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How to debug MQTT session using Proxy channel

Resolving the MQTT connectivity issues faster by analyzing raw MQTT traffic.

Many flespi integrations are accomplished using MQTT API. But each integration is unique: different systems, technologies, architecture solutions, and MQTT libraries may lead to various MQTT connection problems. This article describes how to analyze raw MQTT session traffic which may help you diagnose such problems as:

  • failure to establish the connection

  • unexpected disconnect

  • missing subscription messages

1.Create a channel

Create a proxy channel, specify mqtt.flespi.io:1883 as target URI, make this target Mandatory, and enable Proxy replies back to the client.

create proxy channel

2.Configure MQTT connection

You should use your channel URI to connect the MQTT client to the broker. If you use SSL connection to port 8883, you can hardly see the message details, so we recommend to use the unencrypted session for debug purposes.

configure mqtt connection

3.Test MQTT connection

Subscribe your client for some topic with MQTT API data, do some manual publishing or just try to reproduce the error-causing situation.

test mqtt connection

4.Explore raw MQTT traffic

Use HEX viewer to analyze what’s inside the MQTT connection. E.g. this is the CONNECT packet

explore raw mqtt traffic in hex viewer

This is an example of a published packet:

published mqtt packet in hex viewer

If you need to analyze the raw data that comes inside the connection, you should refer to the MQTT specification of the appropriate protocol version you use in your application.


See also
Obtain telematics data from Jimi Concox devices via API in 5 easy steps.
Using flespi plugins to pack together the data coming from two or more related devices.