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A MQTT Client application that keep connections to one or more MQTT brokers, handles subscriptions, and expose a publisher for publishing messages to the broker.

Amongst other things Tortoise supports:

  • Keeping a connection to a MQTT server (version 3.1.1 for now)
  • Retry connecting with incremental back-off
  • Publishing and subscribing to topics of QoS 0, 1, and 2
  • Connections support last will message
  • Connecting via TCP and SSL
  • The fundamentals are there, but some of the API's might change in the near future
  • A PubSub system where one can listen to system events. For now connection status and ping response times can be subscribed for statistics and administrative purposes.

Most of the public facing interface should be in the Tortoise module. See the GitHub issues for work in progress "known issues in the design", "what needs to be done", and so forth; feel free to open your own issues if something is confusing or broken.

I would love to get some feedback and help building this thing.


A supervised connection can be started like this:

# connect to the server and subscribe to foo/bar with QoS 0
    client_id: "my_client_id",
    handler: {Tortoise.Handler.Logger, []},
    server: {Tortoise.Transport.Tcp, host: 'localhost', port: 1883},
    subscriptions: [{"foo/bar", 0}])

# publish a message on the broker
Tortoise.publish("my_client_id", "foo/bar", "Hello from the World of Tomorrow !", qos: 0)

To connect to a MQTT server using SSL the Tortoise.Transport.SSL transport can be used. This requires configuration of the server's CA certificate, and possibly a client certificate and key. For example, when using the certifi package as the CA trust store:

    client_id: "smart-spoon",
    handler: {Tortoise.Handler.Logger, []},
    server: {
      host: host, port: port,
      cacertfile: :certifi.cacertfile(),
      key: key, cert: cert
    subscriptions: [{"foo/bar", 0}])

Alternatively, for testing purposes, server certificate verification can be disabled by passing verify: :verify_none in the server options. In that case there is no need for CA certificates, but an attacker could intercept the connection without detection!

Look at the connection_test.exs-file for more examples.

Example Handler

defmodule Tortoise.Handler.Example do
  use Tortoise.Handler

  def init(args) do
    {:ok, args}

  def connection(status, state) do
    # `status` will be either `:up` or `:down`; you can use this to
    # inform the rest of your system if the connection is currently
    # open or closed; tortoise should be busy reconnecting if you get
    # a `:down`
    {:ok, state}

  #  topic filter room/+/temp
  def handle_message(["room", room, "temp"], payload, state) do
    # :ok = Temperature.record(room, payload)
    {:ok, state}
  def handle_message(topic, payload, state) do
    # unhandled message! You will crash if you subscribe to something
    # and you don't have a 'catch all' matcher; crashing on unexpected
    # messages could be a strategy though.
    {:ok, state}

  def subscription(status, topic_filter, state) do
    {:ok, state}

  def terminate(reason, state) do
    # tortoise doesn't care about what you return from terminate/2,
    # that is in alignment with other behaviours that implement a
    # terminate-callback

Upgrade path

pre-0.9 to 0.9

The subscribe/3, unsubscribe/3, subscribe_sync/3, and unsubscribe_sync/3 is no longer exposed on the Tortoise module. The functionality has been moved to the Tortoise.Connection module. The functions has the same arities and functionality, so the upgrade path is a simple search and replace:

  • "Tortoise.subscribe(" -> "Tortoise.Connection.subscribe("
  • "Tortoise.subscribe_sync(" -> "Tortoise.Connection.subscribe_sync("
  • "Tortoise.unsubscribe(" -> "Tortoise.Connection.unsubscribe("
  • "Tortoise.unsubscribe_sync(" -> "Tortoise.Connection.unsubscribe_sync("

This change is done because the Tortoise.Connection module should be in charge of changes to the connection life-cycle.


Tortoise can be installed by adding tortoise to your list of dependencies in mix.exs:

def deps do
    {:tortoise, "~> 0.9"}

Documentation should be available at


To start developing, run the following commands:

mix deps.get
MIX_ENV=test mix eqc.install --mini
mix test

Building documentation

To build the documentation run the following command in a terminal emulator:

MIX_ENV=docs mix docs

This will build the documentation in place them in the doc-folder in the root of the project. These docs will also find their way to the Hexdocs website when the project is published on Hex.


Copyright 2018 Martin Gausby

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.