paho.mqtt.golang | repository contains the source code | Pub Sub library
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QUESTION
I want to implement some sort of message fanout using https://github.com/eclipse/paho.mqtt.golang.
I was expecting the client to connect and publish to all the brokers. But I can see in their respective dashboards that it just connects to 1 of those brokers.
...ANSWER
Answered 2021-Nov-09 at 13:35MQTT is a topic-based model, 1 broker has multiple clients, not the other way around.
Some brokers (e.g. mosquitto) support bridging, which allows to build a fanout setup across brokers, but this setup is at broker level, the core MQTT functionality is still 1 broker per client connection. If you want to publish to multiple brokers, you'd need to connect to each one and publish individually.
QUESTION
I've a mosquitto broker that is running in server behind a firewall. Ports needed are open and, from outside, I check that it's working with:
...ANSWER
Answered 2021-Jul-29 at 20:55As per the comments - the issue was due to another client using the same client id. The easiest way to check for this is to read the broker logs (from the clients perspective the connection is just dropped without warning).
The MQTT spec states:
The Server MUST process a second CONNECT Packet sent from a Client as a protocol violation and disconnect the Client [MQTT-3.1.0-2]. See section 4.8 for information about handling errors.
This is a fairly common issue (and is the first thing mentioned in the common problems section of the project readme).
QUESTION
I would like to store a mqtt client in a struct and use this client throughout the application.
My project structure looks like this:
...ANSWER
Answered 2021-Jul-23 at 09:43If you want to have a struct available throughout your code, you might want to use a Singleton Pattern [1].
In Go you basically define an exported global variable in a package which will be available by all code that imports the package.
You can have client live in payload package (or whichever works for you, this is just an example):
QUESTION
I am using the paho.mqtt.golang library to connect to a broker and publish message.
It's working fine except that I don't have errors when the publish failed.
The test I'm doing is as follow:
- I start the broker
- I run my code to connect to the broker. After connection the code waits for an input to proceed to publish
- I kill the broker
- I press enter to proceed to publish the message
I would expect an error with the token returned by the publish function if token.Error() != nil {...} but I got none.
Here is the code of the publish function:
...ANSWER
Answered 2021-May-27 at 20:17From the docs:
QUESTION
I am quite new to MQTT and brokers, but I am having an issue with VerneMQ not sending offline messages to clients. Here is my setup. I have a backend written in Python which is using the Paho Eclipse MQTT library's single() method to send messages to a connected client. The client, a virtual machine on my development station, has a client which is written in go-lang, using paho.mqtt.golang to connect to the broker and subscribe.
The call to single() on the backend looks like this:
...ANSWER
Answered 2020-Nov-19 at 09:03As thrashed out in the comments
Messages will only be queued for an offline client that has subscribed at greater than QOS 0
More details can be found here
QUESTION
I was reviewing MQTT v5 differences and noticed that "header" information can be published outside the body of the message with user properties. Is there support for this in paho.mqtt.golang? Looking at the Publish function, there is only support for client.Publish(topic, qos, retain, message_bytes).
...ANSWER
Answered 2020-Nov-19 at 08:47paho.mqtt.golang only supports MQTT 3/3.1. If you want properties, which were introduced in v5, take a look at paho.golang which is a total rewrite that supports MQTT v5 (and v5 only). Support for properties is demonstrated in the chat example:
QUESTION
I am seeing inconsistent message delivery with message persistence and qos=2 on mosquitto. Is there anything I'm doing wrong?
I have a simple test app that registers a topic for consumption with clientId="receive-client", but immediately disconnects. It then connects as clientId="send-client" and publishes 10 messages, "message #1" ... "message #10". Then disconnects, waits five seconds, and connects to consume with "receive-client" again while printing and counting the messages received.
The result is inconsistent. Sometimes I receive 6 messages, sometimes 8. Typical output is something like this:
...ANSWER
Answered 2020-Oct-28 at 16:00To publish at QOS 2 is a multi step process so the most likely reason is that you are disconnecting the publishing client before all the messages are actually finishing publishing to the broker.
You should probably do that publishing in a loop and using the returned token from the call to client.publish() to wait until it has completed before disconnecting the client.
e.g. as shown in the example:
QUESTION
I am exploring mosquitto as a complete beginner. I have a golang test program that I'm using to see how it manages messages, but subsequent runs of the program show an extra message received.
...ANSWER
Answered 2020-Oct-12 at 23:16Publish is defined as follows:
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