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/discovery.rs

@@ -18,10 +18,11 @@ use futures::prelude::*;
 use libp2p::core::{Multiaddr, PeerId, ProtocolsHandler, PublicKey};
 use libp2p::core::swarm::{ConnectedPoint, NetworkBehaviour, NetworkBehaviourAction};
 use libp2p::core::swarm::PollParameters;
-use libp2p::kad::{Kademlia, KademliaOut};
+use libp2p::kad::{GetValueResult, Kademlia, KademliaOut, PutValueResult};
+use libp2p::multihash::Multihash;
 use libp2p::multiaddr::Protocol;
 use log::{debug, info, trace, warn};
-use std::{cmp, time::Duration};
+use std::{cmp, num::NonZeroU8, time::Duration};
 use tokio_io::{AsyncRead, AsyncWrite};
 use tokio_timer::{Delay, clock::Clock};
 
@@ -81,12 +82,35 @@ impl<TSubstream> DiscoveryBehaviour<TSubstream> {
 	pub fn add_self_reported_address(&mut self, peer_id: &PeerId, addr: Multiaddr) {
 		self.kademlia.add_address(peer_id, addr);
 	}
+
+	/// Get a record from the DHT.
+	pub fn get_value(&mut self, key: &Multihash) {
+		self.kademlia.get_value(key, NonZeroU8::new(10)
+								.expect("Casting 10 to NonZeroU8 should succeed; qed"));
+	}
+
+	/// Put a record into the DHT.
+	pub fn put_value(&mut self, key: Multihash, value: Vec<u8>) {
+		self.kademlia.put_value(key, value);
+	}
 }
 
 /// Event generated by the `DiscoveryBehaviour`.
 pub enum DiscoveryOut {
 	/// We have discovered a node. Can be called multiple times with the same identity.
 	Discovered(PeerId),
+
+	/// The DHT yeided results for the record request, grouped in (key, value) pairs.
+	ValueFound(Vec<(Multihash, Vec<u8>)>),
+
+	/// The record requested was not found in the DHT.
+	ValueNotFound(Multihash),
+
+	/// The record with a given key was successfully inserted into the DHT.
+	ValuePut(Multihash),
+
+	/// Inserting a value into the DHT failed.
+	ValuePutFailed(Multihash),
 }
 
 impl<TSubstream> NetworkBehaviour for DiscoveryBehaviour<TSubstream>
@@ -175,10 +199,35 @@ where
 								results");
 						}
 					}
+					KademliaOut::GetValueResult(res) => {
+						let ev = match res {
+							GetValueResult::Found { results } => {
+								let results = results
+										.into_iter()
+										.map(|r| (r.key, r.value))
+										.collect();
+
+								DiscoveryOut::ValueFound(results)
+							}
+							GetValueResult::NotFound { key, .. } => {
+								DiscoveryOut::ValueNotFound(key)
+							}
+						};
+						return Async::Ready(NetworkBehaviourAction::GenerateEvent(ev));
+					}
+					KademliaOut::PutValueResult(res) => {
+						let ev = match res {
+							PutValueResult::Ok{ key, .. } =>  {
+								DiscoveryOut::ValuePut(key)
+							}
+							PutValueResult::Err { key, .. } => {
+								DiscoveryOut::ValuePutFailed(key)
+							}
+						};
+						return Async::Ready(NetworkBehaviourAction::GenerateEvent(ev));
+					}
 					// We never start any other type of query.
 					KademliaOut::GetProvidersResult { .. } => {}
-					KademliaOut::GetValueResult(_) => {}
-					KademliaOut::PutValueResult(_) => {}
 				}
 			},
 			Async::Ready(NetworkBehaviourAction::DialAddress { address }) =>