add finalize_into methods to DynDigest

Author: newpavlov

digest/src/core_api.rs

@@ -95,7 +95,7 @@ impl<D: FixedOutputCore + Reset> FixedOutput for CoreWrapper<D, D::BlockSize> {
 
     #[inline]
     fn finalize_into(mut self, out: &mut GenericArray<u8, Self::OutputSize>) {
-        let Self { core, buffer} = &mut self;
+        let Self { core, buffer } = &mut self;
         core.finalize_fixed_core(buffer, out);
     }
 
@@ -120,17 +120,23 @@ impl<D: ExtendableOutputCore + Reset> ExtendableOutput for CoreWrapper<D, D::Blo
 
     #[inline]
     fn finalize_xof(mut self) -> Self::Reader {
-        let Self { core, buffer} = &mut self;
+        let Self { core, buffer } = &mut self;
         let reader_core = core.finalize_xof_core(buffer);
-        CoreWrapper { core: reader_core, buffer: Default::default() }
+        CoreWrapper {
+            core: reader_core,
+            buffer: Default::default(),
+        }
     }
 
     #[inline]
     fn finalize_xof_reset(&mut self) -> Self::Reader {
         let Self { core, buffer } = self;
         let reader_core = core.finalize_xof_core(buffer);
         self.reset();
-        CoreWrapper { core: reader_core, buffer: Default::default() }
+        CoreWrapper {
+            core: reader_core,
+            buffer: Default::default(),
+        }
     }
 }
 
@@ -156,4 +162,3 @@ impl<R: XofReaderCore> std::io::Read for CoreWrapper<R, R::BlockSize> {
         Ok(buf.len())
     }
 }
-

digest/src/dyn_digest.rs

@@ -1,8 +1,8 @@
-#![cfg(feature = "alloc")]
 use alloc::boxed::Box;
+use core::fmt;
 
 use super::{FixedOutput, Reset, Update};
-use generic_array::typenum::Unsigned;
+use generic_array::{typenum::Unsigned, GenericArray};
 
 /// The `DynDigest` trait is a modification of `Digest` trait suitable
 /// for trait objects.
@@ -19,6 +19,16 @@ pub trait DynDigest {
     /// Retrieve result and consume boxed hasher instance
     fn finalize(self: Box<Self>) -> Box<[u8]>;
 
+    /// Write result into provided array and consume the hasher instance.
+    ///
+    /// Returns error if buffer length is not equal to `output_size`.
+    fn finalize_into(self, buf: &mut [u8]) -> Result<(), InvalidBufferLength>;
+
+    /// Write result into provided array and reset the hasher instance.
+    ///
+    /// Returns error if buffer length is not equal to `output_size`.
+    fn finalize_into_reset(&mut self, out: &mut [u8]) -> Result<(), InvalidBufferLength>;
+
     /// Reset hasher instance to its initial state.
     fn reset(&mut self);
 
@@ -42,6 +52,24 @@ impl<D: Update + FixedOutput + Reset + Clone + 'static> DynDigest for D {
         self.finalize_fixed().to_vec().into_boxed_slice()
     }
 
+    fn finalize_into(self, buf: &mut [u8]) -> Result<(), InvalidBufferLength> {
+        if buf.len() == self.output_size() {
+            self.finalize_into(GenericArray::from_mut_slice(buf));
+            Ok(())
+        } else {
+            Err(InvalidBufferLength)
+        }
+    }
+
+    fn finalize_into_reset(&mut self, buf: &mut [u8]) -> Result<(), InvalidBufferLength> {
+        if buf.len() == self.output_size() {
+            self.finalize_into_reset(GenericArray::from_mut_slice(buf));
+            Ok(())
+        } else {
+            Err(InvalidBufferLength)
+        }
+    }
+
     fn reset(&mut self) {
         Reset::reset(self);
     }
@@ -60,3 +88,16 @@ impl Clone for Box<dyn DynDigest> {
         self.box_clone()
     }
 }
+
+#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
+#[derive(Default, Debug, Copy, Clone, Eq, PartialEq)]
+pub struct InvalidBufferLength;
+
+impl fmt::Display for InvalidBufferLength {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("invalid buffer length")
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for InvalidBufferLength {}

digest/src/lib.rs

@@ -50,15 +50,16 @@ pub mod dev;
 #[cfg(feature = "core-api")]
 mod core_api;
 mod digest;
+#[cfg(feature = "alloc")]
 mod dyn_digest;
 
-#[cfg(feature = "core-api")]
-pub use block_buffer;
 #[cfg(feature = "core-api")]
 pub use crate::core_api::{CoreWrapper, ExtendableOutputCore, FixedOutputCore, UpdateCore};
 pub use crate::digest::{Digest, Output};
+#[cfg(feature = "core-api")]
+pub use block_buffer;
 #[cfg(feature = "alloc")]
-pub use dyn_digest::DynDigest;
+pub use dyn_digest::{DynDigest, InvalidBufferLength};
 pub use generic_array::{self, typenum::consts, ArrayLength, GenericArray};
 
 /// Trait for updating hasher state with input data.