channeldb: drop unused kvdb.RTx parameter from FetchChannelByID

All four call sites pass nil for tx today (server.go, two in
channeldb/db_test.go, funding/manager_test.go). The internal
channelScanner(nil, selector) call inside FetchChannelByID is preserved
verbatim, so runtime behavior is unchanged.

This is a prerequisite for the upcoming chanstate.ChannelStore
interface: keeping the parameter would leak kvdb into a domain
interface, which the precedent set by invoices/, payments/db/, and
graph/db/ explicitly avoids.

Author: ziggie1984

channeldb/db.go

@@ -729,9 +729,8 @@ func (c *ChannelStateDB) FetchChannel(chanPoint wire.OutPoint) (*OpenChannel,
 
 // FetchChannelByID attempts to locate a channel specified by the passed channel
 // ID. If the channel cannot be found, then an error will be returned.
-// Optionally an existing db tx can be supplied.
-func (c *ChannelStateDB) FetchChannelByID(tx kvdb.RTx, id lnwire.ChannelID) (
-	*OpenChannel, error) {
+func (c *ChannelStateDB) FetchChannelByID(id lnwire.ChannelID) (*OpenChannel,
+	error) {
 
 	selector := func(chainBkt walletdb.ReadBucket) ([]byte, *wire.OutPoint,
 		error) {
@@ -774,7 +773,7 @@ func (c *ChannelStateDB) FetchChannelByID(tx kvdb.RTx, id lnwire.ChannelID) (
 		return targetChanPointBytes, targetChanPoint, nil
 	}
 
-	return c.channelScanner(tx, selector)
+	return c.channelScanner(nil, selector)
 }
 
 // ChanCount is used by the server in determining access control.

channeldb/db_test.go

@@ -253,7 +253,7 @@ func TestFetchChannel(t *testing.T) {
 
 	// Next, attempt to fetch the channel by its channel ID.
 	chanID := lnwire.NewChanIDFromOutPoint(channelState.FundingOutpoint)
-	dbChannel, err = cdb.FetchChannelByID(nil, chanID)
+	dbChannel, err = cdb.FetchChannelByID(chanID)
 	require.NoError(t, err, "unable to fetch channel")
 
 	// The decoded channel state should be identical to what we stored
@@ -272,7 +272,7 @@ func TestFetchChannel(t *testing.T) {
 	require.ErrorIs(t, err, ErrChannelNotFound)
 
 	chanID2 := lnwire.NewChanIDFromOutPoint(channelState2.FundingOutpoint)
-	_, err = cdb.FetchChannelByID(nil, chanID2)
+	_, err = cdb.FetchChannelByID(chanID2)
 	require.ErrorIs(t, err, ErrChannelNotFound)
 }
 

funding/manager_test.go

@@ -1118,7 +1118,7 @@ func assertConfirmationHeight(t *testing.T, node *testNode,
 
 	err := wait.NoError(func() error {
 		pendingChannel, err := node.fundingMgr.cfg.Wallet.Cfg.Database.
-			FetchChannelByID(nil, chanID)
+			FetchChannelByID(chanID)
 		if err != nil {
 			return fmt.Errorf("unable to fetch pending channel: %w",
 				err)

server.go

@@ -1760,9 +1760,7 @@ func newServer(ctx context.Context, cfg *Config, listenAddrs []net.Addr,
 			commitHeight uint64) (*lnwallet.BreachRetribution,
 			channeldb.ChannelType, error) {
 
-			channel, err := s.chanStateDB.FetchChannelByID(
-				nil, chanID,
-			)
+			channel, err := s.chanStateDB.FetchChannelByID(chanID)
 			if err != nil {
 				return nil, 0, err
 			}