Introduce DynSigner, a dynamically dispatched signer

DynSigner provides an abstraction for specifying an external signer
for functional tests.

Author: devrandom

lightning/src/sign/ecdsa.rs

@@ -84,7 +84,7 @@ pub trait EcdsaChannelSigner: ChannelSigner {
 	/// only ever get called once.
 	///
 	/// This method is *not* async as it is intended only for testing purposes.
-	#[cfg(any(test, feature = "unsafe_revoked_tx_signing"))]
+	#[cfg(any(test, feature = "_test_utils", feature = "unsafe_revoked_tx_signing"))]
 	fn unsafe_sign_holder_commitment(
 		&self, channel_parameters: &ChannelTransactionParameters,
 		commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>,

lightning/src/sign/mod.rs

@@ -31,7 +31,6 @@ use bitcoin::hashes::{Hash, HashEngine};
 use bitcoin::secp256k1::ecdh::SharedSecret;
 use bitcoin::secp256k1::ecdsa::{RecoverableSignature, Signature};
 use bitcoin::secp256k1::schnorr;
-#[cfg(taproot)]
 use bitcoin::secp256k1::All;
 use bitcoin::secp256k1::{Keypair, PublicKey, Scalar, Secp256k1, SecretKey, Signing};
 use bitcoin::{secp256k1, Psbt, Sequence, Txid, WPubkeyHash, Witness};
@@ -704,6 +703,13 @@ impl HTLCDescriptor {
 	}
 }
 
+/// Extension trait for [`ChannelSigner`] providing access to additional channel-specific
+/// details.  In particular, this is useful for functional tests.
+pub trait ChannelSignerExt: ChannelSigner {
+	/// Returns the commitment seed for the channel.
+	fn commitment_seed(&self) -> [u8; 32];
+}
+
 /// A trait to handle Lightning channel key material without concretizing the channel type or
 /// the signature mechanism.
 ///
@@ -898,10 +904,10 @@ pub trait OutputSpender {
 	/// Returns `Err(())` if the output value is greater than the input value minus required fee,
 	/// if a descriptor was duplicated, or if an output descriptor `script_pubkey`
 	/// does not match the one we can spend.
-	fn spend_spendable_outputs<C: Signing>(
+	fn spend_spendable_outputs(
 		&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>,
 		change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32,
-		locktime: Option<LockTime>, secp_ctx: &Secp256k1<C>,
+		locktime: Option<LockTime>, secp_ctx: &Secp256k1<All>,
 	) -> Result<Transaction, ()>;
 }
 
@@ -1227,6 +1233,12 @@ impl EntropySource for InMemorySigner {
 	}
 }
 
+impl ChannelSignerExt for InMemorySigner {
+	fn commitment_seed(&self) -> [u8; 32] {
+		self.commitment_seed
+	}
+}
+
 impl ChannelSigner for InMemorySigner {
 	fn get_per_commitment_point(
 		&self, idx: u64, secp_ctx: &Secp256k1<secp256k1::All>,
@@ -1351,7 +1363,7 @@ impl EcdsaChannelSigner for InMemorySigner {
 		))
 	}
 
-	#[cfg(any(test, feature = "unsafe_revoked_tx_signing"))]
+	#[cfg(any(test, feature = "_test_utils", feature = "unsafe_revoked_tx_signing"))]
 	fn unsafe_sign_holder_commitment(
 		&self, channel_parameters: &ChannelTransactionParameters,
 		commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>,
@@ -2044,10 +2056,10 @@ impl OutputSpender for KeysManager {
 	///
 	/// May panic if the [`SpendableOutputDescriptor`]s were not generated by channels which used
 	/// this [`KeysManager`] or one of the [`InMemorySigner`] created by this [`KeysManager`].
-	fn spend_spendable_outputs<C: Signing>(
+	fn spend_spendable_outputs(
 		&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>,
 		change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32,
-		locktime: Option<LockTime>, secp_ctx: &Secp256k1<C>,
+		locktime: Option<LockTime>, secp_ctx: &Secp256k1<All>,
 	) -> Result<Transaction, ()> {
 		let (mut psbt, expected_max_weight) =
 			SpendableOutputDescriptor::create_spendable_outputs_psbt(
@@ -2194,10 +2206,10 @@ impl NodeSigner for PhantomKeysManager {
 impl OutputSpender for PhantomKeysManager {
 	/// See [`OutputSpender::spend_spendable_outputs`] and [`KeysManager::spend_spendable_outputs`]
 	/// for documentation on this method.
-	fn spend_spendable_outputs<C: Signing>(
+	fn spend_spendable_outputs(
 		&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>,
 		change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32,
-		locktime: Option<LockTime>, secp_ctx: &Secp256k1<C>,
+		locktime: Option<LockTime>, secp_ctx: &Secp256k1<All>,
 	) -> Result<Transaction, ()> {
 		self.inner.spend_spendable_outputs(
 			descriptors,