channeldb/channel: add LastChanSync field to CloseChannelSummary

This commit adds an optional field LastChanSyncMsg to the
CloseChannelSummary, which will be used to save the ChannelReestablish
message for the channel at the point of channel close.

channeldb/channel.go

@@ -3,6 +3,7 @@ package channeldb
 import (
 	"bytes"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -1832,6 +1833,10 @@ type ChannelCloseSummary struct {
 
 	// LocalChanCfg is the channel configuration for the local node.
 	LocalChanConfig ChannelConfig
+
+	// LastChanSyncMsg is the ChannelReestablish message for this channel
+	// for the state at the point where it was closed.
+	LastChanSyncMsg *lnwire.ChannelReestablish
 }
 
 // CloseChannel closes a previously active Lightning channel. Closing a channel
@@ -2090,6 +2095,18 @@ func serializeChannelCloseSummary(w io.Writer, cs *ChannelCloseSummary) error {
 		}
 	}
 
+	// Write whether the channel sync message is present.
+	if err := WriteElements(w, cs.LastChanSyncMsg != nil); err != nil {
+		return err
+	}
+
+	// Write the channel sync message, if present.
+	if cs.LastChanSyncMsg != nil {
+		if err := WriteElements(w, cs.LastChanSyncMsg); err != nil {
+			return err
+		}
+	}
+
 	return nil
 }
 
@@ -2162,6 +2179,32 @@ func deserializeCloseChannelSummary(r io.Reader) (*ChannelCloseSummary, error) {
 		}
 	}
 
+	// Check if we have a channel sync message to read.
+	var hasChanSyncMsg bool
+	err = ReadElements(r, &hasChanSyncMsg)
+	if err == io.EOF {
+		return c, nil
+	} else if err != nil {
+		return nil, err
+	}
+
+	// If a chan sync message is present, read it.
+	if hasChanSyncMsg {
+		// We must pass in reference to a lnwire.Message for the codec
+		// to support it.
+		var msg lnwire.Message
+		if err := ReadElements(r, &msg); err != nil {
+			return nil, err
+		}
+
+		chanSync, ok := msg.(*lnwire.ChannelReestablish)
+		if !ok {
+			return nil, errors.New("unable cast db Message to " +
+				"ChannelReestablish")
+		}
+		c.LastChanSyncMsg = chanSync
+	}
+
 	return c, nil
 }