peer: Don't log write errs due to disconnect.

This commit modifies the peer logging so that it will not log an error
when it's due to the remote peer disconnecting or the peer being
forcibly disconnected or shutdown.

peer/peer.go

@@ -1149,10 +1149,10 @@ func (p *Peer) readMessage() (wire.Message, []byte, error) {
 }
 
 // writeMessage sends a bitcoin message to the peer with logging.
-func (p *Peer) writeMessage(msg wire.Message) {
+func (p *Peer) writeMessage(msg wire.Message) error {
 	// Don't do anything if we're disconnecting.
 	if atomic.LoadInt32(&p.disconnect) != 0 {
-		return
+		return nil
 	}
 	if !p.VersionKnown() {
 		switch msg.(type) {
@@ -1163,7 +1163,7 @@ func (p *Peer) writeMessage(msg wire.Message) {
 		default:
 			// Drop all messages other than version and reject if
 			// the handshake has not already been done.
-			return
+			return nil
 		}
 	}
 
@@ -1200,11 +1200,7 @@ func (p *Peer) writeMessage(msg wire.Message) {
 	if p.cfg.Listeners.OnWrite != nil {
 		p.cfg.Listeners.OnWrite(p, n, msg, err)
 	}
-	if err != nil {
-		p.Disconnect()
-		log.Errorf("Can't send message to %s: %v", p, err)
-		return
-	}
+	return err
 }
 
 // isAllowedByRegression returns whether or not the passed error is allowed by
@@ -1806,6 +1802,26 @@ cleanup:
 	log.Tracef("Peer queue handler done for %s", p)
 }
 
+// shouldLogWriteError returns whether or not the passed error, which is
+// expected to have come from writing to the remote peer in the outHandler,
+// should be logged.
+func (p *Peer) shouldLogWriteError(err error) bool {
+	// No logging when the peer is being forcibly disconnected.
+	if atomic.LoadInt32(&p.disconnect) != 0 {
+		return false
+	}
+
+	// No logging when the remote peer has been disconnected.
+	if err == io.EOF {
+		return false
+	}
+	if opErr, ok := err.(*net.OpError); ok && !opErr.Temporary() {
+		return false
+	}
+
+	return true
+}
+
 // outHandler handles all outgoing messages for the peer.  It must be run as a
 // goroutine.  It uses a buffered channel to serialize output messages while
 // allowing the sender to continue running asynchronously.
@@ -1838,7 +1854,24 @@ out:
 			}
 
 			p.stallControl <- stallControlMsg{sccSendMessage, msg.msg}
-			p.writeMessage(msg.msg)
+			err := p.writeMessage(msg.msg)
+			if err != nil {
+				p.Disconnect()
+				if p.shouldLogWriteError(err) {
+					log.Errorf("Failed to send message to "+
+						"%s: %v", p, err)
+				}
+				if msg.doneChan != nil {
+					msg.doneChan <- struct{}{}
+				}
+				continue
+			}
+
+			// At this point, the message was successfully sent, so
+			// update the last send time, signal the sender of the
+			// message that it has been sent (if requested), and
+			// signal the send queue to the deliver the next queued
+			// message.
 			p.statsMtx.Lock()
 			p.lastSend = time.Now()
 			p.statsMtx.Unlock()