sweepbatcher: fix fee rate calculation (publish)

We forgot to account for change outputs when checking the feerate of
signed transaction. The bug resulted in fee rate overestimation in the
log message.

sweepbatcher/presigned.go

@@ -506,7 +506,10 @@ func (b *batch) publishPresigned(ctx context.Context) (btcutil.Amount, error,
 
 	// Find actual fee rate of the signed transaction. It may differ from
 	// the desired fee rate, because SignTx may return a presigned tx.
-	output := btcutil.Amount(tx.TxOut[0].Value)
+	var output btcutil.Amount
+	for _, txOut := range tx.TxOut {
+		output += btcutil.Amount(txOut.Value)
+	}
 	fee = batchAmt - output
 	signedFeeRate := chainfee.NewSatPerKWeight(fee, realWeight)
 

sweepbatcher/sweep_batcher_presigned_test.go

@@ -1270,7 +1270,8 @@ func testPresigned_presigned_group_with_change(t *testing.T,
 }
 
 // testPresigned_fee_portion_with_change ensures that the fee portion reported
-// to clients accounts for change outputs in the presigned transaction.
+// to clients accounts for change outputs in the presigned transaction. It also
+// is a regression test for feerate overestimation when tx is published.
 func testPresigned_fee_portion_with_change(t *testing.T,
 	batcherStore testBatcherStore) {
 
@@ -1350,6 +1351,14 @@ func testPresigned_fee_portion_with_change(t *testing.T,
 	require.Len(t, tx.TxIn, 1)
 	require.Len(t, tx.TxOut, 2)
 
+	// Mine a blocks to trigger republishing.
+	require.NoError(t, lnd.NotifyHeight(601))
+
+	// Make sure it is the same tx.
+	tx2 := <-lnd.TxPublishChannel
+	require.Len(t, tx2.TxOut, len(tx.TxOut))
+	require.Equal(t, tx.TxOut[0].Value, tx2.TxOut[0].Value)
+
 	var (
 		outputSum   int64
 		foundChange bool