Commit d0b2a9b2 authored by antirez's avatar antirez
Browse files

sdsMakeRoomFor() exposed as public API. sdsIncrLen() added. Both the changes...

sdsMakeRoomFor() exposed as public API. sdsIncrLen() added. Both the changes make it possible to copy stuff from a system call to an sds buffer without the need of an additional buffer and copying overhead.
parent 35267245
......@@ -40,6 +40,7 @@
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include "sds.h"
#include "zmalloc.h"
......@@ -107,7 +108,7 @@ void sdsclear(sds s) {
*
* Note: this does not change the *size* of the sds string as returned
* by sdslen(), but only the free buffer space we have. */
static sds sdsMakeRoomFor(sds s, size_t addlen) {
sds sdsMakeRoomFor(sds s, size_t addlen) {
struct sdshdr *sh, *newsh;
size_t free = sdsavail(s);
size_t len, newlen;
......@@ -127,6 +128,37 @@ static sds sdsMakeRoomFor(sds s, size_t addlen) {
return newsh->buf;
}
/* Increment the sds length and decrements the left free space at the
* end of the string accordingly to 'incr'. Also set the null term
* in the new end of the string.
*
* This function is used in order to fix the string length after the
* user calls sdsMakeRoomFor(), writes something after the end of
* the current string, and finally needs to set the new length.
*
* Note: it is possible to use a negative increment in order to
* right-trim the string.
*
* Using sdsIncrLen() and sdsMakeRoomFor() it is possible to mount the
* following schema to cat bytes coming from the kerenl to the end of an
* sds string new things without copying into an intermediate buffer:
*
* oldlen = sdslen(s);
* s = sdsMakeRoomFor(s, BUFFER_SIZE);
* nread = read(fd, s+oldlen, BUFFER_SIZE);
* ... check for nread <= 0 and handle it ...
* sdsIncrLen(s, nhread);
*/
void sdsIncrLen(sds s, int incr) {
struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
assert(sh->free >= incr);
sh->len += incr;
sh->free -= incr;
assert(sh->free >= 0);
s[sh->len] = '\0';
}
/* Grow the sds to have the specified length. Bytes that were not part of
* the original length of the sds will be set to zero. */
sds sdsgrowzero(sds s, size_t len) {
......@@ -615,6 +647,7 @@ sds sdsmapchars(sds s, char *from, char *to, size_t setlen) {
int main(void) {
{
struct sdshdr *sh;
sds x = sdsnew("foo"), y;
test_cond("Create a string and obtain the length",
......@@ -694,7 +727,26 @@ int main(void) {
x = sdsnew("aar");
y = sdsnew("bar");
test_cond("sdscmp(bar,bar)", sdscmp(x,y) < 0)
{
int oldfree;
sdsfree(x);
x = sdsnew("0");
sh = (void*) (x-(sizeof(struct sdshdr)));
test_cond("sdsnew() free/len buffers", sh->len == 1 && sh->free == 0);
x = sdsMakeRoomFor(x,1);
sh = (void*) (x-(sizeof(struct sdshdr)));
test_cond("sdsMakeRoomFor()", sh->len == 1 && sh->free > 0);
oldfree = sh->free;
x[1] = '1';
sdsIncrLen(x,1);
test_cond("sdsIncrLen() -- content", x[0] == '0' && x[1] == '1');
test_cond("sdsIncrLen() -- len", sh->len == 2);
test_cond("sdsIncrLen() -- free", sh->free == oldfree-1);
}
}
test_report()
return 0;
}
#endif
......@@ -88,4 +88,8 @@ sds *sdssplitargs(char *line, int *argc);
void sdssplitargs_free(sds *argv, int argc);
sds sdsmapchars(sds s, char *from, char *to, size_t setlen);
/* Low level functions exposed to the user API */
sds sdsMakeRoomFor(sds s, size_t addlen);
void sdsIncrLen(sds s, int incr);
#endif
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