Merge #440: Add secp256k1_schnorrsig_sign_custom to sys crate

0b27bde Bump secp256k1-sys minor version (Tibo-lg)
4beebd1 Add secp256k1_schnorrsig_sign_custom to sys crate (Tibo-lg)

Pull request description:

  Trying to update to the latest version I noticed that I lost the ability to pass a nonce to the schnorr signing function. This PR restore this ability by adding `secp256k1_schnorrsig_sign_custom` to the sys crate.

  I hid the struct members of `SchnorrSigExtraParams` and added a `new` method to make sure that the `magic` field is properly initialized, I think that make the most sense but happy to hear other opinions.

ACKs for top commit:
  apoelstra:
    ACK 0b27bde

Tree-SHA512: 7181eddb5815ca1a5ae1044f2a6fd8a214f8df9c45352e5f2ab6607f7e0d819cb8856fc2d6596b9d740b859df91d559595e7912332e292079c9ac1d27ec5c00b

Author: apoelstra

secp256k1-sys/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "secp256k1-sys"
-version = "0.5.1"
+version = "0.5.2"
 authors = [ "Dawid Ciężarkiewicz <dpc@ucore.info>",
             "Andrew Poelstra <apoelstra@wpsoftware.net>",
             "Steven Roose <steven@stevenroose.org>" ]

secp256k1-sys/src/lib.rs

@@ -87,12 +87,42 @@ pub type EcdhHashFn = Option<unsafe extern "C" fn(
 pub type SchnorrNonceFn = Option<unsafe extern "C" fn(
     nonce32: *mut c_uchar,
     msg32: *const c_uchar,
+    msg_len: size_t,
     key32: *const c_uchar,
     xonly_pk32: *const c_uchar,
     algo16: *const c_uchar,
+    algo_len: size_t,
     data: *mut c_void,
 ) -> c_int>;
 
+/// Data structure that contains additional arguments for schnorrsig_sign_custom.
+#[repr(C)]
+pub struct SchnorrSigExtraParams {
+    magic: [c_uchar; 4],
+    nonce_fp: SchnorrNonceFn,
+    ndata: *const c_void,
+}
+
+impl SchnorrSigExtraParams {
+    /// Create a new SchnorrSigExtraParams properly initialized.
+    ///
+    /// `nonce_fp`: pointer to a nonce generation function. If NULL
+    /// rustsecp256k1_v0_5_0_nonce_function_bip340 is used
+    ///
+    /// `ndata`: pointer to arbitrary data used by the nonce generation function
+    /// (can be NULL). If it is non-NULL and
+    /// rustsecp256k1_v0_5_0_nonce_function_bip340 is used,
+    /// then ndata must be a pointer to 32-byte auxiliary randomness as per
+    /// BIP-340.
+    pub fn new(nonce_fp: SchnorrNonceFn, ndata: *const c_void) -> Self {
+        SchnorrSigExtraParams {
+            magic: [0xda, 0x6f, 0xb3, 0x8c],
+            nonce_fp,
+            ndata,
+        }
+    }
+}
+
 /// A Secp256k1 context, containing various precomputed values and such
 /// needed to do elliptic curve computations. If you create one of these
 /// with `secp256k1_context_create` you MUST destroy it with
@@ -461,6 +491,17 @@ extern "C" {
         aux_rand32: *const c_uchar
     ) -> c_int;
 
+    // Schnorr Signatures with extra parameters (see [`SchnorrSigExtraParams`])
+    #[cfg_attr(not(rust_secp_no_symbol_renaming), link_name = "rustsecp256k1_v0_5_0_schnorrsig_sign_custom")]
+    pub fn secp256k1_schnorrsig_sign_custom(
+        cx: *const Context,
+        sig: *mut c_uchar,
+        msg: *const c_uchar,
+        msg_len: size_t,
+        keypair: *const KeyPair,
+        extra_params: *const SchnorrSigExtraParams,
+    ) -> c_int;
+
     #[cfg_attr(not(rust_secp_no_symbol_renaming), link_name = "rustsecp256k1_v0_5_0_schnorrsig_verify")]
     pub fn secp256k1_schnorrsig_verify(
         cx: *const Context,