redpanda-data / redpanda-data/connect

Contribution Submission: MQTT v5 Input and Output components

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Dominant language
Go
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Description

Background

We are evaluating Redpanda Connect for use in our data pipelines, but this use case requires MQTT v5 support, which currently does not exist for Redpanda Connect. Currently only MQTT v3.1.1 is supported via the mqtt input and output using the paho.mqtt.golang library.

Prior Work

There were two prior attempts to contribute MQTT v5 support to Redpanda Connect:

  • PR #2197: Was closed due to withdrawal of the contribution on change from Benthos to Redpanda Connect.
  • PR #3731: Was closed due to unaccepted CLA.

Kafka Connect Equivalent

There is no Kafka Connect equivalent since the Kafka Connect MQTT source connector is also based on an MQTT v3.1.1 paho library.

Proposal

We would like to contribute a new mqtt5 input and output component. Per §3.1.1 of the CONTRIBUTING.md, code written by non-Redpanda engineers needs to be reviewed and scoped by Redpanda. We are opening this issue to ask for comments on two points:

  1. Is an MQTT v5 input and output component still desired/wanted by Redpanda?
  2. Is the following scope properly sized for a MQTT v5 input and output component?

Intended Scope

  • A new, separate mqtt5 input and output component.
  • Written in Go and based on paho.golang. This library is written by the same authors as the mqtt.paho.golang library that is already in use with the mqtt connector.
  • Code structure will mirror the existing mqtt connector where it makes sense.
  • All configuration fields shared with the existing mqtt connector are carried over unchanged
  • New mqtt5 input config options:
Field Notes
session_expiry_interval How long the broker retains session state after disconnect.
receive_maximum Maximum in-flight QoS 1/2 messages the broker may send to this client simultaneously.
maximum_packet_size Maximum packet size this client will accept from the broker.
no_local Subscription option: do not receive messages published by this client.
retain_as_published Subscription option: preserve the retain flag from the original publisher.
retain_handling Subscription option: controls whether retained messages are sent on subscribe.
topic_alias_maximum Maximum number of topic aliases this client will accept from the broker. 0 disables topic aliases.
subscription_identifiers Enables the use of subscription identifiers by the client.
will_* Full v5 will message config.
  • Metadata set by the mqtt5 input:
Metadata key Source
mqtt5_user_properties_<key> User Properties from the PUBLISH packet. If a key appears only once, it is stored as-is.
mqtt5_user_properties_<key>_<idx> User Properties from the PUBLISH packet can have the same key multiple times. If this happens they receive a zero-based index as a suffix
mqtt5_content_type Content Type
mqtt5_payload_format_indicator Payload Format Indicator
mqtt5_response_topic Response Topic
mqtt5_correlation_data Correlation Data
mqtt5_subscription_identifier Subscription identifier sent by the broker
  • New mqtt5 output config options:
Field Notes
session_expiry_interval How long the broker retains session state after disconnect.
message_expiry_interval Per-message TTL. Broker drops the message if undelivered before expiry.
topic_alias_maximum Maximum number of topic aliases this client will use when publishing. 0 disables topic aliases.
will_* Full v5 will message config.
  • Metadata read by the mqtt5 output:
Metadata key Written to
mqtt5_user_properties_<key> User Properties on the PUBLISH packet. Plain keys (mqtt5_user_properties_<key>) are written as single entries. Indexed keys (mqtt5_user_properties_<key>_0, _1, etc.) are reassembled into multiple User Properties with the same key, preserving order.
mqtt5_content_type Content Type
mqtt5_payload_format_indicator Payload Format Indicator
mqtt5_response_topic Response Topic
mqtt5_correlation_data Correlation Data
  • Other MQTT v5 Behavior:
    • Shared Subscriptions are supported by the underlying library.
    • Reason codes will be surfaced in error messages.
    • Server-initiated DISCONNECT is handled by the underlying library.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reading CONTRIBUTING.md §3.1.1 and the existing mqtt input and output components, then review the proposed paho.golang-based configuration and metadata scope. Done means Redpanda confirms that MQTT v5 support is wanted, approves the scope, and defines the implementation and testing expectations for the new mqtt5 components.

Written by the indexing model from the issue text.

Assessment

Tech stack
go
Domain
data-engineering, stream-processing
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Quiet
Clarity
Needs clarification
Newbie friendliness
35/100

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