funding: unconditionally forward all received errors to client

Previously, our old lnwire.Error message used a special code to
indicate different types of errors. With the recent push for spec
compatibility, we removed this field and instead stuffed the error into
the first byte of the error data. This works between lnd nodes, but
with other implementations they may send different errors which use a
different error scheme.

To fix this, we’ll now unconditionally return the error to the end
caller (if one exists).

fundingmanager.go

@@ -1894,33 +1894,32 @@ func (f *fundingManager) processFundingError(err *lnwire.Error,
 // depending on the type of error we should do different clean up steps and
 // inform the user about it.
 func (f *fundingManager) handleErrorMsg(fmsg *fundingErrorMsg) {
-	e := fmsg.err
+	protocolErr := fmsg.err
 
-	lnErr := lnwire.ErrorCode(e.Data[0])
-	switch lnErr {
-	case lnwire.ErrChanTooLarge:
-		fallthrough
-	case lnwire.ErrMaxPendingChannels:
-		fallthrough
-	case lnwire.ErrSynchronizingChain:
-		peerKey := fmsg.peerAddress.IdentityKey
-		chanID := fmsg.err.ChanID
-		ctx, err := f.cancelReservationCtx(peerKey, chanID)
-		if err != nil {
-			fndgLog.Warnf("unable to delete reservation: %v", err)
-			ctx.err <- err
-			return
-		}
+	peerKey := fmsg.peerAddress.IdentityKey
+	chanID := fmsg.err.ChanID
 
-		fndgLog.Errorf("Received funding error from %x: %v",
-			peerKey.SerializeCompressed(), lnErr,
-		)
-
-		ctx.err <- grpc.Errorf(lnErr.ToGrpcCode(), lnErr.String())
+	// First, we'll attempt to retrieve the funding workflow that this
+	// error was tied to. If we're unable to do so, then we'll exit early
+	// as this was an unwarranted error.
+	resCtx, err := f.getReservationCtx(peerKey, chanID)
+	if err != nil {
+		fndgLog.Warnf("Received error for non-existent funding "+
+			"flow: %v", protocolErr)
 		return
+	}
 
-	default:
-		fndgLog.Warnf("unknown funding error: %v", spew.Sdump(e.Data))
+	// If we did indeed find the funding workflow, then we'll return the
+	// error back to the caller (if any), and cancel the workflow itself.
+	lnErr := lnwire.ErrorCode(protocolErr.Data[0])
+	fndgLog.Errorf("Received funding error from %x: %v",
+		peerKey.SerializeCompressed(), lnErr,
+	)
+	resCtx.err <- grpc.Errorf(lnErr.ToGrpcCode(), lnErr.String())
+
+	if _, err := f.cancelReservationCtx(peerKey, chanID); err != nil {
+		fndgLog.Warnf("unable to delete reservation: %v", err)
+		return
 	}
 }