From 9069bc0ea8b7fdaa9ee276d78fb0610157edbcf2 Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Thu, 29 Apr 2021 22:29:36 +0000
Subject: [PATCH] Support secp256k1 RecoverableSignatures

---
 c-bindings-gen/src/types.rs             |  6 ++++++
 lightning-c-bindings/src/c_types/mod.rs | 28 +++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/c-bindings-gen/src/types.rs b/c-bindings-gen/src/types.rs
index 9ef83f2..1b38108 100644
--- a/c-bindings-gen/src/types.rs
+++ b/c-bindings-gen/src/types.rs
@@ -781,6 +781,7 @@ impl<'a, 'c: 'a> TypeResolver<'a, 'c> {
 		match ty {
 			"()" => true,
 			"crate::c_types::Signature" => true,
+			"crate::c_types::RecoverableSignature" => true,
 			"crate::c_types::TxOut" => true,
 			_ => false,
 		}
@@ -819,6 +820,7 @@ impl<'a, 'c: 'a> TypeResolver<'a, 'c> {
 			"bitcoin::secp256k1::key::PublicKey"|"bitcoin::secp256k1::PublicKey"|"secp256k1::key::PublicKey"
 				=> Some("crate::c_types::PublicKey"),
 			"bitcoin::secp256k1::Signature" => Some("crate::c_types::Signature"),
+			"bitcoin::secp256k1::recovery::RecoverableSignature" => Some("crate::c_types::RecoverableSignature"),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
 				if is_ref  => Some("*const [u8; 32]"),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
@@ -894,6 +896,7 @@ impl<'a, 'c: 'a> TypeResolver<'a, 'c> {
 				=> Some(""),
 			"bitcoin::secp256k1::Signature" if is_ref => Some("&"),
 			"bitcoin::secp256k1::Signature" => Some(""),
+			"bitcoin::secp256k1::recovery::RecoverableSignature" => Some(""),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
 				if is_ref => Some("&::bitcoin::secp256k1::key::SecretKey::from_slice(&unsafe { *"),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
@@ -954,6 +957,7 @@ impl<'a, 'c: 'a> TypeResolver<'a, 'c> {
 			"bitcoin::secp256k1::key::PublicKey"|"bitcoin::secp256k1::PublicKey"|"secp256k1::key::PublicKey"
 				=> Some(".into_rust()"),
 			"bitcoin::secp256k1::Signature" => Some(".into_rust()"),
+			"bitcoin::secp256k1::recovery::RecoverableSignature" => Some(".into_rust()"),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
 				if !is_ref => Some(".into_rust()"),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
@@ -1033,6 +1037,7 @@ impl<'a, 'c: 'a> TypeResolver<'a, 'c> {
 			"bitcoin::secp256k1::key::PublicKey"|"bitcoin::secp256k1::PublicKey"|"secp256k1::key::PublicKey"
 				=> Some("crate::c_types::PublicKey::from_rust(&"),
 			"bitcoin::secp256k1::Signature" => Some("crate::c_types::Signature::from_rust(&"),
+			"bitcoin::secp256k1::recovery::RecoverableSignature" => Some("crate::c_types::RecoverableSignature::from_rust(&"),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
 				if is_ref => Some(""),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
@@ -1102,6 +1107,7 @@ impl<'a, 'c: 'a> TypeResolver<'a, 'c> {
 			"bitcoin::secp256k1::key::PublicKey"|"bitcoin::secp256k1::PublicKey"|"secp256k1::key::PublicKey"
 				=> Some(")"),
 			"bitcoin::secp256k1::Signature" => Some(")"),
+			"bitcoin::secp256k1::recovery::RecoverableSignature" => Some(")"),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
 				if !is_ref => Some(")"),
 			"bitcoin::secp256k1::key::SecretKey"|"bitcoin::secp256k1::SecretKey"
diff --git a/lightning-c-bindings/src/c_types/mod.rs b/lightning-c-bindings/src/c_types/mod.rs
index cd96dff..b28bc80 100644
--- a/lightning-c-bindings/src/c_types/mod.rs
+++ b/lightning-c-bindings/src/c_types/mod.rs
@@ -9,6 +9,8 @@ use bitcoin::secp256k1::key::PublicKey as SecpPublicKey;
 use bitcoin::secp256k1::key::SecretKey as SecpSecretKey;
 use bitcoin::secp256k1::Signature as SecpSignature;
 use bitcoin::secp256k1::Error as SecpError;
+use bitcoin::secp256k1::recovery::RecoveryId;
+use bitcoin::secp256k1::recovery::RecoverableSignature as SecpRecoverableSignature;
 use bitcoin::bech32;
 
 use std::convert::TryInto; // Bindings need at least rustc 1.34
@@ -85,6 +87,32 @@ impl Signature {
 	#[allow(unused)] pub(crate) fn null() -> Self { Self { compact_form: [0; 64] } }
 }
 
+#[repr(C)]
+#[derive(Clone)]
+/// Represents a secp256k1 signature serialized as two 32-byte numbers as well as a tag which
+/// allows recovering the exact public key which created the signature given the message.
+pub struct RecoverableSignature {
+	/// The bytes of the signature in "compact" form plus a "Recovery ID" which allows for
+	/// recovery.
+	pub serialized_form: [u8; 68],
+}
+impl RecoverableSignature {
+	pub(crate) fn from_rust(pk: &SecpRecoverableSignature) -> Self {
+		let (id, compact_form) = pk.serialize_compact();
+		let mut serialized_form = [0; 68];
+		serialized_form[0..64].copy_from_slice(&compact_form[..]);
+		serialized_form[64..].copy_from_slice(&id.to_i32().to_le_bytes());
+		Self { serialized_form }
+	}
+	pub(crate) fn into_rust(&self) -> SecpRecoverableSignature {
+		let mut id = [0; 4];
+		id.copy_from_slice(&self.serialized_form[64..]);
+		SecpRecoverableSignature::from_compact(&self.serialized_form[0..64],
+				RecoveryId::from_i32(i32::from_le_bytes(id)).expect("Invalid Recovery ID"))
+			.unwrap()
+	}
+}
+
 #[repr(C)]
 /// Represents an error returned from libsecp256k1 during validation of some secp256k1 data
 pub enum Secp256k1Error {
-- 
2.39.5