peer: make peer meet query.Peer interface

query.Peer is used for downloading blocks out of order during headers
first download.  Methods SubscribeRecvMsg() and OnDisconnect() are added
to abide by the interface.

peer/peer.go

@@ -494,6 +494,11 @@ type Peer struct {
 	queueQuit     chan struct{}
 	outQuit       chan struct{}
 	quit          chan struct{}
+
+	// subscribers is a channel for relaying all messages that were received
+	// to this peer.
+	subscribers    map[recvMsgsubscription]struct{}
+	subscriberLock sync.Mutex
 }
 
 // String returns the peer's address and directionality as a human-readable
@@ -1098,6 +1103,35 @@ func (p *Peer) readMessage(encoding wire.MessageEncoding) (wire.Message, []byte,
 	return msg, buf, nil
 }
 
+// recvMsgsubscription is two channels for a subscriber of recevied messages.
+// msgChan for sending the messages and quit for cancelling the subscription.
+type recvMsgsubscription struct {
+	msgChan chan wire.Message
+	quit    chan struct{}
+}
+
+// SubscribeRecvMsg adds a OnRead subscription to the peer.  All bitcoin
+// messages received from this peer will be sent on the returned
+// channel.  A closure is also returned, that should be called to cancel
+// the subscription.
+func (p *Peer) SubscribeRecvMsg() (<-chan wire.Message, func()) {
+	p.subscriberLock.Lock()
+	defer p.subscriberLock.Unlock()
+
+	// No need to buffer this channel as we'll spin up a new goroutine for
+	// every send.
+	msgChan := make(chan wire.Message)
+	quit := make(chan struct{})
+	sub := recvMsgsubscription{
+		msgChan,
+		quit,
+	}
+
+	p.subscribers[sub] = struct{}{}
+
+	return msgChan, func() { close(quit) }
+}
+
 // writeMessage sends a bitcoin message to the peer with logging.
 func (p *Peer) writeMessage(msg wire.Message, enc wire.MessageEncoding) error {
 	// Don't do anything if we're disconnecting.
@@ -1446,6 +1480,27 @@ out:
 			}
 			break out
 		}
+
+		// Send the received message to all the subscribers.
+		for sub := range p.subscribers {
+			select {
+			case <-sub.quit:
+				delete(p.subscribers, sub)
+				continue
+			default:
+			}
+
+			// Spin up a goroutine so that we don't block here.
+			go func(subscription chan wire.Message,
+				quit chan struct{}) {
+
+				select {
+				case subscription <- rmsg:
+				case <-p.quit:
+				}
+
+			}(sub.msgChan, p.quit)
+		}
 		atomic.StoreInt64(&p.lastRecv, time.Now().Unix())
 		p.stallControl <- stallControlMsg{sccReceiveMessage, rmsg}
 
@@ -1961,6 +2016,12 @@ func (p *Peer) Disconnect() {
 	close(p.quit)
 }
 
+// OnDisconnect returns a channel that will be closed when this peer is
+// disconnected.
+func (p *Peer) OnDisconnect() <-chan struct{} {
+	return p.quit
+}
+
 // readRemoteVersionMsg waits for the next message to arrive from the remote
 // peer.  If the next message is not a version message or the version is not
 // acceptable then return an error.
@@ -2397,6 +2458,7 @@ func newPeerBase(origCfg *Config, inbound bool) *Peer {
 		queueQuit:       make(chan struct{}),
 		outQuit:         make(chan struct{}),
 		quit:            make(chan struct{}),
+		subscribers:     make(map[recvMsgsubscription]struct{}),
 		cfg:             cfg, // Copy so caller can't mutate.
 		services:        cfg.Services,
 		protocolVersion: cfg.ProtocolVersion,