Availability recovery subsystem (#2122)

* Adds message types

* Add code skeleton

* Adds subsystem code.

* Adds a first test

* Adds interaction result to availability_lru

* Use LruCache instead of a HashMap

* Whitespaces to tabs

* Do not ignore errors

* Change error type

* Add a timeout to chunk requests

* Add custom errors and log them

* Adds replace_availability_recovery method

* recovery_threshold computed by erasure crate

* change core to std

* adds docs to error type

* Adds a test for invalid reconstruction

* refactors interaction run into multiple methods

* Cleanup AwaitedChunks

* Even more fixes

* Test that recovery with wrong root is an error

* Break to launch another requests

* Styling fixes

* Add SessionIndex to API

* Proper relay parents for MakeRequest

* Remove validator_discovery and use message

* Remove a stream on exhaustion

* On cleanup free the request streams

* Fix merge and refactor

polkadot/node/subsystem/src/messages.rs

@@ -245,6 +245,19 @@ pub enum AvailabilityDistributionMessage {
 	NetworkBridgeUpdateV1(NetworkBridgeEvent<protocol_v1::AvailabilityDistributionMessage>),
 }
 
+/// Availability Recovery Message.
+#[derive(Debug)]
+pub enum AvailabilityRecoveryMessage {
+	/// Recover available data from validators on the network.
+	RecoverAvailableData(
+		CandidateReceipt,
+		SessionIndex,
+		oneshot::Sender<Result<AvailableData, crate::errors::RecoveryError>>,
+	),
+	/// Event from the network bridge.
+	NetworkBridgeUpdateV1(NetworkBridgeEvent<protocol_v1::AvailabilityRecoveryMessage>),
+}
+
 impl AvailabilityDistributionMessage {
 	/// If the current variant contains the relay parent hash, return it.
 	pub fn relay_parent(&self) -> Option<Hash> {
@@ -596,6 +609,8 @@ pub enum AllMessages {
 	StatementDistribution(StatementDistributionMessage),
 	/// Message for the availability distribution subsystem.
 	AvailabilityDistribution(AvailabilityDistributionMessage),
+	/// Message for the availability recovery subsystem.
+	AvailabilityRecovery(AvailabilityRecoveryMessage),
 	/// Message for the bitfield distribution subsystem.
 	BitfieldDistribution(BitfieldDistributionMessage),
 	/// Message for the bitfield signing subsystem.