plugins can modify outgoing messages and subscriptions

[abiliojr]

These changes allow plugins to modify outgoing messages, and subscription topics/qos. Some features that could be built using this changes:

• Dynamically limit the subscription QoS for some clients (example included)
• Topic remapping/jailing (example included)
• MQTT v5 to v3.1.1 translation: properties might be placed in the payload for v3.1.1 clients
• Compression/decompression of retained messages: might be useful on big size/low throughput applications
• Selective modification of properties based on the destination

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[wickywaka]

First time looking at mosquitto code so sorry for my lack of understanding, but my questions is: Would this allow for making changes like adding a new property to an mqtt5 message. I want my bridge on the edge to add timestamps to sensor data before sending it to the cloud.

Edit 1: May be this is what I need: https://github.com/eclipse/mosquitto/blob/master/plugins/message-timestamp/mosquitto_message_timestamp.c

[abiliojr]

I believe these changes will allow you to timestamp outgoing messages only. Of course, you don't want to timestamp all the messages, just the ones going to the cloud. This means you will have to filter by something like clientid (and assign a well known clientid to your bridge connection).

[wickywaka]

This looks like a good idea and can actually work in a cleaner way. Thanks. Also thanks for the reply in the mailing list, it was in my spam.

[chrblabla]

Hi @ralight, I also think this is a reasonable and helpful addition from @abiliojr (thank you!). What would need to happen to get this in?

[abiliojr]

up to date with develop

[Nikolay-Ch]

Sorry, but when this feature will be merged into master? And, when will the new release of Mosquitto?

[ralight]

This has been merged, but github hasn't recognised it as being merged for some reason.