f avoid rounding oddities for fees

Author: dunxen

lightning/src/ln/channel.rs

@@ -3597,24 +3597,24 @@ pub(super) fn maybe_add_funding_change_output<SP: Deref>(
 ) -> Result<Option<TxOut>, ChannelError> where
 	SP::Target: SignerProvider,
 {
-	let our_funding_inputs_weight = funding_inputs_prev_outputs.iter().fold(0u64, |weight, prev_output| {
+	// Add the total estimated weight of our contributed inputs...
+	let mut our_contributed_weight = funding_inputs_prev_outputs.iter().fold(0u64, |weight, prev_output| {
 		weight.saturating_add(estimate_input_weight(prev_output).to_wu())
-	});
-	let our_funding_outputs_weight = funding_outputs.iter().fold(0u64, |weight, txout| {
-		weight.saturating_add(get_output_weight(&txout.script_pubkey).to_wu())
-	});
-	let our_contributed_weight = our_funding_outputs_weight.saturating_add(our_funding_inputs_weight);
-	let mut fees_sats = fee_for_weight(funding_feerate_sat_per_1000_weight, our_contributed_weight);
+	}).saturating_add(
+		// ... with the total weight of our contributed outputs.
+		funding_outputs.iter().fold(0u64, |weight, txout| {
+			weight.saturating_add(get_output_weight(&txout.script_pubkey).to_wu())
+		})
+	);
 
 	// If we are the initiator, we must pay for weight of all common fields in the funding transaction.
 	if is_initiator {
-		let common_fees = fee_for_weight(funding_feerate_sat_per_1000_weight, TX_COMMON_FIELDS_WEIGHT);
-		fees_sats = fees_sats.saturating_add(common_fees);
+		our_contributed_weight += TX_COMMON_FIELDS_WEIGHT;
 	}
 
 	let remaining_value = total_input_satoshis
 		.saturating_sub(our_funding_satoshis)
-		.saturating_sub(fees_sats);
+		.saturating_sub(fee_for_weight(funding_feerate_sat_per_1000_weight, our_contributed_weight));
 
 	if remaining_value < holder_dust_limit_satoshis {
 		Ok(None)