Move syncing code from sc-network-common to sc-network-sync (#1912)

This PR moves syncing-related code from `sc-network-common` to
`sc-network-sync`.

Unfortunately, some parts are tightly integrated with networking, so
they were left in `sc-network-common` for now:

1. `SyncMode` in `common/src/sync.rs` (used in `NetworkConfiguration`).
2. `BlockAnnouncesHandshake`, `BlockRequest`, `BlockResponse`, etc. in
`common/src/sync/message.rs` (used in `src/protocol.rs` and
`src/protocol/message.rs`).

More substantial refactoring is needed to decouple syncing and
networking completely, including getting rid of the hardcoded sync
protocol.

## Release notes

Move syncing-related code from `sc-network-common` to `sc-network-sync`.
Delete `ChainSync` trait as it's never used (the only implementation is
accessed directly from `SyncingEngine` and exposes a lot of public
methods that are not part of the trait). Some new trait(s) for syncing
will likely be introduced as part of Sync 2.0 refactoring to represent
syncing strategies.

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

@@ -18,28 +18,107 @@
 
 //! Warp sync support.
 
+pub use sp_consensus_grandpa::{AuthorityList, SetId};
+
 use crate::{
 	schema::v1::{StateRequest, StateResponse},
 	state::{ImportResult, StateSync},
 };
+use codec::{Decode, Encode};
 use futures::channel::oneshot;
 use log::error;
 use sc_client_api::ProofProvider;
-use sc_network_common::sync::{
-	message::{BlockAttributes, BlockData, BlockRequest, Direction, FromBlock},
-	warp::{
-		EncodedProof, VerificationResult, WarpProofRequest, WarpSyncPhase, WarpSyncProgress,
-		WarpSyncProvider,
-	},
+use sc_network_common::sync::message::{
+	BlockAttributes, BlockData, BlockRequest, Direction, FromBlock,
 };
 use sp_blockchain::HeaderBackend;
-use sp_consensus_grandpa::{AuthorityList, SetId};
 use sp_runtime::traits::{Block as BlockT, Header, NumberFor, Zero};
-use std::sync::Arc;
+use std::{fmt, sync::Arc};
 
 /// Log target for this file.
 const LOG_TARGET: &'static str = "sync";
 
+/// Scale-encoded warp sync proof response.
+pub struct EncodedProof(pub Vec<u8>);
+
+/// Warp sync request
+#[derive(Encode, Decode, Debug)]
+pub struct WarpProofRequest<B: BlockT> {
+	/// Start collecting proofs from this block.
+	pub begin: B::Hash,
+}
+
+/// Proof verification result.
+pub enum VerificationResult<Block: BlockT> {
+	/// Proof is valid, but the target was not reached.
+	Partial(SetId, AuthorityList, Block::Hash),
+	/// Target finality is proved.
+	Complete(SetId, AuthorityList, Block::Header),
+}
+
+/// Warp sync backend. Handles retrieving and verifying warp sync proofs.
+pub trait WarpSyncProvider<Block: BlockT>: Send + Sync {
+	/// Generate proof starting at given block hash. The proof is accumulated until maximum proof
+	/// size is reached.
+	fn generate(
+		&self,
+		start: Block::Hash,
+	) -> Result<EncodedProof, Box<dyn std::error::Error + Send + Sync>>;
+	/// Verify warp proof against current set of authorities.
+	fn verify(
+		&self,
+		proof: &EncodedProof,
+		set_id: SetId,
+		authorities: AuthorityList,
+	) -> Result<VerificationResult<Block>, Box<dyn std::error::Error + Send + Sync>>;
+	/// Get current list of authorities. This is supposed to be genesis authorities when starting
+	/// sync.
+	fn current_authorities(&self) -> AuthorityList;
+}
+
+/// Reported warp sync phase.
+#[derive(Clone, Eq, PartialEq, Debug)]
+pub enum WarpSyncPhase<Block: BlockT> {
+	/// Waiting for peers to connect.
+	AwaitingPeers { required_peers: usize },
+	/// Waiting for target block to be received.
+	AwaitingTargetBlock,
+	/// Downloading and verifying grandpa warp proofs.
+	DownloadingWarpProofs,
+	/// Downloading target block.
+	DownloadingTargetBlock,
+	/// Downloading state data.
+	DownloadingState,
+	/// Importing state.
+	ImportingState,
+	/// Downloading block history.
+	DownloadingBlocks(NumberFor<Block>),
+}
+
+impl<Block: BlockT> fmt::Display for WarpSyncPhase<Block> {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		match self {
+			Self::AwaitingPeers { required_peers } =>
+				write!(f, "Waiting for {required_peers} peers to be connected"),
+			Self::AwaitingTargetBlock => write!(f, "Waiting for target block to be received"),
+			Self::DownloadingWarpProofs => write!(f, "Downloading finality proofs"),
+			Self::DownloadingTargetBlock => write!(f, "Downloading target block"),
+			Self::DownloadingState => write!(f, "Downloading state"),
+			Self::ImportingState => write!(f, "Importing state"),
+			Self::DownloadingBlocks(n) => write!(f, "Downloading block history (#{})", n),
+		}
+	}
+}
+
+/// Reported warp sync progress.
+#[derive(Clone, Eq, PartialEq, Debug)]
+pub struct WarpSyncProgress<Block: BlockT> {
+	/// Estimated download percentage.
+	pub phase: WarpSyncPhase<Block>,
+	/// Total bytes downloaded so far.
+	pub total_bytes: u64,
+}
+
 /// The different types of warp syncing, passed to `build_network`.
 pub enum WarpSyncParams<Block: BlockT> {
 	/// Standard warp sync for the chain.