Add sdsfreeusable()

src/sds.c

@@ -216,6 +216,16 @@ void sdsfree(sds s) {
     s_free((char*)s-sdsHdrSize(s[-1]));
 }
 
+/* Free an sds string. No operation is performed if 's' is NULL.
+ * '*usable' is set to the usable size if non NULL */
+void sdsfreeusable(sds s, size_t *usable) {
+    if (s == NULL) {
+        if (usable) *usable = 0;
+        return;
+    }
+    s_free_usable((char*)s-sdsHdrSize(s[-1]), usable);
+}
+
 /* Generic version of sdsfree. */
 void sdsfreegeneric(void *s) {
     sdsfree((sds)s);

src/sds.h

@@ -218,6 +218,7 @@ sds sdsnewplacement(char *buf, size_t bufsize, char type, const char *init, size
 sds sdsempty(void);
 sds sdsdup(const sds s);
 void sdsfree(sds s);
+void sdsfreeusable(sds s, size_t *usable);
 void sdsfreegeneric(void *s);
 sds sdsgrowzero(sds s, size_t len);
 sds sdscatlen(sds s, const void *t, size_t len);