Requested enhancements to MQTT

Based on a lot of work and discussion within the Industry 4.0/Smart Manufacturing community, Iâd like to present the following recommendations for changes to MQTT to better meet the needs of the user community.

- Move beyond 4 bits for message type (recommended : 8 bits). This is a limitation that will impact the ability to expand/extend the protocol.

- Multi-publish is essential (publish more than one topic in a single message)

- Topics should have durable metadata (could be passed as headers in publish or as its own message type â in effect these are retained user properties for a topic)

- Payloads should have a data type (mime type) to enable parsing/processing by subscribers or intermediaries

- Topic binding should be a built-in broker feature (like a symlink) - topic aliases are not this

- The lack of a capability to query topics is a huge flaw/gap. Ideally these queries should be able to include metadata filters as well. Ideally this will also be bound to a standardized REST or GraphQL API

- MQTT's subscription patterns are extremely limiting. They should support richer match expressions and also metadata filters.

- MQTT should officially support a REST binding for request/response, query (topics, data and metadata), synchronous publish, synchronous read of retained values, subscribe/unsubscribe (via webhooks)

- Handling of RPC/method invocations over MQTT remains quite awkward. This MUST be addressed to enable MQTT to be more effectively utilized as a universal transport for industrial applications.

I would be happy to discuss these in more detail.

Rick Bullotta

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