MQTT Module

Thomas Weber

Edited by

Thomas weber

Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. External Libraries or Applications
3. Parameters
3.1. host (str)
3.2. port (int)
3.3. keepalive (int)
3.4. id (str)
3.5. username (str)
3.6. password (str)
3.7. will_topic (str)
3.8. will (str)
3.9. event_callback (str)
3.10. ca_file (str)
3.11. ca_path (str)
3.12. tls_method (str)
3.13. certificate (str)
3.14. private_key (str)
3.15. cipher_list (str)
3.16. verify_certificate (str)
4. Functions
4.1. mqtt_subscribe(topic, qos)
4.2. mqtt_unsubscribe(topic)
4.3. mqtt_publish(topic, message, qos)
5. Event routes
5.1. mqtt:connected
5.2. mqtt:disconnected
5.3. mqtt:message
6. Exported pseudo-variables

List of Examples

1.1. Set host parameter
1.2. Set port parameter
1.3. Set keepalive parameter
1.4. Set id parameter
1.5. Set username parameter
1.6. Set password parameter
1.7. Set will_topic parameter
1.8. Set will parameter
1.9. Set event_callback parameter
1.10. Set ca_file parameter
1.11. Set ca_path parameter
1.12. Set tls_method parameter
1.13. Set certificate parameter
1.14. Set private_key parameter
1.15. Set cipher_list parameter
1.16. Set verify_certificate parameter
1.17. mqtt_subscribe usage
1.18. mqtt_unsubscribe usage
1.19. mqtt_publish usage

Chapter 1. Admin Guide

1. Overview

The MQTT module allows bidirectional publish/subscribe communication by connecting Kamailio to a MQTT Broker.

Messages can be published from any point in the routing script. Also the subscriptions can be fully controlled by scripting commands.

2. Dependencies

2.1. External Libraries or Applications

The following libraries or applications must be installed before running Kamailio with this module loaded:

3. Parameters

3.1. host (str)

MQTT Broker IP/Hostname.

No default, this parameter is mandatory.

Example 1.1. Set host parameter

modparam("mqtt", "host", "")

3.2. port (int)

MQTT Broker port number.

Default value is 1883.

Example 1.2. Set port parameter

modparam("mqtt", "port", 1883)

3.3. keepalive (int)

The number of seconds after which the broker should send a PING message to the kamailio if no other messages have been exchanged in that time.

Default value is 5.

Example 1.3. Set keepalive parameter

modparam("mqtt", "keepalive", 5)

3.4. id (str)

String to use as the mqtt client id. If NULL, a random client id will be generated.

Default value is NULL.

Example 1.4. Set id parameter

modparam("mqtt", "id", "kamailio123")

3.5. username (str)

The username to send as a string or NULL to disable authentication.

Default value is NULL (no authentication). Must be used together with password.

Example 1.5. Set username parameter

modparam("mqtt", "username", "kamailio-user")

3.6. password (str)

The password to send as a string or NULL to disable authentication.

Default value is NULL (no authentication). Must be used together with username.

Example 1.6. Set password parameter

modparam("mqtt", "password", "supers3cre7")

3.7. will_topic (str)

The topic on which to publish the mqtt will.

Default value is NULL. Must be used together with will.

Example 1.7. Set will_topic parameter

modparam("mqtt", "will_topic", "kamailio123")

3.8. will (str)

The mqtt will payload to be published.

Default value is NULL. Must be used together with will_topic.

Example 1.8. Set will parameter

modparam("mqtt", "will", "gone")

3.9. event_callback (str)

The name of the function in the kemi configuration file (embedded scripting language such as Lua, Python, ...) to be executed instead of event_route[...] blocks.

The function receives a string parameter with the name of the event, the values are: 'mqtt:connected', 'mqtt:disconnected', 'mqtt:message'.

Default value is 'empty' (no function is executed for events).

Example 1.9. Set event_callback parameter

modparam("mqtt", "event_callback", "ksr_mqtt_event")
-- event callback function implemented in Lua
function ksr_mqtt_event(evname)"===== mqtt module triggered event: " .. evname .. "\n");
	return 1;

-- event callback function implemented in Python
function ksr_mqtt_event(self, msg, evname)"===== mqtt module triggered event: %s\n" % evname);
	return 1;

3.10. ca_file (str)

Path to a file containing the PEM encoded trusted CA certificate files.

Default value is NULL. Set either this parameter or ca_path if you want to connect via TLS.

Example 1.10. Set ca_file parameter

modparam("mqtt", "ca_file", "/etc/ssl/certs/myca.pem")

3.11. ca_path (str)

Used to define a directory that contains PEM encoded CA certificates that are trusted. For ca_path to work correctly, the certificates files must have ".pem" as the file ending and you must run "openssl rehash /your/ca_path" each time you add/remove a certificate.

Default value is NULL. Set either this parameter or ca_file if you want to connect via TLS. ca_file and ca_path are mutual exclusive.

Example 1.11. Set ca_path parameter

modparam("mqtt", "ca_path", "/etc/ssl/certs")

3.12. tls_method (str)

The version of the SSL/TLS protocol to use as a string. If NULL, the default value is used. The default value and the available values depend on the version of openssl that libmosquitto was compiled against.

Possible values:

  • tlsv1.3 is available with openssl >= 1.1.1 together with libmosquitto v1.6.8 and newer.

  • For openssl >= 1.0.1, the available options are tlsv1.2, tlsv1.1 and tlsv1, with tlv1.2 as the default.

  • For openssl < 1.0.1, only tlsv1 is available.

Default value is NULL.

Example 1.12. Set tls_method parameter

modparam("mqtt", "tls_method", "tlsv1.3")

3.13. certificate (str)

Path to a file containing the PEM encoded certificate file for a TLS client connection.

Default value is NULL. If NULL, private_key must also be NULL and no client certificate will be used.

Example 1.13. Set certificate parameter

modparam("mqtt", "certificate", "/etc/ssl/certs/myclient.pem")

3.14. private_key (str)

Path to a file containing the PEM encoded private key for a TLS client connection.

Default value is NULL. If NULL, certificate must also be NULL and no client certificate will be used.

Example 1.14. Set private_key parameter

modparam("mqtt", "private_key", "/etc/ssl/private/myclient.key")

3.15. cipher_list (str)

A string describing the ciphers available for use. See the cipher(1) OpenSSL man page. If NULL, the libssl default ciphers will be used.

Default value is NULL.

Example 1.15. Set cipher_list parameter

modparam("mqtt", "cipher_list", "HIGH")

3.16. verify_certificate (str)

Configure verification of the server certificate. If value is set to 0, 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 disable verification in a real system as it makes the connection encryption pointless.

Default value is 1.

Example 1.16. Set verify_certificate parameter

modparam("mqtt", "verify_certificate", "0")

4. Functions

4.1.  mqtt_subscribe(topic, qos)

Subscribe to the given topic. Mqtt qos levels 0, 1 and 2 can be used.

The function is passing the task to mqtt dispatcher process, therefore the SIP worker process is not blocked.

Incoming messages for this topic are then handled by the same process and exposed to the event_route[mqtt:message].

This function can be used from ANY_ROUTE.

Example 1.17. mqtt_subscribe usage

mqtt_subscribe("kamailio/script", 0);

4.2.  mqtt_unsubscribe(topic)

Unsubscribe to a previously subscribed topic. The mqtt broker will stop forwarding messages for this topic.

This function can be used from ANY_ROUTE.

Example 1.18. mqtt_unsubscribe usage


4.3.  mqtt_publish(topic, message, qos)

Send out a message to a topic with a specified mqtt qos level (0, 1, 2). Again the actual sending is done in a mqtt dispatcher process and will not block the SIP worker.

Example 1.19. mqtt_publish usage

mqtt_publish("kamailio/event", "some message", 0);

5. Event routes

5.1.  mqtt:connected

If defined, the module calls event_route[mqtt:connected] when a outgoing broker connection is established.

MQTT subscriptions are not durable, so you should use this event route to manage your subscriptions.

event_route[mqtt:connected] {
        xlog("mqtt connected !\n");
        mqtt_subscribe("kamailio/script", 0);

5.2.  mqtt:disconnected

If defined, the module calls event_route[mqtt:disconnected] when the broker connection is lost.

The module will automatically try to reconnect to the broker every 3 seconds.

event_route[mqtt:disconnected] {
    xlog("Lost mqtt connection !\n");

5.3.  mqtt:message

If defined, the module calls event_route[mqtt:message] when a message is received from the broker.

All incoming messages are handled in a single mqtt dispatcher process.

event_route[mqtt:message] {
	xlog("mqtt message received: $mqtt(topic) -> $mqtt(msg) !\n");

6. Exported pseudo-variables

  • $mqtt(topic) - Received topic (only in mqtt:message)

  • $mqtt(msg) - Received message (only in mqtt:message)

  • $mqtt(qos) - The received message QOS level: 0, 1 ,2 (only in mqtt:message)

Exported pseudo-variables are documented at