Assume splicing input value from channel parameters

Author: wpaulino

lightning/src/sign/ecdsa.rs

@@ -247,15 +247,17 @@ pub trait EcdsaChannelSigner: ChannelSigner {
 	/// In splicing, the previous funding transaction output is spent as the input of
 	/// the new funding transaction, and is a 2-of-2 multisig.
 	///
+	/// `channel_parameters`: The [`ChannelTransactionParameters`] for the channel's current funding
+	/// transaction that is being spent in the splice transaction to sign. A new set of
+	/// [`ChannelTransactionParameters`] will become available for the new funding transaction.
+	///
 	/// `input_index`: The index of the input within the new funding transaction `tx`,
 	///    spending the previous funding transaction's output
 	///
-	/// `input_value`: The value of the previous funding transaction output.
-	///
 	/// This method is *not* asynchronous. If an `Err` is returned, the channel will be immediately
 	/// closed.
 	fn sign_splicing_funding_input(
 		&self, channel_parameters: &ChannelTransactionParameters, tx: &Transaction,
-		input_index: usize, input_value: u64, secp_ctx: &Secp256k1<secp256k1::All>,
+		input_index: usize, secp_ctx: &Secp256k1<secp256k1::All>,
 	) -> Result<Signature, ()>;
 }

lightning/src/sign/mod.rs

@@ -1755,9 +1755,17 @@ impl EcdsaChannelSigner for InMemorySigner {
 
 	fn sign_splicing_funding_input(
 		&self, channel_parameters: &ChannelTransactionParameters, tx: &Transaction,
-		input_index: usize, input_value: u64, secp_ctx: &Secp256k1<secp256k1::All>,
+		input_index: usize, secp_ctx: &Secp256k1<secp256k1::All>,
 	) -> Result<Signature, ()> {
 		assert!(channel_parameters.is_populated(), "Channel parameters must be fully populated");
+		assert_eq!(
+			tx.input[input_index].previous_output,
+			channel_parameters
+				.funding_outpoint
+				.as_ref()
+				.expect("Funding outpoint must be known prior to signing")
+				.into_bitcoin_outpoint()
+		);
 
 		let funding_key = self.funding_key(channel_parameters.splice_parent_funding_txid);
 		let funding_pubkey = funding_key.public_key(secp_ctx);
@@ -1769,7 +1777,7 @@ impl EcdsaChannelSigner for InMemorySigner {
 			.p2wsh_signature_hash(
 				input_index,
 				&funding_redeemscript,
-				Amount::from_sat(input_value),
+				Amount::from_sat(channel_parameters.channel_value_satoshis),
 				EcdsaSighashType::All,
 			)
 			.unwrap()[..];

lightning/src/util/dyn_signer.rs

@@ -160,8 +160,7 @@ delegate!(DynSigner, EcdsaChannelSigner, inner,
 	fn sign_holder_htlc_transaction(, htlc_tx: &Transaction, input: usize,
 		htlc_descriptor: &HTLCDescriptor, secp_ctx: &Secp256k1<All>) -> Result<Signature, ()>,
 	fn sign_splicing_funding_input(, channel_parameters: &ChannelTransactionParameters,
-		tx: &Transaction, input_index: usize, input_value: u64,
-		secp_ctx: &Secp256k1<All>) -> Result<Signature, ()>
+		tx: &Transaction, input_index: usize, secp_ctx: &Secp256k1<All>) -> Result<Signature, ()>
 );
 
 delegate!(DynSigner, ChannelSigner,

lightning/src/util/test_channel_signer.rs

@@ -486,15 +486,9 @@ impl EcdsaChannelSigner for TestChannelSigner {
 
 	fn sign_splicing_funding_input(
 		&self, channel_parameters: &ChannelTransactionParameters, tx: &Transaction,
-		input_index: usize, input_value: u64, secp_ctx: &Secp256k1<secp256k1::All>,
+		input_index: usize, secp_ctx: &Secp256k1<secp256k1::All>,
 	) -> Result<Signature, ()> {
-		self.inner.sign_splicing_funding_input(
-			channel_parameters,
-			tx,
-			input_index,
-			input_value,
-			secp_ctx,
-		)
+		self.inner.sign_splicing_funding_input(channel_parameters, tx, input_index, secp_ctx)
 	}
 }