ffi: make function types nullable

secp256k1-sys/src/lib.rs

@@ -58,36 +58,37 @@ pub const SECP256K1_SER_COMPRESSED: c_uint = (1 << 1) | (1 << 8);
 /// around the FFI functions to use it. And it's an unsafe type.
 /// Nonces are generated deterministically by RFC6979 by
 /// default; there should be no need to ever change this.
-pub type NonceFn = unsafe extern "C" fn(nonce32: *mut c_uchar,
+pub type NonceFn = Option<unsafe extern "C" fn(
+    nonce32: *mut c_uchar,
     msg32: *const c_uchar,
     key32: *const c_uchar,
     algo16: *const c_uchar,
     data: *mut c_void,
     attempt: c_uint,
-) -> c_int;
+) -> c_int>;
 
 /// Hash function to use to post-process an ECDH point to get
 /// a shared secret.
-pub type EcdhHashFn = unsafe extern "C" fn(
+pub type EcdhHashFn = Option<unsafe extern "C" fn(
     output: *mut c_uchar,
     x: *const c_uchar,
     y: *const c_uchar,
     data: *mut c_void,
-) -> c_int;
+) -> c_int>;
 
 ///  Same as secp256k1_nonce function with the exception of accepting an
 ///  additional pubkey argument and not requiring an attempt argument. The pubkey
 ///  argument can protect signature schemes with key-prefixed challenge hash
 ///  inputs against reusing the nonce when signing with the wrong precomputed
 ///  pubkey.
-pub type SchnorrNonceFn = unsafe extern "C" fn(
+pub type SchnorrNonceFn = Option<unsafe extern "C" fn(
     nonce32: *mut c_uchar,
     msg32: *const c_uchar,
     key32: *const c_uchar,
     xonly_pk32: *const c_uchar,
     algo16: *const c_uchar,
     data: *mut c_void,
-) -> c_int;
+) -> c_int>;
 
 /// A Secp256k1 context, containing various precomputed values and such
 /// needed to do elliptic curve computations. If you create one of these

src/ecdh.rs

@@ -151,7 +151,7 @@ impl SharedSecret {
                 xy.as_mut_ptr(),
                 point.as_ptr(),
                 scalar.as_ptr(),
-                c_callback,
+                Some(c_callback),
                 ptr::null_mut(),
             )
         };