Cannot Obtain Packet ID on Publish, Making Concurrent Publishes Difficult

[aa51513]

Description
In rumqttc, when calling AsyncClient::publish(), there is no way to retrieve the MQTT packet identifier (packet_id) assigned to the message. This makes it difficult to implement reliable message tracking and retransmission logic for concurrent publishes, since packet_id is only available later through Event::Outgoing(Outgoing::Publish(publish)).

Steps to Reproduce

1. Create an AsyncClient.

2. Call client.publish(topic, qos, retain, payload).await.

3. There is no return value for packet_id.

Expected Behavior
I would expect publish() to either:

• Return the assigned packet_id immediately, or

• Provide a mechanism to attach user-defined correlation data that can be reliably retrieved with the packet_id in Outgoing::Publish.

This would allow safely implementing concurrent publishes and retransmission logic without relying on a FIFO matching queue.

Actual Behavior

• publish() returns ()

• Packet_id is only visible asynchronously via Event::Outgoing, requiring a pending queue or FIFO matching that blocks true concurrency.

Use Case

• Providing a Future handle upon publish, allowing retrieval of the packet_id used for this send, which would greatly facilitate message retransmission management.

• Supporting fully concurrent publishing while maintaining correct mapping between messages and packet_id.

Suggested Solution

• Either return the assigned packet_id from publish(), or

• Provide a built-in way to attach a correlation ID to a publish message that is guaranteed to appear with its packet_id in Event::Outgoing.

Environment

rumqttc version: [0.25.0]

[giridher-art]

hey @aa51513 , thanks for opening the issue . we are currently working on new architecture of the rumqttc and it aims to include all the required features. and we release new architecture ASAP.