Implements a basic libp2p tcp,secio,mplex,gossipsub swarm.

beacon_node/libp2p/src/behaviour.rs

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+use futures::prelude::*;
+use libp2p::{
+    core::swarm::{NetworkBehaviourAction, NetworkBehaviourEventProcess},
+    gossipsub::{Gossipsub, GossipsubConfig, GossipsubEvent, GossipsubRpc},
+    tokio_io::{AsyncRead, AsyncWrite},
+    NetworkBehaviour, PeerId,
+};
+
+/// Builds the network behaviour for the libp2p Swarm.
+/// Implements gossipsub message routing.
+#[derive(NetworkBehaviour)]
+pub struct Behaviour<TSubstream: AsyncRead + AsyncWrite> {
+    gossipsub: Gossipsub<TSubstream>,
+    // TODO: Add Kademlia for peer discovery
+    /// The events generated by this behaviour to be consumed in the swarm poll.
+    // We use gossipsub events for now, generalise later.
+    #[behaviour(ignore)]
+    events: Vec<GossipsubEvent>,
+}
+
+// Implement the NetworkBehaviourEventProcess trait so that we can derive NetworkBehaviour for Behaviour
+impl<TSubstream: AsyncRead + AsyncWrite> NetworkBehaviourEventProcess<GossipsubEvent>
+    for Behaviour<TSubstream>
+{
+    fn inject_event(&mut self, event: GossipsubEvent) {
+        self.events.push(event);
+    }
+}
+
+impl<TSubstream: AsyncRead + AsyncWrite> Behaviour<TSubstream> {
+    pub fn new(local_peer_id: PeerId, gs_config: GossipsubConfig) -> Self {
+        Behaviour {
+            gossipsub: Gossipsub::new(local_peer_id, gs_config),
+            events: Vec::new(),
+        }
+    }
+
+    /// Consume the events list when polled.
+    fn poll(&mut self) -> Async<NetworkBehaviourAction<GossipsubRpc, GossipsubEvent>> {
+        if !self.events.is_empty() {
+            return Async::Ready(NetworkBehaviourAction::GenerateEvent(self.events.remove(0)));
+        }
+
+        Async::NotReady
+    }
+}