Extract consensus_gossip.rs and put it in its own crate (#4284)

* Extract gossiping system from network

* Finish porting GRANDPA tests

* Try put correct engine ID

* Fix messages encoding

* Fix communication tests

* Use a threads pool to spawn stuff

* Fix compilation everywhere

* Fix bad merge conflict

* Remove dependency on async-std

* Apply suggestions from code review

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

* More suggestions

* Remove network startup GP future

* Update to futures_timer

* adjust wait_when_behind test

* Pass correct Roles after handshake

* Revert "adjust wait_when_behind test"

This reverts commit 23cb3a0a6d25ed732c2cd648607bc44ef2ab0919.

* Crate root documentation

* Remove MessageRecipient

* Address concerns

* Fix more concerns

* Forgot Cargo.lock

substrate/client/network/src/protocol/event.rs

@@ -17,10 +17,15 @@
 //! Network event types. These are are not the part of the protocol, but rather
 //! events that happen on the network like DHT get/put results received.
 
+use crate::config::Roles;
+use bytes::Bytes;
+use libp2p::core::PeerId;
 use libp2p::kad::record::Key;
+use sp_runtime::ConsensusEngineId;
 
 /// Events generated by DHT as a response to get_value and put_value requests.
 #[derive(Debug, Clone)]
+#[must_use]
 pub enum DhtEvent {
 	/// The value was found.
 	ValueFound(Vec<(Key, Vec<u8>)>),
@@ -37,7 +42,37 @@ pub enum DhtEvent {
 
 /// Type for events generated by networking layer.
 #[derive(Debug, Clone)]
+#[must_use]
 pub enum Event {
 	/// Event generated by a DHT.
 	Dht(DhtEvent),
+
+	/// Opened a substream with the given node with the given notifications protocol.
+	///
+	/// The protocol is always one of the notification protocols that have been registered.
+	NotificationStreamOpened {
+		/// Node we opened the substream with.
+		remote: PeerId,
+		/// The concerned protocol. Each protocol uses a different substream.
+		engine_id: ConsensusEngineId,
+		/// Roles that the remote .
+		roles: Roles,
+	},
+
+	/// Closed a substream with the given node. Always matches a corresponding previous
+	/// `NotificationStreamOpened` message.
+	NotificationsStreamClosed {
+		/// Node we closed the substream with.
+		remote: PeerId,
+		/// The concerned protocol. Each protocol uses a different substream.
+		engine_id: ConsensusEngineId,
+	},
+
+	/// Received one or more messages from the given node using the given protocol.
+	NotificationsReceived {
+		/// Node we received the message from.
+		remote: PeerId,
+		/// Concerned protocol and associated message.
+		messages: Vec<(ConsensusEngineId, Bytes)>,
+	},
 }