Add DHT key-value behaviour (#2937)

* Add DHT key-value behaviour

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Apply suggestions from code review

Co-Authored-By: Pierre Krieger <pierre.krieger1708@gmail.com>

* Return which key failed to be inserted

substrate/core/network/src/protocol/event.rs

@@ -0,0 +1,41 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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.
+
+// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Network event types. These are are not the part of the protocol, but rather
+//! events that happen on the network like DHT get/put results received.
+
+use libp2p::multihash::Multihash;
+
+/// Events generated by DHT as a response to get_value and put_value requests.
+pub enum DhtEvent {
+	/// The value was found.
+	ValueFound(Vec<(Multihash, Vec<u8>)>),
+
+	/// The requested record has not been found in the DHT.
+	ValueNotFound(Multihash),
+
+	/// The record has been successfully inserted into the DHT.
+	ValuePut(Multihash),
+
+	/// An error has occured while putting a record into the DHT.
+	ValuePutFailed(Multihash),
+}
+
+/// Type for events generated by networking layer.
+pub enum Event {
+	/// Event generated by a DHT.
+	Dht(DhtEvent),
+}

substrate/core/network/src/protocol/specialization.rs

@@ -39,6 +39,12 @@ pub trait NetworkSpecialization<B: BlockT>: Send + Sync + 'static {
 		message: &mut Option<crate::message::Message<B>>
 	);
 
+	/// Called when a network-specific event arrives.
+	fn on_event(
+		&mut self,
+		event: crate::protocol::event::Event
+	);
+
 	/// Called on abort.
 	#[deprecated(note = "This method is never called; aborting corresponds to dropping the object")]
 	fn on_abort(&mut self) { }
@@ -130,6 +136,13 @@ macro_rules! construct_simple_protocol {
 				$( self.$sub_protocol_name.on_message(_ctx, _who, _message); )*
 			}
 
+			fn on_event(
+				&mut self,
+				_event: $crate::event::Event
+			) {
+				$( self.$sub_protocol_name.on_event(_event); )*
+			}
+
 			fn on_abort(&mut self) {
 				$( self.$sub_protocol_name.on_abort(); )*
 			}