channeldb: fix dangerous type casting hack

channeldb/channel.go

@@ -875,12 +875,43 @@ func fetchChanBucket(tx kvdb.RTx, nodeKey *btcec.PublicKey,
 func fetchChanBucketRw(tx kvdb.RwTx, nodeKey *btcec.PublicKey, // nolint:interfacer
 	outPoint *wire.OutPoint, chainHash chainhash.Hash) (kvdb.RwBucket, error) {
 
-	readBucket, err := fetchChanBucket(tx, nodeKey, outPoint, chainHash)
-	if err != nil {
-		return nil, err
+	// First fetch the top level bucket which stores all data related to
+	// current, active channels.
+	openChanBucket := tx.ReadWriteBucket(openChannelBucket)
+	if openChanBucket == nil {
+		return nil, ErrNoChanDBExists
 	}
 
-	return readBucket.(kvdb.RwBucket), nil
+	// TODO(roasbeef): CreateTopLevelBucket on the interface isn't like
+	// CreateIfNotExists, will return error
+
+	// Within this top level bucket, fetch the bucket dedicated to storing
+	// open channel data specific to the remote node.
+	nodePub := nodeKey.SerializeCompressed()
+	nodeChanBucket := openChanBucket.NestedReadWriteBucket(nodePub)
+	if nodeChanBucket == nil {
+		return nil, ErrNoActiveChannels
+	}
+
+	// We'll then recurse down an additional layer in order to fetch the
+	// bucket for this particular chain.
+	chainBucket := nodeChanBucket.NestedReadWriteBucket(chainHash[:])
+	if chainBucket == nil {
+		return nil, ErrNoActiveChannels
+	}
+
+	// With the bucket for the node and chain fetched, we can now go down
+	// another level, for this channel itself.
+	var chanPointBuf bytes.Buffer
+	if err := writeOutpoint(&chanPointBuf, outPoint); err != nil {
+		return nil, err
+	}
+	chanBucket := chainBucket.NestedReadWriteBucket(chanPointBuf.Bytes())
+	if chanBucket == nil {
+		return nil, ErrChannelNotFound
+	}
+
+	return chanBucket, nil
 }
 
 // fullSync syncs the contents of an OpenChannel while re-using an existing
@@ -965,7 +996,7 @@ func (c *OpenChannel) MarkAsOpen(openLoc lnwire.ShortChannelID) error {
 	defer c.Unlock()
 
 	if err := kvdb.Update(c.Db, func(tx kvdb.RwTx) error {
-		chanBucket, err := fetchChanBucket(
+		chanBucket, err := fetchChanBucketRw(
 			tx, c.IdentityPub, &c.FundingOutpoint, c.ChainHash,
 		)
 		if err != nil {
@@ -980,7 +1011,7 @@ func (c *OpenChannel) MarkAsOpen(openLoc lnwire.ShortChannelID) error {
 		channel.IsPending = false
 		channel.ShortChannelID = openLoc
 
-		return putOpenChannel(chanBucket.(kvdb.RwBucket), channel)
+		return putOpenChannel(chanBucket, channel)
 	}, func() {}); err != nil {
 		return err
 	}