Redis - Simple Dynamic String

1struct sdshdr {
2    unsigned int len;
3    unsigned int free;
4    char buf[];
5};
6 
7static inline size_t sdslen(const sds s)
8{
9    struct sdshdr *sh = (void *)(s - sizeof(struct sdshdr));
10    return sh->len;
11}
12 
13static inline size_t sdsavail(const sds s)
14{
15    struct sdshdr *sh = (void *)(s - sizeof(struct sdshdr));
16    return sh->free;
17}
18 
19sds sdsnewlen(const void *init, size_t initlen)
20{
21    struct sdshdr *sh;
22    sh = malloc(sizeof(struct sdshdr) + initlen + 1);
23    if (sh == NULL) return NULL;
24 
25    sh->len = initlen;
26    sh->free = 0;
27    if (initlen && init)
28        memcpy(sh->buf, init, initlen);
29    sh->buf[initlen] = '\0';
30    return (char *)sh->buf;
31}
32 
33sds sdscat(sds s, const char *t)
34{
35    return sdscatlen(s, t, strlen(t));
36}