Reduce stack usage in loop(). No need to duplicate

topic string onto stack before giving it to callback() Just move it one byte in buffer to add space for 'C' string end \0x00
knolleary · Jun 26, 2016 · d724864 · d724864
1 parent 35ead34
commit d724864
Showing 1 changed file with 4 additions and 6 deletions.
diff --git a/src/PubSubClient.cpp b/src/PubSubClient.cpp
@@ -306,12 +306,10 @@ boolean PubSubClient::loop() {
                 uint8_t type = buffer[0]&0xF0;
                 if (type == MQTTPUBLISH) {
                     if (callback) {
-                        uint16_t tl = (buffer[llen+1]<<8)+buffer[llen+2];
-                        char topic[tl+1];
-                        for (uint16_t i=0;i<tl;i++) {
-                            topic[i] = buffer[llen+3+i];
-                        }
-                        topic[tl] = 0;
+                        uint16_t tl = (buffer[llen+1]<<8)+buffer[llen+2]; /* topic length in bytes */
+                        memmove(buffer+llen+2,buffer+llen+3,tl); /* move topic inside buffer 1 byte to front */
+                        buffer[llen+2+tl] = 0; /* end the topic as a 'C' string with \x00 */
+                        char *topic = (char*) buffer+llen+2;
                         // msgId only present for QOS>0
                         if ((buffer[0]&0x06) == MQTTQOS1) {
                             msgId = (buffer[llen+3+tl]<<8)+buffer[llen+3+tl+1];