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paho-mqtt 0.9

MQTT version 3.1/3.1.1 client class

Latest Version: 1.1

This document describes the source code for the Eclipse Paho MQTT Python client library, which implements versions 3.1 and 3.1.1 of the MQTT protocol.

This code provides a client class which enable applications to connect to an MQTT broker to publish messages, and to subscribe to topics and receive published messages. It also provides some helper functions to make publishing one off messages to an MQTT server very straightforward.

It supports Python 2.7 or 3.x, with limited support for Python 2.6.

The MQTT protocol is a machine-to-machine (M2M)/”Internet of Things” connectivity protocol. Designed as an extremely lightweight publish/subscribe messaging transport, it is useful for connections with remote locations where a small code footprint is required and/or network bandwidth is at a premium.

Paho is an Eclipse Foundation project currently in the incubation phase.

Installation

The latest stable version is available in the Python Package Index (PyPi) and can be installed using

pip install paho-mqtt

Or with virtualenv:

virtualenv paho-mqtt
source paho-mqtt/bin/activate
pip install paho-mqtt

To obtain the full code, including examples and tests, you can clone the git repository:

git clone git://git.eclipse.org/gitroot/paho/org.eclipse.paho.mqtt.python.git

Once you have the code, it can be installed from your repository as well:

cd org.eclipse.paho.mqtt.python
python setup.py install

Usage and API

Detailed API documentation is available through pydoc. Samples are available in the examples directory.

The package provides two modules, a full client and a helper for simple publishing.

Getting Started

Here is a very simple example that subscribes to the broker $SYS topic tree and prints out the resulting messages:

import paho.mqtt.client as mqtt

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, rc):
    print("Connected with result code "+str(rc))

    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    client.subscribe("$SYS/#")

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(msg.topic+" "+str(msg.payload))

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect("iot.eclipse.org", 1883, 60)

# Blocking call that processes network traffic, dispatches callbacks and
# handles reconnecting.
# Other loop*() functions are available that give a threaded interface and a
# manual interface.
client.loop_forever()

Client

You can use the client class as an instance, within a class or by subclassing. The general usage flow is as follows:

  • Create a client instance
  • Connect to a broker using one of the connect*() functions
  • Call one of the loop*() functions to maintain network traffic flow with the broker
  • Use subscribe() to subscribe to a topic and receive messages
  • Use publish() to publish messages to the broker
  • Use disconnect() to disconnect from the broker

Callbacks will be called to allow the application to process events as necessary. These callbacks are described below.

Constructor / reinitialise

Client()
Client(client_id="", clean_session=True, userdata=None, protocol=MQTTv31)

The Client() constructor takes the following arguments:

client_id
the unique client id string used when connecting to the broker. If client_id is zero length or None, then one will be randomly generated. In this case the clean_session parameter must be True.
clean_session

a boolean that determines the client type. If True, the broker will remove all information about this client when it disconnects. If False, the client is a durable client and subscription information and queued messages will be retained when the client disconnects.

Note that a client will never discard its own outgoing messages on disconnect. Calling connect() or reconnect() will cause the messages to be resent. Use reinitialise() to reset a client to its original state.

userdata
user defined data of any type that is passed as the userdata parameter to callbacks. It may be updated at a later point with the user_data_set() function.
protocol
the version of the MQTT protocol to use for this client. Can be either MQTTv31 or MQTTv311
Example
import paho.mqtt.client as mqtt

mqttc = mqtt.Client()
reinitialise()
reinitialise(client_id="", clean_session=True, userdata=None)

The reinitialise() function resets the client to its starting state as if it had just been created. It takes the same arguments as the Client() constructor.

Example
mqttc.reinitialise()

Option functions

These functions represent options that can be set on the client to modify its behaviour. In the majority of cases this must be done before connecting to a broker.

max_inflight_messages_set()
max_inflight_messages_set(self, inflight)

Set the maximum number of messages with QoS>0 that can be part way through their network flow at once.

Defaults to 20. Increasing this value will consume more memory but can increase throughput.

message_retry_set()
::
message_retry_set(retry)

Set the time in seconds before a message with QoS>0 is retried, if the broker does not respond.

This is set to 5 seconds by default and should not normally need changing.

tls_set()
tls_set(ca_certs, certfile=None, keyfile=None, cert_reqs=ssl.CERT_REQUIRED,
    tls_version=ssl.PROTOCOL_TLSv1, ciphers=None)

Configure network encryption and authentication options. Enables SSL/TLS support.

ca_certs
a string path to the Certificate Authority certificate files that are to be treated as trusted by this client. If this is the only option given then the client will operate in a similar manner to a web browser. That is to say it will require the broker to have a certificate signed by the Certificate Authorities in ca_certs and will communicate using TLS v1, but will not attempt any form of authentication. This provides basic network encryption but may not be sufficient depending on how the broker is configured.
certfile, keyfile
strings pointing to the PEM encoded client certificate and private keys respectively. If these arguments are not None then they will be used as client information for TLS based authentication. Support for this feature is broker dependent. Note that if either of these files in encrypted and needs a password to decrypt it, Python will ask for the password at the command line. It is not currently possible to define a callback to provide the password.
cert_reqs
defines the certificate requirements that the client imposes on the broker. By default this is ssl.CERT_REQUIRED, which means that the broker must provide a certificate. See the ssl pydoc for more information on this parameter.
tls_version
specifies the version of the SSL/TLS protocol to be used. By default TLS v1 is used. Previous versions (all versions beginning with SSL) are possible but not recommended due to possible security problems.
ciphers
a string specifying which encryption ciphers are allowable for this connection, or None to use the defaults. See the ssl pydoc for more information.

Must be called before connect*().

tls_insecure_set()
tls_insecure_set(value)

Configure verification of the server hostname in the server certificate.

If value is set to True, it is impossible to guarantee that the host you are connecting to is not impersonating your server. This can be useful in initial server testing, but makes it possible for a malicious third party to impersonate your server through DNS spoofing, for example.

Do not use this function in a real system. Setting value to True means there is no point using encryption.

Must be called before connect*).

username_pw_set()
username_pw_set(username, password=None)

Set a username and optionally a password for broker authentication. Must be called before connect*().

user_data_set()
::
user_data_set(userdata)

Set the private user data that will be passed to callbacks when events are generated. Use this for your own purpose to support your application.

will_set()
::
will_set(topic, payload=None, qos=0, retain=False)

Set a Will to be sent to the broker. If the client disconnects without calling disconnect(), the broker will publish the message on its behalf.

topic
the topic that the will message should be published on.
payload
the message to send as a will. If not given, or set to None a zero length message will be used as the will. Passing an int or float will result in the payload being converted to a string representing that number. If you wish to send a true int/float, use struct.pack() to create the payload you require.
qos
the quality of service level to use for the will.
retain
if set to True, the will message will be set as the “last known good”/retained message for the topic.

Raises a ValueError if qos is not 0, 1 or 2, or if topic is None or has zero string length.

Connect / reconnect / disconnect

connect()
connect(host, port=1883, keepalive=60, bind_address="")

The connect() function connects the client to a broker. This is a blocking function. It takes the following arguments:

host
the hostname or IP address of the remote broker
port
the network port of the server host to connect to. Defaults to 1883. Note that the default port for MQTT over SSL/TLS is 8883 so if you are using tls_set() the port may need providing manually
keepalive
maximum period in seconds allowed between communications with the broker. If no other messages are being exchanged, this controls the rate at which the client will send ping messages to the broker
bind_address
the IP address of a local network interface to bind this client to, assuming multiple interfaces exist
Callback

When the client receives a CONNACK message from the broker in response to the connect it generates an on_connect() callback.

Example
mqttc.connect("iot.eclipse.org")
connect_async()
connect_async(host, port=1883, keepalive=60, bind_address="")

Identical to connect(), but non-blocking. The connection will not complete until one of the loop*() functions is called.

Callback

When the client receives a CONNACK message from the broker in response to the connect it generates an on_connect() callback.

connect_srv()
connect_srv(domain, keepalive=60, bind_address="")

Connect to a broker using an SRV DNS lookup to obtain the broker address. Takes the following arguments:

domain
the DNS domain to search for SRV records. If None, try to determine the local domain name.

See connect() for a description of the keepalive and bind_address arguments.

Callback

When the client receives a CONNACK message from the broker in response to the connect it generates an on_connect() callback.

Example
mqttc.connect_srv("eclipse.org")
reconnect()
reconnect()

Reconnect to a broker using the previously provided details. You must have called connect*() before calling this function.

Callback

When the client receives a CONNACK message from the broker in response to the connect it generates an on_connect() callback.

disconnect()
disconnect()

Disconnect from the broker cleanly. Using disconnect() will not result in a will message being sent by the broker.

Callback

When the client has sent the disconnect message it generates an on_disconnect() callback.

Network loop

These functions are the driving force behind the client. If they are not called, incoming network data will not be processed and outgoing network data may not be sent in a timely fashion. There are four options for managing the network loop. Three are described here, the fourth in “External event loop support” below. Do not mix the different loop functions.

loop()
loop(timeout=1.0, max_packets=1)

Call regularly to process network events. This call waits in select() until the network socket is available for reading or writing, if appropriate, then handles the incoming/outgoing data. This function blocks for up to timeout seconds. timeout must not exceed the keepalive value for the client or your client will be regularly disconnected by the broker.

The max_packets argument is obsolete and should be left unset.

Example
run = True
while run:
    mqttc.loop()
loop_start() / loop_stop()
loop_start()
loop_stop(force=False)

These functions implement a threaded interface to the network loop. Calling loop_start() once, before or after connect*(), runs a thread in the background to call loop() automatically. This frees up the main thread for other work that may be blocking. This call also handles reconnecting to the broker. Call loop_stop() to stop the background thread. The force argument is currently ignored.

Example
mqttc.connect("iot.eclipse.org")
mqttc.loop_start()

while True:
    temperature = sensor.blocking_read()
    mqttc.publish("paho/temperature", temperature)
loop_forever()
loop_forever(timeout=1.0, max_packets=1)

This is a blocking form of the network loop and will not return until the client calls disconnect(). It automatically handles reconnecting.

The timeout and max_packets arguments are obsolete and should be left unset.

Publishing

Send a message from the client to the broker.

publish()
publish(topic, payload=None, qos=0, retain=False)

This causes a message to be sent to the broker and subsequently from the broker to any clients subscribing to matching topics. It takes the following arguments:

topic
the topic that the message should be published on
payload
the actual message to send. If not given, or set to None a zero length message will be used. Passing an int or float will result in the payload being converted to a string representing that number. If you wish to send a true int/float, use struct.pack() to create the payload you require
qos
the quality of service level to use
retain
if set to True, the message will be set as the “last known good”/retained message for the topic.

Returns a tuple (result, mid), where result is MQTT_ERR_SUCCESS to indicate success or MQTT_ERR_NO_CONN if the client is not currently connected. mid is the message ID for the publish request. The mid value can be used to track the publish request by checking against the mid argument in the on_publish() callback if it is defined.

A ValueError will be raised if topic is None, has zero length or is invalid (contains a wildcard), if qos is not one of 0, 1 or 2, or if the length of the payload is greater than 268435455 bytes.

Callback

When the message has been sent to the broker an on_publish() callback will be generated.

Subscribe / Unsubscribe

subscribe()
subscribe(topic, qos=0)

Subscribe the client to one or more topics.

This function may be called in three different ways:

Simple string and integer

e.g. subscribe("my/topic", 2)

topic
a string specifying the subscription topic to subscribe to.
qos
the desired quality of service level for the subscription. Defaults to 0.
String and integer tuple

e.g. subscribe(("my/topic", 1))

topic
a tuple of (topic, qos). Both topic and qos must be present in the tuple.
qos
not used.
List of string and integer tuples

e.g. subscribe([("my/topic", 0), ("another/topic", 2)])

This allows multiple topic subscriptions in a single SUBSCRIPTION command, which is more efficient than using multiple calls to subscribe().

topic
a list of tuple of format (topic, qos). Both topic and qos must be present in all of the tuples.
qos
not used.

The function returns a tuple (result, mid), where result is MQTT_ERR_SUCCESS to indicate success or (MQTT_ERR_NO_CONN, None) if the client is not currently connected. mid is the message ID for the subscribe request. The mid value can be used to track the subscribe request by checking against the mid argument in the on_subscribe() callback if it is defined.

Raises a ValueError if qos is not 0, 1 or 2, or if topic is None or has zero string length, or if topic is not a string, tuple or list.

Callback

When the broker has acknowledged the subscription, an on_subscribe() callback will be generated.

unsubscribe()
unsubscribe(topic)

Unsubscribe the client from one or more topics.

topic
a single string, or list of strings that are the subscription topics to unsubscribe from.

Returns a tuple (result, mid), where result is MQTT_ERR_SUCCESS to indicate success, or (MQTT_ERR_NO_CONN, None) if the client is not currently connected. mid is the message ID for the unsubscribe request. The mid value can be used to track the unsubscribe request by checking against the mid argument in the on_unsubscribe() callback if it is defined.

Raises a ValueError if topic is None or has zero string length, or is not a string or list.

Callback

When the broker has acknowledged the unsubscribe, an on_unsubscribe() callback will be generated.

Callbacks

on_connect()
on_connect(client, userdata, rc)

Called when the broker responds to our connection request.

client
the client instance for this callback
userdata
the private user data as set in Client() or userdata_set()
rc
the connection result

The value of rc indicates success or not:

0: Connection successful 1: Connection refused - incorrect protocol version 2: Connection refused - invalid client identifier 3: Connection refused - server unavailable 4: Connection refused - bad username or password 5: Connection refused - not authorised 6-255: Currently unused.
Example
def on_connect(client, userdata, rc):
    print("Connection returned result: "+connack_string(rc))

mqttc.on_connect = on_connect
...
on_disconnect()
on_disconnect(client, userdata, rc)

Called when the client disconnects from the broker.

client
the client instance for this callback
userdata
the private user data as set in Client() or userdata_set()
rc
the disconnection result

The rc parameter indicates the disconnection state. If MQTT_ERR_SUCCESS (0), the callback was called in response to a disconnect() call. If any other value the disconnection was unexpected, such as might be caused by a network error.

Example
def on_disconnect(client, userdata, rc):
    if rc != 0:
        print("Unexpected disconnection.")

mqttc.on_disconnect = on_disconnect
...
on_message()
on_message(client, userdata, message)

Called when a message has been received on a topic that the client subscribes to. This callback will be called for every message received. Use message_callback_add() to define multiple callbacks that will be called for specific topic filters.

client
the client instance for this callback
userdata
the private user data as set in Client() or userdata_set()
message
an instance of MQTTMessage. This is a class with members topic, payload, qos, retain.
Example
def on_message(client, userdata, message):
    print("Received message '" + str(message.payload) + "' on topic '"
        + message.topic + "' with QoS " + str(message.qos))

mqttc.on_message = on_message
...
message_callback_add()

This function allows you to define callbacks that handle incoming messages for specific subscription filters, including with wildcards. This lets you, for example, subscribe to sensors/# and have one callback to handle sensors/temperature and another to handle sensors/humidity.

message_callback_add(sub, callback)
sub
the subscription filter to match against for this callback. Only one callback may be defined per literal sub string
callback
the callback to be used. Takes the same form as the on_message callback.

If using message_callback_add() and on_message, only messages that do not match a subscription specific filter will be passed to the on_message callback.

message_callback_remove()

Remove a topic/subscription specific callback previously registered using message_callback_add().

message_callback_remove(sub)
sub
the subscription filter to remove
on_publish()
on_publish(client, userdata, mid)

Called when a message that was to be sent using the publish() call has completed transmission to the broker. For messages with QoS levels 1 and 2, this means that the appropriate handshakes have completed. For QoS 0, this simply means that the message has left the client. The mid variable matches the mid variable returned from the corresponding publish() call, to allow outgoing messages to be tracked.

This callback is important because even if the publish() call returns success, it does not always mean that the message has been sent.

on_subscribe()
on_subscribe(client, userdata, mid, granted_qos)

Called when the broker responds to a subscribe request. The mid variable matches the mid variable returned from the corresponding subscribe() call. The granted_qos variable is a list of integers that give the QoS level the broker has granted for each of the different subscription requests.

on_unsubscribe()
on_unsubscribe(client, userdata, mid)

Called when the broker responds to an unsubscribe request. The mid variable matches the mid variable returned from the corresponding unsubscribe() call.

on_log()
on_log(client, userdata, level, buf)

Called when the client has log information. Define to allow debugging. The level variable gives the severity of the message and will be one of MQTT_LOG_INFO, MQTT_LOG_NOTICE, MQTT_LOG_WARNING, MQTT_LOG_ERR, and MQTT_LOG_DEBUG. The message itself is in buf.

External event loop support

loop_read()
loop_read(max_packets=1)

Call when the socket is ready for reading. max_packets is obsolete and should be left unset.

loop_write()
loop_write(max_packets=1)

Call when the socket is ready for writing. max_packets is obsolete and should be left unset.

loop_misc()
loop_misc()

Call every few seconds to handle message retrying and pings.

socket()
socket()

Returns the socket object in use in the client to allow interfacing with other event loops.

want_write()
want_write()

Returns true if there is data waiting to be written, to allow interfacing the client with other event loops.

Global helper functions

The client module also offers some global helper functions.

topic_matches_sub(sub, topic) can be used to check whether a topic matches a subscription.

For example:

the topic foo/bar would match the subscription foo/# or +/bar

the topic non/matching would not match the subscription non/+/+

connack_string(connack_code) returns the error string associated with a CONNACK result.

error_string(mqtt_errno) returns the error string associated with a Paho MQTT error number.

Publish

This module provides some helper functions to allow straightforward publishing of messages in a one-shot manner. In other words, they are useful for the situation where you have a single/multiple messages you want to publish to a broker, then disconnect with nothing else required.

The two functions provided are single() and multiple().

Single

Publish a single message to a broker, then disconnect cleanly.

single(topic, payload=None, qos=0, retain=False, hostname="localhost",
    port=1883, client_id="", keepalive=60, will=None, auth=None, tls=None,
    protocol=mqtt.MQTTv31)
Function arguments
topic
the only required argument must be the topic string to which the payload will be published.
payload
the payload to be published. If “” or None, a zero length payload will be published.
qos
the qos to use when publishing, default to 0.
retain
set the message to be retained (True) or not (False).
hostname
a string containing the address of the broker to connect to. Defaults to localhost.
port
the port to connect to the broker on. Defaults to 1883.
client_id
the MQTT client id to use. If “” or None, the Paho library will generate a client id automatically.
keepalive
the keepalive timeout value for the client. Defaults to 60 seconds.
will

a dict containing will parameters for the client:

will = {‘topic’: “<topic>”, ‘payload’:”<payload”>, ‘qos’:<qos>, ‘retain’:<retain>}.

Topic is required, all other parameters are optional and will default to None, 0 and False respectively.

Defaults to None, which indicates no will should be used.

auth

a dict containing authentication parameters for the client:

auth = {‘username’:”<username>”, ‘password’:”<password>”}

Username is required, password is optional and will default to None if not provided.

Defaults to None, which indicates no authentication is to be used.

tls

a dict containing TLS configuration parameters for the client:

dict = {‘ca_certs’:”<ca_certs>”, ‘certfile’:”<certfile>”, ‘keyfile’:”<keyfile>”, ‘tls_version’:”<tls_version>”, ‘ciphers’:”<ciphers”>}

ca_certs is required, all other parameters are optional and will default to None if not provided, which results in the client using the default behaviour - see the paho.mqtt.client documentation.

Defaults to None, which indicates that TLS should not be used.

protocol
choose the version of the MQTT protocol to use. Use either MQTTv31 or MQTTv311.
Example
import paho.mqtt.publish as publish

publish.single("paho/test/single", "payload", hostname="iot.eclipse.org")

Multiple

Publish multiple messages to a broker, then disconnect cleanly.

multiple(msgs, hostname="localhost", port=1883, client_id="", keepalive=60,
    will=None, auth=None, tls=None, protocol=mqtt.MQTTv31)
Function arguments
msgs

a list of messages to publish. Each message is either a dict or a tuple.

If a dict, only the topic must be present. Default values will be used for any missing arguments. The dict must be of the form:

msg = {‘topic’:”<topic>”, ‘payload’:”<payload>”, ‘qos’:<qos>, ‘retain’:<retain>}

topic must be present and may not be empty. If payload is “”, None or not present then a zero length payload will be published. If qos is not present, the default of 0 is used. If retain is not present, the default of False is used.

If a tuple, then it must be of the form:

(“<topic>”, “<payload>”, qos, retain)

See single() for the description of hostname, port, client_id, keepalive, will, auth, tls, protocol.

Example
import paho.mqtt.publish as publish

msgs = [{'topic':"paho/test/multiple", 'payload':"multiple 1"},
    ("paho/test/multiple", "multiple 2", 0, False)]
publish.multiple(msgs, hostname="iot.eclipse.org")

Reporting bugs

Please report bugs under the “MQTT-Python” Component in Eclipse Bugzilla for the Paho Technology project.

More information

Discussion of the Paho clients takes place on the Eclipse paho-dev mailing list.

General questions about the MQTT protocol are discussed in the MQTT Google Group.

There is much more information available via the MQTT community site.

 
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