Add an as_bytes method to hash types

We now implement `AsRef` for hash types, sometimes usage of `as_ref` may
required type annotations. For such cases we can provide an alternate
way to get the underlying bytes to make the API more ergonomic.

Add a method `as_bytes` for getting a reference to the inner byte array.
Add for new types created by `hash_newtype` also.

Author: tcharding

src/hash160.rs

@@ -36,6 +36,7 @@ pub struct Hash(
 hex_fmt_impl!(Hash);
 serde_impl!(Hash, 20);
 borrow_slice_impl!(Hash);
+as_bytes_impl!(Hash, 20);
 
 impl str::FromStr for Hash {
     type Err = hex::Error;

src/ripemd160.rs

@@ -85,6 +85,7 @@ pub struct Hash(
 hex_fmt_impl!(Hash);
 serde_impl!(Hash, 20);
 borrow_slice_impl!(Hash);
+as_bytes_impl!(Hash, 20);
 
 impl str::FromStr for Hash {
     type Err = hex::Error;

src/sha1.rs

@@ -80,6 +80,7 @@ pub struct Hash(
 hex_fmt_impl!(Hash);
 serde_impl!(Hash, 20);
 borrow_slice_impl!(Hash);
+as_bytes_impl!(Hash, 20);
 
 impl str::FromStr for Hash {
     type Err = hex::Error;

src/sha256.rs

@@ -87,6 +87,7 @@ impl str::FromStr for Hash {
 hex_fmt_impl!(Hash);
 serde_impl!(Hash, 32);
 borrow_slice_impl!(Hash);
+as_bytes_impl!(Hash, 32);
 
 impl crate::Hash for Hash {
     type Engine = HashEngine;
@@ -159,6 +160,7 @@ pub struct Midstate(pub [u8; 32]);
 hex_fmt_impl!(Midstate);
 serde_impl!(Midstate, 32);
 borrow_slice_impl!(Midstate);
+as_bytes_impl!(Midstate, 32);
 
 impl str::FromStr for Midstate {
     type Err = hex::Error;

src/sha256d.rs

@@ -31,6 +31,7 @@ pub struct Hash(
 hex_fmt_impl!(Hash);
 serde_impl!(Hash, 32);
 borrow_slice_impl!(Hash);
+as_bytes_impl!(Hash, 32);
 
 impl str::FromStr for Hash {
     type Err = hex::Error;

src/sha256t.rs

@@ -80,6 +80,7 @@ impl<T: Tag> str::FromStr for Hash<T> {
 
 hex_fmt_impl!(Hash, T:Tag);
 borrow_slice_impl!(Hash, T:Tag);
+as_bytes_impl!(Hash, 32, T:Tag);
 
 impl<T: Tag> crate::Hash for Hash<T> {
     type Engine = sha256::HashEngine;

src/sha512.rs

@@ -136,6 +136,7 @@ impl str::FromStr for Hash {
 hex_fmt_impl!(Hash);
 serde_impl!(Hash, 64);
 borrow_slice_impl!(Hash);
+as_bytes_impl!(Hash, 64);
 
 impl crate::Hash for Hash {
     type Engine = HashEngine;

src/siphash24.rs

@@ -204,6 +204,7 @@ pub struct Hash(
 hex_fmt_impl!(Hash);
 serde_impl!(Hash, 8);
 borrow_slice_impl!(Hash);
+as_bytes_impl!(Hash, 8);
 
 impl str::FromStr for Hash {
     type Err = hex::Error;

src/util.rs

@@ -70,6 +70,22 @@ macro_rules! borrow_slice_impl(
     )
 );
 
+/// Adds a method `as_bytes` to a given type `$ty`.
+#[macro_export]
+macro_rules! as_bytes_impl(
+    ($ty:ident, $len:expr) => (
+        $crate::as_bytes_impl!($ty, $len, );
+    );
+    ($ty:ident, $len:expr, $($gen:ident: $gent:ident),*) => (
+        impl<$($gen: $gent),*> $ty<$($gen),*>  {
+            /// Returns `self` as a byte array reference.
+            pub fn as_bytes(&self) -> &[u8; $len] {
+                &self.0
+            }
+        }
+    );
+);
+
 macro_rules! engine_input_impl(
     () => (
         #[cfg(not(fuzzing))]
@@ -128,6 +144,11 @@ macro_rules! hash_newtype {
                 // Hashes implement Copy so don't need into_hash.
                 self.0
             }
+
+            /// Returns `self` as a byte array reference.
+            pub fn as_bytes(&self) -> &[u8; $len] {
+                &self.0.as_bytes()
+            }
         }
 
         impl $crate::_export::_core::convert::From<$hash> for $newtype {