f use helper

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -672,9 +672,9 @@ impl<Signer: Sign> Channel<Signer> {
 		let feerate = fee_estimator.get_est_sat_per_1000_weight(ConfirmationTarget::Normal);
 
 		let value_to_self_msat = channel_value_satoshis * 1000 - push_msat;
-		let commitment_tx_fee = feerate as u64 * (COMMITMENT_TX_BASE_WEIGHT + 4 * COMMITMENT_TX_WEIGHT_PER_HTLC) / 1000;
-		if value_to_self_msat / 1000 < commitment_tx_fee {
-			return Err(APIError::APIMisuseError{ err: format!("Funding amount ({}) can't even pay fee for initial commitment transaction fee of {}.", value_to_self_msat / 1000, commitment_tx_fee) });
+		let commitment_tx_fee = Self::commit_tx_fee_msat(feerate, 4);
+		if value_to_self_msat < commitment_tx_fee {
+			return Err(APIError::APIMisuseError{ err: format!("Funding amount ({}) can't even pay fee for initial commitment transaction fee of {}.", value_to_self_msat / 1000, commitment_tx_fee / 1000) });
 		}
 
 		let mut secp_ctx = Secp256k1::new();
@@ -932,7 +932,7 @@ impl<Signer: Sign> Channel<Signer> {
 		// for full fee payment. We somewhat arbitrarily pick 4 HTLC outputs here - the funder
 		// should be able to afford at least that many.
 		let funders_amount_msat = msg.funding_satoshis * 1000 - msg.push_msat;
-		let commitment_tx_fee = msg.feerate_per_kw as u64 * (COMMITMENT_TX_BASE_WEIGHT + 4 * COMMITMENT_TX_WEIGHT_PER_HTLC) / 1000;
+		let commitment_tx_fee = Self::commit_tx_fee_msat(msg.feerate_per_kw, 4) / 1000;
 		if funders_amount_msat / 1000 < commitment_tx_fee {
 			return Err(ChannelError::Close(format!("Funding amount ({} sats) can't even pay fee for initial commitment transaction fee of {} sats.", funders_amount_msat / 1000, commitment_tx_fee)));
 		}