lnpeer+peer: use importable lnpeer.ErrPeerExiting

As a prepatory step to making gossip replies synchronous, we will move
the ErrPeerExiting error into the lnpeer package so that it can be
imported by the discovery package. With synchronous sends, this error
can now be detected and handled by goroutines in the syncer, and cause
them to exit instead of continue to sending backlogs.

lnpeer/errors.go

@@ -0,0 +1,8 @@
+package lnpeer
+
+import "fmt"
+
+var (
+	// ErrPeerExiting signals that the peer received a disconnect request.
+	ErrPeerExiting = fmt.Errorf("peer exiting")
+)

peer.go

@@ -32,9 +32,6 @@ import (
 
 var (
 	numNodes int32
-
-	// ErrPeerExiting signals that the peer received a disconnect request.
-	ErrPeerExiting = fmt.Errorf("peer exiting")
 )
 
 const (
@@ -1411,7 +1408,7 @@ func (p *peer) logWireMessage(msg lnwire.Message, read bool) {
 func (p *peer) writeMessage(msg lnwire.Message) error {
 	// Simply exit if we're shutting down.
 	if atomic.LoadInt32(&p.disconnect) != 0 {
-		return ErrPeerExiting
+		return lnpeer.ErrPeerExiting
 	}
 
 	// Only log the message on the first attempt.
@@ -1559,7 +1556,7 @@ out:
 			}
 
 		case <-p.quit:
-			exitErr = ErrPeerExiting
+			exitErr = lnpeer.ErrPeerExiting
 			break out
 		}
 	}
@@ -1691,7 +1688,7 @@ func (p *peer) queue(priority bool, msg lnwire.Message, errChan chan error) {
 	case <-p.quit:
 		peerLog.Tracef("Peer shutting down, could not enqueue msg.")
 		if errChan != nil {
-			errChan <- ErrPeerExiting
+			errChan <- lnpeer.ErrPeerExiting
 		}
 	}
 }
@@ -2504,7 +2501,7 @@ func (p *peer) sendMessage(sync, priority bool, msgs ...lnwire.Message) error {
 		case err := <-errChan:
 			return err
 		case <-p.quit:
-			return ErrPeerExiting
+			return lnpeer.ErrPeerExiting
 		}
 	}
 
@@ -2550,7 +2547,7 @@ func (p *peer) AddNewChannel(channel *channeldb.OpenChannel,
 	case <-cancel:
 		return errors.New("canceled adding new channel")
 	case <-p.quit:
-		return ErrPeerExiting
+		return lnpeer.ErrPeerExiting
 	}
 
 	// We pause here to wait for the peer to recognize the new channel
@@ -2559,7 +2556,7 @@ func (p *peer) AddNewChannel(channel *channeldb.OpenChannel,
 	case err := <-errChan:
 		return err
 	case <-p.quit:
-		return ErrPeerExiting
+		return lnpeer.ErrPeerExiting
 	}
 }