rabbitmq-server/deps/rabbitmq_mqtt

RabbitMQ MQTT adapter

Introduction

This is a protocol adapter that allows MQTT-capable clients to connect to a RabbitMQ broker. The adapter translates MQTT methods into their AMQP equivalents and back.

Supported MQTT features

• QoS0 and QoS1 publish & consume
• Last Will and Testament (LWT)
• SSL
• Session stickiness

Configuration

The main RabbitMQ configuration file also specifies the MQTT configuration. For details see the broker configuration documentation. It is an Erlang-syntax file of the form:

[{section1, [section1-config]},
 {section2, [section2-config]},
 ...
 {sectionN, [sectionN-config]}
].

thus a list of tuples, where the left element of each tuple names the applications being configured. Don't forget the last element of the list doesn't have a trailing comma, and don't forget the full-stop is needed after closing the list. Hence if you configure RabbitMQ-server and the MQTT adapter, then the configuration file may have a structure like this:

[{rabbit,        [configuration-for-RabbitMQ-server]},
 {rabbitmq_mqtt, [configuration-for-RabbitMQ-mqtt-adapter]}
].

Here is a sample configuration that sets every MQTT option:

[{rabbit,        [{tcp_listeners,    [5672]}]},
 {rabbitmq_mqtt, [{default_user,     <<"guest">>},
                  {default_pass,     <<"guest">>},
                  {allow_anonymous,  true},
                  {vhost,            <<"/">>},
                  {exchange,         <<"amq.topic">>},
                  {subscription_ttl, 1800000},
                  {prefetch,         10},
                  {ssl_listeners,    []},
                  {tcp_listeners,    [1883]},
                  {tcp_listen_options, [binary,
                                        {packet,    raw},
                                        {reuseaddr, true},
                                        {backlog,   128},
                                        {nodelay,   true}]}]}
].

The default_user and default_pass options are used to authenticate the adapter in case MQTT clients provide no login credentials. If the allow_anonymous option is set to false then clients MUST provide credentials. The presence of client-supplied credentials over the network overrides the allow_anonymous option.

The vhost option controls which RabbitMQ vhost the adapter connects to and the exchange option determines which exchange messages from MQTT clients are published to. If a non-default exchange is chosen then it must be created before clients publish any messages. The exchange is expected to be an AMQP topic exchange.

The subscription_ttl option controls the lifetime of non-clean sessions. This option is interpreted in the same way as the queue TTL parameter, so the value 1800000 means 30 minutes.

The prefetch option controls the maximum number of unacknowledged messages that will be delivered. This option is interpreted in the same way as the AMQP prefetch-count field, so a value of 0 means "no limit".

The ssl_listeners option controls the endpoint (if any) that the adapter accepts SSL connections on. The default MQTT SSL port is 8883. If this option is non-empty then the rabbit section of the configuration file must contain an ssl_options entry. See the SSL configuration guide for details.

The tcp_listeners and tcp_listen_options options are interpreted in the same way as the corresponding options in the rabbit section, as explained in the broker configuration documentation.

AMQP mapping

This is an outline of the mapping between the MQTT and AMQP methods involved in each of the message flows supported by the adapter. It is not necessary to know this in order to use the adapter.

          (MQTT)    ADAPTER    (AMQP)

• QOS0 flow publish

      PUBLISH   ------>    basic.publish
  

• QOS0 flow receive

      PUBLISH   <------    basic.deliver
  

• QOS1 flow publish (tracked in state.unacked_pub)

      PUBLISH   ------>    basic.publish  --+
                                            |
      PUBACK    <------    basic.ack     <--+
  

• QOS1 flow receive (tracked in state.awaiting_ack)

  +--  PUBLISH   <------    basic.deliver
  |
  +--> PUBACK    ------>    basic.ack