+/* 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) {
+ struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));
+ size_t totlen, curlen = sh->len;
+
+ if (len <= curlen) return s;
+ s = sdsMakeRoomFor(s,len-curlen);
+ if (s == NULL) return NULL;
+
+ /* Make sure added region doesn't contain garbage */
+ sh = (void*)(s-(sizeof(struct sdshdr)));
+ memset(s+curlen,0,(len-curlen+1)); /* also set trailing \0 byte */
+ totlen = sh->len+sh->free;
+ sh->len = len;
+ sh->free = totlen-sh->len;
+ return s;
+}
+