Handle reconnection inside library

Author: Sid23

src/ArduinoCloud.cpp

@@ -14,7 +14,8 @@ const static int thingIdSlot                               = 12;
 
 ArduinoCloudClass::ArduinoCloudClass() :
   _bearSslClient(NULL),
-  _mqttClient(256)
+  // Size of the receive buffer
+  _mqttClient(MQTT_BUFFER_SIZE)
 {
 }
 
@@ -58,17 +59,31 @@ int ArduinoCloudClass::begin(Client& net)
   _bearSslClient = new BearSSLClient(net);
   _bearSslClient->setEccSlot(keySlot, ECCX08Cert.bytes(), ECCX08Cert.length());
 
-  _mqttClient.onMessageAdvanced(ArduinoCloudClass::onMessage);
-  _mqttClient.begin(server, 8883, *_bearSslClient);
-
-  _stdoutTopic = "$aws/things/" + _id + "/stdout";
-  _stdinTopic = "$aws/things/" + _id + "/stdin";
+  // Begin function for the MQTTClient
+  mqttClientBegin(*_bearSslClient);
 
   return 1;
 }
 
+// private class method used to initialize mqttClient class member. (called in the begin class method)
+void ArduinoCloudClass::mqttClientBegin(Client& net)
+{
+  // MQTT topics definition
+  _stdoutTopic = "/a/d/" + _id + "/s/o";
+  _stdinTopic = "/a/d/" + _id + "/s/i";
+
+  // use onMessage as callback for received mqtt messages
+  _mqttClient.onMessageAdvanced(ArduinoCloudClass::onMessage);
+  _mqttClient.begin(server, 8883, net);
+
+  // Set MQTT connection options
+  _mqttClient.setOptions(mqttOpt.keepAlive, mqttOpt.cleanSession, mqttOpt.timeout);
+}
+
 int ArduinoCloudClass::connect()
 {
+  // Username: device id
+  // Password: empty
   if (!_mqttClient.connect(_id.c_str())) {
     return 0;
   }
@@ -78,11 +93,62 @@ int ArduinoCloudClass::connect()
   return 1;
 }
 
+bool ArduinoCloudClass::disconnect()
+{
+    return _mqttClient.disconnect();
+}
+
 void ArduinoCloudClass::poll()
 {
+  // If user call poll() without parameters use the default ones
+  poll(MAX_RETRIES, RECONNECTION_TIMEOUT);
+}
+
+bool ArduinoCloudClass::mqttReconnect(int maxRetries, int timeout)
+{
+  // Counter for reconnection retries
+  int retries = 0;
+  unsigned long start = millis();
+
+  // Check for MQTT broker connection, of if maxReties limit is reached
+  // if MQTTClient is connected , simply do nothing and retun true
+  while(!_mqttClient.connected() && (retries++ < maxRetries) && (millis() - start < timeout)) {
+
+    // Get last MTTQClient error, (a common error may be a buffer overflow)
+    lwmqtt_err_t err = _mqttClient.lastError();
+
+    // try establish the MQTT broker connection
+    connect();
+  }
+
+  // It was impossible to establish a connection, return
+  if ((retries == maxRetries) || (millis() - start >= timeout))
+    return false;
+
+  return true;
+}
+
+void ArduinoCloudClass::poll(int reconnectionMaxRetries, int reconnectionTimeoutMs)
+{
+  // Method's argument controls
+  int maxRetries = (reconnectionMaxRetries > 0) ? reconnectionMaxRetries : MAX_RETRIES;
+  int timeout = (reconnectionTimeoutMs > 0) ? reconnectionTimeoutMs : RECONNECTION_TIMEOUT;
+
+  // If the reconnect() culd not establish the connection, return the control to the user sketch
+  if (!mqttReconnect(maxRetries, timeout))
+    return;
+
+  // MTTQClient connected!, poll() used to retrieve data from MQTT broker
   _mqttClient.loop();
 }
 
+void ArduinoCloudClass::reconnect(Client& net)
+{
+  // Initialize again the MQTTClient, otherwise it would not be able to receive messages through its callback
+  mqttClientBegin(net);
+  connect();
+}
+
 void ArduinoCloudClass::onGetTime(unsigned long(*callback)(void))
 {
   ArduinoBearSSL.onGetTime(callback);

src/ArduinoCloudV2.h

@@ -6,6 +6,13 @@
 
 #include "CloudSerial.h"
 
+// Declaration of the struct for the mqtt connection options
+typedef struct mqtt_opt{
+  int keepAlive;
+  bool cleanSession;
+  int timeout;
+} mqttConnectionOptions;
+
 class ArduinoCloudClass {
 
 public:
@@ -14,33 +21,47 @@ class ArduinoCloudClass {
 
   int begin(Client& net);
 
-  int connect();
+  // Class constant declaration
+  static const int MQTT_BUFFER_SIZE = 256;
+  static const int MAX_RETRIES = 5;
+  static const int RECONNECTION_TIMEOUT = 2000;
+  const mqttConnectionOptions mqttOpt = {120, false, 1000};
 
+  int connect();
+  bool disconnect();
   void poll();
 
+  // defined for users who want to specify max reconnections reties and timeout between them
+  void poll(int reconnectionMaxRetries, int reconnectionTimeoutMs);
+  // It must be a user defined function, in order to avoid ArduinoCloud include specific WiFi file
+  // in this case this library is independent from the WiFi one
   void onGetTime(unsigned long(*)(void));
 
   int connected();
+  // Clean up existing Mqtt connection, create a new one and initialize it
+  void reconnect(Client& net);
 
 protected:
   friend class CloudSerialClass;
   int writeStdout(const byte data[], int length);
+  // Used to initialize MQTTClient
+  void mqttClientBegin(Client& net);
+  // Function in charge of perform MQTT reconnection, basing on class parameters(retries,and timeout)
+  bool mqttReconnect(int maxRetries, int timeout);
 
 private:
   static void onMessage(MQTTClient *client, char topic[], char bytes[], int length);
-
   void handleMessage(char topic[], char bytes[], int length);
 
-private:
   String _id;
   BearSSLClient* _bearSslClient;
   MQTTClient _mqttClient;
 
+  // Class attribute to define MTTQ topics 2 for stdIn/out and 2 for data, in order to avoid getting previous pupblished payload
   String _stdinTopic;
   String _stdoutTopic;
 };
 
-
 extern ArduinoCloudClass ArduinoCloud;
 
 #endif