Support BOLT 12 signing in c_bindings

Replace the Fn trait bound on signing methods with a dedicated trait
since Fn is not supported in bindings. Implement the trait for Fn so
that closures can still be used in Rust.

Author: jkczyz

fuzz/src/invoice_request_deser.rs

@@ -37,17 +37,17 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], _out: Out) {
 			let even_pubkey = x_only_pubkey.public_key(Parity::Even);
 			if signing_pubkey == odd_pubkey || signing_pubkey == even_pubkey {
 				unsigned_invoice
-					.sign::<_, Infallible>(
-						|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-					)
+					.sign(|message: &UnsignedBolt12Invoice| -> Result<_, Infallible> {
+						Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+					})
 					.unwrap()
 					.write(&mut buffer)
 					.unwrap();
 			} else {
 				unsigned_invoice
-					.sign::<_, Infallible>(
-						|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-					)
+					.sign(|message: &UnsignedBolt12Invoice| -> Result<_, Infallible> {
+						Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+					})
 					.unwrap_err();
 			}
 		}

fuzz/src/offer_deser.rs

@@ -29,9 +29,9 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], _out: Out) {
 
 		if let Ok(invoice_request) = build_response(&offer, pubkey) {
 			invoice_request
-				.sign::<_, Infallible>(
-					|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-				)
+				.sign(|message: &UnsignedInvoiceRequest| -> Result<_, Infallible> {
+					Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+				})
 				.unwrap()
 				.write(&mut buffer)
 				.unwrap();

fuzz/src/refund_deser.rs

@@ -33,9 +33,9 @@ pub fn do_test<Out: test_logger::Output>(data: &[u8], _out: Out) {
 
 		if let Ok(invoice) = build_response(&refund, pubkey, &secp_ctx) {
 			invoice
-				.sign::<_, Infallible>(
-					|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-				)
+				.sign(|message: &UnsignedBolt12Invoice| -> Result<_, Infallible> {
+					Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+				})
 				.unwrap()
 				.write(&mut buffer)
 				.unwrap();

lightning/src/ln/channelmanager.rs

@@ -57,7 +57,7 @@ use crate::ln::msgs::{ChannelMessageHandler, DecodeError, LightningError};
 use crate::ln::outbound_payment;
 use crate::ln::outbound_payment::{Bolt12PaymentError, OutboundPayments, PaymentAttempts, PendingOutboundPayment, SendAlongPathArgs, StaleExpiration};
 use crate::ln::wire::Encode;
-use crate::offers::invoice::{BlindedPayInfo, Bolt12Invoice, DEFAULT_RELATIVE_EXPIRY, DerivedSigningPubkey, ExplicitSigningPubkey, InvoiceBuilder};
+use crate::offers::invoice::{BlindedPayInfo, Bolt12Invoice, DEFAULT_RELATIVE_EXPIRY, DerivedSigningPubkey, ExplicitSigningPubkey, InvoiceBuilder, UnsignedBolt12Invoice};
 use crate::offers::invoice_error::InvoiceError;
 use crate::offers::invoice_request::{DerivedPayerId, InvoiceRequestBuilder};
 use crate::offers::merkle::SignError;
@@ -9302,7 +9302,9 @@ where
 						.and_then(|invoice| {
 							#[cfg(c_bindings)]
 							let mut invoice = invoice;
-							match invoice.sign(|invoice| self.node_signer.sign_bolt12_invoice(invoice)) {
+							match invoice.sign(|invoice: &UnsignedBolt12Invoice|
+								self.node_signer.sign_bolt12_invoice(invoice)
+							) {
 								Ok(invoice) => Ok(OffersMessage::Invoice(invoice)),
 								Err(SignError::Signing(())) => Err(OffersMessage::InvoiceError(
 										InvoiceError::from_string("Failed signing invoice".to_string())

lightning/src/offers/invoice.rs

@@ -23,6 +23,7 @@
 //! use bitcoin::hashes::Hash;
 //! use bitcoin::secp256k1::{KeyPair, PublicKey, Secp256k1, SecretKey};
 //! use core::convert::{Infallible, TryFrom};
+//! use lightning::offers::invoice::UnsignedBolt12Invoice;
 //! use lightning::offers::invoice_request::InvoiceRequest;
 //! use lightning::offers::refund::Refund;
 //! use lightning::util::ser::Writeable;
@@ -57,9 +58,9 @@
 //!     .allow_mpp()
 //!     .fallback_v0_p2wpkh(&wpubkey_hash)
 //!     .build()?
-//!     .sign::<_, Infallible>(
-//!         |message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-//!     )
+//!     .sign(|message: &UnsignedBolt12Invoice| -> Result<_, Infallible> {
+//!         Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+//!     })
 //!     .expect("failed verifying signature")
 //!     .write(&mut buffer)
 //!     .unwrap();
@@ -90,9 +91,9 @@
 //!     .allow_mpp()
 //!     .fallback_v0_p2wpkh(&wpubkey_hash)
 //!     .build()?
-//!     .sign::<_, Infallible>(
-//!         |message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-//!     )
+//!     .sign(|message: &UnsignedBolt12Invoice| -> Result<_, Infallible> {
+//!         Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+//!     })
 //!     .expect("failed verifying signature")
 //!     .write(&mut buffer)
 //!     .unwrap();
@@ -119,7 +120,7 @@ use crate::ln::features::{BlindedHopFeatures, Bolt12InvoiceFeatures, InvoiceRequ
 use crate::ln::inbound_payment::ExpandedKey;
 use crate::ln::msgs::DecodeError;
 use crate::offers::invoice_request::{INVOICE_REQUEST_PAYER_ID_TYPE, INVOICE_REQUEST_TYPES, IV_BYTES as INVOICE_REQUEST_IV_BYTES, InvoiceRequest, InvoiceRequestContents, InvoiceRequestTlvStream, InvoiceRequestTlvStreamRef};
-use crate::offers::merkle::{SignError, SignatureTlvStream, SignatureTlvStreamRef, TaggedHash, TlvStream, WithoutSignatures, self};
+use crate::offers::merkle::{SignError, SignFunction, SignatureTlvStream, SignatureTlvStreamRef, TaggedHash, TlvStream, WithoutSignatures, self};
 use crate::offers::offer::{Amount, OFFER_TYPES, OfferTlvStream, OfferTlvStreamRef, Quantity};
 use crate::offers::parse::{Bolt12ParseError, Bolt12SemanticError, ParsedMessage};
 use crate::offers::payer::{PAYER_METADATA_TYPE, PayerTlvStream, PayerTlvStreamRef};
@@ -324,9 +325,9 @@ macro_rules! invoice_derived_signing_pubkey_builder_methods { ($self: ident, $se
 		let mut unsigned_invoice = UnsignedBolt12Invoice::new(invreq_bytes, invoice.clone());
 
 		let invoice = unsigned_invoice
-			.sign::<_, Infallible>(
-				|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-			)
+			.sign(|message: &UnsignedBolt12Invoice| -> Result<_, Infallible> {
+				Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+			})
 			.unwrap();
 		Ok(invoice)
 	}
@@ -534,11 +535,11 @@ macro_rules! unsigned_invoice_sign_method { ($self: ident, $self_type: ty $(, $s
 	/// Signs the [`TaggedHash`] of the invoice using the given function.
 	///
 	/// Note: The hash computation may have included unknown, odd TLV records.
-	///
-	/// This is not exported to bindings users as functions aren't currently mapped.
-	pub fn sign<F, E>($($self_mut)* $self: $self_type, sign: F) -> Result<Bolt12Invoice, SignError<E>>
+	pub fn sign<F>(
+		$($self_mut)* $self: $self_type, sign: F
+	) -> Result<Bolt12Invoice, SignError<F::Error>>
 	where
-		F: FnOnce(&Self) -> Result<Signature, E>
+		F: SignFunction<Self>,
 	{
 		let pubkey = $self.contents.fields().signing_pubkey;
 		let signature = merkle::sign_message(sign, &$self, pubkey)?;
@@ -2013,7 +2014,7 @@ mod tests {
 			.sign(payer_sign).unwrap()
 			.respond_with_no_std(payment_paths(), payment_hash(), now()).unwrap()
 			.build().unwrap()
-			.sign(|_| Err(()))
+			.sign(fail_sign)
 		{
 			Ok(_) => panic!("expected error"),
 			Err(e) => assert_eq!(e, SignError::Signing(())),

lightning/src/offers/invoice_request.rs

@@ -27,6 +27,7 @@
 //! use bitcoin::secp256k1::{KeyPair, PublicKey, Secp256k1, SecretKey};
 //! use core::convert::Infallible;
 //! use lightning::ln::features::OfferFeatures;
+//! use lightning::offers::invoice_request::UnsignedInvoiceRequest;
 //! use lightning::offers::offer::Offer;
 //! use lightning::util::ser::Writeable;
 //!
@@ -47,9 +48,9 @@
 //!     .quantity(5)?
 //!     .payer_note("foo".to_string())
 //!     .build()?
-//!     .sign::<_, Infallible>(
-//!         |message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-//!     )
+//!     .sign(|message: &UnsignedInvoiceRequest| -> Result<_, Infallible> {
+//!         Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+//!     })
 //!     .expect("failed verifying signature")
 //!     .write(&mut buffer)
 //!     .unwrap();
@@ -72,7 +73,7 @@ use crate::ln::features::InvoiceRequestFeatures;
 use crate::ln::inbound_payment::{ExpandedKey, IV_LEN, Nonce};
 use crate::ln::msgs::DecodeError;
 use crate::offers::invoice::BlindedPayInfo;
-use crate::offers::merkle::{SignError, SignatureTlvStream, SignatureTlvStreamRef, TaggedHash, self};
+use crate::offers::merkle::{SignError, SignFunction, SignatureTlvStream, SignatureTlvStreamRef, TaggedHash, self};
 use crate::offers::offer::{Offer, OfferContents, OfferTlvStream, OfferTlvStreamRef};
 use crate::offers::parse::{Bolt12ParseError, ParsedMessage, Bolt12SemanticError};
 use crate::offers::payer::{PayerContents, PayerTlvStream, PayerTlvStreamRef};
@@ -227,9 +228,9 @@ macro_rules! invoice_request_derived_payer_id_builder_methods { (
 		let secp_ctx = secp_ctx.unwrap();
 		let keys = keys.unwrap();
 		let invoice_request = unsigned_invoice_request
-			.sign::<_, Infallible>(
-				|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-			)
+			.sign(|message: &UnsignedInvoiceRequest| -> Result<_, Infallible> {
+				Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+			})
 			.unwrap();
 		Ok(invoice_request)
 	}
@@ -522,11 +523,11 @@ macro_rules! unsigned_invoice_request_sign_method { (
 	/// Signs the [`TaggedHash`] of the invoice request using the given function.
 	///
 	/// Note: The hash computation may have included unknown, odd TLV records.
-	///
-	/// This is not exported to bindings users as functions are not yet mapped.
-	pub fn sign<F, E>($($self_mut)* $self: $self_type, sign: F) -> Result<InvoiceRequest, SignError<E>>
+	pub fn sign<F>(
+		$($self_mut)* $self: $self_type, sign: F
+	) -> Result<InvoiceRequest, SignError<F::Error>>
 	where
-		F: FnOnce(&Self) -> Result<Signature, E>
+		F: SignFunction<Self>,
 	{
 		let pubkey = $self.contents.payer_id;
 		let signature = merkle::sign_message(sign, &$self, pubkey)?;
@@ -1712,7 +1713,7 @@ mod tests {
 			.build().unwrap()
 			.request_invoice(vec![1; 32], payer_pubkey()).unwrap()
 			.build().unwrap()
-			.sign(|_| Err(()))
+			.sign(fail_sign)
 		{
 			Ok(_) => panic!("expected error"),
 			Err(e) => assert_eq!(e, SignError::Signing(())),
@@ -2126,9 +2127,9 @@ mod tests {
 			.build().unwrap()
 			.request_invoice(vec![1; 32], keys.public_key()).unwrap()
 			.build().unwrap()
-			.sign::<_, Infallible>(
-				|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
-			)
+			.sign(|message: &UnsignedInvoiceRequest| -> Result<_, Infallible> {
+				Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &keys))
+			})
 			.unwrap();
 
 		let mut encoded_invoice_request = Vec::new();

lightning/src/offers/merkle.rs

@@ -76,13 +76,34 @@ impl AsRef<TaggedHash> for TaggedHash {
 
 /// Error when signing messages.
 #[derive(Debug, PartialEq)]
-pub enum SignError<E> {
+pub enum SignError<E = ()> {
 	/// User-defined error when signing the message.
 	Signing(E),
 	/// Error when verifying the produced signature using the given pubkey.
 	Verification(secp256k1::Error),
 }
 
+/// A function for signing a [`TaggedHash`].
+pub trait SignFunction<T: AsRef<TaggedHash>> {
+	/// Error type returned by the function.
+	type Error;
+
+	/// Signs a [`TaggedHash`] computed over the merkle root of `message`'s TLV stream.
+	fn sign(&self, message: &T) -> Result<Signature, Self::Error>;
+}
+
+impl<F, T, E> SignFunction<T> for F
+where
+	F: Fn(&T) -> Result<Signature, E>,
+	T: AsRef<TaggedHash>,
+{
+	type Error = E;
+
+	fn sign(&self, message: &T) -> Result<Signature, E> {
+		self(message)
+	}
+}
+
 /// Signs a [`TaggedHash`] computed over the merkle root of `message`'s TLV stream, checking if it
 /// can be verified with the supplied `pubkey`.
 ///
@@ -92,14 +113,14 @@ pub enum SignError<E> {
 ///
 /// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
 /// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
-pub(super) fn sign_message<F, E, T>(
-	sign: F, message: &T, pubkey: PublicKey,
+pub(super) fn sign_message<F, T, E>(
+	f: F, message: &T, pubkey: PublicKey,
 ) -> Result<Signature, SignError<E>>
 where
-	F: FnOnce(&T) -> Result<Signature, E>,
+	F: SignFunction<T, Error = E>,
 	T: AsRef<TaggedHash>,
 {
-	let signature = sign(message).map_err(|e| SignError::Signing(e))?;
+	let signature = f.sign(message).map_err(|e| SignError::Signing(e))?;
 
 	let digest = message.as_ref().as_digest();
 	let pubkey = pubkey.into();
@@ -278,7 +299,7 @@ mod tests {
 	use bitcoin::secp256k1::schnorr::Signature;
 	use core::convert::Infallible;
 	use crate::offers::offer::{Amount, OfferBuilder};
-	use crate::offers::invoice_request::InvoiceRequest;
+	use crate::offers::invoice_request::{InvoiceRequest, UnsignedInvoiceRequest};
 	use crate::offers::parse::Bech32Encode;
 	use crate::offers::test_utils::{payer_pubkey, recipient_pubkey};
 	use crate::util::ser::Writeable;
@@ -321,9 +342,9 @@ mod tests {
 			.build_unchecked()
 			.request_invoice(vec![0; 8], payer_keys.public_key()).unwrap()
 			.build_unchecked()
-			.sign::<_, Infallible>(
-				|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &payer_keys))
-			)
+			.sign(|message: &UnsignedInvoiceRequest| -> Result<_, Infallible> {
+				Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &payer_keys))
+			})
 			.unwrap();
 		assert_eq!(
 			invoice_request.to_string(),
@@ -375,9 +396,9 @@ mod tests {
 			.build_unchecked()
 			.request_invoice(vec![0; 8], payer_keys.public_key()).unwrap()
 			.build_unchecked()
-			.sign::<_, Infallible>(
-				|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &payer_keys))
-			)
+			.sign(|message: &UnsignedInvoiceRequest| -> Result<_, Infallible> {
+				Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &payer_keys))
+			})
 			.unwrap();
 
 		let mut bytes_without_signature = Vec::new();
@@ -407,9 +428,9 @@ mod tests {
 			.build_unchecked()
 			.request_invoice(vec![0; 8], payer_keys.public_key()).unwrap()
 			.build_unchecked()
-			.sign::<_, Infallible>(
-				|message| Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &payer_keys))
-			)
+			.sign(|message: &UnsignedInvoiceRequest| -> Result<_, Infallible> {
+				Ok(secp_ctx.sign_schnorr_no_aux_rand(message.as_ref().as_digest(), &payer_keys))
+			})
 			.unwrap();
 
 		let tlv_stream = TlvStream::new(&invoice_request.bytes).range(0..1)

lightning/src/offers/test_utils.rs

@@ -20,6 +20,10 @@ use crate::ln::features::BlindedHopFeatures;
 use crate::offers::invoice::BlindedPayInfo;
 use crate::offers::merkle::TaggedHash;
 
+pub(crate) fn fail_sign<T: AsRef<TaggedHash>>(_message: &T) -> Result<Signature, ()> {
+	Err(())
+}
+
 pub(crate) fn payer_keys() -> KeyPair {
 	let secp_ctx = Secp256k1::new();
 	KeyPair::from_secret_key(&secp_ctx, &SecretKey::from_slice(&[42; 32]).unwrap())