Let ChannelSigner build the commit tx

lightning/src/ln/chan_utils.rs

@@ -1451,10 +1451,8 @@ impl CommitmentTransaction {
 
 		// Sort outputs and populate output indices while keeping track of the auxiliary data
 		let htlcs: Vec<&mut HTLCOutputInCommitment> = htlcs_with_aux.iter_mut().map(|(htlc, _)| htlc).collect();
-		let (outputs, sorted_htlcs) = signer.build_outputs(&keys.per_commitment_point, to_broadcaster_value_sat, to_countersignatory_value_sat, htlcs, secp_ctx, is_holder_tx, commitment_number).unwrap();
+		let (transaction, sorted_htlcs) = signer.build_transaction(&keys.per_commitment_point, to_broadcaster_value_sat, to_countersignatory_value_sat, htlcs, secp_ctx, is_holder_tx, commitment_number);
 
-		let (obscured_commitment_transaction_number, txins) = signer.build_inputs(commitment_number, is_holder_tx);
-		let transaction = Self::make_transaction(obscured_commitment_transaction_number, txins, outputs);
 		let txid = transaction.compute_txid();
 		CommitmentTransaction {
 			commitment_number,
@@ -1481,13 +1479,10 @@ impl CommitmentTransaction {
 	}
 
 	fn internal_rebuild_transaction<Signer: ChannelSigner>(&self, per_commitment_point: &PublicKey, signer: &Signer, secp_ctx: &Secp256k1<secp256k1::All>, is_holder_tx: bool) -> Result<BuiltCommitmentTransaction, ()> {
-		let (obscured_commitment_transaction_number, txins) = signer.build_inputs(self.commitment_number, is_holder_tx);
-
 		let mut htlcs: Vec<_> = self.htlcs.iter().map(|h| h.clone()).collect();
 		let htlcs: Vec<&mut HTLCOutputInCommitment> = htlcs.iter_mut().collect();
-		let (outputs, _) = signer.build_outputs(per_commitment_point, self.to_broadcaster_value_sat, self.to_countersignatory_value_sat, htlcs, secp_ctx, is_holder_tx, self.commitment_number)?;
+		let (transaction, _) = signer.build_transaction(per_commitment_point, self.to_broadcaster_value_sat, self.to_countersignatory_value_sat, htlcs, secp_ctx, is_holder_tx, self.commitment_number);
 
-		let transaction = Self::make_transaction(obscured_commitment_transaction_number, txins, outputs);
 		let txid = transaction.compute_txid();
 		let built_transaction = BuiltCommitmentTransaction {
 			transaction,
@@ -1496,15 +1491,6 @@ impl CommitmentTransaction {
 		Ok(built_transaction)
 	}
 
-	fn make_transaction(obscured_commitment_transaction_number: u64, txins: Vec<TxIn>, outputs: Vec<TxOut>) -> Transaction {
-		Transaction {
-			version: Version::TWO,
-			lock_time: LockTime::from_consensus(((0x20 as u32) << 8 * 3) | ((obscured_commitment_transaction_number & 0xffffffu64) as u32)),
-			input: txins,
-			output: outputs,
-		}
-	}
-
 	/// The backwards-counting commitment number
 	pub fn commitment_number(&self) -> u64 {
 		self.commitment_number

lightning/src/sign/mod.rs

@@ -1258,6 +1258,39 @@ pub trait ChannelSigner {
 		};
 		(obscured_commitment_transaction_number, txins)
 	}
+
+	/// Builds a commitment transaction
+	fn build_transaction(
+		&self, per_commitment_point: &PublicKey, to_broadcaster_value_sat: Amount,
+		to_countersignatory_value_sat: Amount, htlcs: Vec<&mut HTLCOutputInCommitment>,
+		secp_ctx: &Secp256k1<secp256k1::All>, is_holder_tx: bool, commitment_number: u64,
+	) -> (Transaction, Vec<HTLCOutputInCommitment>) {
+		let (obscured_commitment_transaction_number, txins) =
+			self.build_inputs(commitment_number, is_holder_tx);
+		let (txouts, sorted_htlcs) = self
+			.build_outputs(
+				per_commitment_point,
+				to_broadcaster_value_sat,
+				to_countersignatory_value_sat,
+				htlcs,
+				secp_ctx,
+				is_holder_tx,
+				commitment_number,
+			)
+			.unwrap();
+		(
+			Transaction {
+				version: Version::TWO,
+				lock_time: LockTime::from_consensus(
+					((0x20 as u32) << 8 * 3)
+						| ((obscured_commitment_transaction_number & 0xffffffu64) as u32),
+				),
+				input: txins,
+				output: txouts,
+			},
+			sorted_htlcs,
+		)
+	}
 }
 
 /// Specifies the recipient of an invoice.