enable network to emit events on a bus

network/events.go

+package network
+
+// EvtPeerConnectionStateChange should be emitted when we connect/disconnect from a peer
+type EvtPeerConnectionStateChange struct {
+	Network    Network
+	Connection Conn
+	NewState   Connectedness
+}
+
+// EvtStreamStateChange is emitted when we open/close a stream with a peer
+type EvtStreamStateChange struct {
+	Network  Network
+	Stream   Stream
+	NewState Connectedness
+}

network/network.go

@@ -10,6 +10,7 @@ import (
 	"io"
 
 	"github.com/jbenet/goprocess"
+	"github.com/libp2p/go-libp2p-core/event"
 	"github.com/libp2p/go-libp2p-core/peer"
 	"github.com/libp2p/go-libp2p-core/peerstore"
 
@@ -100,6 +101,11 @@ type Network interface {
 
 	// Process returns the network's Process
 	Process() goprocess.Process
+
+	// EventBus returns the network's Event Bus
+	// we can subscribe to this bus to listen for connection/disconnection of peers,
+	// opening/closing of streams etc etc
+	EventBus() event.Bus
 }
 
 // Dialer represents a service that can dial out to peers