MessageAudit

Overview

mqtt-spy and mqtt-spy-daemon allow you to create message audit logs. These are dedicated log files that only contain received messages (as opposed to diagnostic log, which contains all sorts of information about the internal workings of the application).

The main benefit of having a message log is that you can then perform analysis of the received messages, even hours or days after being the actual message being received.

You can either use mqtt-spy to browse a message audit log offline, and then use all the filtering and searching functionality, or write your own scripts or tools to analyse them. Each logged message contains an index (or ID), a timestamp and all the usual message properties (e.g. topic, QoS, payload).

Further to that, you can also replay those messages at different speeds by running a replay script in mqtt-spy or mqtt-spy-daemon.

Creating message log

For details on how to perform the replay see the Message Audit Recording wiki.

Message log replay

For details on how to perform the replay see the Message Audit Replay wiki.

Off-line analysis (mqtt-spy only)

To browse a message log file, from the main menu select Window -> Open view -> Message audit log browser. When prompted, selected the message audit log file (normally with .messages extension). Once the file has been loaded, a new tab will appear. Logged messages can be now browsed in the same way as during normal broker connection, including filtering and searching.

Message audit log format

Messages are written to a text file, one message per line. Each line is an XML document with MqttMessage element. The value of the element is the payload of the message. The attributes describe various properties of the message, e.g. its ID (set to 1 at start-up), timestamp (in milliseconds), topic, quality of service, retained flag, connection name, subscription and encoded flag. Some of these fields are optional and might not be included.

Message payload can be either written as Base64 encoded string (e.g. when binary messages are handled), or as plain text wrapped in XML CDATA tags if necessary.

Sample message log

<MqttMessage id="1" timestamp="1415830549180" topic="/home/bedroom/current" qos="0" retained="false" ><![CDATA[<temp>20.5</temp><energy>110</energy>]]></MqttMessage>
<MqttMessage id="2" timestamp="1415830550249" topic="/home/bedroom/current" qos="0" retained="false" ><![CDATA[<temp>20.8</temp><energy>102</energy>]]></MqttMessage>
<MqttMessage id="3" timestamp="1415830551255" topic="/home/bedroom/current" qos="0" retained="false" ><![CDATA[<temp>20.9</temp><energy>104</energy>]]></MqttMessage>
<MqttMessage id="4" timestamp="1415830552256" topic="/home/bedroom/current" qos="0" retained="false" ><![CDATA[<temp>20.6</temp><energy>108</energy>]]></MqttMessage>