Extract syncing protocol from sc-network (#12828)

* Move import queue out of `sc-network`

Add supplementary asynchronous API for the import queue which means
it can be run as an independent task and communicated with through
the `ImportQueueService`.

This commit removes removes block and justification imports from
`sc-network` and provides `ChainSync` with a handle to import queue so
it can import blocks and justifications. Polling of the import queue is
moved complete out of `sc-network` and `sc_consensus::Link` is
implemented for `ChainSyncInterfaceHandled` so the import queue
can still influence the syncing process.

* Move stuff to SyncingEngine

* Move `ChainSync` instanation to `SyncingEngine`

Some of the tests have to be rewritten

* Move peer hashmap to `SyncingEngine`

* Let `SyncingEngine` to implement `ChainSyncInterface`

* Introduce `SyncStatusProvider`

* Move `sync_peer_(connected|disconnected)` to `SyncingEngine`

* Implement `SyncEventStream`

Remove `SyncConnected`/`SyncDisconnected` events from
`NetworkEvenStream` and provide those events through
`ChainSyncInterface` instead.

Modify BEEFY/GRANDPA/transactions protocol and `NetworkGossip` to take
`SyncEventStream` object which they listen to for incoming sync peer
events.

* Introduce `ChainSyncInterface`

This interface provides a set of miscellaneous functions that other
subsystems can use to query, for example, the syncing status.

* Move event stream polling to `SyncingEngine`

Subscribe to `NetworkStreamEvent` and poll the incoming notifications
and substream events from `SyncingEngine`.

The code needs refactoring.

* Make `SyncingEngine` into an asynchronous runner

This commits removes the last hard dependency of syncing from
`sc-network` meaning the protocol now lives completely outside of
`sc-network`, ignoring the hardcoded peerset entry which will be
addressed in the future.

Code needs a lot of refactoring.

* Fix warnings

* Code refactoring

* Use `SyncingService` for BEEFY

* Use `SyncingService` for GRANDPA

* Remove call delegation from `NetworkService`

* Remove `ChainSyncService`

* Remove `ChainSync` service tests

They were written for the sole purpose of verifying that `NetworWorker`
continues to function while the calls are being dispatched to
`ChainSync`.

* Refactor code

* Refactor code

* Update client/finality-grandpa/src/communication/tests.rs

Co-authored-by: Anton <anton.kalyaev@gmail.com>

* Fix warnings

* Apply review comments

* Fix docs

* Fix test

* cargo-fmt

* Update client/network/sync/src/engine.rs

Co-authored-by: Anton <anton.kalyaev@gmail.com>

* Update client/network/sync/src/engine.rs

Co-authored-by: Anton <anton.kalyaev@gmail.com>

* Add missing docs

* Refactor code

---------

Co-authored-by: Anton <anton.kalyaev@gmail.com>

substrate/client/network/common/src/sync.rs

@@ -22,7 +22,11 @@ pub mod message;
 pub mod metrics;
 pub mod warp;
 
+use crate::protocol::role::Roles;
+use futures::Stream;
+
 use libp2p::PeerId;
+
 use message::{BlockAnnounce, BlockData, BlockRequest, BlockResponse};
 use sc_consensus::{import_queue::RuntimeOrigin, IncomingBlock};
 use sp_consensus::BlockOrigin;
@@ -30,9 +34,10 @@ use sp_runtime::{
 	traits::{Block as BlockT, NumberFor},
 	Justifications,
 };
-use std::{any::Any, fmt, fmt::Formatter, task::Poll};
 use warp::WarpSyncProgress;
 
+use std::{any::Any, fmt, fmt::Formatter, pin::Pin, sync::Arc, task::Poll};
+
 /// The sync status of a peer we are trying to sync with
 #[derive(Debug)]
 pub struct PeerInfo<Block: BlockT> {
@@ -42,6 +47,17 @@ pub struct PeerInfo<Block: BlockT> {
 	pub best_number: NumberFor<Block>,
 }
 
+/// Info about a peer's known state (both full and light).
+#[derive(Clone, Debug)]
+pub struct ExtendedPeerInfo<B: BlockT> {
+	/// Roles
+	pub roles: Roles,
+	/// Peer best block hash
+	pub best_hash: B::Hash,
+	/// Peer best block number
+	pub best_number: NumberFor<B>,
+}
+
 /// Reported sync state.
 #[derive(Clone, Eq, PartialEq, Debug)]
 pub enum SyncState<BlockNumber> {
@@ -251,6 +267,49 @@ impl fmt::Debug for OpaqueBlockResponse {
 	}
 }
 
+/// Provides high-level status of syncing.
+#[async_trait::async_trait]
+pub trait SyncStatusProvider<Block: BlockT>: Send + Sync {
+	/// Get high-level view of the syncing status.
+	async fn status(&self) -> Result<SyncStatus<Block>, ()>;
+}
+
+#[async_trait::async_trait]
+impl<T, Block> SyncStatusProvider<Block> for Arc<T>
+where
+	T: ?Sized,
+	T: SyncStatusProvider<Block>,
+	Block: BlockT,
+{
+	async fn status(&self) -> Result<SyncStatus<Block>, ()> {
+		T::status(self).await
+	}
+}
+
+/// Syncing-related events that other protocols can subscribe to.
+pub enum SyncEvent {
+	/// Peer that the syncing implementation is tracking connected.
+	PeerConnected(PeerId),
+
+	/// Peer that the syncing implementation was tracking disconnected.
+	PeerDisconnected(PeerId),
+}
+
+pub trait SyncEventStream: Send + Sync {
+	/// Subscribe to syncing-related events.
+	fn event_stream(&self, name: &'static str) -> Pin<Box<dyn Stream<Item = SyncEvent> + Send>>;
+}
+
+impl<T> SyncEventStream for Arc<T>
+where
+	T: ?Sized,
+	T: SyncEventStream,
+{
+	fn event_stream(&self, name: &'static str) -> Pin<Box<dyn Stream<Item = SyncEvent> + Send>> {
+		T::event_stream(self, name)
+	}
+}
+
 /// Something that represents the syncing strategy to download past and future blocks of the chain.
 pub trait ChainSync<Block: BlockT>: Send {
 	/// Returns the state of the sync of the given peer.