Implement Buf for std::io::Take<&[u8]>.

Author: smarnach

src/buf/buf_impl.rs

@@ -864,6 +864,30 @@ impl Buf for &[u8] {
     }
 }
 
+impl<'a> Buf for io::Take<&'a [u8]> {
+    #[inline]
+    fn remaining(&self) -> usize {
+        let len = self.get_ref().len() as u64;
+        let limit = self.limit();
+        // The smaller of the two values will always fit in usize.
+        cmp::min(len, limit) as usize
+    }
+
+    fn bytes(&self) -> &[u8] {
+        &self.get_ref()[..self.remaining()]
+    }
+
+    fn advance(&mut self, cnt: usize) {
+        let remaining = self.remaining();
+        assert!(cnt <= remaining);
+        // Use the actual number of remaining bytes as new limit, even if limit
+        // was greater than remaining before.
+        self.set_limit((remaining - cnt) as u64);
+        let slice = self.get_mut();
+        *slice = &slice[cnt..];
+    }
+}
+
 impl Buf for Option<[u8; 1]> {
     fn remaining(&self) -> usize {
         if self.is_some() {

tests/test_buf.rs

@@ -69,3 +69,41 @@ fn test_vec_deque() {
     buffer.copy_to_slice(&mut out);
     assert_eq!(b"world piece", &out[..]);
 }
+
+#[test]
+fn test_take() {
+    // Pulling Read into the scope would result in a conflict between
+    // Buf::bytes() from Read::bytes().
+    let mut buf = std::io::Read::take(&b"hello world"[..], 5);
+    assert_eq!(buf.bytes(), b"hello");
+    assert_eq!(buf.remaining(), 5);
+
+    buf.advance(3);
+    assert_eq!(buf.bytes(), b"lo");
+    assert_eq!(buf.remaining(), 2);
+
+    buf.advance(2);
+    assert_eq!(buf.bytes(), b"");
+    assert_eq!(buf.remaining(), 0);
+}
+
+#[test]
+#[should_panic]
+fn test_take_advance_too_far() {
+    let mut buf = std::io::Read::take(&b"hello world"[..], 5);
+    buf.advance(10);
+}
+
+#[test]
+fn test_take_limit_gt_length() {
+    // The byte array has only 11 bytes, but we take 15 bytes.
+    let mut buf = std::io::Read::take(&b"hello world"[..], 15);
+    assert_eq!(buf.remaining(), 11);
+    assert_eq!(buf.limit(), 15);
+
+    buf.advance(5);
+    assert_eq!(buf.remaining(), 6);
+    // The limit is reduced my more than the number of bytes we advanced, to
+    // the actual number of remaining bytes in the buffer.
+    assert_eq!(buf.limit(), 6);
+}