Hermes: Conditionally spawn the relayer worker only if there are outstanding packets

[adizere]

Crate

relayer

Summary

We should optimize the starting of a worker for a UnidirectionalChannelPath, so that the worker only get spawned if there is any outstanding packets to relay (e.g., unreceived packets or unreceived acks).

Problem Definition

Currently, within the multi-start command, the workers for UnidirectionalChannelPath get spawned as soon as Hermes detects an open channel. This worker, however, might not have any job to do if there are no outstanding packets to relay.

https://github.com/informalsystems/ibc-rs/blob/13f592b8a4db47356a057470949c41361391564a/relayer/src/supervisor.rs#L231-L238

Proposal

Prior to spawning the worker for UnidirectionalChannelPath, we should detect if there are unreceived packets (or acks). To detect this, we can reuse functionality from query CLIs UnreceivedPackets (and UnreceivedAcks), see . The query CLI implementation, however, spawns its own runtimes and consequently it is awkward to reuse it.

Acceptance Criteria

We should probably proceed as follows:

• refactor the logic in CLIs for UnreceivedPackets and UnreceivedAcks. Ideally, we should encapsulate the logic for detecting outstanding packets in some methods, and reuse those methods both from the CLI queries and from multi-start command.
• adapt the behavior for the multi-start command, in the supervisor to conditionally spawn a worker for UnidirectionalChannelPath only if there are outstanding packets to relay.
• the same modifications should occur for the start command

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate milestone (priority) applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned