Merge #828: Add arbitrary impl for types used in PSBTs

02ac1f2 Add `Arbitrary` impl for SecretKey, Parity, and XOnlyPublicKey (Shing Him Ng)

Pull request description:

  


ACKs for top commit:
  tcharding:
    ACK 02ac1f2
  apoelstra:
    ACK 02ac1f2; successfully ran local tests; nice!!


Tree-SHA512: bc6248e54770e27dbc72a5e1e72e7918fe6916cdae2208f2841833d56b214e95025a9a4c8ddb991dd99910a58e28d04c283ecf7bc74f60eb1e265b82e4778381

Author: apoelstra

src/key.rs

@@ -1658,17 +1658,50 @@ impl<C: Verification> Secp256k1<C> {
 #[cfg(feature = "arbitrary")]
 impl<'a> Arbitrary<'a> for PublicKey {
     fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
-        let mut bytes = [0u8; 33];
+        Ok(PublicKey::from_x_only_public_key(u.arbitrary()?, u.arbitrary()?))
+    }
+}
+
+#[cfg(feature = "arbitrary")]
+impl<'a> Arbitrary<'a> for Parity {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        match bool::arbitrary(u)? {
+            true => Ok(Parity::Even),
+            false => Ok(Parity::Odd),
+        }
+    }
+}
+
+#[cfg(feature = "arbitrary")]
+impl<'a> Arbitrary<'a> for SecretKey {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        let mut bytes = [0u8; constants::SECRET_KEY_SIZE];
         loop {
             // Unstructured::fill_buffer pads the buffer with zeroes if it runs out of data
-            if u.len() < 33 {
+            if u.len() < constants::SECRET_KEY_SIZE {
                 return Err(arbitrary::Error::NotEnoughData);
             }
+            u.fill_buffer(&mut bytes[..])?;
 
-            bytes[0] = if u.arbitrary::<bool>()? { 0x02 } else { 0x03 };
-            u.fill_buffer(&mut bytes[1..])?;
+            if let Ok(sk) = SecretKey::from_byte_array(bytes) {
+                return Ok(sk);
+            }
+        }
+    }
+}
+
+#[cfg(feature = "arbitrary")]
+impl<'a> Arbitrary<'a> for XOnlyPublicKey {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        let mut bytes = [0u8; 32];
+        loop {
+            // Unstructured::fill_buffer pads the buffer with zeroes if it runs out of data
+            if u.len() < 32 {
+                return Err(arbitrary::Error::NotEnoughData);
+            }
 
-            if let Ok(pk) = PublicKey::from_slice(&bytes) {
+            u.fill_buffer(&mut bytes[..])?;
+            if let Ok(pk) = XOnlyPublicKey::from_byte_array(bytes) {
                 return Ok(pk);
             }
         }