Merge #393: Add custom Debug impl for RecoverableSignature

4c43d5e Add custom Debug impl for RecoverableSignature (Tobin Harding)

Pull request description:

  Currently when debug printing the `RecoverableSignature` we do so byte by byte, this means that the output differs depending on the endianess of the machine. If instead we serialize the signature in compact form then the output is the same irrespective of the endianess.

  With this applied the following two commands now pass:

  ```
  cargo test test_debug_output --features=recovery
  ```
  ```
  cross test --target powerpc-unknown-linux-gnu test_debug_output --features=recovery
  ```

  Fixes: #375

ACKs for top commit:
  apoelstra:
    ACK 4c43d5e

Tree-SHA512: 073c2e0e23ce41a2b35f1b1193b07a755b726bf565d61e6bcb23b6bdaab31ba3591f31aa92230b07f7dfc018de0401eba09a6858dc261e66dacb331355f40d76

secp256k1-sys/src/recovery.rs

@@ -16,13 +16,13 @@
 //! # FFI of the recovery module
 
 use ::types::*;
-use {Context, Signature, NonceFn, PublicKey};
+use ::core::fmt;
+use {Context, Signature, NonceFn, PublicKey, CPtr};
 
 /// Library-internal representation of a Secp256k1 signature + recovery ID
 #[repr(C)]
 pub struct RecoverableSignature([c_uchar; 65]);
 impl_array_newtype!(RecoverableSignature, c_uchar, 65);
-impl_raw_debug!(RecoverableSignature);
 
 impl RecoverableSignature {
     /// Create a new (zeroed) signature usable for the FFI interface
@@ -35,6 +35,30 @@ impl Default for RecoverableSignature {
     }
 }
 
+impl fmt::Debug for RecoverableSignature {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut ret = [0u8; 64];
+        let mut recid = 0i32;
+
+        unsafe {
+            let err = secp256k1_ecdsa_recoverable_signature_serialize_compact(
+                super::secp256k1_context_no_precomp,
+                ret.as_mut_c_ptr(),
+                &mut recid,
+                self,
+            );
+            assert!(err == 1);
+        }
+
+        for byte in ret.iter() {
+            write!(f, "{:02x}", byte)?;
+        }
+        write!(f, "{:02x}", recid as u8)?;
+
+        Ok(())
+    }
+}
+
 extern "C" {
     #[cfg_attr(not(rust_secp_no_symbol_renaming), link_name = "rustsecp256k1_v0_4_1_ecdsa_recoverable_signature_parse_compact")]
     pub fn secp256k1_ecdsa_recoverable_signature_parse_compact(cx: *const Context, sig: *mut RecoverableSignature,

src/ecdsa/recovery.rs

@@ -346,7 +346,7 @@ mod tests {
             0xff, 0x20, 0x80, 0xc4, 0xa3, 0x9a, 0xae, 0x06,
             0x8d, 0x12, 0xee, 0xd0, 0x09, 0xb6, 0x8c, 0x89],
             RecoveryId(1)).unwrap();
-        assert_eq!(&format!("{:?}", sig), "RecoverableSignature(98882e09f4ed6dc3659e43fc771e0cafa60b1f926f2b77041f744721adff7366898cb609d0ee128d06ae9aa3c48020ff9f705e02f80e1280a8ade05216971a4c01)");
+        assert_eq!(&format!("{:?}", sig), "RecoverableSignature(6673ffad2147741f04772b6f921f0ba6af0c1e77fc439e65c36dedf4092e88984c1a971652e0ada880120ef8025e709fff2080c4a39aae068d12eed009b68c8901)");
     }
 
     #[test]