Request based PoV distribution (#2640)

* Indentation fix.

* Prepare request-response for PoV fetching.

* Drop old PoV distribution.

* WIP: Fetch PoV directly from backing.

* Backing compiles.

* Runtime access and connection management for PoV distribution.

* Get rid of seemingly dead code.

* Implement PoV fetching.

Backing does not yet use it.

* Don't send `ConnectToValidators` for empty list.

* Even better - no need to check over and over again.

* PoV fetching implemented.

+ Typechecks
+ Should work

Missing:

- Guide
- Tests
- Do fallback fetching in case fetching from seconding validator fails.

* Check PoV hash upon reception.

* Implement retry of PoV fetching in backing.

* Avoid pointless validation spawning.

* Add jaeger span to pov requesting.

* Add back tracing.

* Review remarks.

* Whitespace.

* Whitespace again.

* Cleanup + fix tests.

* Log to log target in overseer.

* Fix more tests.

* Don't fail if group cannot be found.

* Simple test for PoV fetcher.

* Handle missing group membership better.

* Add test for retry functionality.

* Fix flaky test.

* Spaces again.

* Guide updates.

* Spaces.

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

@@ -289,7 +289,7 @@ pub mod v1 {
 	use std::convert::TryFrom;
 
 	use polkadot_primitives::v1::{
-		CandidateIndex, CollatorId, CompressedPoV, Hash, Id as ParaId, SignedAvailabilityBitfield,
+		CandidateIndex, CollatorId, Hash, Id as ParaId, SignedAvailabilityBitfield,
 		CollatorSignature,
 	};
 	use polkadot_node_primitives::{
@@ -305,19 +305,6 @@ pub mod v1 {
 		Bitfield(Hash, SignedAvailabilityBitfield),
 	}
 
-	/// Network messages used by the PoV distribution subsystem.
-	#[derive(Debug, Clone, Encode, Decode, PartialEq, Eq)]
-	pub enum PoVDistributionMessage {
-		/// Notification that we are awaiting the given PoVs (by hash) against a
-		/// specific relay-parent hash.
-		#[codec(index = 0)]
-		Awaiting(Hash, Vec<Hash>),
-		/// Notification of an awaited PoV, in a given relay-parent context.
-		/// (relay_parent, pov_hash, compressed_pov)
-		#[codec(index = 1)]
-		SendPoV(Hash, Hash, CompressedPoV),
-	}
-
 	/// Network messages used by the statement distribution subsystem.
 	#[derive(Debug, Clone, Encode, Decode, PartialEq, Eq)]
 	pub enum StatementDistributionMessage {
@@ -361,9 +348,6 @@ pub mod v1 {
 		/// Bitfield distribution messages
 		#[codec(index = 1)]
 		BitfieldDistribution(BitfieldDistributionMessage),
-		/// PoV Distribution messages
-		#[codec(index = 2)]
-		PoVDistribution(PoVDistributionMessage),
 		/// Statement distribution messages
 		#[codec(index = 3)]
 		StatementDistribution(StatementDistributionMessage),
@@ -373,7 +357,6 @@ pub mod v1 {
 	}
 
 	impl_try_from!(ValidationProtocol, BitfieldDistribution, BitfieldDistributionMessage);
-	impl_try_from!(ValidationProtocol, PoVDistribution, PoVDistributionMessage);
 	impl_try_from!(ValidationProtocol, StatementDistribution, StatementDistributionMessage);
 	impl_try_from!(ValidationProtocol, ApprovalDistribution, ApprovalDistributionMessage);