examples/gossipsub-chat: Add mDNS peer discovery

[andrewdavidmackenzie]

Description

This PR adds the discovery of other peers using mDNS to the gossipsub example, allowing each peer to not have to know the address of the first peer to connect to.

Links to any relevant issues

N/A

Open Questions

N/A

Change checklist

• [ X ] I have performed a self-review of my own code
• [ X ] I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[thomaseizinger]

Just one comment, otherwise LGTM!

[andrewdavidmackenzie]

I synced my fork and pulled master and getting errors running cargo test, cargo build seems to be fine.

running 9 tests
test src/tutorials/hole_punching.rs - tutorials::hole_punching (line 165) ... ignored
test src/tutorials/hole_punching.rs - tutorials::hole_punching (line 173) ... ignored
test src/tutorials/hole_punching.rs - tutorials::hole_punching (line 181) ... ignored
test src/tutorials/ping.rs - tutorials::ping (line 176) ... FAILED
test src/tutorials/ping.rs - tutorials::ping (line 106) ... FAILED
test src/tutorials/ping.rs - tutorials::ping (line 272) - compile ... FAILED
test src/tutorials/ping.rs - tutorials::ping (line 228) ... FAILED
test src/tutorials/ping.rs - tutorials::ping (line 144) ... FAILED
test src/tutorials/ping.rs - tutorials::ping (line 72) ... ok

failures:

---- src/tutorials/ping.rs - tutorials::ping (line 176) stdout ----
error[E0432]: unresolved import `libp2p::ping`
 --> src/tutorials/ping.rs:177:32
  |
3 | use libp2p::{identity, PeerId, ping};
  |                                ^^^^ no `ping` in the root

error[E0425]: cannot find function `development_transport` in crate `libp2p`
  --> src/tutorials/ping.rs:187:29
   |
13 |     let transport = libp2p::development_transport(local_key).await?;
   |                             ^^^^^^^^^^^^^^^^^^^^^ not found in `libp2p`

Is master building OK?

Maybe some refactor needs updating of doc tests?
(do you run doc tests in CI?)

[thomaseizinger]

You probably have to run it with --all-features. Unfortunately our CI currently runs on the entire workspace at once so this isn't checked.

[andrewdavidmackenzie]

Removing #[behaviour(out_event = "MyBehaviourEvent")] to leave :

    #[derive(NetworkBehaviour)]
    struct MyBehaviour {
        gossipsub: Gossipsub,
        mdns: Mdns,
    }

you get

cargo run --example gossipsub-chat --features="full"
   Compiling libp2p v0.49.0 (/Users/andrew/workspace/rust-libp2p)
error[E0428]: the name `MyBehaviourEvent` is defined multiple times
  --> examples/gossipsub-chat.rs:83:5
   |
77 |     #[derive(NetworkBehaviour)]
   |              ---------------- previous definition of the type `MyBehaviourEvent` here
...
83 |     enum MyBehaviourEvent {
   |     ^^^^^^^^^^^^^^^^^^^^^ `MyBehaviourEvent` redefined here
   |
   = note: `MyBehaviourEvent` must be defined only once in the type namespace of this block

[thomaseizinger]

Removing #[behaviour(out_event = "MyBehaviourEvent")] to leave :

    #[derive(NetworkBehaviour)]
    struct MyBehaviour {
        gossipsub: Gossipsub,
        mdns: Mdns,
    }

you get

cargo run --example gossipsub-chat --features="full"
   Compiling libp2p v0.49.0 (/Users/andrew/workspace/rust-libp2p)
error[E0428]: the name `MyBehaviourEvent` is defined multiple times
  --> examples/gossipsub-chat.rs:83:5
   |
77 |     #[derive(NetworkBehaviour)]
   |              ---------------- previous definition of the type `MyBehaviourEvent` here
...
83 |     enum MyBehaviourEvent {
   |     ^^^^^^^^^^^^^^^^^^^^^ `MyBehaviourEvent` redefined here
   |
   = note: `MyBehaviourEvent` must be defined only once in the type namespace of this block

Yep, it generates the event for you so you can delete the definition below :)

[andrewdavidmackenzie]

Accepted suggested comment change.
Removed the struct definition that is not needed.

[mxinden]

Looks good to me. @thomaseizinger can you merge in case you have no more comments?