MQTT Inbound Protocol

MQ Telemetry Transport (MQTT) is a lightweight broker-based publish/subscribe messaging protocol, designed to be open, simple, lightweight and easy to implement. These characteristics make it ideal for use in constrained environments.

For example,

When the network is expensive, has low bandwidth or is unreliable.
When running on an embedded device with limited processor or memory resources.

To configure the MQTT inbound endpoint, you need to specify XML fragments that represents various parameters.

Following is a sample MQTT inbound endpoint configuration that can subscribe to messages using the specified topic:

<inboundEndpoint xmlns="http://ws.apache.org/ns/synapse" name="Test" sequence="TestIn" onError="fault" protocol="mqtt" suspend="false">
   <parameters>
 	  <parameter name="sequential">true</parameter>
      <parameter name="mqtt.connection.factory">mqttFactory</parameter>
      <parameter name="mqtt.server.host.name">localhost</parameter>
      <parameter name="mqtt.server.port">1883</parameter>
      <parameter name="mqtt.topic.name">ei.test2</parameter>
      <parameter name="mqtt.subscription.qos">2</parameter>
      <parameter name="content.type">application/xml</parameter>
      <parameter name="mqtt.session.clean">false</parameter>
      <parameter name="mqtt.ssl.enable">false</parameter>
      <parameter name="mqtt.subscription.username">client</parameter>
      <parameter name="mqtt.subscription.password">e13</parameter>
      <parameter name="mqtt.temporary.store.directory">m1y</parameter>
      <parameter name="mqtt.reconnection.interval">5</parameter>
   </parameters>
</inboundEndpoint>

MQTT inbound endpoint parameters

Parameter	Description	Required
sequential	The behaviour when executing the given sequence.	Yes
coordination	In a cluster setup, if set to true, the inbound endpoint will run only in a single worker node. If set to false, it will run on all worker nodes.	Yes
suspend	If set to true, the inbound listener will not accept incoming request messages from clients and will not inject messages to the synapse message mediation. If set to false, incoming messages will be accepted.	Yes
mqtt.connection.factory	Name of the connection factory.	Yes
mqtt.server.host.name	Address of the message broker (eg., localhost).	Yes
mqtt.server.port	Port of the message broker (e.g., 1883).	Yes
mqtt.topic.name	MQTT topic to which the message should be published.	Yes
mqtt.subscription.qos	The quality of service level that need to be maintained with the subscription. The quality of service level can be either 0,1 or 2. 0 - Specifying this level ensures that the message delivery is efficient. However, specifying this level does not guarantee that the message will be delivered to its recipient. 1 - Specifying this level ensures that the message is delivered at least once, but this can lead to messages being duplicated. 2 - This is the highest level of quality of service. Specifying this guarantees that the message is delivered and that it is delivered only once.	No
mqtt.client.id	The id of the client.	No
content.type	The content type of the message. (i.e., XML or JSON)	Yes
mqtt.session.clean	Whether the client and server should remember the state across restarts and reconnects.	No
mqtt.ssl.enable	Whether to use tcp connection or ssl connection.	No
mqtt.subscription.username	The username for the subscription.	No
mqtt.subscription.password	The password for the subscription.	No
mqtt.temporary.store.directory	Path of the directory to be used as the persistent data store for quality of service purposes.	No
mqtt.reconnection.interval	The retry interval to reconnect to the MQTT server.	No

Samples

For a sample that demonstrates how the MQTT connector publishes a message on a particular topic and how a MQTT client that is subscribed to that topic receives it, see Sample 906: MQTT Inbound Endpoint Sample.