Add peek methods to Reader

wincode/src/io/cursor.rs

@@ -161,7 +161,7 @@ where
         self.pos = unsafe { self.pos.unchecked_add(amt) };
     }
 
-    #[expect(deprecated)]
+    #[inline]
     fn consume(&mut self, amt: usize) -> ReadResult<()> {
         if self.cur_len() < amt {
             return Err(read_size_limit(amt));

wincode/src/io/mod.rs

@@ -90,7 +90,7 @@ pub trait Reader<'a> {
     /// Return exactly `N` bytes as `&[u8; N]` without advancing.
     ///
     /// Errors if fewer than `N` bytes are available.
-    #[deprecated(since = "0.4.6", note = "use `take_array`.")]
+    #[deprecated(since = "0.4.6", note = "use `peek_array`.")]
     #[expect(deprecated)]
     fn fill_array<const N: usize>(&mut self) -> ReadResult<&[u8; N]> {
         let src = self.fill_exact(N)?;
@@ -99,6 +99,18 @@ pub trait Reader<'a> {
         Ok(unsafe { &*src.as_ptr().cast::<[u8; N]>() })
     }
 
+    /// Return exactly `N` bytes as `&[u8; N]` without advancing.
+    ///
+    /// Errors if fewer than `N` bytes are available.
+    #[inline]
+    #[expect(deprecated)]
+    fn peek_array<const N: usize>(&mut self) -> ReadResult<&[u8; N]> {
+        let src = self.fill_exact(N)?;
+        // SAFETY:
+        // - `fill_exact` ensures we read N bytes.
+        Ok(unsafe { &*src.as_ptr().cast::<[u8; N]>() })
+    }
+
     /// Return exactly `N` bytes as `[u8; N]` and advance by `N`.
     ///
     /// Errors if fewer than `N` bytes are available.
@@ -202,17 +214,9 @@ pub trait Reader<'a> {
     /// # Safety
     ///
     /// - `amt` must be less than or equal to the number of bytes remaining in the reader.
-    #[deprecated(
-        since = "0.4.6",
-        note = "use one of the `take_*` methods, which automatically advance the reader."
-    )]
     unsafe fn consume_unchecked(&mut self, amt: usize);
 
     /// Advance the reader exactly `amt` bytes, returning an error if the source does not have enough bytes.
-    #[deprecated(
-        since = "0.4.6",
-        note = "use one of the `take_*` methods, which automatically advance the reader."
-    )]
     fn consume(&mut self, amt: usize) -> ReadResult<()>;
 
     /// Advance the parent by `n_bytes` and return a [`Reader`] that can elide bounds checks within
@@ -249,12 +253,20 @@ pub trait Reader<'a> {
     ///
     /// May buffer more bytes if necessary. Errors if no bytes remain.
     #[inline]
-    #[deprecated(since = "0.4.6", note = "use `take_byte`.")]
+    #[deprecated(since = "0.4.6", note = "use `peek_byte`.")]
     #[expect(deprecated)]
     fn peek(&mut self) -> ReadResult<&u8> {
         self.fill_buf(1)?.first().ok_or_else(|| read_size_limit(1))
     }
 
+    /// Get the next byte without advancing.
+    ///
+    /// Errors if no bytes remain.
+    #[inline]
+    fn peek_byte(&mut self) -> ReadResult<u8> {
+        Ok(self.peek_array::<1>()?[0])
+    }
+
     /// Get a mutable reference to the [`Reader`].
     ///
     /// Useful in situations where one only has an `impl Reader<'de>` that
@@ -386,6 +398,11 @@ impl<'a, R: Reader<'a> + ?Sized> Reader<'a> for &mut R {
         (*self).fill_array()
     }
 
+    #[inline(always)]
+    fn peek_array<const N: usize>(&mut self) -> ReadResult<&[u8; N]> {
+        (*self).peek_array()
+    }
+
     #[inline(always)]
     fn take_array<const N: usize>(&mut self) -> ReadResult<[u8; N]> {
         (*self).take_array()
@@ -424,13 +441,11 @@ impl<'a, R: Reader<'a> + ?Sized> Reader<'a> for &mut R {
     }
 
     #[inline(always)]
-    #[expect(deprecated)]
     unsafe fn consume_unchecked(&mut self, amt: usize) {
         (*self).consume_unchecked(amt)
     }
 
     #[inline(always)]
-    #[expect(deprecated)]
     fn consume(&mut self, amt: usize) -> ReadResult<()> {
         (*self).consume(amt)
     }
@@ -446,6 +461,11 @@ impl<'a, R: Reader<'a> + ?Sized> Reader<'a> for &mut R {
         (*self).peek()
     }
 
+    #[inline(always)]
+    fn peek_byte(&mut self) -> ReadResult<u8> {
+        (*self).peek_byte()
+    }
+
     #[inline(always)]
     fn copy_into_slice(&mut self, dst: &mut [MaybeUninit<u8>]) -> ReadResult<()> {
         (*self).copy_into_slice(dst)

wincode/src/io/slice.rs

@@ -177,7 +177,6 @@ impl<'a> Reader<'a> for TrustedSliceReaderZeroCopyMut<'a> {
     }
 
     #[inline]
-    #[expect(deprecated)]
     fn consume(&mut self, amt: usize) -> ReadResult<()> {
         unsafe { Self::consume_unchecked(self, amt) };
         Ok(())
@@ -308,7 +307,6 @@ impl<'a> Reader<'a> for &'a [u8] {
     }
 
     #[inline]
-    #[expect(deprecated)]
     fn consume(&mut self, amt: usize) -> ReadResult<()> {
         if self.len() < amt {
             return Err(read_size_limit(amt));
@@ -376,7 +374,6 @@ impl<'a> Reader<'a> for &'a mut [u8] {
     }
 
     #[inline]
-    #[expect(deprecated)]
     fn consume(&mut self, amt: usize) -> ReadResult<()> {
         if self.len() < amt {
             return Err(read_size_limit(amt));