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MQTT library for Erlang *JUST USABLE*
Erlang Perl
Branch: master

Remove spurious help text

Topics are now given with -t
latest commit 514f01d272
@squaremo authored
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include Specs for the public API
src Supplied client ID and disabling the clean session flag
test Add public API (erlmqtt) and rename other src files
.gitignore Bring tests up to date and add properties
LICENSE License under MIT terms
Makefile Mention erlmqtt_pub and erlmqtt_sub
erlmqtt_sub Remove spurious help text
rebar.config Add PropEr as dependency and only test erlmqtt


An Erlang client library for MQTT 3.1 (but not for MQTT 3.1.1, yet).


$ make


$ make test && make dialyse

Trying out

This API may change, especially with respect to receiving messages.

(Assuming RabbitMQ or another MQTT broker is running on localhost:1883)

$ erl -pa ebin

Opening a connection and subscribing

1> {ok, C} = erlmqtt:open_clean("localhost", []).
2> {ok, _} = erlmqtt:subscribe(C, [{"topic/#", at_most_once}]).

open_clean starts a fresh connection that doesn't keep state around when disconnected. The second argument is a proplist of options, for example, [{keep_alive, 600}].

Also exported are open/2 and open/3, which start connections with persistent state (though resumption of those after disconnection is not fully implemented yet).

Publishing messages

3> erlmqtt:publish(C, "topic/a/b", <<"payload">>).

There's also a publish/4 which accepts a proplist of options, e.g., [retain, at_least_once], and publish_sync/4 and publish_sync/5, which publish a message using guaranteed delivery and return when the message has been delivered (or in the case of publish_sync/5, if it has timed out).

4> erlmqtt:publish_sync(C, "/dev/null", <<"payload">>, at_least_once).

Currently, using "quality of service" (guaranteed delivery) other than at_most_once does not get you a lot; the connection will enact the correct protocol, but if it crashes you will still lose the state.

Receiving messages

5> erlmqtt:recv_message(1000).
6> erlmqtt:recv_message(1000).
7> erlmqtt:publish(C, "topic/foo", <<"payload">>).
8> erlmqtt:poll_message().
9> erlmqtt:poll_message().

When a connection is opened, the calling process is volunteered as the message consumer. This means the connection will deliver messages to its mailbox. recv_message/0 and recv_message/1 wait for a message to arrive (in the latter case, for a limited time) and return it as a pair of topic and payload. poll_message/0 returns a pair of topic and payload if a message is available in the mailbox now, otherwise 'none'.


The scripts erlmqtt_pub and erlmqtt_sub give examples of publishing and subscribing respectively. Presently they must be run from the repository directory. Use the argument --help with either to see its usage.

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