From 445924b7a9f79d71a7d217df3fb1f67a80089ea9 Mon Sep 17 00:00:00 2001
From: Steven Roose <stevenroose@gmail.com>
Date: Thu, 5 Apr 2018 18:52:35 +0200
Subject: [PATCH] rpcserver: Clarify failure closing offline channel

---
 htlcswitch/interfaces.go |  2 +-
 htlcswitch/switch.go     |  4 ++--
 lnwire/channel_id.go     |  2 ++
 rpcserver.go             | 10 ++++++++++
 4 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/htlcswitch/interfaces.go b/htlcswitch/interfaces.go
index 51a5146e..a1b36ed7 100644
--- a/htlcswitch/interfaces.go
+++ b/htlcswitch/interfaces.go
@@ -30,7 +30,7 @@ type InvoiceDatabase interface {
 //       |
 //       | (Switch)		     (Switch)		       (Switch)
 //       |  Alice <-- channel link --> Bob <-- channel link --> Carol
-//	 |
+//       |
 //       | - - - - - - - - - - - - - TCP - - - - - - - - - - - - - - -
 //       |
 //       |  (Peer) 		     (Peer)	                (Peer)
diff --git a/htlcswitch/switch.go b/htlcswitch/switch.go
index b794d19b..377222ca 100644
--- a/htlcswitch/switch.go
+++ b/htlcswitch/switch.go
@@ -1284,8 +1284,8 @@ func (s *Switch) htlcForwarder() {
 			chanID := lnwire.NewChanIDFromOutPoint(req.ChanPoint)
 			link, ok := s.linkIndex[chanID]
 			if !ok {
-				req.Err <- errors.Errorf("channel with "+
-					"chan_id=%x not found", chanID[:])
+				req.Err <- errors.Errorf("no peer for channel with "+
+					"chan_id=%x", chanID[:])
 				continue
 			}
 
diff --git a/lnwire/channel_id.go b/lnwire/channel_id.go
index 3033f401..1997ba51 100644
--- a/lnwire/channel_id.go
+++ b/lnwire/channel_id.go
@@ -22,6 +22,8 @@ const (
 // within the network. The ChannelID is computed using the outpoint of the
 // funding transaction (the txid, and output index). Given a funding output the
 // ChannelID can be calculated by XOR'ing the big-endian serialization of the
+// txid and the big-endian serialization of the output index, truncated to
+// 2 bytes.
 type ChannelID [32]byte
 
 // ConnectionWideID is an all-zero ChannelID, which is used to represent a
diff --git a/rpcserver.go b/rpcserver.go
index cec89b6c..f93df730 100644
--- a/rpcserver.go
+++ b/rpcserver.go
@@ -1071,6 +1071,16 @@ func (r *rpcServer) CloseChannel(in *lnrpc.CloseChannelRequest,
 				}
 			})
 	} else {
+		// If the link is not known by the switch, we cannot gracefully close
+		// the channel.
+		channelID := lnwire.NewChanIDFromOutPoint(chanPoint)
+		if _, err := r.server.htlcSwitch.GetLink(channelID); err != nil {
+			rpcsLog.Debugf("Trying to non-force close offline channel with "+
+				"chan_point=%v", chanPoint)
+			return fmt.Errorf("unable to gracefully close channel while peer "+
+				"is offline (try force closing it instead): %v", err)
+		}
+
 		// Based on the passed fee related parameters, we'll determine
 		// an appropriate fee rate for the cooperative closure
 		// transaction.