channeldb: add new method to db, MarkChanFullyClosed

This commit adds a new method to the database which allows callers to
mark a channel as fully closed once certain conditions have been
reached. If a channel was cooperatively closed, then it can be marked
as fully closed as soon as the channel has been confirmed. If the
channel was marked as force closed, then it should be marked as closed
as soon as _all_ the funds in limbo have been swept.

channeldb/db.go

@@ -430,6 +430,38 @@ func (d *DB) FetchClosedChannels(pendingOnly bool) ([]*ChannelCloseSummary, erro
 
 	return chanSummaries, nil
 }
+
+// MarkChanFullyClosed marks a channel as fully closed within the database. A
+// channel should be marked as fully closed if the channel was initially
+// cooperatively closed and it's reach a single confirmation, or after all the
+// pending funds in a channel that has been forcibly closed have been swept.
+func (d *DB) MarkChanFullyClosed(chanPoint *wire.OutPoint) error {
+	return d.Update(func(tx *bolt.Tx) error {
+		var b bytes.Buffer
+		if err := writeOutpoint(&b, chanPoint); err != nil {
+			return err
+		}
+
+		chanID := b.Bytes()
+
+		closedChanBucket, err := tx.CreateBucketIfNotExists(closedChannelBucket)
+		if err != nil {
+			return err
+		}
+
+		chanSummary := closedChanBucket.Get(chanID)
+		if chanSummary == nil {
+			return fmt.Errorf("no closed channel by that chanID found")
+		}
+
+		newSummary := make([]byte, len(chanSummary))
+		copy(newSummary[:], chanSummary[:])
+		newSummary[0] = 0x00
+
+		return closedChanBucket.Put(chanID, newSummary)
+	})
+}
+
 // syncVersions function is used for safe db version synchronization. It applies
 // migration functions to the current database and recovers the previous
 // state of db if at least one error/panic appeared during migration.