\r\n";
        else
            err = "-ERR max number of clients reached\r\n";

        /* That's a best effort error message, don't check write errors.
         * Note that for TLS connections, no handshake was done yet so nothing
         * is written and the connection will just drop. */
        if (connWrite(conn,err,strlen(err)) == -1) {
            /* Nothing to do, Just to avoid the warning... */
        }
        server.stat_rejected_conn++;
        connClose(conn);
        return;
    }

    /* Create connection and client */
    if ((c = createClient(conn)) == NULL) {
        serverLog(LL_WARNING,
            "Error registering fd event for the new client: %s (conn: %s)",
            connGetLastError(conn),
            connGetInfo(conn, conninfo, sizeof(conninfo)));
        connClose(conn); /* May be already closed, just ignore errors */
        return;
    }

    /* Last chance to keep flags */
    c->flags |= flags;

    /* Initiate accept.
     *
     * Note that connAccept() is free to do two things here:
     * 1. Call clientAcceptHandler() immediately;
     * 2. Schedule a future call to clientAcceptHandler().
     *
     * Because of that, we must do nothing else afterwards.
     */
    if (connAccept(conn, clientAcceptHandler) == C_ERR) {
        char conninfo[100];
        if (connGetState(conn) == CONN_STATE_ERROR)
            serverLog(LL_WARNING,
                    "Error accepting a client connection: %s (conn: %s)",
                    connGetLastError(conn), connGetInfo(conn, conninfo, sizeof(conninfo)));
        freeClient(connGetPrivateData(conn));
        return;
    }
}

void freeClientOriginalArgv(client *c) {
    /* We didn't rewrite this client */
    if (!c->original_argv) return;

    for (int j = 0; j < c->original_argc; j++)
        decrRefCount(c->original_argv[j]);
    zfree(c->original_argv);
    c->original_argv = NULL;
    c->original_argc = 0;
}

void freeClientArgv(client *c) {
    int j;
    for (j = 0; j < c->argc; j++)
        decrRefCount(c->argv[j]);
    c->argc = 0;
    c->cmd = NULL;
    c->argv_len_sum = 0;
    c->argv_len = 0;
    zfree(c->argv);
    c->argv = NULL;
}

/* Close all the slaves connections. This is useful in chained replication
 * when we resync with our own master and want to force all our slaves to
 * resync with us as well. */
void disconnectSlaves(void) {
    listIter li;
    listNode *ln;
    listRewind(server.slaves,&li);
    while((ln = listNext(&li))) {
        freeClient((client*)ln->value);
    }
}

/* Check if there is any other slave waiting dumping RDB finished expect me.
 * This function is useful to judge current dumping RDB can be used for full
 * synchronization or not. */
int anyOtherSlaveWaitRdb(client *except_me) {
    listIter li;
    listNode *ln;

    listRewind(server.slaves, &li);
    while((ln = listNext(&li))) {
        client *slave = ln->value;
        if (slave != except_me &&
            slave->replstate == SLAVE_STATE_WAIT_BGSAVE_END)
        {
            return 1;
        }
    }
    return 0;
}

/* Remove the specified client from global lists where the client could
 * be referenced, not including the Pub/Sub channels.
 * This is used by freeClient() and replicationCacheMaster(). */
void unlinkClient(client *c) {
    listNode *ln;

    /* If this is marked as current client unset it. */
    if (server.current_client == c) server.current_client = NULL;

    /* Certain operations must be done only if the client has an active connection.
     * If the client was already unlinked or if it's a "fake client" the
     * conn is already set to NULL. */
    if (c->conn) {
        /* Remove from the list of active clients. */
        if (c->client_list_node) {
            uint64_t id = htonu64(c->id);
            raxRemove(server.clients_index,(unsigned char*)&id,sizeof(id),NULL);
            listDelNode(server.clients,c->client_list_node);
            c->client_list_node = NULL;
        }

        /* Check if this is a replica waiting for diskless replication (rdb pipe),
         * in which case it needs to be cleaned from that list */
        if (c->flags & CLIENT_SLAVE &&
            c->replstate == SLAVE_STATE_WAIT_BGSAVE_END &&
            server.rdb_pipe_conns)
        {
            int i;
            for (i=0; i < server.rdb_pipe_numconns; i++) {
                if (server.rdb_pipe_conns[i] == c->conn) {
                    rdbPipeWriteHandlerConnRemoved(c->conn);
                    server.rdb_pipe_conns[i] = NULL;
                    break;
                }
            }
        }
        connClose(c->conn);
        c->conn = NULL;
    }

    /* Remove from the list of pending writes if needed. */
    if (c->flags & CLIENT_PENDING_WRITE) {
        serverAssert(&c->clients_pending_write_node.next != NULL || 
                     &c->clients_pending_write_node.prev != NULL);
        listUnlinkNode(server.clients_pending_write, &c->clients_pending_write_node);
        c->flags &= ~CLIENT_PENDING_WRITE;
    }

    /* Remove from the list of pending reads if needed. */
    serverAssert(io_threads_op == IO_THREADS_OP_IDLE);
    if (c->pending_read_list_node != NULL) {
        listDelNode(server.clients_pending_read,c->pending_read_list_node);
        c->pending_read_list_node = NULL;
    }


    /* When client was just unblocked because of a blocking operation,
     * remove it from the list of unblocked clients. */
    if (c->flags & CLIENT_UNBLOCKED) {
        ln = listSearchKey(server.unblocked_clients,c);
        serverAssert(ln != NULL);
        listDelNode(server.unblocked_clients,ln);
        c->flags &= ~CLIENT_UNBLOCKED;
    }

    /* Clear the tracking status. */
    if (c->flags & CLIENT_TRACKING) disableTracking(c);
}

/* Clear the client state to resemble a newly connected client. */
void clearClientConnectionState(client *c) {
    listNode *ln;

    /* MONITOR clients are also marked with CLIENT_SLAVE, we need to
     * distinguish between the two.
     */
    if (c->flags & CLIENT_MONITOR) {
        ln = listSearchKey(server.monitors,c);
        serverAssert(ln != NULL);
        listDelNode(server.monitors,ln);

        c->flags &= ~(CLIENT_MONITOR|CLIENT_SLAVE);
    }

    serverAssert(!(c->flags &(CLIENT_SLAVE|CLIENT_MASTER)));

    if (c->flags & CLIENT_TRACKING) disableTracking(c);
    selectDb(c,0);
    c->resp = 2;

    clientSetDefaultAuth(c);
    moduleNotifyUserChanged(c);
    discardTransaction(c);

    pubsubUnsubscribeAllChannels(c,0);
    pubsubUnsubscribeShardAllChannels(c, 0);
    pubsubUnsubscribeAllPatterns(c,0);

    if (c->name) {
        decrRefCount(c->name);
        c->name = NULL;
    }

    /* Selectively clear state flags not covered above */
    c->flags &= ~(CLIENT_ASKING|CLIENT_READONLY|CLIENT_PUBSUB|
                  CLIENT_REPLY_OFF|CLIENT_REPLY_SKIP_NEXT);
}

void freeClient(client *c) {
    listNode *ln;

    /* If a client is protected, yet we need to free it right now, make sure
     * to at least use asynchronous freeing. */
    if (c->flags & CLIENT_PROTECTED) {
        freeClientAsync(c);
        return;
    }

    /* For connected clients, call the disconnection event of modules hooks. */
    if (c->conn) {
        moduleFireServerEvent(REDISMODULE_EVENT_CLIENT_CHANGE,
                              REDISMODULE_SUBEVENT_CLIENT_CHANGE_DISCONNECTED,
                              c);
    }

    /* Notify module system that this client auth status changed. */
    moduleNotifyUserChanged(c);

    /* If this client was scheduled for async freeing we need to remove it
     * from the queue. Note that we need to do this here, because later
     * we may call replicationCacheMaster() and the client should already
     * be removed from the list of clients to free. */
    if (c->flags & CLIENT_CLOSE_ASAP) {
        ln = listSearchKey(server.clients_to_close,c);
        serverAssert(ln != NULL);
        listDelNode(server.clients_to_close,ln);
    }

    /* If it is our master that's being disconnected we should make sure
     * to cache the state to try a partial resynchronization later.
     *
     * Note that before doing this we make sure that the client is not in
     * some unexpected state, by checking its flags. */
    if (server.master && c->flags & CLIENT_MASTER) {
        serverLog(LL_WARNING,"Connection with master lost.");
        if (!(c->flags & (CLIENT_PROTOCOL_ERROR|CLIENT_BLOCKED))) {
            c->flags &= ~(CLIENT_CLOSE_ASAP|CLIENT_CLOSE_AFTER_REPLY);
            replicationCacheMaster(c);
            return;
        }
    }

    /* Log link disconnection with slave */
    if (getClientType(c) == CLIENT_TYPE_SLAVE) {
        serverLog(LL_WARNING,"Connection with replica %s lost.",
            replicationGetSlaveName(c));
    }

    /* Free the query buffer */
    sdsfree(c->querybuf);
    c->querybuf = NULL;

    /* Deallocate structures used to block on blocking ops. */
    if (c->flags & CLIENT_BLOCKED) unblockClient(c);
    dictRelease(c->bpop.keys);

    /* UNWATCH all the keys */
    unwatchAllKeys(c);
    listRelease(c->watched_keys);

    /* Unsubscribe from all the pubsub channels */
    pubsubUnsubscribeAllChannels(c,0);
    pubsubUnsubscribeShardAllChannels(c, 0);
    pubsubUnsubscribeAllPatterns(c,0);
    dictRelease(c->pubsub_channels);
    listRelease(c->pubsub_patterns);
    dictRelease(c->pubsubshard_channels);

    /* Free data structures. */
    listRelease(c->reply);
    zfree(c->buf);
    freeReplicaReferencedReplBuffer(c);
    freeClientArgv(c);
    freeClientOriginalArgv(c);
    if (c->deferred_reply_errors)
        listRelease(c->deferred_reply_errors);

    /* Unlink the client: this will close the socket, remove the I/O
     * handlers, and remove references of the client from different
     * places where active clients may be referenced. */
    unlinkClient(c);

    /* Master/slave cleanup Case 1:
     * we lost the connection with a slave. */
    if (c->flags & CLIENT_SLAVE) {
        /* If there is no any other slave waiting dumping RDB finished, the
         * current child process need not continue to dump RDB, then we kill it.
         * So child process won't use more memory, and we also can fork a new
         * child process asap to dump rdb for next full synchronization or bgsave.
         * But we also need to check if users enable 'save' RDB, if enable, we
         * should not remove directly since that means RDB is important for users
         * to keep data safe and we may delay configured 'save' for full sync. */
        if (server.saveparamslen == 0 &&
            c->replstate == SLAVE_STATE_WAIT_BGSAVE_END &&
            server.child_type == CHILD_TYPE_RDB &&
            server.rdb_child_type == RDB_CHILD_TYPE_DISK &&
            anyOtherSlaveWaitRdb(c) == 0)
        {
            killRDBChild();
        }
        if (c->replstate == SLAVE_STATE_SEND_BULK) {
            if (c->repldbfd != -1) close(c->repldbfd);
            if (c->replpreamble) sdsfree(c->replpreamble);
        }
        list *l = (c->flags & CLIENT_MONITOR) ? server.monitors : server.slaves;
        ln = listSearchKey(l,c);
        serverAssert(ln != NULL);
        listDelNode(l,ln);
        /* We need to remember the time when we started to have zero
         * attached slaves, as after some time we'll free the replication
         * backlog. */
        if (getClientType(c) == CLIENT_TYPE_SLAVE && listLength(server.slaves) == 0)
            server.repl_no_slaves_since = server.unixtime;
        refreshGoodSlavesCount();
        /* Fire the replica change modules event. */
        if (c->replstate == SLAVE_STATE_ONLINE)
            moduleFireServerEvent(REDISMODULE_EVENT_REPLICA_CHANGE,
                                  REDISMODULE_SUBEVENT_REPLICA_CHANGE_OFFLINE,
                                  NULL);
    }

    /* Master/slave cleanup Case 2:
     * we lost the connection with the master. */
    if (c->flags & CLIENT_MASTER) replicationHandleMasterDisconnection();

    /* Remove the contribution that this client gave to our
     * incrementally computed memory usage. */
    server.stat_clients_type_memory[c->last_memory_type] -=
        c->last_memory_usage;
    /* Remove client from memory usage buckets */
    if (c->mem_usage_bucket) {
        c->mem_usage_bucket->mem_usage_sum -= c->last_memory_usage;
        listDelNode(c->mem_usage_bucket->clients, c->mem_usage_bucket_node);
    }

    /* Release other dynamically allocated client structure fields,
     * and finally release the client structure itself. */
    if (c->name) decrRefCount(c->name);
    freeClientMultiState(c);
    sdsfree(c->peerid);
    sdsfree(c->sockname);
    sdsfree(c->slave_addr);
    zfree(c);
}

/* Schedule a client to free it at a safe time in the serverCron() function.
 * This function is useful when we need to terminate a client but we are in
 * a context where calling freeClient() is not possible, because the client
 * should be valid for the continuation of the flow of the program. */
void freeClientAsync(client *c) {
    /* We need to handle concurrent access to the server.clients_to_close list
     * only in the freeClientAsync() function, since it's the only function that
     * may access the list while Redis uses I/O threads. All the other accesses
     * are in the context of the main thread while the other threads are
     * idle. */
    if (c->flags & CLIENT_CLOSE_ASAP || c->flags & CLIENT_SCRIPT) return;
    c->flags |= CLIENT_CLOSE_ASAP;
    if (server.io_threads_num == 1) {
        /* no need to bother with locking if there's just one thread (the main thread) */
        listAddNodeTail(server.clients_to_close,c);
        return;
    }
    static pthread_mutex_t async_free_queue_mutex = PTHREAD_MUTEX_INITIALIZER;
    pthread_mutex_lock(&async_free_queue_mutex);
    listAddNodeTail(server.clients_to_close,c);
    pthread_mutex_unlock(&async_free_queue_mutex);
}

/* Log errors for invalid use and free the client in async way.
 * We will add additional information about the client to the message. */
void logInvalidUseAndFreeClientAsync(client *c, const char *fmt, ...) {
    va_list ap;
    va_start(ap, fmt);
    sds info = sdscatvprintf(sdsempty(), fmt, ap);
    va_end(ap);

    sds client = catClientInfoString(sdsempty(), c);
    serverLog(LL_WARNING, "%s, disconnecting it: %s", info, client);

    sdsfree(info);
    sdsfree(client);
    freeClientAsync(c);
}

/* Perform processing of the client before moving on to processing the next client
 * this is useful for performing operations that affect the global state but can't
 * wait until we're done with all clients. In other words can't wait until beforeSleep()
 * return C_ERR in case client is no longer valid after call.
 * The input client argument: c, may be NULL in case the previous client was
 * freed before the call. */
int beforeNextClient(client *c) {
    /* Skip the client processing if we're in an IO thread, in that case we'll perform
       this operation later (this function is called again) in the fan-in stage of the threading mechanism */
    if (io_threads_op != IO_THREADS_OP_IDLE)
        return C_OK;
    /* Handle async frees */
    /* Note: this doesn't make the server.clients_to_close list redundant because of
     * cases where we want an async free of a client other than myself. For example
     * in ACL modifications we disconnect clients authenticated to non-existent
     * users (see ACL LOAD). */
    if (c && (c->flags & CLIENT_CLOSE_ASAP)) {
        freeClient(c);
        return C_ERR;
    }
    return C_OK;
}

/* Free the clients marked as CLOSE_ASAP, return the number of clients
 * freed. */
int freeClientsInAsyncFreeQueue(void) {
    int freed = 0;
    listIter li;
    listNode *ln;

    listRewind(server.clients_to_close,&li);
    while ((ln = listNext(&li)) != NULL) {
        client *c = listNodeValue(ln);

        if (c->flags & CLIENT_PROTECTED) continue;

        c->flags &= ~CLIENT_CLOSE_ASAP;
        freeClient(c);
        listDelNode(server.clients_to_close,ln);
        freed++;
    }
    return freed;
}

/* Return a client by ID, or NULL if the client ID is not in the set
 * of registered clients. Note that "fake clients", created with -1 as FD,
 * are not registered clients. */
client *lookupClientByID(uint64_t id) {
    id = htonu64(id);
    client *c = raxFind(server.clients_index,(unsigned char*)&id,sizeof(id));
    return (c == raxNotFound) ? NULL : c;
}

/* This function should be called from _writeToClient when the reply list is not empty,
 * it gathers the scattered buffers from reply list and sends them away with connWritev.
 * If we write successfully, it returns C_OK, otherwise, C_ERR is returned,
 * and 'nwritten' is an output parameter, it means how many bytes server write
 * to client. */
static int _writevToClient(client *c, ssize_t *nwritten) {
    struct iovec iov[IOV_MAX];
    int iovcnt = 0;
    size_t iov_bytes_len = 0;
    /* If the static reply buffer is not empty, 
     * add it to the iov array for writev() as well. */
    if (c->bufpos > 0) {
        iov[iovcnt].iov_base = c->buf + c->sentlen;
        iov[iovcnt].iov_len = c->bufpos - c->sentlen;
        iov_bytes_len += iov[iovcnt++].iov_len;
    }
    /* The first node of reply list might be incomplete from the last call,
     * thus it needs to be calibrated to get the actual data address and length. */
    size_t offset = c->bufpos > 0 ? 0 : c->sentlen;
    listIter iter;
    listNode *next;
    clientReplyBlock *o;
    listRewind(c->reply, &iter);
    while ((next = listNext(&iter)) && iovcnt < IOV_MAX && iov_bytes_len < NET_MAX_WRITES_PER_EVENT) {
        o = listNodeValue(next);
        if (o->used == 0) { /* empty node, just release it and skip. */
            c->reply_bytes -= o->size;
            listDelNode(c->reply, next);
            offset = 0;
            continue;
        }

        iov[iovcnt].iov_base = o->buf + offset;
        iov[iovcnt].iov_len = o->used - offset;
        iov_bytes_len += iov[iovcnt++].iov_len;
        offset = 0;
    }
    if (iovcnt == 0) return C_OK;
    *nwritten = connWritev(c->conn, iov, iovcnt);
    if (*nwritten <= 0) return C_ERR;

    /* Locate the new node which has leftover data and
     * release all nodes in front of it. */
    ssize_t remaining = *nwritten;
    if (c->bufpos > 0) { /* deal with static reply buffer first. */
        int buf_len = c->bufpos - c->sentlen;
        c->sentlen += remaining;
        /* If the buffer was sent, set bufpos to zero to continue with
         * the remainder of the reply. */
        if (remaining >= buf_len) {
            c->bufpos = 0;
            c->sentlen = 0;
        }
        remaining -= buf_len;
    }
    listRewind(c->reply, &iter);
    while (remaining > 0) {
        next = listNext(&iter);
        o = listNodeValue(next);
        if (remaining < (ssize_t)(o->used - c->sentlen)) {
            c->sentlen += remaining;
            break;
        }
        remaining -= (ssize_t)(o->used - c->sentlen);
        c->reply_bytes -= o->size;
        listDelNode(c->reply, next);
        c->sentlen = 0;
    }

    return C_OK;
}

/* This function does actual writing output buffers to different types of
 * clients, it is called by writeToClient.
 * If we write successfully, it returns C_OK, otherwise, C_ERR is returned,
 * and 'nwritten' is an output parameter, it means how many bytes server write
 * to client. */
int _writeToClient(client *c, ssize_t *nwritten) {
    *nwritten = 0;
    if (getClientType(c) == CLIENT_TYPE_SLAVE) {
        serverAssert(c->bufpos == 0 && listLength(c->reply) == 0);

        replBufBlock *o = listNodeValue(c->ref_repl_buf_node);
        serverAssert(o->used >= c->ref_block_pos);
        /* Send current block if it is not fully sent. */
        if (o->used > c->ref_block_pos) {
            *nwritten = connWrite(c->conn, o->buf+c->ref_block_pos,
                                  o->used-c->ref_block_pos);
            if (*nwritten <= 0) return C_ERR;
            c->ref_block_pos += *nwritten;
        }

        /* If we fully sent the object on head, go to the next one. */
        listNode *next = listNextNode(c->ref_repl_buf_node);
        if (next && c->ref_block_pos == o->used) {
            o->refcount--;
            ((replBufBlock *)(listNodeValue(next)))->refcount++;
            c->ref_repl_buf_node = next;
            c->ref_block_pos = 0;
            incrementalTrimReplicationBacklog(REPL_BACKLOG_TRIM_BLOCKS_PER_CALL);
        }
        return C_OK;
    }

    /* When the reply list is not empty, it's better to use writev to save us some
     * system calls and TCP packets. */
    if (listLength(c->reply) > 0) {
        int ret = _writevToClient(c, nwritten);
        if (ret != C_OK) return ret;

        /* If there are no longer objects in the list, we expect
         * the count of reply bytes to be exactly zero. */
        if (listLength(c->reply) == 0)
            serverAssert(c->reply_bytes == 0);
    } else if (c->bufpos > 0) {
        *nwritten = connWrite(c->conn, c->buf + c->sentlen, c->bufpos - c->sentlen);
        if (*nwritten <= 0) return C_ERR;
        c->sentlen += *nwritten;

        /* If the buffer was sent, set bufpos to zero to continue with
         * the remainder of the reply. */
        if ((int)c->sentlen == c->bufpos) {
            c->bufpos = 0;
            c->sentlen = 0;
        }
    } 

    return C_OK;
}

/* Write data in output buffers to client. Return C_OK if the client
 * is still valid after the call, C_ERR if it was freed because of some
 * error.  If handler_installed is set, it will attempt to clear the
 * write event.
 *
 * This function is called by threads, but always with handler_installed
 * set to 0. So when handler_installed is set to 0 the function must be
 * thread safe. */
int writeToClient(client *c, int handler_installed) {
    /* Update total number of writes on server */
    atomicIncr(server.stat_total_writes_processed, 1);

    ssize_t nwritten = 0, totwritten = 0;

    while(clientHasPendingReplies(c)) {
        int ret = _writeToClient(c, &nwritten);
        if (ret == C_ERR) break;
        totwritten += nwritten;
        /* Note that we avoid to send more than NET_MAX_WRITES_PER_EVENT
         * bytes, in a single threaded server it's a good idea to serve
         * other clients as well, even if a very large request comes from
         * super fast link that is always able to accept data (in real world
         * scenario think about 'KEYS *' against the loopback interface).
         *
         * However if we are over the maxmemory limit we ignore that and
         * just deliver as much data as it is possible to deliver.
         *
         * Moreover, we also send as much as possible if the client is
         * a slave or a monitor (otherwise, on high-speed traffic, the
         * replication/output buffer will grow indefinitely) */
        if (totwritten > NET_MAX_WRITES_PER_EVENT &&
            (server.maxmemory == 0 ||
             zmalloc_used_memory() < server.maxmemory) &&
            !(c->flags & CLIENT_SLAVE)) break;
    }

    if (getClientType(c) == CLIENT_TYPE_SLAVE) {
        atomicIncr(server.stat_net_repl_output_bytes, totwritten);
    } else {
        atomicIncr(server.stat_net_output_bytes, totwritten);
    }

    if (nwritten == -1) {
        if (connGetState(c->conn) != CONN_STATE_CONNECTED) {
            serverLog(LL_VERBOSE,
                "Error writing to client: %s", connGetLastError(c->conn));
            freeClientAsync(c);
            return C_ERR;
        }
    }
    if (totwritten > 0) {
        /* For clients representing masters we don't count sending data
         * as an interaction, since we always send REPLCONF ACK commands
         * that take some time to just fill the socket output buffer.
         * We just rely on data / pings received for timeout detection. */
        if (!(c->flags & CLIENT_MASTER)) c->lastinteraction = server.unixtime;
    }
    if (!clientHasPendingReplies(c)) {
        c->sentlen = 0;
        /* Note that writeToClient() is called in a threaded way, but
         * aeDeleteFileEvent() is not thread safe: however writeToClient()
         * is always called with handler_installed set to 0 from threads
         * so we are fine. */
        if (handler_installed) {
            serverAssert(io_threads_op == IO_THREADS_OP_IDLE);
            connSetWriteHandler(c->conn, NULL);
        }

        /* Close connection after entire reply has been sent. */
        if (c->flags & CLIENT_CLOSE_AFTER_REPLY) {
            freeClientAsync(c);
            return C_ERR;
        }
    }
    /* Update client's memory usage after writing.
     * Since this isn't thread safe we do this conditionally. In case of threaded writes this is done in
     * handleClientsWithPendingWritesUsingThreads(). */
    if (io_threads_op == IO_THREADS_OP_IDLE)
        updateClientMemUsage(c);
    return C_OK;
}

/* Write event handler. Just send data to the client. */
void sendReplyToClient(connection *conn) {
    client *c = connGetPrivateData(conn);
    writeToClient(c,1);
}

/* This function is called just before entering the event loop, in the hope
 * we can just write the replies to the client output buffer without any
 * need to use a syscall in order to install the writable event handler,
 * get it called, and so forth. */
int handleClientsWithPendingWrites(void) {
    listIter li;
    listNode *ln;
    int processed = listLength(server.clients_pending_write);

    listRewind(server.clients_pending_write,&li);
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
        c->flags &= ~CLIENT_PENDING_WRITE;
        listUnlinkNode(server.clients_pending_write,ln);

        /* If a client is protected, don't do anything,
         * that may trigger write error or recreate handler. */
        if (c->flags & CLIENT_PROTECTED) continue;

        /* Don't write to clients that are going to be closed anyway. */
        if (c->flags & CLIENT_CLOSE_ASAP) continue;

        /* Try to write buffers to the client socket. */
        if (writeToClient(c,0) == C_ERR) continue;

        /* If after the synchronous writes above we still have data to
         * output to the client, we need to install the writable handler. */
        if (clientHasPendingReplies(c)) {
            installClientWriteHandler(c);
        }
    }
    return processed;
}

/* resetClient prepare the client to process the next command */
void resetClient(client *c) {
    redisCommandProc *prevcmd = c->cmd ? c->cmd->proc : NULL;

    freeClientArgv(c);
    c->reqtype = 0;
    c->multibulklen = 0;
    c->bulklen = -1;
    c->slot = -1;

    if (c->deferred_reply_errors)
        listRelease(c->deferred_reply_errors);
    c->deferred_reply_errors = NULL;

    /* We clear the ASKING flag as well if we are not inside a MULTI, and
     * if what we just executed is not the ASKING command itself. */
    if (!(c->flags & CLIENT_MULTI) && prevcmd != askingCommand)
        c->flags &= ~CLIENT_ASKING;

    /* We do the same for the CACHING command as well. It also affects
     * the next command or transaction executed, in a way very similar
     * to ASKING. */
    if (!(c->flags & CLIENT_MULTI) && prevcmd != clientCommand)
        c->flags &= ~CLIENT_TRACKING_CACHING;

    /* Remove the CLIENT_REPLY_SKIP flag if any so that the reply
     * to the next command will be sent, but set the flag if the command
     * we just processed was "CLIENT REPLY SKIP". */
    c->flags &= ~CLIENT_REPLY_SKIP;
    if (c->flags & CLIENT_REPLY_SKIP_NEXT) {
        c->flags |= CLIENT_REPLY_SKIP;
        c->flags &= ~CLIENT_REPLY_SKIP_NEXT;
    }
}

/* This function is used when we want to re-enter the event loop but there
 * is the risk that the client we are dealing with will be freed in some
 * way. This happens for instance in:
 *
 * * DEBUG RELOAD and similar.
 * * When a Lua script is in -BUSY state.
 *
 * So the function will protect the client by doing two things:
 *
 * 1) It removes the file events. This way it is not possible that an
 *    error is signaled on the socket, freeing the client.
 * 2) Moreover it makes sure that if the client is freed in a different code
 *    path, it is not really released, but only marked for later release. */
void protectClient(client *c) {
    c->flags |= CLIENT_PROTECTED;
    if (c->conn) {
        connSetReadHandler(c->conn,NULL);
        connSetWriteHandler(c->conn,NULL);
    }
}

/* This will undo the client protection done by protectClient() */
void unprotectClient(client *c) {
    if (c->flags & CLIENT_PROTECTED) {
        c->flags &= ~CLIENT_PROTECTED;
        if (c->conn) {
            connSetReadHandler(c->conn,readQueryFromClient);
            if (clientHasPendingReplies(c)) putClientInPendingWriteQueue(c);
        }
    }
}

/* Like processMultibulkBuffer(), but for the inline protocol instead of RESP,
 * this function consumes the client query buffer and creates a command ready
 * to be executed inside the client structure. Returns C_OK if the command
 * is ready to be executed, or C_ERR if there is still protocol to read to
 * have a well formed command. The function also returns C_ERR when there is
 * a protocol error: in such a case the client structure is setup to reply
 * with the error and close the connection. */
int processInlineBuffer(client *c) {
    char *newline;
    int argc, j, linefeed_chars = 1;
    sds *argv, aux;
    size_t querylen;

    /* Search for end of line */
    newline = strchr(c->querybuf+c->qb_pos,'\n');

    /* Nothing to do without a \r\n */
    if (newline == NULL) {
        if (sdslen(c->querybuf)-c->qb_pos > PROTO_INLINE_MAX_SIZE) {
            addReplyError(c,"Protocol error: too big inline request");
            setProtocolError("too big inline request",c);
        }
        return C_ERR;
    }

    /* Handle the \r\n case. */
    if (newline != c->querybuf+c->qb_pos && *(newline-1) == '\r')
        newline--, linefeed_chars++;

    /* Split the input buffer up to the \r\n */
    querylen = newline-(c->querybuf+c->qb_pos);
    aux = sdsnewlen(c->querybuf+c->qb_pos,querylen);
    argv = sdssplitargs(aux,&argc);
    sdsfree(aux);
    if (argv == NULL) {
        addReplyError(c,"Protocol error: unbalanced quotes in request");
        setProtocolError("unbalanced quotes in inline request",c);
        return C_ERR;
    }

    /* Newline from slaves can be used to refresh the last ACK time.
     * This is useful for a slave to ping back while loading a big
     * RDB file. */
    if (querylen == 0 && getClientType(c) == CLIENT_TYPE_SLAVE)
        c->repl_ack_time = server.unixtime;

    /* Masters should never send us inline protocol to run actual
     * commands. If this happens, it is likely due to a bug in Redis where
     * we got some desynchronization in the protocol, for example
     * because of a PSYNC gone bad.
     *
     * However there is an exception: masters may send us just a newline
     * to keep the connection active. */
    if (querylen != 0 && c->flags & CLIENT_MASTER) {
        sdsfreesplitres(argv,argc);
        serverLog(LL_WARNING,"WARNING: Receiving inline protocol from master, master stream corruption? Closing the master connection and discarding the cached master.");
        setProtocolError("Master using the inline protocol. Desync?",c);
        return C_ERR;
    }

    /* Move querybuffer position to the next query in the buffer. */
    c->qb_pos += querylen+linefeed_chars;

    /* Setup argv array on client structure */
    if (argc) {
        if (c->argv) zfree(c->argv);
        c->argv_len = argc;
        c->argv = zmalloc(sizeof(robj*)*c->argv_len);
        c->argv_len_sum = 0;
    }

    /* Create redis objects for all arguments. */
    for (c->argc = 0, j = 0; j < argc; j++) {
        c->argv[c->argc] = createObject(OBJ_STRING,argv[j]);
        c->argc++;
        c->argv_len_sum += sdslen(argv[j]);
    }
    zfree(argv);
    return C_OK;
}

/* Helper function. Record protocol error details in server log,
 * and set the client as CLIENT_CLOSE_AFTER_REPLY and
 * CLIENT_PROTOCOL_ERROR. */
#define PROTO_DUMP_LEN 128
static void setProtocolError(const char *errstr, client *c) {
    if (server.verbosity <= LL_VERBOSE || c->flags & CLIENT_MASTER) {
        sds client = catClientInfoString(sdsempty(),c);

        /* Sample some protocol to given an idea about what was inside. */
        char buf[256];
        if (sdslen(c->querybuf)-c->qb_pos < PROTO_DUMP_LEN) {
            snprintf(buf,sizeof(buf),"Query buffer during protocol error: '%s'", c->querybuf+c->qb_pos);
        } else {
            snprintf(buf,sizeof(buf),"Query buffer during protocol error: '%.*s' (... more %zu bytes ...) '%.*s'", PROTO_DUMP_LEN/2, c->querybuf+c->qb_pos, sdslen(c->querybuf)-c->qb_pos-PROTO_DUMP_LEN, PROTO_DUMP_LEN/2, c->querybuf+sdslen(c->querybuf)-PROTO_DUMP_LEN/2);
        }

        /* Remove non printable chars. */
        char *p = buf;
        while (*p != '\0') {
            if (!isprint(*p)) *p = '.';
            p++;
        }

        /* Log all the client and protocol info. */
        int loglevel = (c->flags & CLIENT_MASTER) ? LL_WARNING :
                                                    LL_VERBOSE;
        serverLog(loglevel,
            "Protocol error (%s) from client: %s. %s", errstr, client, buf);
        sdsfree(client);
    }
    c->flags |= (CLIENT_CLOSE_AFTER_REPLY|CLIENT_PROTOCOL_ERROR);
}

/* Process the query buffer for client 'c', setting up the client argument
 * vector for command execution. Returns C_OK if after running the function
 * the client has a well-formed ready to be processed command, otherwise
 * C_ERR if there is still to read more buffer to get the full command.
 * The function also returns C_ERR when there is a protocol error: in such a
 * case the client structure is setup to reply with the error and close
 * the connection.
 *
 * This function is called if processInputBuffer() detects that the next
 * command is in RESP format, so the first byte in the command is found
 * to be '*'. Otherwise for inline commands processInlineBuffer() is called. */
int processMultibulkBuffer(client *c) {
    char *newline = NULL;
    int ok;
    long long ll;

    if (c->multibulklen == 0) {
        /* The client should have been reset */
        serverAssertWithInfo(c,NULL,c->argc == 0);

        /* Multi bulk length cannot be read without a \r\n */
        newline = strchr(c->querybuf+c->qb_pos,'\r');
        if (newline == NULL) {
            if (sdslen(c->querybuf)-c->qb_pos > PROTO_INLINE_MAX_SIZE) {
                addReplyError(c,"Protocol error: too big mbulk count string");
                setProtocolError("too big mbulk count string",c);
            }
            return C_ERR;
        }

        /* Buffer should also contain \n */
        if (newline-(c->querybuf+c->qb_pos) > (ssize_t)(sdslen(c->querybuf)-c->qb_pos-2))
            return C_ERR;

        /* We know for sure there is a whole line since newline != NULL,
         * so go ahead and find out the multi bulk length. */
        serverAssertWithInfo(c,NULL,c->querybuf[c->qb_pos] == '*');
        ok = string2ll(c->querybuf+1+c->qb_pos,newline-(c->querybuf+1+c->qb_pos),&ll);
        if (!ok || ll > INT_MAX) {
            addReplyError(c,"Protocol error: invalid multibulk length");
            setProtocolError("invalid mbulk count",c);
            return C_ERR;
        } else if (ll > 10 && authRequired(c)) {
            addReplyError(c, "Protocol error: unauthenticated multibulk length");
            setProtocolError("unauth mbulk count", c);
            return C_ERR;
        }

        c->qb_pos = (newline-c->querybuf)+2;

        if (ll <= 0) return C_OK;

        c->multibulklen = ll;

        /* Setup argv array on client structure */
        if (c->argv) zfree(c->argv);
        c->argv_len = min(c->multibulklen, 1024);
        c->argv = zmalloc(sizeof(robj*)*c->argv_len);
        c->argv_len_sum = 0;
    }

    serverAssertWithInfo(c,NULL,c->multibulklen > 0);
    while(c->multibulklen) {
        /* Read bulk length if unknown */
        if (c->bulklen == -1) {
            newline = strchr(c->querybuf+c->qb_pos,'\r');
            if (newline == NULL) {
                if (sdslen(c->querybuf)-c->qb_pos > PROTO_INLINE_MAX_SIZE) {
                    addReplyError(c,
                        "Protocol error: too big bulk count string");
                    setProtocolError("too big bulk count string",c);
                    return C_ERR;
                }
                break;
            }

            /* Buffer should also contain \n */
            if (newline-(c->querybuf+c->qb_pos) > (ssize_t)(sdslen(c->querybuf)-c->qb_pos-2))
                break;

            if (c->querybuf[c->qb_pos] != '$') {
                addReplyErrorFormat(c,
                    "Protocol error: expected '$', got '%c'",
                    c->querybuf[c->qb_pos]);
                setProtocolError("expected $ but got something else",c);
                return C_ERR;
            }

            ok = string2ll(c->querybuf+c->qb_pos+1,newline-(c->querybuf+c->qb_pos+1),&ll);
            if (!ok || ll < 0 ||
                (!(c->flags & CLIENT_MASTER) && ll > server.proto_max_bulk_len)) {
                addReplyError(c,"Protocol error: invalid bulk length");
                setProtocolError("invalid bulk length",c);
                return C_ERR;
            } else if (ll > 16384 && authRequired(c)) {
                addReplyError(c, "Protocol error: unauthenticated bulk length");
                setProtocolError("unauth bulk length", c);
                return C_ERR;
            }

            c->qb_pos = newline-c->querybuf+2;
            if (!(c->flags & CLIENT_MASTER) && ll >= PROTO_MBULK_BIG_ARG) {
                /* When the client is not a master client (because master
                 * client's querybuf can only be trimmed after data applied
                 * and sent to replicas).
                 *
                 * If we are going to read a large object from network
                 * try to make it likely that it will start at c->querybuf
                 * boundary so that we can optimize object creation
                 * avoiding a large copy of data.
                 *
                 * But only when the data we have not parsed is less than
                 * or equal to ll+2. If the data length is greater than
                 * ll+2, trimming querybuf is just a waste of time, because
                 * at this time the querybuf contains not only our bulk. */
                if (sdslen(c->querybuf)-c->qb_pos <= (size_t)ll+2) {
                    sdsrange(c->querybuf,c->qb_pos,-1);
                    c->qb_pos = 0;
                    /* Hint the sds library about the amount of bytes this string is
                     * going to contain. */
                    c->querybuf = sdsMakeRoomForNonGreedy(c->querybuf,ll+2-sdslen(c->querybuf));
                }
            }
            c->bulklen = ll;
        }

        /* Read bulk argument */
        if (sdslen(c->querybuf)-c->qb_pos < (size_t)(c->bulklen+2)) {
            /* Not enough data (+2 == trailing \r\n) */
            break;
        } else {
            /* Check if we have space in argv, grow if needed */
            if (c->argc >= c->argv_len) {
                c->argv_len = min(c->argv_len < INT_MAX/2 ? c->argv_len*2 : INT_MAX, c->argc+c->multibulklen);
                c->argv = zrealloc(c->argv, sizeof(robj*)*c->argv_len);
            }

            /* Optimization: if a non-master client's buffer contains JUST our bulk element
             * instead of creating a new object by *copying* the sds we
             * just use the current sds string. */
            if (!(c->flags & CLIENT_MASTER) &&
                c->qb_pos == 0 &&
                c->bulklen >= PROTO_MBULK_BIG_ARG &&
                sdslen(c->querybuf) == (size_t)(c->bulklen+2))
            {
                c->argv[c->argc++] = createObject(OBJ_STRING,c->querybuf);
                c->argv_len_sum += c->bulklen;
                sdsIncrLen(c->querybuf,-2); /* remove CRLF */
                /* Assume that if we saw a fat argument we'll see another one
                 * likely... */
                c->querybuf = sdsnewlen(SDS_NOINIT,c->bulklen+2);
                sdsclear(c->querybuf);
            } else {
                c->argv[c->argc++] =
                    createStringObject(c->querybuf+c->qb_pos,c->bulklen);
                c->argv_len_sum += c->bulklen;
                c->qb_pos += c->bulklen+2;
            }
            c->bulklen = -1;
            c->multibulklen--;
        }
    }

    /* We're done when c->multibulk == 0 */
    if (c->multibulklen == 0) return C_OK;

    /* Still not ready to process the command */
    return C_ERR;
}

/* Perform necessary tasks after a command was executed:
 *
 * 1. The client is reset unless there are reasons to avoid doing it.
 * 2. In the case of master clients, the replication offset is updated.
 * 3. Propagate commands we got from our master to replicas down the line. */
void commandProcessed(client *c) {
    /* If client is blocked(including paused), just return avoid reset and replicate.
     *
     * 1. Don't reset the client structure for blocked clients, so that the reply
     *    callback will still be able to access the client argv and argc fields.
     *    The client will be reset in unblockClient().
     * 2. Don't update replication offset or propagate commands to replicas,
     *    since we have not applied the command. */
    if (c->flags & CLIENT_BLOCKED) return;

    resetClient(c);

    long long prev_offset = c->reploff;
    if (c->flags & CLIENT_MASTER && !(c->flags & CLIENT_MULTI)) {
        /* Update the applied replication offset of our master. */
        c->reploff = c->read_reploff - sdslen(c->querybuf) + c->qb_pos;
    }

    /* If the client is a master we need to compute the difference
     * between the applied offset before and after processing the buffer,
     * to understand how much of the replication stream was actually
     * applied to the master state: this quantity, and its corresponding
     * part of the replication stream, will be propagated to the
     * sub-replicas and to the replication backlog. */
    if (c->flags & CLIENT_MASTER) {
        long long applied = c->reploff - prev_offset;
        if (applied) {
            replicationFeedStreamFromMasterStream(c->querybuf+c->repl_applied,applied);
            c->repl_applied += applied;
        }
    }
}

/* This function calls processCommand(), but also performs a few sub tasks
 * for the client that are useful in that context:
 *
 * 1. It sets the current client to the client 'c'.
 * 2. calls commandProcessed() if the command was handled.
 *
 * The function returns C_ERR in case the client was freed as a side effect
 * of processing the command, otherwise C_OK is returned. */
int processCommandAndResetClient(client *c) {
    int deadclient = 0;
    client *old_client = server.current_client;
    server.current_client = c;
    if (processCommand(c) == C_OK) {
        commandProcessed(c);
        /* Update the client's memory to include output buffer growth following the
         * processed command. */
        updateClientMemUsage(c);
    }

    if (server.current_client == NULL) deadclient = 1;
    /*
     * Restore the old client, this is needed because when a script
     * times out, we will get into this code from processEventsWhileBlocked.
     * Which will cause to set the server.current_client. If not restored
     * we will return 1 to our caller which will falsely indicate the client
     * is dead and will stop reading from its buffer.
     */
    server.current_client = old_client;
    /* performEvictions may flush slave output buffers. This may
     * result in a slave, that may be the active client, to be
     * freed. */
    return deadclient ? C_ERR : C_OK;
}


/* This function will execute any fully parsed commands pending on
 * the client. Returns C_ERR if the client is no longer valid after executing
 * the command, and C_OK for all other cases. */
int processPendingCommandAndInputBuffer(client *c) {
    if (c->flags & CLIENT_PENDING_COMMAND) {
        c->flags &= ~CLIENT_PENDING_COMMAND;
        if (processCommandAndResetClient(c) == C_ERR) {
            return C_ERR;
        }
    }

    /* Now process client if it has more data in it's buffer.
     *
     * Note: when a master client steps into this function,
     * it can always satisfy this condition, because its querbuf
     * contains data not applied. */
    if (c->querybuf && sdslen(c->querybuf) > 0) {
        return processInputBuffer(c);
    }
    return C_OK;
}

/* This function is called every time, in the client structure 'c', there is
 * more query buffer to process, because we read more data from the socket
 * or because a client was blocked and later reactivated, so there could be
 * pending query buffer, already representing a full command, to process.
 * return C_ERR in case the client was freed during the processing */
int processInputBuffer(client *c) {
    /* Keep processing while there is something in the input buffer */
    while(c->qb_pos < sdslen(c->querybuf)) {
        /* Immediately abort if the client is in the middle of something. */
        if (c->flags & CLIENT_BLOCKED) break;

        /* Don't process more buffers from clients that have already pending
         * commands to execute in c->argv. */
        if (c->flags & CLIENT_PENDING_COMMAND) break;

        /* Don't process input from the master while there is a busy script
         * condition on the slave. We want just to accumulate the replication
         * stream (instead of replying -BUSY like we do with other clients) and
         * later resume the processing. */
        if (isInsideYieldingLongCommand() && c->flags & CLIENT_MASTER) break;

        /* CLIENT_CLOSE_AFTER_REPLY closes the connection once the reply is
         * written to the client. Make sure to not let the reply grow after
         * this flag has been set (i.e. don't process more commands).
         *
         * The same applies for clients we want to terminate ASAP. */
        if (c->flags & (CLIENT_CLOSE_AFTER_REPLY|CLIENT_CLOSE_ASAP)) break;

        /* Determine request type when unknown. */
        if (!c->reqtype) {
            if (c->querybuf[c->qb_pos] == '*') {
                c->reqtype = PROTO_REQ_MULTIBULK;
            } else {
                c->reqtype = PROTO_REQ_INLINE;
            }
        }

        if (c->reqtype == PROTO_REQ_INLINE) {
            if (processInlineBuffer(c) != C_OK) break;
        } else if (c->reqtype == PROTO_REQ_MULTIBULK) {
            if (processMultibulkBuffer(c) != C_OK) break;
        } else {
            serverPanic("Unknown request type");
        }

        /* Multibulk processing could see a <= 0 length. */
        if (c->argc == 0) {
            resetClient(c);
        } else {
            /* If we are in the context of an I/O thread, we can't really
             * execute the command here. All we can do is to flag the client
             * as one that needs to process the command. */
            if (io_threads_op != IO_THREADS_OP_IDLE) {
                serverAssert(io_threads_op == IO_THREADS_OP_READ);
                c->flags |= CLIENT_PENDING_COMMAND;
                break;
            }

            /* We are finally ready to execute the command. */
            if (processCommandAndResetClient(c) == C_ERR) {
                /* If the client is no longer valid, we avoid exiting this
                 * loop and trimming the client buffer later. So we return
                 * ASAP in that case. */
                return C_ERR;
            }
        }
    }

    if (c->flags & CLIENT_MASTER) {
        /* If the client is a master, trim the querybuf to repl_applied,
         * since master client is very special, its querybuf not only
         * used to parse command, but also proxy to sub-replicas.
         *
         * Here are some scenarios we cannot trim to qb_pos:
         * 1. we don't receive complete command from master
         * 2. master client blocked cause of client pause
         * 3. io threads operate read, master client flagged with CLIENT_PENDING_COMMAND
         *
         * In these scenarios, qb_pos points to the part of the current command
         * or the beginning of next command, and the current command is not applied yet,
         * so the repl_applied is not equal to qb_pos. */
        if (c->repl_applied) {
            sdsrange(c->querybuf,c->repl_applied,-1);
            c->qb_pos -= c->repl_applied;
            c->repl_applied = 0;
        }
    } else if (c->qb_pos) {
        /* Trim to pos */
        sdsrange(c->querybuf,c->qb_pos,-1);
        c->qb_pos = 0;
    }

    /* Update client memory usage after processing the query buffer, this is
     * important in case the query buffer is big and wasn't drained during
     * the above loop (because of partially sent big commands). */
    if (io_threads_op == IO_THREADS_OP_IDLE)
        updateClientMemUsage(c);

    return C_OK;
}

void readQueryFromClient(connection *conn) {
    client *c = connGetPrivateData(conn);
    int nread, big_arg = 0;
    size_t qblen, readlen;

    /* Check if we want to read from the client later when exiting from
     * the event loop. This is the case if threaded I/O is enabled. */
    if (postponeClientRead(c)) return;

    /* Update total number of reads on server */
    atomicIncr(server.stat_total_reads_processed, 1);

    readlen = PROTO_IOBUF_LEN;
    /* If this is a multi bulk request, and we are processing a bulk reply
     * that is large enough, try to maximize the probability that the query
     * buffer contains exactly the SDS string representing the object, even
     * at the risk of requiring more read(2) calls. This way the function
     * processMultiBulkBuffer() can avoid copying buffers to create the
     * Redis Object representing the argument. */
    if (c->reqtype == PROTO_REQ_MULTIBULK && c->multibulklen && c->bulklen != -1
        && c->bulklen >= PROTO_MBULK_BIG_ARG)
    {
        ssize_t remaining = (size_t)(c->bulklen+2)-(sdslen(c->querybuf)-c->qb_pos);
        big_arg = 1;

        /* Note that the 'remaining' variable may be zero in some edge case,
         * for example once we resume a blocked client after CLIENT PAUSE. */
        if (remaining > 0) readlen = remaining;

        /* Master client needs expand the readlen when meet BIG_ARG(see #9100),
         * but doesn't need align to the next arg, we can read more data. */
        if (c->flags & CLIENT_MASTER && readlen < PROTO_IOBUF_LEN)
            readlen = PROTO_IOBUF_LEN;
    }

    qblen = sdslen(c->querybuf);
    if (!(c->flags & CLIENT_MASTER) && // master client's querybuf can grow greedy.
        (big_arg || sdsalloc(c->querybuf) < PROTO_IOBUF_LEN)) {
        /* When reading a BIG_ARG we won't be reading more than that one arg
         * into the query buffer, so we don't need to pre-allocate more than we
         * need, so using the non-greedy growing. For an initial allocation of
         * the query buffer, we also don't wanna use the greedy growth, in order
         * to avoid collision with the RESIZE_THRESHOLD mechanism. */
        c->querybuf = sdsMakeRoomForNonGreedy(c->querybuf, readlen);
    } else {
        c->querybuf = sdsMakeRoomFor(c->querybuf, readlen);

        /* Read as much as possible from the socket to save read(2) system calls. */
        readlen = sdsavail(c->querybuf);
    }
    nread = connRead(c->conn, c->querybuf+qblen, readlen);
    if (nread == -1) {
        if (connGetState(conn) == CONN_STATE_CONNECTED) {
            return;
        } else {
            serverLog(LL_VERBOSE, "Reading from client: %s",connGetLastError(c->conn));
            freeClientAsync(c);
            goto done;
        }
    } else if (nread == 0) {
        if (server.verbosity <= LL_VERBOSE) {
            sds info = catClientInfoString(sdsempty(), c);
            serverLog(LL_VERBOSE, "Client closed connection %s", info);
            sdsfree(info);
        }
        freeClientAsync(c);
        goto done;
    }

    sdsIncrLen(c->querybuf,nread);
    qblen = sdslen(c->querybuf);
    if (c->querybuf_peak < qblen) c->querybuf_peak = qblen;

    c->lastinteraction = server.unixtime;
    if (c->flags & CLIENT_MASTER) {
        c->read_reploff += nread;
        atomicIncr(server.stat_net_repl_input_bytes, nread);
    } else {
        atomicIncr(server.stat_net_input_bytes, nread);
    }

    if (!(c->flags & CLIENT_MASTER) && sdslen(c->querybuf) > server.client_max_querybuf_len) {
        sds ci = catClientInfoString(sdsempty(),c), bytes = sdsempty();

        bytes = sdscatrepr(bytes,c->querybuf,64);
        serverLog(LL_WARNING,"Closing client that reached max query buffer length: %s (qbuf initial bytes: %s)", ci, bytes);
        sdsfree(ci);
        sdsfree(bytes);
        freeClientAsync(c);
        goto done;
    }

    /* There is more data in the client input buffer, continue parsing it
     * and check if there is a full command to execute. */
    if (processInputBuffer(c) == C_ERR)
         c = NULL;

done:
    beforeNextClient(c);
}

/* A Redis "Address String" is a colon separated ip:port pair.
 * For IPv4 it's in the form x.y.z.k:port, example: "127.0.0.1:1234".
 * For IPv6 addresses we use [] around the IP part, like in "[::1]:1234".
 * For Unix sockets we use path:0, like in "/tmp/redis:0".
 *
 * An Address String always fits inside a buffer of NET_ADDR_STR_LEN bytes,
 * including the null term.
 *
 * On failure the function still populates 'addr' with the "?:0" string in case
 * you want to relax error checking or need to display something anyway (see
 * anetFdToString implementation for more info). */
void genClientAddrString(client *client, char *addr,
                         size_t addr_len, int remote) {
    if (client->flags & CLIENT_UNIX_SOCKET) {
        /* Unix socket client. */
        snprintf(addr,addr_len,"%s:0",server.unixsocket);
    } else {
        /* TCP client. */
        connFormatAddr(client->conn,addr,addr_len,remote);
    }
}

/* This function returns the client peer id, by creating and caching it
 * if client->peerid is NULL, otherwise returning the cached value.
 * The Peer ID never changes during the life of the client, however it
 * is expensive to compute. */
char *getClientPeerId(client *c) {
    char peerid[NET_ADDR_STR_LEN] = {0};

    if (c->peerid == NULL) {
        genClientAddrString(c,peerid,sizeof(peerid),1);
        c->peerid = sdsnew(peerid);
    }
    return c->peerid;
}

/* This function returns the client bound socket name, by creating and caching
 * it if client->sockname is NULL, otherwise returning the cached value.
 * The Socket Name never changes during the life of the client, however it
 * is expensive to compute. */
char *getClientSockname(client *c) {
    char sockname[NET_ADDR_STR_LEN] = {0};

    if (c->sockname == NULL) {
        genClientAddrString(c,sockname,sizeof(sockname),0);
        c->sockname = sdsnew(sockname);
    }
    return c->sockname;
}

/* Concatenate a string representing the state of a client in a human
 * readable format, into the sds string 's'. */
sds catClientInfoString(sds s, client *client) {
    char flags[16], events[3], conninfo[CONN_INFO_LEN], *p;

    p = flags;
    if (client->flags & CLIENT_SLAVE) {
        if (client->flags & CLIENT_MONITOR)
            *p++ = 'O';
        else
            *p++ = 'S';
    }
    if (client->flags & CLIENT_MASTER) *p++ = 'M';
    if (client->flags & CLIENT_PUBSUB) *p++ = 'P';
    if (client->flags & CLIENT_MULTI) *p++ = 'x';
    if (client->flags & CLIENT_BLOCKED) *p++ = 'b';
    if (client->flags & CLIENT_TRACKING) *p++ = 't';
    if (client->flags & CLIENT_TRACKING_BROKEN_REDIR) *p++ = 'R';
    if (client->flags & CLIENT_TRACKING_BCAST) *p++ = 'B';
    if (client->flags & CLIENT_DIRTY_CAS) *p++ = 'd';
    if (client->flags & CLIENT_CLOSE_AFTER_REPLY) *p++ = 'c';
    if (client->flags & CLIENT_UNBLOCKED) *p++ = 'u';
    if (client->flags & CLIENT_CLOSE_ASAP) *p++ = 'A';
    if (client->flags & CLIENT_UNIX_SOCKET) *p++ = 'U';
    if (client->flags & CLIENT_READONLY) *p++ = 'r';
    if (client->flags & CLIENT_NO_EVICT) *p++ = 'e';
    if (p == flags) *p++ = 'N';
    *p++ = '\0';

    p = events;
    if (client->conn) {
        if (connHasReadHandler(client->conn)) *p++ = 'r';
        if (connHasWriteHandler(client->conn)) *p++ = 'w';
    }
    *p = '\0';

    /* Compute the total memory consumed by this client. */
    size_t obufmem, total_mem = getClientMemoryUsage(client, &obufmem);

    size_t used_blocks_of_repl_buf = 0;
    if (client->ref_repl_buf_node) {
        replBufBlock *last = listNodeValue(listLast(server.repl_buffer_blocks));
        replBufBlock *cur = listNodeValue(client->ref_repl_buf_node);
        used_blocks_of_repl_buf = last->id - cur->id + 1;
    }

    sds ret = sdscatfmt(s,
        "id=%U addr=%s laddr=%s %s name=%s age=%I idle=%I flags=%s db=%i sub=%i psub=%i ssub=%i multi=%i qbuf=%U qbuf-free=%U argv-mem=%U multi-mem=%U rbs=%U rbp=%U obl=%U oll=%U omem=%U tot-mem=%U events=%s cmd=%s user=%s redir=%I resp=%i",
        (unsigned long long) client->id,
        getClientPeerId(client),
        getClientSockname(client),
        connGetInfo(client->conn, conninfo, sizeof(conninfo)),
        client->name ? (char*)client->name->ptr : "",
        (long long)(server.unixtime - client->ctime),
        (long long)(server.unixtime - client->lastinteraction),
        flags,
        client->db->id,
        (int) dictSize(client->pubsub_channels),
        (int) listLength(client->pubsub_patterns),
        (int) dictSize(client->pubsubshard_channels),
        (client->flags & CLIENT_MULTI) ? client->mstate.count : -1,
        (unsigned long long) sdslen(client->querybuf),
        (unsigned long long) sdsavail(client->querybuf),
        (unsigned long long) client->argv_len_sum,
        (unsigned long long) client->mstate.argv_len_sums,
        (unsigned long long) client->buf_usable_size,
        (unsigned long long) client->buf_peak,
        (unsigned long long) client->bufpos,
        (unsigned long long) listLength(client->reply) + used_blocks_of_repl_buf,
        (unsigned long long) obufmem, /* should not include client->buf since we want to see 0 for static clients. */
        (unsigned long long) total_mem,
        events,
        client->lastcmd ? client->lastcmd->fullname : "NULL",
        client->user ? client->user->name : "(superuser)",
        (client->flags & CLIENT_TRACKING) ? (long long) client->client_tracking_redirection : -1,
        client->resp);
    return ret;
}

sds getAllClientsInfoString(int type) {
    listNode *ln;
    listIter li;
    client *client;
    sds o = sdsnewlen(SDS_NOINIT,200*listLength(server.clients));
    sdsclear(o);
    listRewind(server.clients,&li);
    while ((ln = listNext(&li)) != NULL) {
        client = listNodeValue(ln);
        if (type != -1 && getClientType(client) != type) continue;
        o = catClientInfoString(o,client);
        o = sdscatlen(o,"\n",1);
    }
    return o;
}

/* Returns C_OK if the name has been set or C_ERR if the name is invalid. */
int clientSetName(client *c, robj *name) {
    int len = (name != NULL) ? sdslen(name->ptr) : 0;

    /* Setting the client name to an empty string actually removes
     * the current name. */
    if (len == 0) {
        if (c->name) decrRefCount(c->name);
        c->name = NULL;
        return C_OK;
    }

    /* Otherwise check if the charset is ok. We need to do this otherwise
     * CLIENT LIST format will break. You should always be able to
     * split by space to get the different fields. */
    char *p = name->ptr;
    for (int j = 0; j < len; j++) {
        if (p[j] < '!' || p[j] > '~') { /* ASCII is assumed. */
            return C_ERR;
        }
    }
    if (c->name) decrRefCount(c->name);
    c->name = name;
    incrRefCount(name);
    return C_OK;
}

/* This function implements CLIENT SETNAME, including replying to the
 * user with an error if the charset is wrong (in that case C_ERR is
 * returned). If the function succeeded C_OK is returned, and it's up
 * to the caller to send a reply if needed.
 *
 * Setting an empty string as name has the effect of unsetting the
 * currently set name: the client will remain unnamed.
 *
 * This function is also used to implement the HELLO SETNAME option. */
int clientSetNameOrReply(client *c, robj *name) {
    int result = clientSetName(c, name);
    if (result == C_ERR) {
        addReplyError(c,
                      "Client names cannot contain spaces, "
                      "newlines or special characters.");
    }
    return result;
}

/* Reset the client state to resemble a newly connected client.
 */
void resetCommand(client *c) {
    /* MONITOR clients are also marked with CLIENT_SLAVE, we need to
     * distinguish between the two.
     */
    uint64_t flags = c->flags;
    if (flags & CLIENT_MONITOR) flags &= ~(CLIENT_MONITOR|CLIENT_SLAVE);

    if (flags & (CLIENT_SLAVE|CLIENT_MASTER|CLIENT_MODULE)) {
        addReplyError(c,"can only reset normal client connections");
        return;
    }

    clearClientConnectionState(c);
    addReplyStatus(c,"RESET");
}

/* Disconnect the current client */
void quitCommand(client *c) {
    addReply(c,shared.ok);
    c->flags |= CLIENT_CLOSE_AFTER_REPLY;
}

void clientCommand(client *c) {
    listNode *ln;
    listIter li;

    if (c->argc == 2 && !strcasecmp(c->argv[1]->ptr,"help")) {
        const char *help[] = {
"CACHING (YES|NO)",
"    Enable/disable tracking of the keys for next command in OPTIN/OPTOUT modes.",
"GETREDIR",
"    Return the client ID we are redirecting to when tracking is enabled.",
"GETNAME",
"    Return the name of the current connection.",
"ID",
"    Return the ID of the current connection.",
"INFO",
"    Return information about the current client connection.",
"KILL <ip:port>",
"    Kill connection made from <ip:port>.",
"KILL <option> <value> [<option> <value> [...]]",
"    Kill connections. Options are:",
"    * ADDR (<ip:port>|<unixsocket>:0)",
"      Kill connections made from the specified address",
"    * LADDR (<ip:port>|<unixsocket>:0)",
"      Kill connections made to specified local address",
"    * TYPE (NORMAL|MASTER|REPLICA|PUBSUB)",
"      Kill connections by type.",
"    * USER <username>",
"      Kill connections authenticated by <username>.",
"    * SKIPME (YES|NO)",
"      Skip killing current connection (default: yes).",
"LIST [options ...]",
"    Return information about client connections. Options:",
"    * TYPE (NORMAL|MASTER|REPLICA|PUBSUB)",
"      Return clients of specified type.",
"UNPAUSE",
"    Stop the current client pause, resuming traffic.",
"PAUSE <timeout> [WRITE|ALL]",
"    Suspend all, or just write, clients for <timeout> milliseconds.",
"REPLY (ON|OFF|SKIP)",
"    Control the replies sent to the current connection.",
"SETNAME <name>",
"    Assign the name <name> to the current connection.",
"UNBLOCK <clientid> [TIMEOUT|ERROR]",
"    Unblock the specified blocked client.",
"TRACKING (ON|OFF) [REDIRECT <id>] [BCAST] [PREFIX <prefix> [...]]",
"         [OPTIN] [OPTOUT] [NOLOOP]",
"    Control server assisted client side caching.",
"TRACKINGINFO",
"    Report tracking status for the current connection.",
"NO-EVICT (ON|OFF)",
"    Protect current client connection from eviction.",
NULL
        };
        addReplyHelp(c, help);
    } else if (!strcasecmp(c->argv[1]->ptr,"id") && c->argc == 2) {
        /* CLIENT ID */
        addReplyLongLong(c,c->id);
    } else if (!strcasecmp(c->argv[1]->ptr,"info") && c->argc == 2) {
        /* CLIENT INFO */
        sds o = catClientInfoString(sdsempty(), c);
        o = sdscatlen(o,"\n",1);
        addReplyVerbatim(c,o,sdslen(o),"txt");
        sdsfree(o);
    } else if (!strcasecmp(c->argv[1]->ptr,"list")) {
        /* CLIENT LIST */
        int type = -1;
        sds o = NULL;
        if (c->argc == 4 && !strcasecmp(c->argv[2]->ptr,"type")) {
            type = getClientTypeByName(c->argv[3]->ptr);
            if (type == -1) {
                addReplyErrorFormat(c,"Unknown client type '%s'",
                    (char*) c->argv[3]->ptr);
                return;
            }
        } else if (c->argc > 3 && !strcasecmp(c->argv[2]->ptr,"id")) {
            int j;
            o = sdsempty();
            for (j = 3; j < c->argc; j++) {
                long long cid;
                if (getLongLongFromObjectOrReply(c, c->argv[j], &cid,
                            "Invalid client ID")) {
                    sdsfree(o);
                    return;
                }
                client *cl = lookupClientByID(cid);
                if (cl) {
                    o = catClientInfoString(o, cl);
                    o = sdscatlen(o, "\n", 1);
                }
            }
        } else if (c->argc != 2) {
            addReplyErrorObject(c,shared.syntaxerr);
            return;
        }

        if (!o)
            o = getAllClientsInfoString(type);
        addReplyVerbatim(c,o,sdslen(o),"txt");
        sdsfree(o);
    } else if (!strcasecmp(c->argv[1]->ptr,"reply") && c->argc == 3) {
        /* CLIENT REPLY ON|OFF|SKIP */
        if (!strcasecmp(c->argv[2]->ptr,"on")) {
            c->flags &= ~(CLIENT_REPLY_SKIP|CLIENT_REPLY_OFF);
            addReply(c,shared.ok);
        } else if (!strcasecmp(c->argv[2]->ptr,"off")) {
            c->flags |= CLIENT_REPLY_OFF;
        } else if (!strcasecmp(c->argv[2]->ptr,"skip")) {
            if (!(c->flags & CLIENT_REPLY_OFF))
                c->flags |= CLIENT_REPLY_SKIP_NEXT;
        } else {
            addReplyErrorObject(c,shared.syntaxerr);
            return;
        }
    } else if (!strcasecmp(c->argv[1]->ptr,"no-evict") && c->argc == 3) {
        /* CLIENT NO-EVICT ON|OFF */
        if (!strcasecmp(c->argv[2]->ptr,"on")) {
            c->flags |= CLIENT_NO_EVICT;
            addReply(c,shared.ok);
        } else if (!strcasecmp(c->argv[2]->ptr,"off")) {
            c->flags &= ~CLIENT_NO_EVICT;
            addReply(c,shared.ok);
        } else {
            addReplyErrorObject(c,shared.syntaxerr);
            return;
        }
    } else if (!strcasecmp(c->argv[1]->ptr,"kill")) {
        /* CLIENT KILL <ip:port>
         * CLIENT KILL <option> [value] ... <option> [value] */
        char *addr = NULL;
        char *laddr = NULL;
        user *user = NULL;
        int type = -1;
        uint64_t id = 0;
        int skipme = 1;
        int killed = 0, close_this_client = 0;

        if (c->argc == 3) {
            /* Old style syntax: CLIENT KILL <addr> */
            addr = c->argv[2]->ptr;
            skipme = 0; /* With the old form, you can kill yourself. */
        } else if (c->argc > 3) {
            int i = 2; /* Next option index. */

            /* New style syntax: parse options. */
            while(i < c->argc) {
                int moreargs = c->argc > i+1;

                if (!strcasecmp(c->argv[i]->ptr,"id") && moreargs) {
                    long tmp;

                    if (getRangeLongFromObjectOrReply(c, c->argv[i+1], 1, LONG_MAX, &tmp,
                                                      "client-id should be greater than 0") != C_OK)
                        return;
                    id = tmp;
                } else if (!strcasecmp(c->argv[i]->ptr,"type") && moreargs) {
                    type = getClientTypeByName(c->argv[i+1]->ptr);
                    if (type == -1) {
                        addReplyErrorFormat(c,"Unknown client type '%s'",
                            (char*) c->argv[i+1]->ptr);
                        return;
                    }
                } else if (!strcasecmp(c->argv[i]->ptr,"addr") && moreargs) {
                    addr = c->argv[i+1]->ptr;
                } else if (!strcasecmp(c->argv[i]->ptr,"laddr") && moreargs) {
                    laddr = c->argv[i+1]->ptr;
                } else if (!strcasecmp(c->argv[i]->ptr,"user") && moreargs) {
                    user = ACLGetUserByName(c->argv[i+1]->ptr,
                                            sdslen(c->argv[i+1]->ptr));
                    if (user == NULL) {
                        addReplyErrorFormat(c,"No such user '%s'",
                            (char*) c->argv[i+1]->ptr);
                        return;
                    }
                } else if (!strcasecmp(c->argv[i]->ptr,"skipme") && moreargs) {
                    if (!strcasecmp(c->argv[i+1]->ptr,"yes")) {
                        skipme = 1;
                    } else if (!strcasecmp(c->argv[i+1]->ptr,"no")) {
                        skipme = 0;
                    } else {
                        addReplyErrorObject(c,shared.syntaxerr);
                        return;
                    }
                } else {
                    addReplyErrorObject(c,shared.syntaxerr);
                    return;
                }
                i += 2;
            }
        } else {
            addReplyErrorObject(c,shared.syntaxerr);
            return;
        }

        /* Iterate clients killing all the matching clients. */
        listRewind(server.clients,&li);
        while ((ln = listNext(&li)) != NULL) {
            client *client = listNodeValue(ln);
            if (addr && strcmp(getClientPeerId(client),addr) != 0) continue;
            if (laddr && strcmp(getClientSockname(client),laddr) != 0) continue;
            if (type != -1 && getClientType(client) != type) continue;
            if (id != 0 && client->id != id) continue;
            if (user && client->user != user) continue;
            if (c == client && skipme) continue;

            /* Kill it. */
            if (c == client) {
                close_this_client = 1;
            } else {
                freeClient(client);
            }
            killed++;
        }

        /* Reply according to old/new format. */
        if (c->argc == 3) {
            if (killed == 0)
                addReplyError(c,"No such client");
            else
                addReply(c,shared.ok);
        } else {
            addReplyLongLong(c,killed);
        }

        /* If this client has to be closed, flag it as CLOSE_AFTER_REPLY
         * only after we queued the reply to its output buffers. */
        if (close_this_client) c->flags |= CLIENT_CLOSE_AFTER_REPLY;
    } else if (!strcasecmp(c->argv[1]->ptr,"unblock") && (c->argc == 3 ||
                                                          c->argc == 4))
    {
        /* CLIENT UNBLOCK <id> [timeout|error] */
        long long id;
        int unblock_error = 0;

        if (c->argc == 4) {
            if (!strcasecmp(c->argv[3]->ptr,"timeout")) {
                unblock_error = 0;
            } else if (!strcasecmp(c->argv[3]->ptr,"error")) {
                unblock_error = 1;
            } else {
                addReplyError(c,
                    "CLIENT UNBLOCK reason should be TIMEOUT or ERROR");
                return;
            }
        }
        if (getLongLongFromObjectOrReply(c,c->argv[2],&id,NULL)
            != C_OK) return;
        struct client *target = lookupClientByID(id);
        /* Note that we never try to unblock a client blocked on a module command, which
         * doesn't have a timeout callback (even in the case of UNBLOCK ERROR).
         * The reason is that we assume that if a command doesn't expect to be timedout,
         * it also doesn't expect to be unblocked by CLIENT UNBLOCK */
        if (target && target->flags & CLIENT_BLOCKED && moduleBlockedClientMayTimeout(target)) {
            if (unblock_error)
                addReplyError(target,
                    "-UNBLOCKED client unblocked via CLIENT UNBLOCK");
            else
                replyToBlockedClientTimedOut(target);
            unblockClient(target);
            updateStatsOnUnblock(target, 0, 0, 1);
            addReply(c,shared.cone);
        } else {
            addReply(c,shared.czero);
        }
    } else if (!strcasecmp(c->argv[1]->ptr,"setname") && c->argc == 3) {
        /* CLIENT SETNAME */
        if (clientSetNameOrReply(c,c->argv[2]) == C_OK)
            addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"getname") && c->argc == 2) {
        /* CLIENT GETNAME */
        if (c->name)
            addReplyBulk(c,c->name);
        else
            addReplyNull(c);
    } else if (!strcasecmp(c->argv[1]->ptr,"unpause") && c->argc == 2) {
        /* CLIENT UNPAUSE */
        unpauseClients(PAUSE_BY_CLIENT_COMMAND);
        addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"pause") && (c->argc == 3 ||
                                                        c->argc == 4))
    {
        /* CLIENT PAUSE TIMEOUT [WRITE|ALL] */
        mstime_t end;
        int type = CLIENT_PAUSE_ALL;
        if (c->argc == 4) {
            if (!strcasecmp(c->argv[3]->ptr,"write")) {
                type = CLIENT_PAUSE_WRITE;
            } else if (!strcasecmp(c->argv[3]->ptr,"all")) {
                type = CLIENT_PAUSE_ALL;
            } else {
                addReplyError(c,
                    "CLIENT PAUSE mode must be WRITE or ALL");  
                return;       
            }
        }

        if (getTimeoutFromObjectOrReply(c,c->argv[2],&end,
            UNIT_MILLISECONDS) != C_OK) return;
        pauseClients(PAUSE_BY_CLIENT_COMMAND, end, type);
        addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"tracking") && c->argc >= 3) {
        /* CLIENT TRACKING (on|off) [REDIRECT <id>] [BCAST] [PREFIX first]
         *                          [PREFIX second] [OPTIN] [OPTOUT] [NOLOOP]... */
        long long redir = 0;
        uint64_t options = 0;
        robj **prefix = NULL;
        size_t numprefix = 0;

        /* Parse the options. */
        for (int j = 3; j < c->argc; j++) {
            int moreargs = (c->argc-1) - j;

            if (!strcasecmp(c->argv[j]->ptr,"redirect") && moreargs) {
                j++;
                if (redir != 0) {
                    addReplyError(c,"A client can only redirect to a single "
                                    "other client");
                    zfree(prefix);
                    return;
                }

                if (getLongLongFromObjectOrReply(c,c->argv[j],&redir,NULL) !=
                    C_OK)
                {
                    zfree(prefix);
                    return;
                }
                /* We will require the client with the specified ID to exist
                 * right now, even if it is possible that it gets disconnected
                 * later. Still a valid sanity check. */
                if (lookupClientByID(redir) == NULL) {
                    addReplyError(c,"The client ID you want redirect to "
                                    "does not exist");
                    zfree(prefix);
                    return;
                }
            } else if (!strcasecmp(c->argv[j]->ptr,"bcast")) {
                options |= CLIENT_TRACKING_BCAST;
            } else if (!strcasecmp(c->argv[j]->ptr,"optin")) {
                options |= CLIENT_TRACKING_OPTIN;
            } else if (!strcasecmp(c->argv[j]->ptr,"optout")) {
                options |= CLIENT_TRACKING_OPTOUT;
            } else if (!strcasecmp(c->argv[j]->ptr,"noloop")) {
                options |= CLIENT_TRACKING_NOLOOP;
            } else if (!strcasecmp(c->argv[j]->ptr,"prefix") && moreargs) {
                j++;
                prefix = zrealloc(prefix,sizeof(robj*)*(numprefix+1));
                prefix[numprefix++] = c->argv[j];
            } else {
                zfree(prefix);
                addReplyErrorObject(c,shared.syntaxerr);
                return;
            }
        }

        /* Options are ok: enable or disable the tracking for this client. */
        if (!strcasecmp(c->argv[2]->ptr,"on")) {
            /* Before enabling tracking, make sure options are compatible
             * among each other and with the current state of the client. */
            if (!(options & CLIENT_TRACKING_BCAST) && numprefix) {
                addReplyError(c,
                    "PREFIX option requires BCAST mode to be enabled");
                zfree(prefix);
                return;
            }

            if (c->flags & CLIENT_TRACKING) {
                int oldbcast = !!(c->flags & CLIENT_TRACKING_BCAST);
                int newbcast = !!(options & CLIENT_TRACKING_BCAST);
                if (oldbcast != newbcast) {
                    addReplyError(c,
                    "You can't switch BCAST mode on/off before disabling "
                    "tracking for this client, and then re-enabling it with "
                    "a different mode.");
                    zfree(prefix);
                    return;
                }
            }

            if (options & CLIENT_TRACKING_BCAST &&
                options & (CLIENT_TRACKING_OPTIN|CLIENT_TRACKING_OPTOUT))
            {
                addReplyError(c,
                "OPTIN and OPTOUT are not compatible with BCAST");
                zfree(prefix);
                return;
            }

            if (options & CLIENT_TRACKING_OPTIN && options & CLIENT_TRACKING_OPTOUT)
            {
                addReplyError(c,
                "You can't specify both OPTIN mode and OPTOUT mode");
                zfree(prefix);
                return;
            }

            if ((options & CLIENT_TRACKING_OPTIN && c->flags & CLIENT_TRACKING_OPTOUT) ||
                (options & CLIENT_TRACKING_OPTOUT && c->flags & CLIENT_TRACKING_OPTIN))
            {
                addReplyError(c,
                "You can't switch OPTIN/OPTOUT mode before disabling "
                "tracking for this client, and then re-enabling it with "
                "a different mode.");
                zfree(prefix);
                return;
            }

            if (options & CLIENT_TRACKING_BCAST) {
                if (!checkPrefixCollisionsOrReply(c,prefix,numprefix)) {
                    zfree(prefix);
                    return;
                }
            }

            enableTracking(c,redir,options,prefix,numprefix);
        } else if (!strcasecmp(c->argv[2]->ptr,"off")) {
            disableTracking(c);
        } else {
            zfree(prefix);
            addReplyErrorObject(c,shared.syntaxerr);
            return;
        }
        zfree(prefix);
        addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"caching") && c->argc >= 3) {
        if (!(c->flags & CLIENT_TRACKING)) {
            addReplyError(c,"CLIENT CACHING can be called only when the "
                            "client is in tracking mode with OPTIN or "
                            "OPTOUT mode enabled");
            return;
        }

        char *opt = c->argv[2]->ptr;
        if (!strcasecmp(opt,"yes")) {
            if (c->flags & CLIENT_TRACKING_OPTIN) {
                c->flags |= CLIENT_TRACKING_CACHING;
            } else {
                addReplyError(c,"CLIENT CACHING YES is only valid when tracking is enabled in OPTIN mode.");
                return;
            }
        } else if (!strcasecmp(opt,"no")) {
            if (c->flags & CLIENT_TRACKING_OPTOUT) {
                c->flags |= CLIENT_TRACKING_CACHING;
            } else {
                addReplyError(c,"CLIENT CACHING NO is only valid when tracking is enabled in OPTOUT mode.");
                return;
            }
        } else {
            addReplyErrorObject(c,shared.syntaxerr);
            return;
        }

        /* Common reply for when we succeeded. */
        addReply(c,shared.ok);
    } else if (!strcasecmp(c->argv[1]->ptr,"getredir") && c->argc == 2) {
        /* CLIENT GETREDIR */
        if (c->flags & CLIENT_TRACKING) {
            addReplyLongLong(c,c->client_tracking_redirection);
        } else {
            addReplyLongLong(c,-1);
        }
    } else if (!strcasecmp(c->argv[1]->ptr,"trackinginfo") && c->argc == 2) {
        addReplyMapLen(c,3);

        /* Flags */
        addReplyBulkCString(c,"flags");
        void *arraylen_ptr = addReplyDeferredLen(c);
        int numflags = 0;
        addReplyBulkCString(c,c->flags & CLIENT_TRACKING ? "on" : "off");
        numflags++;
        if (c->flags & CLIENT_TRACKING_BCAST) {
            addReplyBulkCString(c,"bcast");
            numflags++;
        }
        if (c->flags & CLIENT_TRACKING_OPTIN) {
            addReplyBulkCString(c,"optin");
            numflags++;
            if (c->flags & CLIENT_TRACKING_CACHING) {
                addReplyBulkCString(c,"caching-yes");
                numflags++;        
            }
        }
        if (c->flags & CLIENT_TRACKING_OPTOUT) {
            addReplyBulkCString(c,"optout");
            numflags++;
            if (c->flags & CLIENT_TRACKING_CACHING) {
                addReplyBulkCString(c,"caching-no");
                numflags++;        
            }
        }
        if (c->flags & CLIENT_TRACKING_NOLOOP) {
            addReplyBulkCString(c,"noloop");
            numflags++;
        }
        if (c->flags & CLIENT_TRACKING_BROKEN_REDIR) {
            addReplyBulkCString(c,"broken_redirect");
            numflags++;
        }
        setDeferredSetLen(c,arraylen_ptr,numflags);

        /* Redirect */
        addReplyBulkCString(c,"redirect");
        if (c->flags & CLIENT_TRACKING) {
            addReplyLongLong(c,c->client_tracking_redirection);
        } else {
            addReplyLongLong(c,-1);
        }

        /* Prefixes */
        addReplyBulkCString(c,"prefixes");
        if (c->client_tracking_prefixes) {
            addReplyArrayLen(c,raxSize(c->client_tracking_prefixes));
            raxIterator ri;
            raxStart(&ri,c->client_tracking_prefixes);
            raxSeek(&ri,"^",NULL,0);
            while(raxNext(&ri)) {
                addReplyBulkCBuffer(c,ri.key,ri.key_len);
            }
            raxStop(&ri);
        } else {
            addReplyArrayLen(c,0);
        }
    } else {
        addReplySubcommandSyntaxError(c);
    }
}

/* HELLO [<protocol-version> [AUTH <user> <password>] [SETNAME <name>] ] */
void helloCommand(client *c) {
    long long ver = 0;
    int next_arg = 1;

    if (c->argc >= 2) {
        if (getLongLongFromObjectOrReply(c, c->argv[next_arg++], &ver,
            "Protocol version is not an integer or out of range") != C_OK) {
            return;
        }

        if (ver < 2 || ver > 3) {
            addReplyError(c,"-NOPROTO unsupported protocol version");
            return;
        }
    }

    for (int j = next_arg; j < c->argc; j++) {
        int moreargs = (c->argc-1) - j;
        const char *opt = c->argv[j]->ptr;
        if (!strcasecmp(opt,"AUTH") && moreargs >= 2) {
            redactClientCommandArgument(c, j+1);
            redactClientCommandArgument(c, j+2);
            if (ACLAuthenticateUser(c, c->argv[j+1], c->argv[j+2]) == C_ERR) {
                addReplyError(c,"-WRONGPASS invalid username-password pair or user is disabled.");
                return;
            }
            j += 2;
        } else if (!strcasecmp(opt,"SETNAME") && moreargs) {
            if (clientSetNameOrReply(c, c->argv[j+1]) == C_ERR) return;
            j++;
        } else {
            addReplyErrorFormat(c,"Syntax error in HELLO option '%s'",opt);
            return;
        }
    }

    /* At this point we need to be authenticated to continue. */
    if (!c->authenticated) {
        addReplyError(c,"-NOAUTH HELLO must be called with the client already "
                        "authenticated, otherwise the HELLO AUTH <user> <pass> "
                        "option can be used to authenticate the client and "
                        "select the RESP protocol version at the same time");
        return;
    }

    /* Let's switch to the specified RESP mode. */
    if (ver) c->resp = ver;
    addReplyMapLen(c,6 + !server.sentinel_mode);

    addReplyBulkCString(c,"server");
    addReplyBulkCString(c,"redis");

    addReplyBulkCString(c,"version");
    addReplyBulkCString(c,REDIS_VERSION);

    addReplyBulkCString(c,"proto");
    addReplyLongLong(c,c->resp);

    addReplyBulkCString(c,"id");
    addReplyLongLong(c,c->id);

    addReplyBulkCString(c,"mode");
    if (server.sentinel_mode) addReplyBulkCString(c,"sentinel");
    else if (server.cluster_enabled) addReplyBulkCString(c,"cluster");
    else addReplyBulkCString(c,"standalone");

    if (!server.sentinel_mode) {
        addReplyBulkCString(c,"role");
        addReplyBulkCString(c,server.masterhost ? "replica" : "master");
    }

    addReplyBulkCString(c,"modules");
    addReplyLoadedModules(c);
}

/* This callback is bound to POST and "Host:" command names. Those are not
 * really commands, but are used in security attacks in order to talk to
 * Redis instances via HTTP, with a technique called "cross protocol scripting"
 * which exploits the fact that services like Redis will discard invalid
 * HTTP headers and will process what follows.
 *
 * As a protection against this attack, Redis will terminate the connection
 * when a POST or "Host:" header is seen, and will log the event from
 * time to time (to avoid creating a DOS as a result of too many logs). */
void securityWarningCommand(client *c) {
    static time_t logged_time = 0;
    time_t now = time(NULL);

    if (llabs(now-logged_time) > 60) {
        serverLog(LL_WARNING,"Possible SECURITY ATTACK detected. It looks like somebody is sending POST or Host: commands to Redis. This is likely due to an attacker attempting to use Cross Protocol Scripting to compromise your Redis instance. Connection aborted.");
        logged_time = now;
    }
    freeClientAsync(c);
}

/* Keep track of the original command arguments so that we can generate
 * an accurate slowlog entry after the command has been executed. */
static void retainOriginalCommandVector(client *c) {
    /* We already rewrote this command, so don't rewrite it again */
    if (c->original_argv) return;
    c->original_argc = c->argc;
    c->original_argv = zmalloc(sizeof(robj*)*(c->argc));
    for (int j = 0; j < c->argc; j++) {
        c->original_argv[j] = c->argv[j];
        incrRefCount(c->argv[j]);
    }
}

/* Redact a given argument to prevent it from being shown
 * in the slowlog. This information is stored in the
 * original_argv array. */
void redactClientCommandArgument(client *c, int argc) {
    retainOriginalCommandVector(c);
    if (c->original_argv[argc] == shared.redacted) {
        /* This argument has already been redacted */
        return;
    }
    decrRefCount(c->original_argv[argc]);
    c->original_argv[argc] = shared.redacted;
}

/* Rewrite the command vector of the client. All the new objects ref count
 * is incremented. The old command vector is freed, and the old objects
 * ref count is decremented. */
void rewriteClientCommandVector(client *c, int argc, ...) {
    va_list ap;
    int j;
    robj **argv; /* The new argument vector */

    argv = zmalloc(sizeof(robj*)*argc);
    va_start(ap,argc);
    for (j = 0; j < argc; j++) {
        robj *a;

        a = va_arg(ap, robj*);
        argv[j] = a;
        incrRefCount(a);
    }
    replaceClientCommandVector(c, argc, argv);
    va_end(ap);
}

/* Completely replace the client command vector with the provided one. */
void replaceClientCommandVector(client *c, int argc, robj **argv) {
    int j;
    retainOriginalCommandVector(c);
    freeClientArgv(c);
    c->argv = argv;
    c->argc = argc;
    c->argv_len_sum = 0;
    for (j = 0; j < c->argc; j++)
        if (c->argv[j])
            c->argv_len_sum += getStringObjectLen(c->argv[j]);
    c->cmd = lookupCommandOrOriginal(c->argv,c->argc);
    serverAssertWithInfo(c,NULL,c->cmd != NULL);
}

/* Rewrite a single item in the command vector.
 * The new val ref count is incremented, and the old decremented.
 *
 * It is possible to specify an argument over the current size of the
 * argument vector: in this case the array of objects gets reallocated
 * and c->argc set to the max value. However it's up to the caller to
 *
 * 1. Make sure there are no "holes" and all the arguments are set.
 * 2. If the original argument vector was longer than the one we
 *    want to end with, it's up to the caller to set c->argc and
 *    free the no longer used objects on c->argv. */
void rewriteClientCommandArgument(client *c, int i, robj *newval) {
    robj *oldval;
    retainOriginalCommandVector(c);

    /* We need to handle both extending beyond argc (just update it and
     * initialize the new element) or beyond argv_len (realloc is needed).
     */
    if (i >= c->argc) {
        if (i >= c->argv_len) {
            c->argv = zrealloc(c->argv,sizeof(robj*)*(i+1));
            c->argv_len = i+1;
        }
        c->argc = i+1;
        c->argv[i] = NULL;
    }
    oldval = c->argv[i];
    if (oldval) c->argv_len_sum -= getStringObjectLen(oldval);
    if (newval) c->argv_len_sum += getStringObjectLen(newval);
    c->argv[i] = newval;
    incrRefCount(newval);
    if (oldval) decrRefCount(oldval);

    /* If this is the command name make sure to fix c->cmd. */
    if (i == 0) {
        c->cmd = lookupCommandOrOriginal(c->argv,c->argc);
        serverAssertWithInfo(c,NULL,c->cmd != NULL);
    }
}

/* This function returns the number of bytes that Redis is
 * using to store the reply still not read by the client.
 *
 * Note: this function is very fast so can be called as many time as
 * the caller wishes. The main usage of this function currently is
 * enforcing the client output length limits. */
size_t getClientOutputBufferMemoryUsage(client *c) {
    if (getClientType(c) == CLIENT_TYPE_SLAVE) {
        size_t repl_buf_size = 0;
        size_t repl_node_num = 0;
        size_t repl_node_size = sizeof(listNode) + sizeof(replBufBlock);
        if (c->ref_repl_buf_node) {
            replBufBlock *last = listNodeValue(listLast(server.repl_buffer_blocks));
            replBufBlock *cur = listNodeValue(c->ref_repl_buf_node);
            repl_buf_size = last->repl_offset + last->size - cur->repl_offset;
            repl_node_num = last->id - cur->id + 1;
        }
        return repl_buf_size + (repl_node_size*repl_node_num);
    } else { 
        size_t list_item_size = sizeof(listNode) + sizeof(clientReplyBlock);
        return c->reply_bytes + (list_item_size*listLength(c->reply));
    }
}

/* Returns the total client's memory usage.
 * Optionally, if output_buffer_mem_usage is not NULL, it fills it with
 * the client output buffer memory usage portion of the total. */
size_t getClientMemoryUsage(client *c, size_t *output_buffer_mem_usage) {
    size_t mem = getClientOutputBufferMemoryUsage(c);
    if (output_buffer_mem_usage != NULL)
        *output_buffer_mem_usage = mem;
    mem += sdsZmallocSize(c->querybuf);
    mem += zmalloc_size(c);
    mem += c->buf_usable_size;
    /* For efficiency (less work keeping track of the argv memory), it doesn't include the used memory
     * i.e. unused sds space and internal fragmentation, just the string length. but this is enough to
     * spot problematic clients. */
    mem += c->argv_len_sum + sizeof(robj*)*c->argc;
    mem += multiStateMemOverhead(c);

    /* Add memory overhead of pubsub channels and patterns. Note: this is just the overhead of the robj pointers
     * to the strings themselves because they aren't stored per client. */
    mem += pubsubMemOverhead(c);

    /* Add memory overhead of the tracking prefixes, this is an underestimation so we don't need to traverse the entire rax */
    if (c->client_tracking_prefixes)
        mem += c->client_tracking_prefixes->numnodes * (sizeof(raxNode) * sizeof(raxNode*));

    return mem;
}

/* Get the class of a client, used in order to enforce limits to different
 * classes of clients.
 *
 * The function will return one of the following:
 * CLIENT_TYPE_NORMAL -> Normal client
 * CLIENT_TYPE_SLAVE  -> Slave
 * CLIENT_TYPE_PUBSUB -> Client subscribed to Pub/Sub channels
 * CLIENT_TYPE_MASTER -> The client representing our replication master.
 */
int getClientType(client *c) {
    if (c->flags & CLIENT_MASTER) return CLIENT_TYPE_MASTER;
    /* Even though MONITOR clients are marked as replicas, we
     * want the expose them as normal clients. */
    if ((c->flags & CLIENT_SLAVE) && !(c->flags & CLIENT_MONITOR))
        return CLIENT_TYPE_SLAVE;
    if (c->flags & CLIENT_PUBSUB) return CLIENT_TYPE_PUBSUB;
    return CLIENT_TYPE_NORMAL;
}

int getClientTypeByName(char *name) {
    if (!strcasecmp(name,"normal")) return CLIENT_TYPE_NORMAL;
    else if (!strcasecmp(name,"slave")) return CLIENT_TYPE_SLAVE;
    else if (!strcasecmp(name,"replica")) return CLIENT_TYPE_SLAVE;
    else if (!strcasecmp(name,"pubsub")) return CLIENT_TYPE_PUBSUB;
    else if (!strcasecmp(name,"master")) return CLIENT_TYPE_MASTER;
    else return -1;
}

char *getClientTypeName(int class) {
    switch(class) {
    case CLIENT_TYPE_NORMAL: return "normal";
    case CLIENT_TYPE_SLAVE:  return "slave";
    case CLIENT_TYPE_PUBSUB: return "pubsub";
    case CLIENT_TYPE_MASTER: return "master";
    default:                       return NULL;
    }
}

/* The function checks if the client reached output buffer soft or hard
 * limit, and also update the state needed to check the soft limit as
 * a side effect.
 *
 * Return value: non-zero if the client reached the soft or the hard limit.
 *               Otherwise zero is returned. */
int checkClientOutputBufferLimits(client *c) {
    int soft = 0, hard = 0, class;
    unsigned long used_mem = getClientOutputBufferMemoryUsage(c);

    class = getClientType(c);
    /* For the purpose of output buffer limiting, masters are handled
     * like normal clients. */
    if (class == CLIENT_TYPE_MASTER) class = CLIENT_TYPE_NORMAL;

    /* Note that it doesn't make sense to set the replica clients output buffer
     * limit lower than the repl-backlog-size config (partial sync will succeed
     * and then replica will get disconnected).
     * Such a configuration is ignored (the size of repl-backlog-size will be used).
     * This doesn't have memory consumption implications since the replica client
     * will share the backlog buffers memory. */
    size_t hard_limit_bytes = server.client_obuf_limits[class].hard_limit_bytes;
    if (class == CLIENT_TYPE_SLAVE && hard_limit_bytes &&
        (long long)hard_limit_bytes < server.repl_backlog_size)
        hard_limit_bytes = server.repl_backlog_size;
    if (server.client_obuf_limits[class].hard_limit_bytes &&
        used_mem >= hard_limit_bytes)
        hard = 1;
    if (server.client_obuf_limits[class].soft_limit_bytes &&
        used_mem >= server.client_obuf_limits[class].soft_limit_bytes)
        soft = 1;

    /* We need to check if the soft limit is reached continuously for the
     * specified amount of seconds. */
    if (soft) {
        if (c->obuf_soft_limit_reached_time == 0) {
            c->obuf_soft_limit_reached_time = server.unixtime;
            soft = 0; /* First time we see the soft limit reached */
        } else {
            time_t elapsed = server.unixtime - c->obuf_soft_limit_reached_time;

            if (elapsed <=
                server.client_obuf_limits[class].soft_limit_seconds) {
                soft = 0; /* The client still did not reached the max number of
                             seconds for the soft limit to be considered
                             reached. */
            }
        }
    } else {
        c->obuf_soft_limit_reached_time = 0;
    }
    return soft || hard;
}

/* Asynchronously close a client if soft or hard limit is reached on the
 * output buffer size. The caller can check if the client will be closed
 * checking if the client CLIENT_CLOSE_ASAP flag is set.
 *
 * Note: we need to close the client asynchronously because this function is
 * called from contexts where the client can't be freed safely, i.e. from the
 * lower level functions pushing data inside the client output buffers.
 * When `async` is set to 0, we close the client immediately, this is
 * useful when called from cron.
 *
 * Returns 1 if client was (flagged) closed. */
int closeClientOnOutputBufferLimitReached(client *c, int async) {
    if (!c->conn) return 0; /* It is unsafe to free fake clients. */
    serverAssert(c->reply_bytes < SIZE_MAX-(1024*64));
    /* Note that c->reply_bytes is irrelevant for replica clients
     * (they use the global repl buffers). */
    if ((c->reply_bytes == 0 && getClientType(c) != CLIENT_TYPE_SLAVE) ||
        c->flags & CLIENT_CLOSE_ASAP) return 0;
    if (checkClientOutputBufferLimits(c)) {
        sds client = catClientInfoString(sdsempty(),c);

        if (async) {
            freeClientAsync(c);
            serverLog(LL_WARNING,
                      "Client %s scheduled to be closed ASAP for overcoming of output buffer limits.",
                      client);
        } else {
            freeClient(c);
            serverLog(LL_WARNING,
                      "Client %s closed for overcoming of output buffer limits.",
                      client);
        }
        sdsfree(client);
        return  1;
    }
    return 0;
}

/* Helper function used by performEvictions() in order to flush slaves
 * output buffers without returning control to the event loop.
 * This is also called by SHUTDOWN for a best-effort attempt to send
 * slaves the latest writes. */
void flushSlavesOutputBuffers(void) {
    listIter li;
    listNode *ln;

    listRewind(server.slaves,&li);
    while((ln = listNext(&li))) {
        client *slave = listNodeValue(ln);
        int can_receive_writes = connHasWriteHandler(slave->conn) ||
                                 (slave->flags & CLIENT_PENDING_WRITE);

        /* We don't want to send the pending data to the replica in a few
         * cases:
         *
         * 1. For some reason there is neither the write handler installed
         *    nor the client is flagged as to have pending writes: for some
         *    reason this replica may not be set to receive data. This is
         *    just for the sake of defensive programming.
         *
         * 2. The put_online_on_ack flag is true. To know why we don't want
         *    to send data to the replica in this case, please grep for the
         *    flag for this flag.
         *
         * 3. Obviously if the slave is not ONLINE.
         */
        if (slave->replstate == SLAVE_STATE_ONLINE &&
            can_receive_writes &&
            !slave->repl_start_cmd_stream_on_ack &&
            clientHasPendingReplies(slave))
        {
            writeToClient(slave,0);
        }
    }
}

/* Compute current most restrictive pause type and its end time, aggregated for
 * all pause purposes. */
static void updateClientPauseTypeAndEndTime(void) {
    pause_type old_type = server.client_pause_type;
    pause_type type = CLIENT_PAUSE_OFF;
    mstime_t end = 0;
    for (int i = 0; i < NUM_PAUSE_PURPOSES; i++) {
        pause_event *p = server.client_pause_per_purpose[i];
        if (p == NULL) {
            /* Nothing to do. */
        } else if (p->end < server.mstime) {
            /* This one expired. */
            zfree(p);
            server.client_pause_per_purpose[i] = NULL;
        } else if (p->type > type) {
            /* This type is the most restrictive so far. */
            type = p->type;
        }
    }

    /* Find the furthest end time among the pause purposes of the most
     * restrictive type */
    for (int i = 0; i < NUM_PAUSE_PURPOSES; i++) {
        pause_event *p = server.client_pause_per_purpose[i];
        if (p != NULL && p->type == type && p->end > end) end = p->end;
    }
    server.client_pause_type = type;
    server.client_pause_end_time = end;

    /* If the pause type is less restrictive than before, we unblock all clients
     * so they are reprocessed (may get re-paused). */
    if (type < old_type) {
        unblockPostponedClients();
    }
}

/* Unblock all paused clients (ones that where blocked by BLOCKED_POSTPONE (possibly in processCommand).
 * This means they'll get re-processed in beforeSleep, and may get paused again if needed. */
void unblockPostponedClients() {
    listNode *ln;
    listIter li;
    listRewind(server.postponed_clients, &li);
    while ((ln = listNext(&li)) != NULL) {
        client *c = listNodeValue(ln);
        unblockClient(c);
    }
}

/* Pause clients up to the specified unixtime (in ms) for a given type of
 * commands.
 *
 * A main use case of this function is to allow pausing replication traffic
 * so that a failover without data loss to occur. Replicas will continue to receive
 * traffic to facilitate this functionality.
 * 
 * This function is also internally used by Redis Cluster for the manual
 * failover procedure implemented by CLUSTER FAILOVER.
 *
 * The function always succeed, even if there is already a pause in progress.
 * In such a case, the duration is set to the maximum and new end time and the
 * type is set to the more restrictive type of pause. */
void pauseClients(pause_purpose purpose, mstime_t end, pause_type type) {
    /* Manage pause type and end time per pause purpose. */
    if (server.client_pause_per_purpose[purpose] == NULL) {
        server.client_pause_per_purpose[purpose] = zmalloc(sizeof(pause_event));
        server.client_pause_per_purpose[purpose]->type = type;
        server.client_pause_per_purpose[purpose]->end = end;
    } else {
        pause_event *p = server.client_pause_per_purpose[purpose];
        p->type = max(p->type, type);
        p->end = max(p->end, end);
    }
    updateClientPauseTypeAndEndTime();

    /* We allow write commands that were queued
     * up before and after to execute. We need
     * to track this state so that we don't assert
     * in propagateNow(). */
    if (server.in_exec) {
        server.client_pause_in_transaction = 1;
    }
}

/* Unpause clients and queue them for reprocessing. */
void unpauseClients(pause_purpose purpose) {
    if (server.client_pause_per_purpose[purpose] == NULL) return;
    zfree(server.client_pause_per_purpose[purpose]);
    server.client_pause_per_purpose[purpose] = NULL;
    updateClientPauseTypeAndEndTime();
}

/* Returns true if clients are paused and false otherwise. */ 
int areClientsPaused(void) {
    return server.client_pause_type != CLIENT_PAUSE_OFF;
}

/* Checks if the current client pause has elapsed and unpause clients
 * if it has. Also returns true if clients are now paused and false 
 * otherwise. */
int checkClientPauseTimeoutAndReturnIfPaused(void) {
    if (!areClientsPaused())
        return 0;
    if (server.client_pause_end_time < server.mstime) {
        updateClientPauseTypeAndEndTime();
    }
    return areClientsPaused();
}

/* This function is called by Redis in order to process a few events from
 * time to time while blocked into some not interruptible operation.
 * This allows to reply to clients with the -LOADING error while loading the
 * data set at startup or after a full resynchronization with the master
 * and so forth.
 *
 * It calls the event loop in order to process a few events. Specifically we
 * try to call the event loop 4 times as long as we receive acknowledge that
 * some event was processed, in order to go forward with the accept, read,
 * write, close sequence needed to serve a client.
 *
 * The function returns the total number of events processed. */
void processEventsWhileBlocked(void) {
    int iterations = 4; /* See the function top-comment. */

    /* Update our cached time since it is used to create and update the last
     * interaction time with clients and for other important things. */
    updateCachedTime(0);

    /* Note: when we are processing events while blocked (for instance during
     * busy Lua scripts), we set a global flag. When such flag is set, we
     * avoid handling the read part of clients using threaded I/O.
     * See https://github.com/redis/redis/issues/6988 for more info.
     * Note that there could be cases of nested calls to this function,
     * specifically on a busy script during async_loading rdb, and scripts
     * that came from AOF. */
    ProcessingEventsWhileBlocked++;
    while (iterations--) {
        long long startval = server.events_processed_while_blocked;
        long long ae_events = aeProcessEvents(server.el,
            AE_FILE_EVENTS|AE_DONT_WAIT|
            AE_CALL_BEFORE_SLEEP|AE_CALL_AFTER_SLEEP);
        /* Note that server.events_processed_while_blocked will also get
         * incremented by callbacks called by the event loop handlers. */
        server.events_processed_while_blocked += ae_events;
        long long events = server.events_processed_while_blocked - startval;
        if (!events) break;
    }

    whileBlockedCron();

    ProcessingEventsWhileBlocked--;
    serverAssert(ProcessingEventsWhileBlocked >= 0);
}

/* ==========================================================================
 * Threaded I/O
 * ========================================================================== */

#define IO_THREADS_MAX_NUM 128
#ifndef CACHE_LINE_SIZE
#if defined(__aarch64__) && defined(__APPLE__)
#define CACHE_LINE_SIZE 128
#else
#define CACHE_LINE_SIZE 64
#endif
#endif

typedef struct __attribute__((aligned(CACHE_LINE_SIZE))) threads_pending {
    redisAtomic unsigned long value;
} threads_pending;

pthread_t io_threads[IO_THREADS_MAX_NUM];
pthread_mutex_t io_threads_mutex[IO_THREADS_MAX_NUM];
threads_pending io_threads_pending[IO_THREADS_MAX_NUM];
int io_threads_op;      /* IO_THREADS_OP_IDLE, IO_THREADS_OP_READ or IO_THREADS_OP_WRITE. */ // TODO: should access to this be atomic??!

/* This is the list of clients each thread will serve when threaded I/O is
 * used. We spawn io_threads_num-1 threads, since one is the main thread
 * itself. */
list *io_threads_list[IO_THREADS_MAX_NUM];

static inline unsigned long getIOPendingCount(int i) {
    unsigned long count = 0;
    atomicGetWithSync(io_threads_pending[i].value, count);
    return count;
}

static inline void setIOPendingCount(int i, unsigned long count) {
    atomicSetWithSync(io_threads_pending[i].value, count);
}

void *IOThreadMain(void *myid) {
    /* The ID is the thread number (from 0 to server.iothreads_num-1), and is
     * used by the thread to just manipulate a single sub-array of clients. */
    long id = (unsigned long)myid;
    char thdname[16];

    snprintf(thdname, sizeof(thdname), "io_thd_%ld", id);
    redis_set_thread_title(thdname);
    redisSetCpuAffinity(server.server_cpulist);
    makeThreadKillable();

    while(1) {
        /* Wait for start */
        for (int j = 0; j < 1000000; j++) {
            if (getIOPendingCount(id) != 0) break;
        }

        /* Give the main thread a chance to stop this thread. */
        if (getIOPendingCount(id) == 0) {
            pthread_mutex_lock(&io_threads_mutex[id]);
            pthread_mutex_unlock(&io_threads_mutex[id]);
            continue;
        }

        serverAssert(getIOPendingCount(id) != 0);

        /* Process: note that the main thread will never touch our list
         * before we drop the pending count to 0. */
        listIter li;
        listNode *ln;
        listRewind(io_threads_list[id],&li);
        while((ln = listNext(&li))) {
            client *c = listNodeValue(ln);
            if (io_threads_op == IO_THREADS_OP_WRITE) {
                writeToClient(c,0);
            } else if (io_threads_op == IO_THREADS_OP_READ) {
                readQueryFromClient(c->conn);
            } else {
                serverPanic("io_threads_op value is unknown");
            }
        }
        listEmpty(io_threads_list[id]);
        setIOPendingCount(id, 0);
    }
}

/* Initialize the data structures needed for threaded I/O. */
void initThreadedIO(void) {
    server.io_threads_active = 0; /* We start with threads not active. */

    /* Indicate that io-threads are currently idle */
    io_threads_op = IO_THREADS_OP_IDLE;

    /* Don't spawn any thread if the user selected a single thread:
     * we'll handle I/O directly from the main thread. */
    if (server.io_threads_num == 1) return;

    if (server.io_threads_num > IO_THREADS_MAX_NUM) {
        serverLog(LL_WARNING,"Fatal: too many I/O threads configured. "
                             "The maximum number is %d.", IO_THREADS_MAX_NUM);
        exit(1);
    }

    /* Spawn and initialize the I/O threads. */
    for (int i = 0; i < server.io_threads_num; i++) {
        /* Things we do for all the threads including the main thread. */
        io_threads_list[i] = listCreate();
        if (i == 0) continue; /* Thread 0 is the main thread. */

        /* Things we do only for the additional threads. */
        pthread_t tid;
        pthread_mutex_init(&io_threads_mutex[i],NULL);
        setIOPendingCount(i, 0);
        pthread_mutex_lock(&io_threads_mutex[i]); /* Thread will be stopped. */
        if (pthread_create(&tid,NULL,IOThreadMain,(void*)(long)i) != 0) {
            serverLog(LL_WARNING,"Fatal: Can't initialize IO thread.");
            exit(1);
        }
        io_threads[i] = tid;
    }
}

void killIOThreads(void) {
    int err, j;
    for (j = 0; j < server.io_threads_num; j++) {
        if (io_threads[j] == pthread_self()) continue;
        if (io_threads[j] && pthread_cancel(io_threads[j]) == 0) {
            if ((err = pthread_join(io_threads[j],NULL)) != 0) {
                serverLog(LL_WARNING,
                    "IO thread(tid:%lu) can not be joined: %s",
                        (unsigned long)io_threads[j], strerror(err));
            } else {
                serverLog(LL_WARNING,
                    "IO thread(tid:%lu) terminated",(unsigned long)io_threads[j]);
            }
        }
    }
}

void startThreadedIO(void) {
    serverAssert(server.io_threads_active == 0);
    for (int j = 1; j < server.io_threads_num; j++)
        pthread_mutex_unlock(&io_threads_mutex[j]);
    server.io_threads_active = 1;
}

void stopThreadedIO(void) {
    /* We may have still clients with pending reads when this function
     * is called: handle them before stopping the threads. */
    handleClientsWithPendingReadsUsingThreads();
    serverAssert(server.io_threads_active == 1);
    for (int j = 1; j < server.io_threads_num; j++)
        pthread_mutex_lock(&io_threads_mutex[j]);
    server.io_threads_active = 0;
}

/* This function checks if there are not enough pending clients to justify
 * taking the I/O threads active: in that case I/O threads are stopped if
 * currently active. We track the pending writes as a measure of clients
 * we need to handle in parallel, however the I/O threading is disabled
 * globally for reads as well if we have too little pending clients.
 *
 * The function returns 0 if the I/O threading should be used because there
 * are enough active threads, otherwise 1 is returned and the I/O threads
 * could be possibly stopped (if already active) as a side effect. */
int stopThreadedIOIfNeeded(void) {
    int pending = listLength(server.clients_pending_write);

    /* Return ASAP if IO threads are disabled (single threaded mode). */
    if (server.io_threads_num == 1) return 1;

    if (pending < (server.io_threads_num*2)) {
        if (server.io_threads_active) stopThreadedIO();
        return 1;
    } else {
        return 0;
    }
}

/* This function achieves thread safety using a fan-out -> fan-in paradigm:
 * Fan out: The main thread fans out work to the io-threads which block until
 * setIOPendingCount() is called with a value larger than 0 by the main thread.
 * Fan in: The main thread waits until getIOPendingCount() returns 0. Then
 * it can safely perform post-processing and return to normal synchronous
 * work. */
int handleClientsWithPendingWritesUsingThreads(void) {
    int processed = listLength(server.clients_pending_write);
    if (processed == 0) return 0; /* Return ASAP if there are no clients. */

    /* If I/O threads are disabled or we have few clients to serve, don't
     * use I/O threads, but the boring synchronous code. */
    if (server.io_threads_num == 1 || stopThreadedIOIfNeeded()) {
        return handleClientsWithPendingWrites();
    }

    /* Start threads if needed. */
    if (!server.io_threads_active) startThreadedIO();

    /* Distribute the clients across N different lists. */
    listIter li;
    listNode *ln;
    listRewind(server.clients_pending_write,&li);
    int item_id = 0;
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
        c->flags &= ~CLIENT_PENDING_WRITE;

        /* Remove clients from the list of pending writes since
         * they are going to be closed ASAP. */
        if (c->flags & CLIENT_CLOSE_ASAP) {
            listUnlinkNode(server.clients_pending_write, ln);
            continue;
        }

        /* Since all replicas and replication backlog use global replication
         * buffer, to guarantee data accessing thread safe, we must put all
         * replicas client into io_threads_list[0] i.e. main thread handles
         * sending the output buffer of all replicas. */
        if (getClientType(c) == CLIENT_TYPE_SLAVE) {
            listAddNodeTail(io_threads_list[0],c);
            continue;
        }

        int target_id = item_id % server.io_threads_num;
        listAddNodeTail(io_threads_list[target_id],c);
        item_id++;
    }

    /* Give the start condition to the waiting threads, by setting the
     * start condition atomic var. */
    io_threads_op = IO_THREADS_OP_WRITE;
    for (int j = 1; j < server.io_threads_num; j++) {
        int count = listLength(io_threads_list[j]);
        setIOPendingCount(j, count);
    }

    /* Also use the main thread to process a slice of clients. */
    listRewind(io_threads_list[0],&li);
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
        writeToClient(c,0);
    }
    listEmpty(io_threads_list[0]);

    /* Wait for all the other threads to end their work. */
    while(1) {
        unsigned long pending = 0;
        for (int j = 1; j < server.io_threads_num; j++)
            pending += getIOPendingCount(j);
        if (pending == 0) break;
    }

    io_threads_op = IO_THREADS_OP_IDLE;

    /* Run the list of clients again to install the write handler where
     * needed. */
    listRewind(server.clients_pending_write,&li);
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);

        /* Update the client in the mem usage after we're done processing it in the io-threads */
        updateClientMemUsage(c);

        /* Install the write handler if there are pending writes in some
         * of the clients. */
        if (clientHasPendingReplies(c)) {
            installClientWriteHandler(c);
        }
    }
    while(listLength(server.clients_pending_write) > 0) {
        listUnlinkNode(server.clients_pending_write, server.clients_pending_write->head);
    }

    /* Update processed count on server */
    server.stat_io_writes_processed += processed;

    return processed;
}

/* Return 1 if we want to handle the client read later using threaded I/O.
 * This is called by the readable handler of the event loop.
 * As a side effect of calling this function the client is put in the
 * pending read clients and flagged as such. */
int postponeClientRead(client *c) {
    if (server.io_threads_active &&
        server.io_threads_do_reads &&
        !ProcessingEventsWhileBlocked &&
        !(c->flags & (CLIENT_MASTER|CLIENT_SLAVE|CLIENT_BLOCKED)) &&
        io_threads_op == IO_THREADS_OP_IDLE)
    {
        listAddNodeHead(server.clients_pending_read,c);
        c->pending_read_list_node = listFirst(server.clients_pending_read);
        return 1;
    } else {
        return 0;
    }
}

/* When threaded I/O is also enabled for the reading + parsing side, the
 * readable handler will just put normal clients into a queue of clients to
 * process (instead of serving them synchronously). This function runs
 * the queue using the I/O threads, and process them in order to accumulate
 * the reads in the buffers, and also parse the first command available
 * rendering it in the client structures.
 * This function achieves thread safety using a fan-out -> fan-in paradigm:
 * Fan out: The main thread fans out work to the io-threads which block until
 * setIOPendingCount() is called with a value larger than 0 by the main thread.
 * Fan in: The main thread waits until getIOPendingCount() returns 0. Then
 * it can safely perform post-processing and return to normal synchronous
 * work. */
int handleClientsWithPendingReadsUsingThreads(void) {
    if (!server.io_threads_active || !server.io_threads_do_reads) return 0;
    int processed = listLength(server.clients_pending_read);
    if (processed == 0) return 0;

    /* Distribute the clients across N different lists. */
    listIter li;
    listNode *ln;
    listRewind(server.clients_pending_read,&li);
    int item_id = 0;
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
        int target_id = item_id % server.io_threads_num;
        listAddNodeTail(io_threads_list[target_id],c);
        item_id++;
    }

    /* Give the start condition to the waiting threads, by setting the
     * start condition atomic var. */
    io_threads_op = IO_THREADS_OP_READ;
    for (int j = 1; j < server.io_threads_num; j++) {
        int count = listLength(io_threads_list[j]);
        setIOPendingCount(j, count);
    }

    /* Also use the main thread to process a slice of clients. */
    listRewind(io_threads_list[0],&li);
    while((ln = listNext(&li))) {
        client *c = listNodeValue(ln);
        readQueryFromClient(c->conn);
    }
    listEmpty(io_threads_list[0]);

    /* Wait for all the other threads to end their work. */
    while(1) {
        unsigned long pending = 0;
        for (int j = 1; j < server.io_threads_num; j++)
            pending += getIOPendingCount(j);
        if (pending == 0) break;
    }

    io_threads_op = IO_THREADS_OP_IDLE;

    /* Run the list of clients again to process the new buffers. */
    while(listLength(server.clients_pending_read)) {
        ln = listFirst(server.clients_pending_read);
        client *c = listNodeValue(ln);
        listDelNode(server.clients_pending_read,ln);
        c->pending_read_list_node = NULL;

        serverAssert(!(c->flags & CLIENT_BLOCKED));

        if (beforeNextClient(c) == C_ERR) {
            /* If the client is no longer valid, we avoid
             * processing the client later. So we just go
             * to the next. */
            continue;
        }

        /* Once io-threads are idle we can update the client in the mem usage */
        updateClientMemUsage(c);

        if (processPendingCommandAndInputBuffer(c) == C_ERR) {
            /* If the client is no longer valid, we avoid
             * processing the client later. So we just go
             * to the next. */
            continue;
        }

        /* We may have pending replies if a thread readQueryFromClient() produced
         * replies and did not put the client in pending write queue (it can't).
         */
        if (!(c->flags & CLIENT_PENDING_WRITE) && clientHasPendingReplies(c))
            putClientInPendingWriteQueue(c);
    }

    /* Update processed count on server */
    server.stat_io_reads_processed += processed;

    return processed;
}

/* Returns the actual client eviction limit based on current configuration or
 * 0 if no limit. */
size_t getClientEvictionLimit(void) {
    size_t maxmemory_clients_actual = SIZE_MAX;

    /* Handle percentage of maxmemory*/
    if (server.maxmemory_clients < 0 && server.maxmemory > 0) {
        unsigned long long maxmemory_clients_bytes = (unsigned long long)((double)server.maxmemory * -(double) server.maxmemory_clients / 100);
        if (maxmemory_clients_bytes <= SIZE_MAX)
            maxmemory_clients_actual = maxmemory_clients_bytes;
    }
    else if (server.maxmemory_clients > 0)
        maxmemory_clients_actual = server.maxmemory_clients;
    else
        return 0;

    /* Don't allow a too small maxmemory-clients to avoid cases where we can't communicate
     * at all with the server because of bad configuration */
    if (maxmemory_clients_actual < 1024*128)
        maxmemory_clients_actual = 1024*128;

    return maxmemory_clients_actual;
}

void evictClients(void) {
    /* Start eviction from topmost bucket (largest clients) */
    int curr_bucket = CLIENT_MEM_USAGE_BUCKETS-1;
    listIter bucket_iter;
    listRewind(server.client_mem_usage_buckets[curr_bucket].clients, &bucket_iter);
    size_t client_eviction_limit = getClientEvictionLimit();
    if (client_eviction_limit == 0)
        return;
    while (server.stat_clients_type_memory[CLIENT_TYPE_NORMAL] +
           server.stat_clients_type_memory[CLIENT_TYPE_PUBSUB] >= client_eviction_limit) {
        listNode *ln = listNext(&bucket_iter);
        if (ln) {
            client *c = ln->value;
            sds ci = catClientInfoString(sdsempty(),c);
            serverLog(LL_NOTICE, "Evicting client: %s", ci);
            freeClient(c);
            sdsfree(ci);
            server.stat_evictedclients++;
        } else {
            curr_bucket--;
            if (curr_bucket < 0) {
                serverLog(LL_WARNING, "Over client maxmemory after evicting all evictable clients");
                break;
            }
            listRewind(server.client_mem_usage_buckets[curr_bucket].clients, &bucket_iter);
        }
    }
}
