mg_set_option(): allow NULL as value. Fast success if old_value == new_value.

mongoose.c

@@ -4415,15 +4415,26 @@ const char *mg_set_option(struct mg_server *server, const char *name,
                           const char *value) {
   int ind = get_option_index(name);
   const char *error_msg = NULL;
+  char **v = NULL;
 
-  if (ind < 0) {
-    error_msg = "No such option";
-  } else {
-    if (server->config_options[ind] != NULL) {
-      free(server->config_options[ind]);
+  if (ind < 0) return  "No such option";
+  v = &server->config_options[ind];
+
+  // Return success immediately if setting to the same value
+  if ((*v == NULL && value == NULL) ||
+      (value != NULL && *v != NULL && !strcmp(value, *v))) {
+    return NULL;
+  }
+
+  if (*v != NULL) {
+    free(*v);
+    *v = NULL;
   }
-    server->config_options[ind] = mg_strdup(value);
-    DBG(("%s [%s]", name, value));
+
+  if (value == NULL) return NULL;
+
+  *v = mg_strdup(value);
+  DBG(("%s [%s]", name, *v));
 
   if (ind == LISTENING_PORT) {
     int port = ns_bind(&server->ns_server, value);
@@ -4435,8 +4446,8 @@ const char *mg_set_option(struct mg_server *server, const char *name,
       if (!strcmp(value, "0")) {
         char buf[10];
         mg_snprintf(buf, sizeof(buf), "%d", port);
-          free(server->config_options[ind]);
-          server->config_options[ind] = mg_strdup(buf);
+        free(*v);
+        *v = mg_strdup(buf);
       }
     }
 #ifndef _WIN32
@@ -4462,7 +4473,6 @@ const char *mg_set_option(struct mg_server *server, const char *name,
     }
 #endif
   }
-  }
 
   return error_msg;
 }