MQTTv5 support in rumqttd

[swanandx]

This issue is for tracking the progress of MQTTv5 support in our broker ( rumqttd ) 🚀

We encourage everyone to try out MQTTv5 and help us with your valuable feedback & contributions. Feel free to comment below <3

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Features

Done

• Topic Alias ( Topic alias and message expiry support in broker #616 )
• Message Expiry ( Topic alias and message expiry support in broker #616 )
• Shared Subscriptions ( Shared subscriptions with random strategy #628 --> Shared subscriptions with configurable strategy #668 )
• Subscription IDs ( Subscription IDs support in broker #632 )
• Request / Response pattern
• Will delay ( Will messages and will delay interval #686 )

WIP / Under Review

• Session Expiry ( Session expiry and clean start in rumqttd #691 )
• Flow Control ( Flow control in rumqttd #695 )
• Subscription Options ( Subscription options support in rumqttd #701 )
• Assign client ID ( feat(rumqttd): assign random client identifier to clients #709 )
• Maximum Packet Size ( Maximum packet size in MQTTv5 #714 )
• Payload format and content-type ( Payload format indicator in Publish and LastWill #715 )
• Server Disconnect

TODO

• Reason code and string on ACKs
• Enhanced Auth

Supported, but not in use

• Server reference / redirect
• Server Keep Alive
• Optional Server feature availability
• User Properties

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NOTE: Features having partial support aren't marked as Done, like server disconnect etc. e.g. we have ability to send Disconnect packets, but we aren't sending them everywhere yet.
Support for some features can be very subjective, e.g. User Properties or Enhanced Auth.

[tmbull]

Hi @swanandx . I was wondering if there was any blocker (other than the maintainers' time) to merging these features in? I am interested in using rumqttd, primarily due to the embeddable nature of the service, but I have clients that are already leveraging MQTT5 features.

[swanandx]

Hey @tmbull, as you mentioned already, maintainers' time is the blocker, and I think getting those PRs reviewed before merging would be better, but if its urgent, we can try to figure out some workaround like merging without review ( though I don't support it much 🤣 ) or prioritize reviews.

Can you please let me know specifically which MQTTv5 features are required by those clients, so those can be prioritized?

Thank you for your interest 💯

[tmbull]

Thanks for the quick reply! Shared subscriptions are the big feature for me, which you already have merged in. Session expiry and max packet size would be nice to have, but it is not an urgent matter so please take your time!