Silky smooth discovery (#1274)

* Initial structural re-write

* Improving discovery update and correcting attestation service logic

* Rework discovery.mod

* Handling lifetimes of query futures

* Discovery update first draft

* format fixes

* Stabalise discv5 update

* Formatting corrections

* Limit FindPeers queries and bug correction

* Update to stable release discv5

* Remove unnecessary pin

* formatting

beacon_node/eth2_libp2p/src/behaviour/handler/mod.rs

@@ -0,0 +1,139 @@
+use crate::rpc::*;
+use delegate::DelegatingHandler;
+pub(super) use delegate::{
+    DelegateError, DelegateIn, DelegateInProto, DelegateOut, DelegateOutInfo, DelegateOutProto,
+};
+use libp2p::{
+    core::upgrade::{InboundUpgrade, OutboundUpgrade},
+    gossipsub::Gossipsub,
+    identify::Identify,
+    swarm::protocols_handler::{
+        KeepAlive, ProtocolsHandlerEvent, ProtocolsHandlerUpgrErr, SubstreamProtocol,
+    },
+    swarm::{NegotiatedSubstream, ProtocolsHandler},
+};
+use std::task::{Context, Poll};
+use types::EthSpec;
+
+mod delegate;
+
+/// Handler that combines Lighthouse's Behaviours' handlers in a delegating manner.
+pub struct BehaviourHandler<TSpec: EthSpec> {
+    /// Handler combining all sub behaviour's handlers.
+    delegate: DelegatingHandler<TSpec>,
+    /// Flag indicating if the handler is shutting down.
+    shutting_down: bool,
+}
+
+impl<TSpec: EthSpec> BehaviourHandler<TSpec> {
+    pub fn new(gossipsub: &mut Gossipsub, rpc: &mut RPC<TSpec>, identify: &mut Identify) -> Self {
+        BehaviourHandler {
+            delegate: DelegatingHandler::new(gossipsub, rpc, identify),
+            shutting_down: false,
+        }
+    }
+}
+
+#[derive(Clone)]
+pub enum BehaviourHandlerIn<TSpec: EthSpec> {
+    Delegate(DelegateIn<TSpec>),
+    /// Start the shutdown process.
+    Shutdown(Option<(RequestId, RPCRequest<TSpec>)>),
+}
+
+pub enum BehaviourHandlerOut<TSpec: EthSpec> {
+    Delegate(DelegateOut<TSpec>),
+    // TODO: replace custom with events to send
+    Custom,
+}
+
+impl<TSpec: EthSpec> ProtocolsHandler for BehaviourHandler<TSpec> {
+    type InEvent = BehaviourHandlerIn<TSpec>;
+    type OutEvent = BehaviourHandlerOut<TSpec>;
+    type Error = DelegateError<TSpec>;
+    type InboundProtocol = DelegateInProto<TSpec>;
+    type OutboundProtocol = DelegateOutProto<TSpec>;
+    type OutboundOpenInfo = DelegateOutInfo<TSpec>;
+
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
+        self.delegate.listen_protocol()
+    }
+
+    fn inject_fully_negotiated_inbound(
+        &mut self,
+        out: <Self::InboundProtocol as InboundUpgrade<NegotiatedSubstream>>::Output,
+    ) {
+        self.delegate.inject_fully_negotiated_inbound(out)
+    }
+
+    fn inject_fully_negotiated_outbound(
+        &mut self,
+        out: <Self::OutboundProtocol as OutboundUpgrade<NegotiatedSubstream>>::Output,
+        info: Self::OutboundOpenInfo,
+    ) {
+        self.delegate.inject_fully_negotiated_outbound(out, info)
+    }
+
+    fn inject_event(&mut self, event: Self::InEvent) {
+        match event {
+            BehaviourHandlerIn::Delegate(delegated_ev) => self.delegate.inject_event(delegated_ev),
+            /* Events comming from the behaviour */
+            BehaviourHandlerIn::Shutdown(last_message) => {
+                self.shutting_down = true;
+                self.delegate.rpc_mut().shutdown(last_message);
+            }
+        }
+    }
+
+    fn inject_dial_upgrade_error(
+        &mut self,
+        info: Self::OutboundOpenInfo,
+        err: ProtocolsHandlerUpgrErr<
+            <Self::OutboundProtocol as OutboundUpgrade<NegotiatedSubstream>>::Error,
+        >,
+    ) {
+        self.delegate.inject_dial_upgrade_error(info, err)
+    }
+
+    fn connection_keep_alive(&self) -> KeepAlive {
+        if self.shutting_down {
+            let rpc_keep_alive = self.delegate.rpc().connection_keep_alive();
+            let identify_keep_alive = self.delegate.identify().connection_keep_alive();
+            rpc_keep_alive.max(identify_keep_alive)
+        } else {
+            KeepAlive::Yes
+        }
+    }
+
+    fn poll(
+        &mut self,
+        cx: &mut Context,
+    ) -> Poll<
+        ProtocolsHandlerEvent<
+            Self::OutboundProtocol,
+            Self::OutboundOpenInfo,
+            Self::OutEvent,
+            Self::Error,
+        >,
+    > {
+        match self.delegate.poll(cx) {
+            Poll::Ready(ProtocolsHandlerEvent::Custom(event)) => {
+                return Poll::Ready(ProtocolsHandlerEvent::Custom(
+                    BehaviourHandlerOut::Delegate(event),
+                ))
+            }
+            Poll::Ready(ProtocolsHandlerEvent::Close(err)) => {
+                return Poll::Ready(ProtocolsHandlerEvent::Close(err))
+            }
+            Poll::Ready(ProtocolsHandlerEvent::OutboundSubstreamRequest { protocol, info }) => {
+                return Poll::Ready(ProtocolsHandlerEvent::OutboundSubstreamRequest {
+                    protocol,
+                    info,
+                });
+            }
+            Poll::Pending => (),
+        }
+
+        Poll::Pending
+    }
+}