Support publishing and receiving large messages. Send multiple 250 byte packets (ref PR#113) for larger messages. Correctly identify topic start position for >127byte messages (ref PR#166). Resolves issue #102

Adafruit_MQTT.cpp

@@ -233,7 +233,7 @@ uint16_t Adafruit_MQTT::readFullPacket(uint8_t *buffer, uint16_t maxsize,
   // will read a packet and Do The Right Thing with length
   uint8_t *pbuff = buffer;
 
-  uint8_t rlen;
+  uint16_t rlen;
 
   // read the packet type:
   rlen = readPacket(pbuff, 1, timeout);
@@ -473,6 +473,22 @@ Adafruit_MQTT_Subscribe *Adafruit_MQTT::readSubscription(int16_t timeout) {
   return handleSubscriptionPacket(len);
 }
 
+namespace {
+
+uint16_t topicOffsetFromLenth(uint16_t const len) 
+{
+  if (len < 128) {            // 7 bits (+1 continuation bit)
+    return 0;
+  } else if (len < 16384) {   // 14 bits (+2 continuation bits)
+    return 1;
+  } else if (len < 2097152) { // 21 bits
+    return 2;
+  }
+  return 3;
+}
+
+} // anon
+
 Adafruit_MQTT_Subscribe *Adafruit_MQTT::handleSubscriptionPacket(uint16_t len) {
   uint16_t i, topiclen, datalen;
 
@@ -491,7 +507,9 @@ Adafruit_MQTT_Subscribe *Adafruit_MQTT::handleSubscriptionPacket(uint16_t len) {
   }
 
   // Parse out length of packet.
-  topiclen = buffer[3];
+  uint16_t const topicoffset = topicOffsetFromLength(len);
+  uint16_t const topicstart = topicoffset + 4;
+  topiclen = buffer[3+topicoffset];
   DEBUG_PRINT(F("Looking for subscription len "));
   DEBUG_PRINTLN(topiclen);
 
@@ -504,7 +522,7 @@ Adafruit_MQTT_Subscribe *Adafruit_MQTT::handleSubscriptionPacket(uint16_t len) {
         continue;
       // Stop if the subscription topic matches the received topic. Be careful
       // to make comparison case insensitive.
-      if (strncasecmp((char *)buffer + 4, subscriptions[i]->topic, topiclen) ==
+      if (strncasecmp((char *)buffer + topicstart, subscriptions[i]->topic, topiclen) ==
           0) {
         DEBUG_PRINT(F("Found sub #"));
         DEBUG_PRINTLN(i);
@@ -520,20 +538,20 @@ Adafruit_MQTT_Subscribe *Adafruit_MQTT::handleSubscriptionPacket(uint16_t len) {
   // Check if it is QoS 1, TODO: we dont support QoS 2
   if ((buffer[0] & 0x6) == 0x2) {
     packet_id_len = 2;
-    packetid = buffer[topiclen + 4];
+    packetid = buffer[topiclen + topicstart];
     packetid <<= 8;
-    packetid |= buffer[topiclen + 5];
+    packetid |= buffer[topiclen + topicstart + 1];
   }
 
   // zero out the old data
   memset(subscriptions[i]->lastread, 0, SUBSCRIPTIONDATALEN);
 
-  datalen = len - topiclen - packet_id_len - 4;
+  datalen = len - topiclen - packet_id_len - topicstart;
   if (datalen > SUBSCRIPTIONDATALEN) {
     datalen = SUBSCRIPTIONDATALEN - 1; // cut it off
   }
   // extract out just the data, into the subscription object itself
-  memmove(subscriptions[i]->lastread, buffer + 4 + topiclen + packet_id_len,
+  memmove(subscriptions[i]->lastread, buffer + topicstart + topiclen + packet_id_len,
           datalen);
   subscriptions[i]->datalen = datalen;
   DEBUG_PRINT(F("Data len: "));

Adafruit_MQTT_Client.cpp

@@ -83,18 +83,19 @@ uint16_t Adafruit_MQTT_Client::readPacket(uint8_t *buffer, uint16_t maxlen,
 
 bool Adafruit_MQTT_Client::sendPacket(uint8_t *buffer, uint16_t len) {
   uint16_t ret = 0;
-
+  uint16_t offset = 0;
   while (len > 0) {
     if (client->connected()) {
       // send 250 bytes at most at a time, can adjust this later based on Client
 
       uint16_t sendlen = len > 250 ? 250 : len;
       // Serial.print("Sending: "); Serial.println(sendlen);
-      ret = client->write(buffer, sendlen);
+      ret = client->write(buffer + offset, sendlen);
       DEBUG_PRINT(F("Client sendPacket returned: "));
       DEBUG_PRINTLN(ret);
       len -= ret;
-
+      offset += ret;
+      
       if (ret != sendlen) {
         DEBUG_PRINTLN("Failed to send packet.");
         return false;