digest: add CoreProxy::compose/decompose methods (#1898)

Author: newpavlov

digest/src/block_api.rs

@@ -97,8 +97,13 @@ pub enum TruncSide {
     Right,
 }
 
-/// A proxy trait to a core type.
+/// A proxy trait to the core block-level type.
 pub trait CoreProxy {
-    /// Wrapped block-level type.
-    type Core;
+    /// Core block-level type.
+    type Core: BufferKindUser;
+
+    /// Create `Self` from core and buffer.
+    fn compose(core: Self::Core, buffer: Buffer<Self::Core>) -> Self;
+    /// Decompose `self` into core and buffer.
+    fn decompose(self) -> (Self::Core, Buffer<Self::Core>);
 }

digest/src/buffer_macros/fixed.rs

@@ -179,6 +179,13 @@ macro_rules! buffer_fixed {
     ) => {
         impl$(< $( $lt $( : $clt $(+ $dlt )* )? ),+ >)? $crate::block_api::CoreProxy for $name$(< $( $lt ),+ >)? {
             type Core = $core_ty;
+            fn compose(core: Self::Core, buffer: $crate::block_api::Buffer<Self::Core>) -> Self {
+                Self { core, buffer }
+            }
+            fn decompose(self) -> (Self::Core, $crate::block_api::Buffer<Self::Core>) {
+                let Self { core, buffer } = self;
+                (core, buffer)
+            }
         }
 
         $crate::buffer_fixed!(impl_inner: $name$(< $( $lt $( : $clt $(+ $dlt )* )? ),+ >)?($core_ty); $($trait_name)*;);

digest/src/buffer_macros/variable_ct.rs

@@ -112,6 +112,13 @@ macro_rules! buffer_ct_variable {
             $out_size: $crate::array::ArraySize + $crate::typenum::IsLessOrEqual<$max_size, Output = $crate::typenum::True>,
         {
             type Core = $crate::block_api::CtOutWrapper<$core_ty, $out_size>;
+            fn compose(core: Self::Core, buffer: $crate::block_api::Buffer<Self::Core>) -> Self {
+                Self { core, buffer }
+            }
+            fn decompose(self) -> (Self::Core, $crate::block_api::Buffer<Self::Core>) {
+                let Self { core, buffer } = self;
+                (core, buffer)
+            }
         }
 
         impl<$out_size> $crate::Update for $name<$out_size>

digest/src/buffer_macros/xof.rs

@@ -87,7 +87,7 @@ macro_rules! buffer_xof {
     ) => {
         $crate::buffer_xof!(
             impl_inner: $name($core_ty);
-            Debug Clone BlockSizeUser CoreProxy
+            Debug Clone BlockSizeUser
             $($trait_name)*;);
     };
 
@@ -194,6 +194,13 @@ macro_rules! buffer_xof {
     ) => {
         impl $crate::block_api::CoreProxy for $name {
             type Core = $core_ty;
+            fn compose(core: Self::Core, buffer: $crate::block_api::Buffer<Self::Core>) -> Self {
+                Self { core, buffer }
+            }
+            fn decompose(self) -> (Self::Core, $crate::block_api::Buffer<Self::Core>) {
+                let Self { core, buffer } = self;
+                (core, buffer)
+            }
         }
 
         $crate::buffer_xof!(impl_inner: $name($core_ty); $($trait_name)*;);