channeldb+funding: move opening channel state to DB

The funding manager doesn't need to know the details of the underlying
storage of the opening channel state, so we move the actual store and
retrieval into the channel database.

channeldb/db.go

@@ -209,6 +209,11 @@ var (
 	// Big endian is the preferred byte order, due to cursor scans over
 	// integer keys iterating in order.
 	byteOrder = binary.BigEndian
+
+	// channelOpeningStateBucket is the database bucket used to store the
+	// channelOpeningState for each channel that is currently in the process
+	// of being opened.
+	channelOpeningStateBucket = []byte("channelOpeningState")
 )
 
 // DB is the primary datastore for the lnd daemon. The database stores
@@ -1197,6 +1202,56 @@ func (d *DB) AbandonChannel(chanPoint *wire.OutPoint, bestHeight uint32) error {
 	return dbChan.CloseChannel(summary, ChanStatusLocalCloseInitiator)
 }
 
+// SaveChannelOpeningState saves the serialized channel state for the provided
+// chanPoint to the channelOpeningStateBucket.
+func (d *DB) SaveChannelOpeningState(outPoint, serializedState []byte) error {
+	return kvdb.Update(d, func(tx kvdb.RwTx) error {
+		bucket, err := tx.CreateTopLevelBucket(channelOpeningStateBucket)
+		if err != nil {
+			return err
+		}
+
+		return bucket.Put(outPoint, serializedState)
+	}, func() {})
+}
+
+// GetChannelOpeningState fetches the serialized channel state for the provided
+// outPoint from the database, or returns ErrChannelNotFound if the channel
+// is not found.
+func (d *DB) GetChannelOpeningState(outPoint []byte) ([]byte, error) {
+	var serializedState []byte
+	err := kvdb.View(d, func(tx kvdb.RTx) error {
+		bucket := tx.ReadBucket(channelOpeningStateBucket)
+		if bucket == nil {
+			// If the bucket does not exist, it means we never added
+			//  a channel to the db, so return ErrChannelNotFound.
+			return ErrChannelNotFound
+		}
+
+		serializedState = bucket.Get(outPoint)
+		if serializedState == nil {
+			return ErrChannelNotFound
+		}
+
+		return nil
+	}, func() {
+		serializedState = nil
+	})
+	return serializedState, err
+}
+
+// DeleteChannelOpeningState removes any state for outPoint from the database.
+func (d *DB) DeleteChannelOpeningState(outPoint []byte) error {
+	return kvdb.Update(d, func(tx kvdb.RwTx) error {
+		bucket := tx.ReadWriteBucket(channelOpeningStateBucket)
+		if bucket == nil {
+			return ErrChannelNotFound
+		}
+
+		return bucket.Delete(outPoint)
+	}, func() {})
+}
+
 // 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.