Network sync refactoring (part 6) (#11940)

* Extract `NetworkKVProvider` trait in `sc-authority-discovery` and remove unnecessary dependency

* Extract `NetworkSyncForkRequest` trait in `sc-finality-grandpa`

* Relax requirements on `SyncOracle` trait, remove extra native methods from `NetworkService` that are already provided by trait impls

* Move `NetworkSigner` trait from `sc-authority-discovery` into `sc-network-common` and de-duplicate methods on `NetworkService`

* Move `NetworkKVProvider` trait from `sc-authority-discovery` into `sc-network-common` and de-duplicate methods on `NetworkService`

* Minimize `sc-authority-discovery` dependency on `sc-network`

* Move `NetworkSyncForkRequest` trait from `sc-finality-grandpa` to `sc-network-common` and de-duplicate methods in `NetworkService`

* Extract `NetworkStatusProvider` trait and de-duplicate methods on `NetworkService`

* Extract `NetworkPeers` trait and de-duplicate methods on `NetworkService`

* Extract `NetworkEventStream` trait and de-duplicate methods on `NetworkService`

* Move more methods from `NetworkService` into `NetworkPeers` trait

* Move `NetworkStateInfo` trait into `sc-network-common`

* Extract `NetworkNotification` trait and de-duplicate methods on `NetworkService`

* Extract `NetworkRequest` trait and de-duplicate methods on `NetworkService`

* Remove `NetworkService::local_peer_id()`, it is already provided by `NetworkStateInfo` impl

* Extract `NetworkTransaction` trait and de-duplicate methods on `NetworkService`

* Extract `NetworkBlock` trait and de-duplicate methods on `NetworkService`

* Remove dependencies on `NetworkService` from most of the methods of `sc-service`

* Address simple review comments

substrate/client/network/common/src/request_responses.rs

@@ -19,7 +19,7 @@
 //! Collection of generic data structures for request-response protocols.
 
 use futures::channel::{mpsc, oneshot};
-use libp2p::PeerId;
+use libp2p::{request_response::OutboundFailure, PeerId};
 use sc_peerset::ReputationChange;
 use std::{borrow::Cow, time::Duration};
 
@@ -115,3 +115,40 @@ pub struct OutgoingResponse {
 	/// >			written to the buffer managed by the operating system.
 	pub sent_feedback: Option<oneshot::Sender<()>>,
 }
+
+/// When sending a request, what to do on a disconnected recipient.
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum IfDisconnected {
+	/// Try to connect to the peer.
+	TryConnect,
+	/// Just fail if the destination is not yet connected.
+	ImmediateError,
+}
+
+/// Convenience functions for `IfDisconnected`.
+impl IfDisconnected {
+	/// Shall we connect to a disconnected peer?
+	pub fn should_connect(self) -> bool {
+		match self {
+			Self::TryConnect => true,
+			Self::ImmediateError => false,
+		}
+	}
+}
+
+/// Error in a request.
+#[derive(Debug, thiserror::Error)]
+#[allow(missing_docs)]
+pub enum RequestFailure {
+	#[error("We are not currently connected to the requested peer.")]
+	NotConnected,
+	#[error("Given protocol hasn't been registered.")]
+	UnknownProtocol,
+	#[error("Remote has closed the substream before answering, thereby signaling that it considers the request as valid, but refused to answer it.")]
+	Refused,
+	#[error("The remote replied, but the local node is no longer interested in the response.")]
+	Obsolete,
+	/// Problem on the network.
+	#[error("Problem on the network: {0}")]
+	Network(OutboundFailure),
+}