Approve multiple candidates with a single signature (#1191)

Initial implementation for the plan discussed here: https://github.com/paritytech/polkadot-sdk/issues/701
Built on top of https://github.com/paritytech/polkadot-sdk/pull/1178
v0: https://github.com/paritytech/polkadot/pull/7554,

## Overall idea

When approval-voting checks a candidate and is ready to advertise the
approval, defer it in a per-relay chain block until we either have
MAX_APPROVAL_COALESCE_COUNT candidates to sign or a candidate has stayed
MAX_APPROVALS_COALESCE_TICKS in the queue, in both cases we sign what
candidates we have available.

This should allow us to reduce the number of approvals messages we have
to create/send/verify. The parameters are configurable, so we should
find some values that balance:

- Security of the network: Delaying broadcasting of an approval
shouldn't but the finality at risk and to make sure that never happens
we won't delay sending a vote if we are past 2/3 from the no-show time.
- Scalability of the network: MAX_APPROVAL_COALESCE_COUNT = 1 &
MAX_APPROVALS_COALESCE_TICKS =0, is what we have now and we know from
the measurements we did on versi, it bottlenecks
approval-distribution/approval-voting when increase significantly the
number of validators and parachains
- Block storage: In case of disputes we have to import this votes on
chain and that increase the necessary storage with
MAX_APPROVAL_COALESCE_COUNT * CandidateHash per vote. Given that
disputes are not the normal way of the network functioning and we will
limit MAX_APPROVAL_COALESCE_COUNT in the single digits numbers, this
should be good enough. Alternatively, we could try to create a better
way to store this on-chain through indirection, if that's needed.

## Other fixes:
- Fixed the fact that we were sending random assignments to
non-validators, that was wrong because those won't do anything with it
and they won't gossip it either because they do not have a grid topology
set, so we would waste the random assignments.
- Added metrics to be able to debug potential no-shows and
mis-processing of approvals/assignments.

## TODO:
- [x] Get feedback, that this is moving in the right direction. @ordian
@sandreim @eskimor @burdges, let me know what you think.
- [x] More and more testing.
- [x]  Test in versi.
- [x] Make MAX_APPROVAL_COALESCE_COUNT &
MAX_APPROVAL_COALESCE_WAIT_MILLIS a parachain host configuration.
- [x] Make sure the backwards compatibility works correctly
- [x] Make sure this direction is compatible with other streams of work:
https://github.com/paritytech/polkadot-sdk/issues/635 &
https://github.com/paritytech/polkadot-sdk/issues/742
- [x] Final versi burn-in before merging

---------

Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>

polkadot/node/network/protocol/src/peer_set.rs

@@ -73,7 +73,11 @@ impl PeerSet {
 		// Networking layer relies on `get_main_name()` being the main name of the protocol
 		// for peersets and connection management.
 		let protocol = peerset_protocol_names.get_main_name(self);
-		let fallback_names = PeerSetProtocolNames::get_fallback_names(self);
+		let fallback_names = PeerSetProtocolNames::get_fallback_names(
+			self,
+			&peerset_protocol_names.genesis_hash,
+			peerset_protocol_names.fork_id.as_deref(),
+		);
 		let max_notification_size = self.get_max_notification_size(is_authority);
 
 		match self {
@@ -127,15 +131,8 @@ impl PeerSet {
 	/// Networking layer relies on `get_main_version()` being the version
 	/// of the main protocol name reported by [`PeerSetProtocolNames::get_main_name()`].
 	pub fn get_main_version(self) -> ProtocolVersion {
-		#[cfg(not(feature = "network-protocol-staging"))]
 		match self {
-			PeerSet::Validation => ValidationVersion::V2.into(),
-			PeerSet::Collation => CollationVersion::V2.into(),
-		}
-
-		#[cfg(feature = "network-protocol-staging")]
-		match self {
-			PeerSet::Validation => ValidationVersion::VStaging.into(),
+			PeerSet::Validation => ValidationVersion::V3.into(),
 			PeerSet::Collation => CollationVersion::V2.into(),
 		}
 	}
@@ -163,7 +160,7 @@ impl PeerSet {
 					Some("validation/1")
 				} else if version == ValidationVersion::V2.into() {
 					Some("validation/2")
-				} else if version == ValidationVersion::VStaging.into() {
+				} else if version == ValidationVersion::V3.into() {
 					Some("validation/3")
 				} else {
 					None
@@ -236,9 +233,10 @@ pub enum ValidationVersion {
 	V1 = 1,
 	/// The second version.
 	V2 = 2,
-	/// The staging version to gather changes
-	/// that before the release become v3.
-	VStaging = 3,
+	/// The third version where changes to ApprovalDistributionMessage had been made.
+	/// The changes are translatable to V2 format untill assignments v2 and approvals
+	/// coalescing is enabled through a runtime upgrade.
+	V3 = 3,
 }
 
 /// Supported collation protocol versions. Only versions defined here must be used in the codebase.
@@ -299,6 +297,8 @@ impl From<CollationVersion> for ProtocolVersion {
 pub struct PeerSetProtocolNames {
 	protocols: HashMap<ProtocolName, (PeerSet, ProtocolVersion)>,
 	names: HashMap<(PeerSet, ProtocolVersion), ProtocolName>,
+	genesis_hash: Hash,
+	fork_id: Option<String>,
 }
 
 impl PeerSetProtocolNames {
@@ -333,7 +333,7 @@ impl PeerSetProtocolNames {
 			}
 			Self::register_legacy_protocol(&mut protocols, protocol);
 		}
-		Self { protocols, names }
+		Self { protocols, names, genesis_hash, fork_id: fork_id.map(|fork_id| fork_id.into()) }
 	}
 
 	/// Helper function to register main protocol.
@@ -437,9 +437,30 @@ impl PeerSetProtocolNames {
 	}
 
 	/// Get the protocol fallback names. Currently only holds the legacy name
-	/// for `LEGACY_PROTOCOL_VERSION` = 1.
-	fn get_fallback_names(protocol: PeerSet) -> Vec<ProtocolName> {
-		std::iter::once(Self::get_legacy_name(protocol)).collect()
+	/// for `LEGACY_PROTOCOL_VERSION` = 1 and v2 for validation.
+	fn get_fallback_names(
+		protocol: PeerSet,
+		genesis_hash: &Hash,
+		fork_id: Option<&str>,
+	) -> Vec<ProtocolName> {
+		let mut fallbacks = vec![Self::get_legacy_name(protocol)];
+		match protocol {
+			PeerSet::Validation => {
+				// Fallbacks are tried one by one, till one matches so push v2 at the top, so
+				// that it is used ahead of the legacy one(v1).
+				fallbacks.insert(
+					0,
+					Self::generate_name(
+						genesis_hash,
+						fork_id,
+						protocol,
+						ValidationVersion::V2.into(),
+					),
+				)
+			},
+			PeerSet::Collation => {},
+		};
+		fallbacks
 	}
 }