Add Hash type and finalize method to HashEngine

Add an associated const `Hash` to the `HashEngine` trait. Also add a
`finalize` method that converts the engine to the associated hash.

For now just use the existent `from_engine` stuff. We can refactor
later.

hashes/src/hash160/mod.rs

@@ -38,9 +38,12 @@ impl Default for HashEngine {
 }
 
 impl crate::HashEngine for HashEngine {
+    type Hash = Hash;
     const BLOCK_SIZE: usize = 64; // Same as sha256::HashEngine::BLOCK_SIZE;
+
     fn input(&mut self, data: &[u8]) { self.0.input(data) }
     fn n_bytes_hashed(&self) -> u64 { self.0.n_bytes_hashed() }
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }
 
 #[cfg(test)]

hashes/src/hmac/mod.rs

@@ -92,11 +92,12 @@ impl<T: GeneralHash> HmacEngine<T> {
 }
 
 impl<T: GeneralHash> HashEngine for HmacEngine<T> {
+    type Hash = Hmac<T>;
     const BLOCK_SIZE: usize = T::Engine::BLOCK_SIZE;
 
     fn n_bytes_hashed(&self) -> u64 { self.iengine.n_bytes_hashed() }
-
     fn input(&mut self, buf: &[u8]) { self.iengine.input(buf) }
+    fn finalize(self) -> Self::Hash { Hmac::from_engine(self) }
 }
 
 impl<T: GeneralHash + fmt::Debug> fmt::Debug for Hmac<T> {

hashes/src/lib.rs

@@ -186,6 +186,9 @@ pub type HkdfSha512 = Hkdf<sha512::Hash>;
 
 /// A hashing engine which bytes can be serialized into.
 pub trait HashEngine: Clone {
+    /// The `Hash` type returned when finalizing this engine.
+    type Hash: Hash;
+
     /// Length of the hash's internal block size, in bytes.
     const BLOCK_SIZE: usize;
 
@@ -194,6 +197,9 @@ pub trait HashEngine: Clone {
 
     /// Return the number of bytes already input into the engine.
     fn n_bytes_hashed(&self) -> u64;
+
+    /// Finalizes this engine.
+    fn finalize(self) -> Self::Hash;
 }
 
 /// Trait describing hash digests which can be constructed by hashing arbitrary data.

hashes/src/ripemd160/mod.rs

@@ -87,9 +87,10 @@ impl Default for HashEngine {
 }
 
 impl crate::HashEngine for HashEngine {
+    type Hash = Hash;
     const BLOCK_SIZE: usize = 64;
 
     fn n_bytes_hashed(&self) -> u64 { self.bytes_hashed }
-
     crate::internal_macros::engine_input_impl!();
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }

hashes/src/sha1/mod.rs

@@ -79,9 +79,12 @@ impl Default for HashEngine {
 }
 
 impl crate::HashEngine for HashEngine {
+    type Hash = Hash;
     const BLOCK_SIZE: usize = 64;
 
     fn n_bytes_hashed(&self) -> u64 { self.bytes_hashed }
 
     crate::internal_macros::engine_input_impl!();
+
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }

hashes/src/sha256/mod.rs

@@ -128,11 +128,12 @@ impl Default for HashEngine {
 }
 
 impl crate::HashEngine for HashEngine {
+    type Hash = Hash;
     const BLOCK_SIZE: usize = 64;
 
     fn n_bytes_hashed(&self) -> u64 { self.bytes_hashed }
-
     crate::internal_macros::engine_input_impl!();
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }
 
 impl Hash {

hashes/src/sha256d/mod.rs

@@ -33,9 +33,12 @@ impl Default for HashEngine {
 }
 
 impl crate::HashEngine for HashEngine {
+    type Hash = Hash;
     const BLOCK_SIZE: usize = 64; // Same as sha256::HashEngine::BLOCK_SIZE;
+
     fn input(&mut self, data: &[u8]) { self.0.input(data) }
     fn n_bytes_hashed(&self) -> u64 { self.0.n_bytes_hashed() }
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }
 
 #[cfg(test)]

hashes/src/sha256t/mod.rs

@@ -133,9 +133,12 @@ impl<T: Tag> Clone for HashEngine<T> {
 }
 
 impl<T: Tag> crate::HashEngine for HashEngine<T> {
+    type Hash = Hash<T>;
     const BLOCK_SIZE: usize = 64; // Same as sha256::HashEngine::BLOCK_SIZE;
+
     fn input(&mut self, data: &[u8]) { self.0.input(data) }
     fn n_bytes_hashed(&self) -> u64 { self.0.n_bytes_hashed() }
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }
 
 crate::internal_macros::impl_write!(

hashes/src/sha384/mod.rs

@@ -30,11 +30,12 @@ impl Default for HashEngine {
 }
 
 impl crate::HashEngine for HashEngine {
+    type Hash = Hash;
     const BLOCK_SIZE: usize = sha512::BLOCK_SIZE;
 
     fn n_bytes_hashed(&self) -> u64 { self.0.n_bytes_hashed() }
-
     fn input(&mut self, inp: &[u8]) { self.0.input(inp); }
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }
 
 #[cfg(test)]

hashes/src/sha512/mod.rs

@@ -120,9 +120,10 @@ impl HashEngine {
 }
 
 impl crate::HashEngine for HashEngine {
+    type Hash = Hash;
     const BLOCK_SIZE: usize = 128;
 
     fn n_bytes_hashed(&self) -> u64 { self.bytes_hashed }
-
     crate::internal_macros::engine_input_impl!();
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }

hashes/src/sha512_256/mod.rs

@@ -40,11 +40,12 @@ impl Default for HashEngine {
 }
 
 impl crate::HashEngine for HashEngine {
+    type Hash = Hash;
     const BLOCK_SIZE: usize = sha512::BLOCK_SIZE;
 
     fn n_bytes_hashed(&self) -> u64 { self.0.n_bytes_hashed() }
-
     fn input(&mut self, inp: &[u8]) { self.0.input(inp); }
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }
 
 #[cfg(test)]

hashes/src/siphash24/mod.rs

@@ -121,6 +121,7 @@ impl HashEngine {
 }
 
 impl crate::HashEngine for HashEngine {
+    type Hash = Hash;
     const BLOCK_SIZE: usize = 8;
 
     #[inline]
@@ -165,6 +166,8 @@ impl crate::HashEngine for HashEngine {
     }
 
     fn n_bytes_hashed(&self) -> u64 { self.bytes_hashed }
+
+    fn finalize(self) -> Self::Hash { Hash::from_engine(self) }
 }
 
 impl Hash {