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>
2026-06-14 06:21:11 +00:00 · 2021-02-03 21:21:09 +01:00
parent 41eeb5716f
commit 0cb1ccd122
25 changed files with 964 additions and 260 deletions
@@ -22,13 +22,14 @@ use polkadot_node_network_protocol::{
 	peer_set::PeerSet, v1 as protocol_v1, PeerId, ReputationChange,
 };
 use polkadot_primitives::v1::{AuthorityDiscoveryId, BlockNumber};
-use polkadot_subsystem::messages::NetworkBridgeMessage;
+use polkadot_subsystem::messages::{AllMessages, NetworkBridgeMessage};
 use polkadot_subsystem::{ActiveLeavesUpdate, FromOverseer, OverseerSignal};
 use sc_network::Event as NetworkEvent;

-use polkadot_node_network_protocol::ObservedRole;
+use polkadot_node_network_protocol::{request_response::Requests, ObservedRole};

-use super::{WireMessage, LOG_TARGET, MALFORMED_MESSAGE_COST};
+use super::multiplexer::RequestMultiplexError;
+use super::{WireMessage, MALFORMED_MESSAGE_COST};

 /// Internal type combining all actions a `NetworkBridge` might perform.
 ///
@@ -43,6 +44,9 @@ pub(crate) enum Action {
 	/// Ask network to send a collation message.
 	SendCollationMessages(Vec<(Vec<PeerId>, protocol_v1::CollationProtocol)>),

+	/// Ask network to send requests.
+	SendRequests(Vec<Requests>),
+
 	/// Ask network to connect to validators.
 	ConnectToValidators {
 		validator_ids: Vec<AuthorityDiscoveryId>,
@@ -76,13 +80,32 @@ pub(crate) enum Action {
 		Vec<WireMessage<protocol_v1::CollationProtocol>>,
 	),

-	Abort,
+	/// Send a message to another subsystem or the overseer.
+	///
+	/// Used for handling incoming requests.
+	SendMessage(AllMessages),
+
+	/// Abort with reason.
+	Abort(AbortReason),
 	Nop,
 }

+#[derive(Debug)]
+pub(crate) enum AbortReason {
+	/// Received error from overseer:
+	SubsystemError(polkadot_subsystem::SubsystemError),
+	/// The stream of incoming events concluded.
+	EventStreamConcluded,
+	/// The stream of incoming requests concluded.
+	RequestStreamConcluded,
+	/// We received OverseerSignal::Conclude
+	OverseerConcluded,
+}
+
 impl From<polkadot_subsystem::SubsystemResult<FromOverseer<NetworkBridgeMessage>>> for Action {
-	#[tracing::instrument(level = "trace", fields(subsystem = LOG_TARGET))]
-	fn from(res: polkadot_subsystem::SubsystemResult<FromOverseer<NetworkBridgeMessage>>) -> Self {
+	fn from(
+		res: polkadot_subsystem::SubsystemResult<FromOverseer<NetworkBridgeMessage>>,
+	) -> Self {
 		match res {
 			Ok(FromOverseer::Signal(OverseerSignal::ActiveLeaves(active_leaves))) => {
 				Action::ActiveLeaves(active_leaves)
@@ -90,7 +113,9 @@ impl From<polkadot_subsystem::SubsystemResult<FromOverseer<NetworkBridgeMessage>
 			Ok(FromOverseer::Signal(OverseerSignal::BlockFinalized(_hash, number))) => {
 				Action::BlockFinalized(number)
 			}
-			Ok(FromOverseer::Signal(OverseerSignal::Conclude)) => Action::Abort,
+			Ok(FromOverseer::Signal(OverseerSignal::Conclude)) => {
+				Action::Abort(AbortReason::OverseerConcluded)
+			}
 			Ok(FromOverseer::Communication { msg }) => match msg {
 				NetworkBridgeMessage::ReportPeer(peer, rep) => Action::ReportPeer(peer, rep),
 				NetworkBridgeMessage::SendValidationMessage(peers, msg) => {
@@ -99,6 +124,7 @@ impl From<polkadot_subsystem::SubsystemResult<FromOverseer<NetworkBridgeMessage>
 				NetworkBridgeMessage::SendCollationMessage(peers, msg) => {
 					Action::SendCollationMessages(vec![(peers, msg)])
 				}
+				NetworkBridgeMessage::SendRequests(reqs) => Action::SendRequests(reqs),
 				NetworkBridgeMessage::SendValidationMessages(msgs) => {
 					Action::SendValidationMessages(msgs)
 				}
@@ -113,25 +139,15 @@ impl From<polkadot_subsystem::SubsystemResult<FromOverseer<NetworkBridgeMessage>
 					connected,
 				},
 			},
-			Err(e) => {
-				tracing::warn!(target: LOG_TARGET, err = ?e, "Shutting down Network Bridge due to error");
-				Action::Abort
-			}
+			Err(e) => Action::Abort(AbortReason::SubsystemError(e)),
 		}
 	}
 }

 impl From<Option<NetworkEvent>> for Action {
-	#[tracing::instrument(level = "trace", fields(subsystem = LOG_TARGET))]
 	fn from(event: Option<NetworkEvent>) -> Action {
 		match event {
-			None => {
-				tracing::info!(
-					target: LOG_TARGET,
-					"Shutting down Network Bridge: underlying event stream concluded"
-				);
-				Action::Abort
-			}
+			None => Action::Abort(AbortReason::EventStreamConcluded),
 			Some(NetworkEvent::Dht(_))
 			| Some(NetworkEvent::SyncConnected { .. })
 			| Some(NetworkEvent::SyncDisconnected { .. }) => Action::Nop,
@@ -153,7 +169,9 @@ impl From<Option<NetworkEvent>> for Action {
 			Some(NetworkEvent::NotificationsReceived { remote, messages }) => {
 				let v_messages: Result<Vec<_>, _> = messages
 					.iter()
-					.filter(|(protocol, _)| protocol == &PeerSet::Validation.into_protocol_name())
+					.filter(|(protocol, _)| {
+						protocol == &PeerSet::Validation.into_protocol_name()
+					})
 					.map(|(_, msg_bytes)| WireMessage::decode(&mut msg_bytes.as_ref()))
 					.collect();

@@ -164,7 +182,9 @@ impl From<Option<NetworkEvent>> for Action {

 				let c_messages: Result<Vec<_>, _> = messages
 					.iter()
-					.filter(|(protocol, _)| protocol == &PeerSet::Collation.into_protocol_name())
+					.filter(|(protocol, _)| {
+						protocol == &PeerSet::Collation.into_protocol_name()
+					})
 					.map(|(_, msg_bytes)| WireMessage::decode(&mut msg_bytes.as_ref()))
 					.collect();

@@ -182,3 +202,13 @@ impl From<Option<NetworkEvent>> for Action {
 		}
 	}
 }
+
+impl From<Option<Result<AllMessages, RequestMultiplexError>>> for Action {
+	fn from(event: Option<Result<AllMessages, RequestMultiplexError>>) -> Self {
+		match event {
+			None => Action::Abort(AbortReason::RequestStreamConcluded),
+			Some(Err(err)) => Action::ReportPeer(err.peer, MALFORMED_MESSAGE_COST),
+			Some(Ok(msg)) => Action::SendMessage(msg),
+		}
+	}
+}
@@ -30,11 +30,11 @@ use polkadot_subsystem::{
 use polkadot_subsystem::messages::{
 	NetworkBridgeMessage, AllMessages, AvailabilityDistributionMessage,
 	BitfieldDistributionMessage, PoVDistributionMessage, StatementDistributionMessage,
-	CollatorProtocolMessage, ApprovalDistributionMessage,
+	CollatorProtocolMessage, ApprovalDistributionMessage, NetworkBridgeEvent,
 };
 use polkadot_primitives::v1::{Hash, BlockNumber};
 use polkadot_node_network_protocol::{
-	ReputationChange, PeerId, peer_set::PeerSet, View, NetworkBridgeEvent, v1 as protocol_v1, OurView,
+	ReputationChange, PeerId, peer_set::PeerSet, View, v1 as protocol_v1, OurView,
 };

 /// Peer set infos for network initialization.
@@ -53,7 +53,7 @@ mod validator_discovery;
 /// All requested `NetworkBridgeMessage` user actions  and `NetworkEvent` network messages are
 /// translated to `Action` before being processed by `run_network`.
 mod action;
-use action::Action;
+use action::{Action, AbortReason};

 /// Actual interfacing to the network based on the `Network` trait.
 ///
@@ -61,6 +61,10 @@ use action::Action;
 mod network;
 use network::{Network, send_message};

+/// Request multiplexer for combining the multiple request sources into a single `Stream` of `AllMessages`.
+mod multiplexer;
+pub use multiplexer::RequestMultiplexer;
+

 /// The maximum amount of heads a peer is allowed to have in their view at any time.
 ///
@@ -95,6 +99,7 @@ pub struct NetworkBridge<N, AD> {
 	/// `Network` trait implementing type.
 	network_service: N,
 	authority_discovery_service: AD,
+	request_multiplexer: RequestMultiplexer,
 }

 impl<N, AD> NetworkBridge<N, AD> {
@@ -102,10 +107,11 @@ impl<N, AD> NetworkBridge<N, AD> {
 	///
 	/// This assumes that the network service has had the notifications protocol for the network
 	/// bridge already registered. See [`peers_sets_info`](peers_sets_info).
-	pub fn new(network_service: N, authority_discovery_service: AD) -> Self {
+	pub fn new(network_service: N, authority_discovery_service: AD, request_multiplexer: RequestMultiplexer) -> Self {
 		NetworkBridge {
 			network_service,
 			authority_discovery_service,
+			request_multiplexer,
 		}
 	}
 }
@@ -119,12 +125,7 @@ impl<Net, AD, Context> Subsystem<Context> for NetworkBridge<Net, AD>
 	fn start(self, ctx: Context) -> SpawnedSubsystem {
 		// Swallow error because failure is fatal to the node and we log with more precision
 		// within `run_network`.
-		let Self { network_service, authority_discovery_service } = self;
-		let future = run_network(
-				network_service,
-				authority_discovery_service,
-				ctx,
-			)
+		let future = run_network(self, ctx)
 			.map_err(|e| {
 				SubsystemError::with_origin("network-bridge", e)
 			})
@@ -142,17 +143,16 @@ struct PeerData {
 }

 /// Main driver, processing network events and messages from other subsystems.
-#[tracing::instrument(skip(network_service, authority_discovery_service, ctx), fields(subsystem = LOG_TARGET))]
+#[tracing::instrument(skip(bridge, ctx), fields(subsystem = LOG_TARGET))]
 async fn run_network<N, AD>(
-	mut network_service: N,
-	mut authority_discovery_service: AD,
+	mut bridge: NetworkBridge<N, AD>,
 	mut ctx: impl SubsystemContext<Message=NetworkBridgeMessage>,
 ) -> SubsystemResult<()>
 where
 	N: Network + validator_discovery::Network,
 	AD: validator_discovery::AuthorityDiscovery,
 {
-	let mut event_stream = network_service.event_stream().fuse();
+	let mut event_stream = bridge.network_service.event_stream().fuse();

 	// Most recent heads are at the back.
 	let mut live_heads: Vec<(Hash, Arc<JaegerSpan>)> = Vec::with_capacity(MAX_VIEW_HEADS);
@@ -169,22 +169,55 @@ where
 		let action = {
 			let subsystem_next = ctx.recv().fuse();
 			let mut net_event_next = event_stream.next().fuse();
+			let mut req_res_event_next = bridge.request_multiplexer.next().fuse();
 			futures::pin_mut!(subsystem_next);

 			futures::select! {
 				subsystem_msg = subsystem_next => Action::from(subsystem_msg),
 				net_event = net_event_next => Action::from(net_event),
+				req_res_event = req_res_event_next  => Action::from(req_res_event),
 			}
 		};

 		match action {
 			Action::Nop => {}
-			Action::Abort => return Ok(()),
+			Action::Abort(reason) => match reason {
+				AbortReason::SubsystemError(err) => {
+					tracing::warn!(
+						target: LOG_TARGET,
+						err = ?err,
+						"Shutting down Network Bridge due to error"
+					);
+					return Err(SubsystemError::Context(format!(
+						"Received SubsystemError from overseer: {:?}",
+						err
+					)));
+				}
+				AbortReason::EventStreamConcluded => {
+					tracing::info!(
+						target: LOG_TARGET,
+						"Shutting down Network Bridge: underlying request stream concluded"
+					);
+					return Err(SubsystemError::Context(
+						"Incoming network event stream concluded.".to_string(),
+					));
+				}
+				AbortReason::RequestStreamConcluded => {
+					tracing::info!(
+						target: LOG_TARGET,
+						"Shutting down Network Bridge: underlying request stream concluded"
+					);
+					return Err(SubsystemError::Context(
+						"Incoming network request stream concluded".to_string(),
+					));
+				}
+				AbortReason::OverseerConcluded => return Ok(()),
+			}

 			Action::SendValidationMessages(msgs) => {
 				for (peers, msg) in msgs {
 					send_message(
-							&mut network_service,
+							&mut bridge.network_service,
 							peers,
 							PeerSet::Validation,
 							WireMessage::ProtocolMessage(msg),
@@ -195,7 +228,7 @@ where
 			Action::SendCollationMessages(msgs) => {
 				for (peers, msg) in msgs {
 					send_message(
-							&mut network_service,
+							&mut bridge.network_service,
 							peers,
 							PeerSet::Collation,
 							WireMessage::ProtocolMessage(msg),
@@ -203,6 +236,12 @@ where
 				}
 			}

+			Action::SendRequests(reqs) => {
+				for req in reqs {
+					bridge.network_service.start_request(req);
+				}
+			},
+
 			Action::ConnectToValidators {
 				validator_ids,
 				connected,
@@ -210,21 +249,28 @@ where
 				let (ns, ads) = validator_discovery.on_request(
 					validator_ids,
 					connected,
-					network_service,
-					authority_discovery_service,
+					bridge.network_service,
+					bridge.authority_discovery_service,
 				).await;
-				network_service = ns;
-				authority_discovery_service = ads;
+				bridge.network_service = ns;
+				bridge.authority_discovery_service = ads;
 			},

-			Action::ReportPeer(peer, rep) => network_service.report_peer(peer, rep).await?,
+			Action::ReportPeer(peer, rep) => {
+				tracing::debug!(
+					target: LOG_TARGET,
+					peer = ?peer,
+					"Peer sent us an invalid request",
+				);
+				bridge.network_service.report_peer(peer, rep).await?
+			}

 			Action::ActiveLeaves(ActiveLeavesUpdate { activated, deactivated }) => {
 				live_heads.extend(activated);
 				live_heads.retain(|h| !deactivated.contains(&h.0));

 				update_our_view(
-					&mut network_service,
+					&mut bridge.network_service,
 					&mut ctx,
 					&live_heads,
 					&mut local_view,
@@ -250,7 +296,7 @@ where
 					PeerSet::Collation => &mut collation_peers,
 				};

-				validator_discovery.on_peer_connected(&peer, &mut authority_discovery_service).await;
+				validator_discovery.on_peer_connected(&peer, &mut bridge.authority_discovery_service).await;

 				match peer_map.entry(peer.clone()) {
 					hash_map::Entry::Occupied(_) => continue,
@@ -311,7 +357,7 @@ where
 						peer.clone(),
 						&mut validation_peers,
 						v_messages,
-						&mut network_service,
+						&mut bridge.network_service,
 					).await?;

 					dispatch_validation_events_to_all(events, &mut ctx).await;
@@ -322,12 +368,13 @@ where
 						peer.clone(),
 						&mut collation_peers,
 						c_messages,
-						&mut network_service,
+						&mut bridge.network_service,
 					).await?;

 					dispatch_collation_events_to_all(events, &mut ctx).await;
 				}
 			},
+			Action::SendMessage(msg) => ctx.send_message(msg).await,
 		}
 	}
 }
@@ -562,9 +609,10 @@ mod tests {
 	use polkadot_node_subsystem_util::metered;
 	use polkadot_node_network_protocol::view;
 	use sc_network::Multiaddr;
+	use sc_network::config::RequestResponseConfig;
 	use sp_keyring::Sr25519Keyring;
 	use polkadot_primitives::v1::AuthorityDiscoveryId;
-	use polkadot_node_network_protocol::ObservedRole;
+	use polkadot_node_network_protocol::{ObservedRole, request_response::request::Requests};

 	use crate::network::{Network, NetworkAction};

@@ -572,6 +620,7 @@ mod tests {
 	struct TestNetwork {
 		net_events: Arc<Mutex<Option<SingleItemStream<NetworkEvent>>>>,
 		action_tx: metered::UnboundedMeteredSender<NetworkAction>,
+		_req_configs: Vec<RequestResponseConfig>,
 	}

 	struct TestAuthorityDiscovery;
@@ -583,7 +632,7 @@ mod tests {
 		net_tx: SingleItemSink<NetworkEvent>,
 	}

-	fn new_test_network() -> (
+	fn new_test_network(req_configs: Vec<RequestResponseConfig>) -> (
 		TestNetwork,
 		TestNetworkHandle,
 		TestAuthorityDiscovery,
@@ -595,6 +644,7 @@ mod tests {
 			TestNetwork {
 				net_events: Arc::new(Mutex::new(Some(net_rx))),
 				action_tx,
+				_req_configs: req_configs,
 			},
 			TestNetworkHandle {
 				action_rx,
@@ -617,6 +667,9 @@ mod tests {
 		{
 			Box::pin((&mut self.action_tx).sink_map_err(Into::into))
 		}
+
+		fn start_request(&self, _: Requests) {
+		}
 	}

 	#[async_trait]
@@ -698,12 +751,18 @@ mod tests {

 	fn test_harness<T: Future<Output=()>>(test: impl FnOnce(TestHarness) -> T) {
 		let pool = sp_core::testing::TaskExecutor::new();
-		let (network, network_handle, discovery) = new_test_network();
+		let (request_multiplexer, req_configs) = RequestMultiplexer::new();
+		let (network, network_handle, discovery) = new_test_network(req_configs);
 		let (context, virtual_overseer) = polkadot_node_subsystem_test_helpers::make_subsystem_context(pool);

+		let bridge = NetworkBridge {
+			network_service: network,
+			authority_discovery_service: discovery,
+			request_multiplexer,
+		};
+
 		let network_bridge = run_network(
-			network,
-			discovery,
+			bridge,
 			context,
 		)
 			.map_err(|_| panic!("subsystem execution failed"))
@@ -0,0 +1,132 @@
+// Copyright 2021 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+use std::pin::Pin;
+
+use futures::channel::mpsc;
+use futures::stream::Stream;
+use futures::task::{Context, Poll};
+use strum::IntoEnumIterator;
+
+use parity_scale_codec::{Decode, Error as DecodingError};
+
+use sc_network::config as network;
+use sc_network::PeerId;
+
+use polkadot_node_network_protocol::request_response::{
+	request::IncomingRequest, v1, Protocol, RequestResponseConfig,
+};
+use polkadot_subsystem::messages::AllMessages;
+
+/// Multiplex incoming network requests.
+///
+/// This multiplexer consumes all request streams and makes them a `Stream` of a single message
+/// type, useful for the network bridge to send them via the `Overseer` to other subsystems.
+pub struct RequestMultiplexer {
+	receivers: Vec<(Protocol, mpsc::Receiver<network::IncomingRequest>)>,
+	next_poll: usize,
+}
+
+/// Multiplexing can fail in case of invalid messages.
+pub struct RequestMultiplexError {
+	/// The peer that sent the invalid message.
+	pub peer: PeerId,
+	/// The error that occurred.
+	pub error: DecodingError,
+}
+
+impl RequestMultiplexer {
+	/// Create a new `RequestMultiplexer`.
+	///
+	/// This function uses `Protocol::get_config` for each available protocol and creates a
+	/// `RequestMultiplexer` from it. The returned `RequestResponseConfig`s must be passed to the
+	/// network implementation.
+	pub fn new() -> (Self, Vec<RequestResponseConfig>) {
+		let (receivers, cfgs): (Vec<_>, Vec<_>) = Protocol::iter()
+			.map(|p| {
+				let (rx, cfg) = p.get_config();
+				((p, rx), cfg)
+			})
+			.unzip();
+
+		(
+			Self {
+				receivers,
+				next_poll: 0,
+			},
+			cfgs,
+		)
+	}
+}
+
+impl Stream for RequestMultiplexer {
+	type Item = Result<AllMessages, RequestMultiplexError>;
+
+	fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+		let len = self.receivers.len();
+		let mut count = len;
+		let mut i = self.next_poll;
+		let mut result = Poll::Ready(None);
+		// Poll streams in round robin fashion:
+		while count > 0 {
+			// % safe, because count initialized to len, loop would not be entered if 0, also
+			// length of receivers is fixed.
+			let (p, rx): &mut (_, _) = &mut self.receivers[i % len];
+			i += 1;
+			count -= 1;
+			match Pin::new(rx).poll_next(cx) {
+				// If at least one stream is pending, then we are not done yet (No
+				// Ready(None)).
+				Poll::Pending => result = Poll::Pending,
+				// Receiver is a fused stream, which allows for this simple handling of 
+				// exhausted ones.
+				Poll::Ready(None) => {}
+				Poll::Ready(Some(v)) => {
+					result = Poll::Ready(Some(multiplex_single(*p, v)));
+					break;
+				}
+			}
+		}
+		self.next_poll = i;
+		result
+	}
+}
+
+/// Convert a single raw incoming request into a `MultiplexMessage`.
+fn multiplex_single(
+	p: Protocol,
+	network::IncomingRequest {
+		payload,
+		peer,
+		pending_response,
+	}: network::IncomingRequest,
+) -> Result<AllMessages, RequestMultiplexError> {
+	let r = match p {
+		Protocol::AvailabilityFetching => From::from(IncomingRequest::new(
+			peer,
+			decode_with_peer::<v1::AvailabilityFetchingRequest>(peer, payload)?,
+			pending_response,
+		)),
+	};
+	Ok(r)
+}
+
+fn decode_with_peer<Req: Decode>(
+	peer: PeerId,
+	payload: Vec<u8>,
+) -> Result<Req, RequestMultiplexError> {
+	Req::decode(&mut payload.as_ref()).map_err(|error| RequestMultiplexError { peer, error })
+}
@@ -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,
+		);
+	}
 }