Merge pull request #1462 from wpaulino/verack-version-handshake

peer: include verack as part of version handshake

peer/peer.go

@@ -1377,20 +1377,12 @@ out:
 			break out
 
 		case *wire.MsgVerAck:
-
-			// No read lock is necessary because verAckReceived is not written
-			// to in any other goroutine.
-			if p.verAckReceived {
-				log.Infof("Already received 'verack' from peer %v -- "+
-					"disconnecting", p)
-				break out
-			}
-			p.flagsMtx.Lock()
-			p.verAckReceived = true
-			p.flagsMtx.Unlock()
-			if p.cfg.Listeners.OnVerAck != nil {
-				p.cfg.Listeners.OnVerAck(p, msg)
-			}
+			// Limit to one verack message per peer.
+			p.PushRejectMsg(
+				msg.Command(), wire.RejectDuplicate,
+				"duplicate verack message", nil, true,
+			)
+			break out
 
 		case *wire.MsgGetAddr:
 			if p.cfg.Listeners.OnGetAddr != nil {
@@ -1974,6 +1966,40 @@ func (p *Peer) readRemoteVersionMsg() error {
 	return nil
 }
 
+// readRemoteVerAckMsg waits for the next message to arrive from the remote
+// peer. If this message is not a verack message, then an error is returned.
+// This method is to be used as part of the version negotiation upon a new
+// connection.
+func (p *Peer) readRemoteVerAckMsg() error {
+	// Read the next message from the wire.
+	remoteMsg, _, err := p.readMessage(wire.LatestEncoding)
+	if err != nil {
+		return err
+	}
+
+	// It should be a verack message, otherwise send a reject message to the
+	// peer explaining why.
+	msg, ok := remoteMsg.(*wire.MsgVerAck)
+	if !ok {
+		reason := "a verack message must follow version"
+		rejectMsg := wire.NewMsgReject(
+			msg.Command(), wire.RejectMalformed, reason,
+		)
+		_ = p.writeMessage(rejectMsg, wire.LatestEncoding)
+		return errors.New(reason)
+	}
+
+	p.flagsMtx.Lock()
+	p.verAckReceived = true
+	p.flagsMtx.Unlock()
+
+	if p.cfg.Listeners.OnVerAck != nil {
+		p.cfg.Listeners.OnVerAck(p, msg)
+	}
+
+	return nil
+}
+
 // localVersionMsg creates a version message that can be used to send to the
 // remote peer.
 func (p *Peer) localVersionMsg() (*wire.MsgVersion, error) {
@@ -2046,26 +2072,53 @@ func (p *Peer) writeLocalVersionMsg() error {
 	return p.writeMessage(localVerMsg, wire.LatestEncoding)
 }
 
-// negotiateInboundProtocol waits to receive a version message from the peer
-// then sends our version message. If the events do not occur in that order then
-// it returns an error.
+// negotiateInboundProtocol performs the negotiation protocol for an inbound
+// peer. The events should occur in the following order, otherwise an error is
+// returned:
+//
+//   1. Remote peer sends their version.
+//   2. We send our version.
+//   3. We send our verack.
+//   4. Remote peer sends their verack.
 func (p *Peer) negotiateInboundProtocol() error {
 	if err := p.readRemoteVersionMsg(); err != nil {
 		return err
 	}
 
-	return p.writeLocalVersionMsg()
+	if err := p.writeLocalVersionMsg(); err != nil {
+		return err
+	}
+
+	err := p.writeMessage(wire.NewMsgVerAck(), wire.LatestEncoding)
+	if err != nil {
+		return err
+	}
+
+	return p.readRemoteVerAckMsg()
 }
 
-// negotiateOutboundProtocol sends our version message then waits to receive a
-// version message from the peer.  If the events do not occur in that order then
-// it returns an error.
+// negotiateOutoundProtocol performs the negotiation protocol for an outbound
+// peer. The events should occur in the following order, otherwise an error is
+// returned:
+//
+//   1. We send our version.
+//   2. Remote peer sends their version.
+//   3. Remote peer sends their verack.
+//   4. We send our verack.
 func (p *Peer) negotiateOutboundProtocol() error {
 	if err := p.writeLocalVersionMsg(); err != nil {
 		return err
 	}
 
-	return p.readRemoteVersionMsg()
+	if err := p.readRemoteVersionMsg(); err != nil {
+		return err
+	}
+
+	if err := p.readRemoteVerAckMsg(); err != nil {
+		return err
+	}
+
+	return p.writeMessage(wire.NewMsgVerAck(), wire.LatestEncoding)
 }
 
 // start begins processing input and output messages.
@@ -2102,8 +2155,6 @@ func (p *Peer) start() error {
 	go p.outHandler()
 	go p.pingHandler()
 
-	// Send our verack message now that the IO processing machinery has started.
-	p.QueueMessage(wire.NewMsgVerAck(), nil)
 	return nil
 }
 

wire/message.go

@@ -321,9 +321,13 @@ func WriteMessageWithEncodingN(w io.Writer, msg Message, pver uint32,
 		return totalBytes, err
 	}
 
-	// Write payload.
-	n, err = w.Write(payload)
-	totalBytes += n
+	// Only write the payload if there is one, e.g., verack messages don't
+	// have one.
+	if len(payload) > 0 {
+		n, err = w.Write(payload)
+		totalBytes += n
+	}
+
 	return totalBytes, err
 }