Add Update::chain and Digest::new_with_prefix (#846)

digest/CHANGELOG.md

@@ -5,6 +5,16 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 0.10.1 (2021-12-14)
+### Added
+- `Update::chain` and `Digest::new_with_prefix` methods. ([#846])
+
+### Fixed
+- Doc cfg attribute for CtOutput and MacError. ([#842])
+
+[#842]: https://github.com/RustCrypto/traits/pull/842
+[#846]: https://github.com/RustCrypto/traits/pull/846
+
 ## 0.10.0 (2021-12-07)
 ### Changed
 - Dirty traits are removed and instead block-level traits are introduced.

digest/src/digest.rs

@@ -14,9 +14,12 @@ pub trait HashMarker {}
 /// This trait wraps [`Update`], [`FixedOutput`], [`Default`], and
 /// [`HashMarker`] traits and provides additional convenience methods.
 pub trait Digest: OutputSizeUser {
-    /// Create new hasher instance
+    /// Create new hasher instance.
     fn new() -> Self;
 
+    /// Create new hasher instance which has processed the provided data.
+    fn new_with_prefix(data: impl AsRef<[u8]>) -> Self;
+
     /// Process data, updating the internal state.
     fn update(&mut self, data: impl AsRef<[u8]>);
 
@@ -57,6 +60,16 @@ impl<D: FixedOutput + Default + Update + HashMarker> Digest for D {
         Self::default()
     }
 
+    #[inline]
+    fn new_with_prefix(data: impl AsRef<[u8]>) -> Self
+    where
+        Self: Default + Sized,
+    {
+        let mut h = Self::default();
+        h.update(data.as_ref());
+        h
+    }
+
     #[inline]
     fn update(&mut self, data: impl AsRef<[u8]>) {
         Update::update(self, data.as_ref());

digest/src/lib.rs

@@ -72,6 +72,15 @@ use core::fmt;
 pub trait Update {
     /// Update state using the provided data.
     fn update(&mut self, data: &[u8]);
+
+    /// Digest input data in a chained manner.
+    fn chain(mut self, data: impl AsRef<[u8]>) -> Self
+    where
+        Self: Sized,
+    {
+        self.update(data.as_ref());
+        self
+    }
 }
 
 /// Trait for hash functions with fixed-size output.