config: add support for lastWill and keep alive

By default, MQTT keep-alive is 1200 seconds and AWS broker add a
1.5x factor, so it takes generally 15 min to discover that a device
is disconnected (30 min in the worst case)

This patch allow a user to configure a last will and change the
default timeout (30 seconds will be the minimum authorized by AWS)

New config will have for example:

	"last-will-topic": "things/myDevice/shadow/name/demo-shadow/update",
        "last-will-message": "{\"state\":{\"reported\":{\"connected\":false}}}",
        "connect-timeout": 0,
        "keep-alive": 30,

Author: AmarOk1412

source/SharedCrtResourceManager.cpp

@@ -455,13 +455,29 @@ int SharedCrtResourceManager::establishConnection(const PlainConfig &config)
     connection->OnConnectionInterrupted = move(OnConnectionInterrupted);
     connection->OnConnectionResumed = move(OnConnectionResumed);
 
+    if (config.lastWillTopic.has_value() && config.lastWillMessage.has_value()) {
+        Aws::Crt::ByteBuf payload = Aws::Crt::ByteBufFromCString(config.lastWillMessage->c_str());
+        connection->SetWill(config.lastWillTopic->c_str(), Aws::Crt::Mqtt::QOS::AWS_MQTT_QOS_AT_LEAST_ONCE, false, payload);
+    }
+
     LOGM_INFO(TAG, "Establishing MQTT connection with client id %s...", config.thingName->c_str());
     if (!connection->SetReconnectTimeout(15, 240))
     {
         LOG_ERROR(TAG, "Device Client is not able to set reconnection settings. Device Client will retry again.");
         return RETRY;
     }
-    if (!connection->Connect(config.thingName->c_str(), false))
+
+    int keepAliveTimeSecs = 0;
+    if (config.connectKeepAlive.has_value()) {
+        keepAliveTimeSecs = *config.connectKeepAlive;
+    }
+
+    int pingTimeoutMs = 0;
+    if (config.connectTimeout.has_value()) {
+        pingTimeoutMs = *config.connectTimeout;
+    }
+
+    if (!connection->Connect(config.thingName->c_str(), false, keepAliveTimeSecs, pingTimeoutMs))
     {
         LOGM_ERROR(TAG, "MQTT Connection failed with error: %s", ErrorDebugString(connection->LastError()));
         return RETRY;

source/config/Config.cpp

@@ -62,6 +62,10 @@ constexpr char PlainConfig::JSON_KEY_FLEET_PROVISIONING[];
 constexpr char PlainConfig::JSON_KEY_RUNTIME_CONFIG[];
 constexpr char PlainConfig::JSON_KEY_SAMPLES[];
 constexpr char PlainConfig::JSON_KEY_PUB_SUB[];
+constexpr char PlainConfig::JSON_KEY_LAST_WILL_TOPIC[];
+constexpr char PlainConfig::JSON_KEY_LAST_WILL_MESSAGE[];
+constexpr char PlainConfig::JSON_KEY_CONNECT_TIMEOUT[];
+constexpr char PlainConfig::JSON_KEY_CONNECT_KEEPALIVE[];
 constexpr char PlainConfig::JSON_KEY_SAMPLE_SHADOW[];
 constexpr char PlainConfig::JSON_KEY_CONFIG_SHADOW[];
 constexpr char PlainConfig::JSON_KEY_SECURE_ELEMENT[];
@@ -208,6 +212,30 @@ bool PlainConfig::LoadFromJson(const Crt::JsonView &json)
         }
     }
 
+    jsonKey = JSON_KEY_LAST_WILL_TOPIC;
+    if (json.ValueExists(jsonKey))
+    {
+        lastWillTopic = json.GetString(jsonKey).c_str();
+    }
+
+    jsonKey = JSON_KEY_LAST_WILL_MESSAGE;
+    if (json.ValueExists(jsonKey))
+    {
+        lastWillMessage = json.GetString(jsonKey).c_str();
+    }
+
+    jsonKey = JSON_KEY_CONNECT_TIMEOUT;
+    if (json.ValueExists(jsonKey))
+    {
+        connectTimeout = json.GetInteger(jsonKey);
+    }
+
+    jsonKey = JSON_KEY_CONNECT_KEEPALIVE;
+    if (json.ValueExists(jsonKey))
+    {
+        connectKeepAlive = json.GetInteger(jsonKey);
+    }
+
     jsonKey = JSON_KEY_SAMPLE_SHADOW;
     if (json.ValueExists(jsonKey))
     {
@@ -436,6 +464,22 @@ void PlainConfig::SerializeToObject(Crt::JsonObject &object) const
     {
         object.WithString(JSON_KEY_THING_NAME, thingName->c_str());
     }
+    if (lastWillTopic.has_value() && lastWillTopic->c_str())
+    {
+        object.WithString(JSON_KEY_LAST_WILL_TOPIC, lastWillTopic->c_str());
+    }
+    if (lastWillMessage.has_value() && lastWillMessage->c_str())
+    {
+        object.WithString(JSON_KEY_LAST_WILL_MESSAGE, lastWillMessage->c_str());
+    }
+    if (connectTimeout.has_value() && connectTimeout)
+    {
+        object.WithInteger(JSON_KEY_CONNECT_TIMEOUT, *connectTimeout);
+    }
+    if (connectKeepAlive.has_value() && connectKeepAlive)
+    {
+        object.WithInteger(JSON_KEY_CONNECT_KEEPALIVE, *connectKeepAlive);
+    }
 
     Crt::JsonObject loggingObject;
     logConfig.SerializeToObject(loggingObject);

source/config/Config.h

@@ -94,6 +94,12 @@ namespace Aws
                 static constexpr char JSON_KEY_SAMPLES[] = "samples";
                 static constexpr char JSON_KEY_PUB_SUB[] = "pub-sub";
 
+                static constexpr char JSON_KEY_LAST_WILL_TOPIC[] = "last-will-topic";
+                static constexpr char JSON_KEY_LAST_WILL_MESSAGE[] = "last-will-message";
+
+                static constexpr char JSON_KEY_CONNECT_TIMEOUT[] = "connect-timeout";
+                static constexpr char JSON_KEY_CONNECT_KEEPALIVE[] = "keep-alive";
+
                 static constexpr char JSON_KEY_SAMPLE_SHADOW[] = "sample-shadow";
                 static constexpr char JSON_KEY_CONFIG_SHADOW[] = "config-shadow";
                 static constexpr char JSON_KEY_SENSOR_PUBLISH[] = "sensor-publish";
@@ -107,6 +113,10 @@ namespace Aws
                 Aws::Crt::Optional<std::string> key;
                 Aws::Crt::Optional<std::string> rootCa;
                 Aws::Crt::Optional<std::string> thingName;
+                Aws::Crt::Optional<std::string> lastWillTopic;
+                Aws::Crt::Optional<std::string> lastWillMessage;
+                Aws::Crt::Optional<int> connectTimeout;
+                Aws::Crt::Optional<int> connectKeepAlive;
 
                 std::string lockFilePath{DEFAULT_LOCK_FILE_PATH};