Add fallible Bytes slicing

src/bytes.rs

@@ -385,6 +385,13 @@ impl Bytes {
         ret
     }
 
+    /// Returns a slice of self for the provided range, or `None` if the range
+    /// is out of bounds.
+    pub fn try_slice(&self, range: impl RangeBounds<usize>) -> Option<Self> {
+        let (begin, end) = crate::try_range(range, self.len())?;
+        Some(self.slice(begin..end))
+    }
+
     /// Returns a slice of self that is equivalent to the given `subset`.
     ///
     /// When processing a `Bytes` buffer with other tools, one often gets a

src/lib.rs

@@ -166,6 +166,30 @@ fn range(range: impl core::ops::RangeBounds<usize>, len: usize) -> (usize, usize
     (begin, end)
 }
 
+/// Performs bounds checking of a range without panicking.
+#[inline(always)]
+fn try_range(range: impl core::ops::RangeBounds<usize>, len: usize) -> Option<(usize, usize)> {
+    use core::ops::Bound;
+
+    let begin = match range.start_bound() {
+        Bound::Included(&n) => n,
+        Bound::Excluded(&n) => n.checked_add(1)?,
+        Bound::Unbounded => 0,
+    };
+
+    let end = match range.end_bound() {
+        Bound::Included(&n) => n.checked_add(1)?,
+        Bound::Excluded(&n) => n,
+        Bound::Unbounded => len,
+    };
+
+    if begin <= end && end <= len {
+        Some((begin, end))
+    } else {
+        None
+    }
+}
+
 /// Error type for the `try_get_` methods of [`Buf`].
 /// Indicates that there were not enough remaining
 /// bytes in the buffer while attempting

tests/test_bytes.rs

@@ -141,6 +141,26 @@ fn slice() {
     assert_eq!(b, b"lo world"[..]);
 }
 
+#[test]
+fn try_slice() {
+    let a = Bytes::from(&b"hello world"[..]);
+
+    assert_eq!(a.try_slice(3..5), Some(Bytes::from(&b"lo"[..])));
+    assert_eq!(a.try_slice(..5), Some(Bytes::from(&b"hello"[..])));
+    assert_eq!(a.try_slice(3..), Some(Bytes::from(&b"lo world"[..])));
+    assert_eq!(a.try_slice(3..3), Some(Bytes::new()));
+}
+
+#[test]
+fn try_slice_invalid_range() {
+    let a = Bytes::from(&b"hello world"[..]);
+
+    assert_eq!(a.try_slice(5..44), None);
+    assert_eq!(a.try_slice(44..49), None);
+    assert_eq!(a.try_slice(5..3), None);
+    assert_eq!(a.try_slice(..=usize::MAX), None);
+}
+
 #[test]
 #[should_panic]
 fn slice_oob_1() {