Generic request/response infrastructure for Polkadot (#2352)

* Move NetworkBridgeEvent to subsystem::messages.

It is not protocol related at all, it is in fact only part of the
subsystem communication as it gets wrapped into messages of each
subsystem.

* Request/response infrastructure is taking shape.

WIP: Does not compile.

* Multiplexer variant not supported by Rusts type system.

* request_response::request type checks.

* Cleanup.

* Minor fixes for request_response.

* Implement request sending + move multiplexer.

Request multiplexer is moved to bridge, as there the implementation is
more straight forward as we can specialize on `AllMessages` for the
multiplexing target.

Sending of requests is mostly complete, apart from a few `From`
instances. Receiving is also almost done, initializtion needs to be
fixed and the multiplexer needs to be invoked.

* Remove obsolete multiplexer.

* Initialize bridge with multiplexer.

* Finish generic request sending/receiving.

Subsystems are now able to receive and send requests and responses via
the overseer.

* Doc update.

* Fixes.

* Link issue for not yet implemented code.

* Fixes suggested by @ordian - thanks!

- start encoding at 0
- don't crash on zero protocols
- don't panic on not yet implemented request handling

* Update node/network/protocol/src/request_response/v1.rs

Use index 0 instead of 1.

Co-authored-by: Andronik Ordian <write@reusable.software>

* Update node/network/protocol/src/request_response.rs

Co-authored-by: Andronik Ordian <write@reusable.software>

* Fix existing tests.

* Better avoidance of division by zoro errors.

* Doc fixes.

* send_request -> start_request.

* Fix missing renamings.

* Update substrate.

* Pass TryConnect instead of true.

* Actually import `IfDisconnected`.

* Fix wrong import.

* Update node/network/bridge/src/lib.rs

typo

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

* Update node/network/bridge/src/multiplexer.rs

Remove redundant import.

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

* Stop doing tracing from within `From` instance.

Thanks for the catch @tomaka!

* Get rid of redundant import.

* Formatting cleanup.

* Fix tests.

* Add link to issue.

* Clarify comments some more.

* Fix tests.

* Formatting fix.

* tabs

* Fix link

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* Use map_err.

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* Improvements inspired by suggestions by @drahnr.

- Channel size is now determined by function.
- Explicitely scope NetworkService::start_request.

Co-authored-by: Andronik Ordian <write@reusable.software>
Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>
Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

polkadot/node/network/bridge/src/network.rs

@@ -24,12 +24,18 @@ use futures::stream::BoxStream;
 use parity_scale_codec::Encode;
 
 use sc_network::Event as NetworkEvent;
+use sc_network::{NetworkService, IfDisconnected};
 
-use super::LOG_TARGET;
-use polkadot_node_network_protocol::{peer_set::PeerSet, PeerId, ReputationChange};
+use polkadot_node_network_protocol::{
+	peer_set::PeerSet,
+	request_response::{OutgoingRequest, Requests},
+	PeerId, ReputationChange,
+};
 use polkadot_primitives::v1::{Block, Hash};
 use polkadot_subsystem::{SubsystemError, SubsystemResult};
 
+use super::LOG_TARGET;
+
 /// Send a message to the network.
 ///
 /// This function is only used internally by the network-bridge, which is responsible to only send
@@ -86,7 +92,6 @@ pub enum NetworkAction {
 }
 
 /// An abstraction over networking for the purposes of this subsystem.
-///
 pub trait Network: Send + 'static {
 	/// Get a stream of all events occurring on the network. This may include events unrelated
 	/// to the Polkadot protocol - the user of this function should filter only for events related
@@ -99,6 +104,9 @@ pub trait Network: Send + 'static {
 		&'a mut self,
 	) -> Pin<Box<dyn Sink<NetworkAction, Error = SubsystemError> + Send + 'a>>;
 
+	/// Send a request to a remote peer.
+	fn start_request(&self, req: Requests);
+
 	/// Report a given peer as either beneficial (+) or costly (-) according to the given scalar.
 	fn report_peer(
 		&mut self,
@@ -129,9 +137,9 @@ pub trait Network: Send + 'static {
 	}
 }
 
-impl Network for Arc<sc_network::NetworkService<Block, Hash>> {
+impl Network for Arc<NetworkService<Block, Hash>> {
 	fn event_stream(&mut self) -> BoxStream<'static, NetworkEvent> {
-		sc_network::NetworkService::event_stream(self, "polkadot-network-bridge").boxed()
+		NetworkService::event_stream(self, "polkadot-network-bridge").boxed()
 	}
 
 	#[tracing::instrument(level = "trace", skip(self), fields(subsystem = LOG_TARGET))]
@@ -141,7 +149,7 @@ impl Network for Arc<sc_network::NetworkService<Block, Hash>> {
 		use futures::task::{Context, Poll};
 
 		// wrapper around a NetworkService to make it act like a sink.
-		struct ActionSink<'b>(&'b sc_network::NetworkService<Block, Hash>);
+		struct ActionSink<'b>(&'b NetworkService<Block, Hash>);
 
 		impl<'b> Sink<NetworkAction> for ActionSink<'b> {
 			type Error = SubsystemError;
@@ -180,4 +188,23 @@ impl Network for Arc<sc_network::NetworkService<Block, Hash>> {
 
 		Box::pin(ActionSink(&**self))
 	}
+
+	fn start_request(&self, req: Requests) {
+		let (
+			protocol,
+			OutgoingRequest {
+				peer,
+				payload,
+				pending_response,
+			},
+		) = req.encode_request();
+
+		NetworkService::start_request(&*self,
+			peer,
+			protocol.into_protocol_name(),
+			payload,
+			pending_response,
+			IfDisconnected::TryConnect,
+		);
+	}
 }