peer: Separate ping ticker functionality from outHandler.

This is part of a series of commits to make the internals of the peer
package more modular, testable and tunable. No functionality has changed.

peer/peer.go

@@ -1746,10 +1746,6 @@ func (p *Peer) shouldLogWriteError(err error) bool {
 // goroutine.  It uses a buffered channel to serialize output messages while
 // allowing the sender to continue running asynchronously.
 func (p *Peer) outHandler() {
-	// pingTicker is used to periodically send pings to the remote peer.
-	pingTicker := time.NewTicker(pingInterval)
-	defer pingTicker.Stop()
-
 out:
 	for {
 		select {
@@ -1790,14 +1786,6 @@ out:
 			}
 			p.sendDoneQueue <- struct{}{}
 
-		case <-pingTicker.C:
-			nonce, err := wire.RandomUint64()
-			if err != nil {
-				log.Errorf("Not sending ping to %s: %v", p, err)
-				continue
-			}
-			p.QueueMessage(wire.NewMsgPing(nonce), nil)
-
 		case <-p.quit:
 			break out
 		}
@@ -1825,6 +1813,28 @@ cleanup:
 	log.Tracef("Peer output handler done for %s", p)
 }
 
+// pingHandler periodically pings the peer.  It must be run as a goroutine.
+func (p *Peer) pingHandler() {
+	pingTicker := time.NewTicker(pingInterval)
+	defer pingTicker.Stop()
+
+out:
+	for {
+		select {
+		case <-pingTicker.C:
+			nonce, err := wire.RandomUint64()
+			if err != nil {
+				log.Errorf("Not sending ping to %s: %v", p, err)
+				continue
+			}
+			p.QueueMessage(wire.NewMsgPing(nonce), nil)
+
+		case <-p.quit:
+			break out
+		}
+	}
+}
+
 // QueueMessage adds the passed bitcoin message to the peer send queue.
 //
 // This function is safe for concurrent access.
@@ -1952,6 +1962,7 @@ func (p *Peer) start() error {
 	go p.inHandler()
 	go p.queueHandler()
 	go p.outHandler()
+	go p.pingHandler()
 
 	// Send our verack message now that the IO processing machinery has started.
 	p.QueueMessage(wire.NewMsgVerAck(), nil)