htlcswitch+channel: add channel states synchronization

In this commit BOLT№2 retranmission logic for the channel link have
been added. Now if channel link have been initialised with the
'SyncState' field than it will send the lnwire.ChannelReestablish
message and will be waiting for receiving the same message from remote
side. Exchange of this message allow both sides understand which
updates they should exchange with each other in order sync their
states.

htlcswitch/switch.go

@@ -211,14 +211,16 @@ func (s *Switch) SendHTLC(nextNode [33]byte, htlc *lnwire.UpdateAddHTLC,
 	case e := <-payment.err:
 		err = e
 	case <-s.quit:
-		return zeroPreimage, errors.New("switch is shutting down")
+		return zeroPreimage, errors.New("htlc switch have been stopped " +
+			"while waiting for payment result")
 	}
 
 	select {
 	case p := <-payment.preimage:
 		preimage = p
 	case <-s.quit:
-		return zeroPreimage, errors.New("switch is shutting down")
+		return zeroPreimage, errors.New("htlc switch have been stopped " +
+			"while waiting for payment result")
 	}
 
 	return preimage, err
@@ -316,7 +318,8 @@ func (s *Switch) forward(packet *htlcPacket) error {
 	case err := <-command.err:
 		return err
 	case <-s.quit:
-		return errors.New("Htlc Switch was stopped")
+		return errors.New("unable to forward htlc packet htlc switch was " +
+			"stopped")
 	}
 }
 
@@ -803,7 +806,7 @@ func (s *Switch) htlcForwarder() {
 func (s *Switch) Start() error {
 	if !atomic.CompareAndSwapInt32(&s.started, 0, 1) {
 		log.Warn("Htlc Switch already started")
-		return nil
+		return errors.New("htlc switch already started")
 	}
 
 	log.Infof("Starting HTLC Switch")
@@ -819,10 +822,10 @@ func (s *Switch) Start() error {
 func (s *Switch) Stop() error {
 	if !atomic.CompareAndSwapInt32(&s.shutdown, 0, 1) {
 		log.Warn("Htlc Switch already stopped")
-		return nil
+		return errors.New("htlc switch already shutdown")
 	}
 
-	log.Infof("HLTC Switch shutting down")
+	log.Infof("HTLC Switch shutting down")
 
 	close(s.quit)
 	s.wg.Wait()
@@ -849,7 +852,7 @@ func (s *Switch) AddLink(link ChannelLink) error {
 	case s.linkControl <- command:
 		return <-command.err
 	case <-s.quit:
-		return errors.New("Htlc Switch was stopped")
+		return errors.New("unable to add link htlc switch was stopped")
 	}
 }
 
@@ -903,7 +906,7 @@ func (s *Switch) GetLink(chanID lnwire.ChannelID) (ChannelLink, error) {
 	case s.linkControl <- command:
 		return <-command.done, <-command.err
 	case <-s.quit:
-		return nil, errors.New("Htlc Switch was stopped")
+		return nil, errors.New("unable to get link htlc switch was stopped")
 	}
 }
 
@@ -947,7 +950,7 @@ func (s *Switch) RemoveLink(chanID lnwire.ChannelID) error {
 	case s.linkControl <- command:
 		return <-command.err
 	case <-s.quit:
-		return errors.New("Htlc Switch was stopped")
+		return errors.New("unable to remove link htlc switch was stopped")
 	}
 }
 
@@ -994,7 +997,7 @@ func (s *Switch) GetLinksByInterface(hop [33]byte) ([]ChannelLink, error) {
 	case s.linkControl <- command:
 		return <-command.done, <-command.err
 	case <-s.quit:
-		return nil, errors.New("Htlc Switch was stopped")
+		return nil, errors.New("unable to get links htlc switch was stopped")
 	}
 }