How to implement fire-and-forget pattern

[oskin1]

Some sub-protocols in my application require sending to concrete peers just a single message. Does libp2p-rust allow to send a message to some PeerId without negotiating a substream?

[thomaseizinger]

If you use the Upgrade::V1Lazy strategy, negotiating substreams is 0RTT. The OneShotHandler may be useful for your usecase: https://github.com/libp2p/rust-libp2p/blob/master/swarm/src/handler/one_shot.rs

[oskin1]

@thomaseizinger Thanks!
Where do I specify upgrade strategy? Also, can I somehow combine Upgrade::V1Lazy and Upgrade::V1 to support both one-shot protocols and protocols that require negotiation?

[thomaseizinger]

V1Lazy is backwards-compatible to V1, see its docs: https://docs.rs/libp2p/0.51.3/libp2p/core/upgrade/enum.Version.html

See the identify example for how to use it: https://github.com/libp2p/rust-libp2p/blob/master/examples/identify/src/main.rs#L55

[oskin1]

@thomaseizinger Yes, in the documentation for V1Lazy it is said that "This strategy is only applicable for the node with the role of “dialer” in the negotiation and only if the dialer supports just a single application protocol.", while in my case the node should still support both dialing and listening for a number of other protocols.

[thomaseizinger]

The configuration option is ignored for listening so you are all good. You can set it to V1Lazy without problems. In fact, we want to make it the default: #3563