Previously, the `DummyConnectionHandler` offered a "keep alive" functionality,
i.e. it allowed users to set the value of what is returned from
`ConnectionHandler::keep_alive`. This handler is primarily used in tests or
`NetworkBehaviour`s that don't open any connections (like mDNS). In all of these
cases, it is statically known whether we want to keep connections alive. As
such, this functionality is better represented by a static
`KeepAliveConnectionHandler` that always returns `KeepAlive::Yes` and a
`DummyConnectionHandler` that always returns `KeepAlive::No`.
To follow the naming conventions described in
https://github.com/libp2p/rust-libp2p/issues/2217, we introduce a top-level
`keep_alive` and `dummy` behaviour in `libp2p-swarm` that contains both the
`NetworkBehaviour` and `ConnectionHandler` implementation for either case.
Remove default features. You need to enable required features
explicitly now. As a quick workaround, you may want to use the
new `full` feature which activates all features.
Allow users to choose between async-io and tokio runtime
in the mdns protocol implementation. `async-io` is a default
feature, with an additional `tokio` feature.
Fix high CPU usage with Tokio library.
Instead of having a mix of `poll_event`, `poll_outbound` and `poll_close`, we
flatten the entire interface of `StreamMuxer` into 4 individual functions:
- `poll_inbound`
- `poll_outbound`
- `poll_address_change`
- `poll_close`
This design is closer to the design of other async traits like `AsyncRead` and
`AsyncWrite`. It also allows us to delete the `StreamMuxerEvent`.
* misc/metrics: Explicitly delegate event recording to each recorder
This allows delegating a single event to multiple `Recorder`s. That enables e.g. the
`identify::Metrics` `Recorder` to act both on `IdentifyEvent` and `SwarmEvent`. The latter enables
it to garbage collect per peer data on disconnects.
* protocols/dcutr: Expose PROTOCOL_NAME
* protocols/identify: Expose PROTOCOL_NAME and PUSH_PROTOCOL_NAME
* protocols/ping: Expose PROTOCOL_NAME
* protocols/relay: Expose HOP_PROTOCOL_NAME and STOP_PROTOCOL_NAME
* misc/metrics: Track # connected nodes supporting specific protocol
An example metric exposed with this patch:
```
libp2p_identify_protocols{protocol="/ipfs/ping/1.0.0"} 10
```
This implies that 10 of the currently connected nodes support the ping protocol.
Remove the concept of individual `Transport::Listener` streams from `Transport`.
Instead the `Transport` is polled directly via `Transport::poll`. The
`Transport` is now responsible for driving its listeners.
**Summary** of the plot of the `discover_peer_after_disconnect` test:
1. `swarm2` connects to `swarm1`.
2. `swarm2` requests an identify response from `swarm1`.
3. `swarm1` sends the response to `swarm2`.
4. `swarm2` disconnects from `swarm1`.
5. `swarm2` tries to disconnect.
**Problem**
`libp2p-identify` sets `KeepAlive::No` when it identified the remote. Thus `swarm1` might
identify` `swarm2` before `swarm2` identified `swarm1`. `swarm1` then sets `KeepAlive::No` and thus closes the
connection to `swarm2` before `swarm2` identified `swarm1`. In such case the unit test
`discover_peer_after_disconnect hangs indefinitely.
**Solution**
Add an initial delay to `swarm1` requesting an identification from `swarm2`, thus ensuring `swarm2`
is always able to identify `swarm1`.
