block-buffer: add try_new method (#799)

try_new creates BlockBuffer or returns an error.

Author: rpiasetskyi

block-buffer/src/lib.rs

@@ -8,7 +8,7 @@
 
 pub use generic_array;
 
-use core::{marker::PhantomData, slice};
+use core::{fmt, marker::PhantomData, slice};
 use generic_array::{
     typenum::{IsLess, Le, NonZero, U256},
     ArrayLength, GenericArray,
@@ -40,6 +40,16 @@ pub type EagerBuffer<B> = BlockBuffer<B, Eager>;
 /// Lazy block buffer.
 pub type LazyBuffer<B> = BlockBuffer<B, Lazy>;
 
+/// Block buffer error.
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+pub struct Error;
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        f.write_str("Block buffer error")
+    }
+}
+
 /// Buffer for block processing of data.
 #[derive(Debug)]
 pub struct BlockBuffer<BlockSize, Kind>
@@ -95,15 +105,25 @@ where
     /// If slice length is not valid for used buffer kind.
     #[inline(always)]
     pub fn new(buf: &[u8]) -> Self {
+        Self::try_new(buf).unwrap()
+    }
+
+    /// Create new buffer from slice.
+    ///
+    /// Returns an error if slice length is not valid for used buffer kind.
+    #[inline(always)]
+    pub fn try_new(buf: &[u8]) -> Result<Self, Error> {
         let pos = buf.len();
-        assert!(Kind::invariant(pos, BlockSize::USIZE));
+        if !Kind::invariant(pos, BlockSize::USIZE) {
+            return Err(Error);
+        }
         let mut buffer = Block::<BlockSize>::default();
         buffer[..pos].copy_from_slice(buf);
-        Self {
+        Ok(Self {
             buffer,
             pos: pos as u8,
             _pd: PhantomData,
-        }
+        })
     }
 
     /// Digest data in `input` in blocks of size `BlockSize` using

block-buffer/tests/mod.rs

@@ -186,3 +186,11 @@ fn test_eager_paddings() {
         [0x42, 0xff, 0x10, 0x11],
     );
 }
+
+#[test]
+fn test_try_new() {
+    assert!(EagerBuffer::<U4>::try_new(&[0; 3]).is_ok());
+    assert!(EagerBuffer::<U4>::try_new(&[0; 4]).is_err());
+    assert!(LazyBuffer::<U4>::try_new(&[0; 4]).is_ok());
+    assert!(LazyBuffer::<U4>::try_new(&[0; 5]).is_err());
+}