Using `store_offset` with `OwnedMessage`

[bruceg]

I would like to use the Consumer::store_offset interface to update the offset asynchronously after a message has been fully processed. Currently, this interface takes a BorrowedMessage parameter, but I have not figured a way to use this type due to needing a static lifetime on the async block. I could detach the borrowed message into an OwnedMessage to satisfy the static lifetime requirement, but store_offset takes a BorrowedMessage parameter and there is no way to produce one from an OwnedMessage. Even if this was possible, it is far from ideal, as store_offset only actually requires the topic, partition, and offset data, and storing the entire message just to access those is rather inefficient.

Is there another way to achieve this process?

[bruceg]

IMO ideally Consumer::store_offset would take a generic parameter that is Into some intermediate type that stores references to the three pieces of data required. This intermediate type could then be implemented for BorrowedMessage, OwnedMessage, and hopefully a new type that just stored the topic, partition, and offset. This would make it a different interface, but one that should only break code that implements trait Consumer, which I would expect to be rare in consumers of this crate.

[binarylogic]

@fede1024 thanks for your work on this library. It looks like @blt, another Vector engineer, filed a similar issue (#89). If you could approve this direction we'd be happy to contribute the change.

[benesch]

If you have a minute, #376 should do what you need!