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https://github.com/fluencelabs/redis
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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.
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54
src/sds.c
54
src/sds.c
@ -40,6 +40,7 @@
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#include <stdlib.h>
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#include <string.h>
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#include <ctype.h>
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#include <assert.h>
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#include "sds.h"
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#include "zmalloc.h"
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@ -107,7 +108,7 @@ void sdsclear(sds s) {
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*
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* Note: this does not change the *size* of the sds string as returned
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* by sdslen(), but only the free buffer space we have. */
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static sds sdsMakeRoomFor(sds s, size_t addlen) {
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sds sdsMakeRoomFor(sds s, size_t addlen) {
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struct sdshdr *sh, *newsh;
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size_t free = sdsavail(s);
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size_t len, newlen;
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@ -127,6 +128,37 @@ static sds sdsMakeRoomFor(sds s, size_t addlen) {
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return newsh->buf;
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}
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/* Increment the sds length and decrements the left free space at the
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* end of the string accordingly to 'incr'. Also set the null term
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* in the new end of the string.
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*
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* This function is used in order to fix the string length after the
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* user calls sdsMakeRoomFor(), writes something after the end of
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* the current string, and finally needs to set the new length.
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*
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* Note: it is possible to use a negative increment in order to
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* right-trim the string.
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*
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* Using sdsIncrLen() and sdsMakeRoomFor() it is possible to mount the
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* following schema to cat bytes coming from the kerenl to the end of an
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* sds string new things without copying into an intermediate buffer:
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*
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* oldlen = sdslen(s);
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* s = sdsMakeRoomFor(s, BUFFER_SIZE);
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* nread = read(fd, s+oldlen, BUFFER_SIZE);
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* ... check for nread <= 0 and handle it ...
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* sdsIncrLen(s, nhread);
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*/
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void sdsIncrLen(sds s, int incr) {
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struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
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assert(sh->free >= incr);
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sh->len += incr;
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sh->free -= incr;
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assert(sh->free >= 0);
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s[sh->len] = '\0';
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}
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/* Grow the sds to have the specified length. Bytes that were not part of
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* the original length of the sds will be set to zero. */
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sds sdsgrowzero(sds s, size_t len) {
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@ -615,6 +647,7 @@ sds sdsmapchars(sds s, char *from, char *to, size_t setlen) {
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int main(void) {
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{
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struct sdshdr *sh;
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sds x = sdsnew("foo"), y;
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test_cond("Create a string and obtain the length",
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@ -694,7 +727,26 @@ int main(void) {
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x = sdsnew("aar");
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y = sdsnew("bar");
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test_cond("sdscmp(bar,bar)", sdscmp(x,y) < 0)
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{
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int oldfree;
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sdsfree(x);
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x = sdsnew("0");
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sh = (void*) (x-(sizeof(struct sdshdr)));
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test_cond("sdsnew() free/len buffers", sh->len == 1 && sh->free == 0);
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x = sdsMakeRoomFor(x,1);
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sh = (void*) (x-(sizeof(struct sdshdr)));
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test_cond("sdsMakeRoomFor()", sh->len == 1 && sh->free > 0);
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oldfree = sh->free;
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x[1] = '1';
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sdsIncrLen(x,1);
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test_cond("sdsIncrLen() -- content", x[0] == '0' && x[1] == '1');
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test_cond("sdsIncrLen() -- len", sh->len == 2);
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test_cond("sdsIncrLen() -- free", sh->free == oldfree-1);
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}
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}
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test_report()
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return 0;
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}
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#endif
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@ -88,4 +88,8 @@ sds *sdssplitargs(char *line, int *argc);
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void sdssplitargs_free(sds *argv, int argc);
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sds sdsmapchars(sds s, char *from, char *to, size_t setlen);
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/* Low level functions exposed to the user API */
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sds sdsMakeRoomFor(sds s, size_t addlen);
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void sdsIncrLen(sds s, int incr);
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#endif
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