Implement chunks_vectored for VecDeque<u8>

Author: paolobarbolini

src/buf/vec_deque.rs

@@ -1,4 +1,6 @@
 use alloc::collections::VecDeque;
+#[cfg(feature = "std")]
+use std::io;
 
 use super::Buf;
 
@@ -16,6 +18,22 @@ impl Buf for VecDeque<u8> {
         }
     }
 
+    #[cfg(feature = "std")]
+    fn chunks_vectored<'a>(&'a self, dst: &mut [io::IoSlice<'a>]) -> usize {
+        if self.is_empty() || dst.is_empty() {
+            return 0;
+        }
+
+        let (s1, s2) = self.as_slices();
+        dst[0] = io::IoSlice::new(s1);
+        if s2.is_empty() || dst.len() == 1 {
+            return 1;
+        }
+
+        dst[1] = io::IoSlice::new(s2);
+        2
+    }
+
     fn advance(&mut self, cnt: usize) {
         self.drain(..cnt);
     }

tests/test_buf.rs

@@ -1,5 +1,7 @@
 #![warn(rust_2018_idioms)]
 
+use std::collections::VecDeque;
+
 use bytes::Buf;
 #[cfg(feature = "std")]
 use std::io::IoSlice;
@@ -58,9 +60,7 @@ fn test_bufs_vec() {
 
 #[test]
 fn test_vec_deque() {
-    use std::collections::VecDeque;
-
-    let mut buffer: VecDeque<u8> = VecDeque::new();
+    let mut buffer = VecDeque::new();
     buffer.extend(b"hello world");
     assert_eq!(11, buffer.remaining());
     assert_eq!(b"hello world", buffer.chunk());
@@ -72,6 +72,41 @@ fn test_vec_deque() {
     assert_eq!(b"world piece", &out[..]);
 }
 
+#[cfg(feature = "std")]
+#[test]
+fn test_vec_deque_vectored() {
+    let mut buffer = VecDeque::new();
+    buffer.reserve_exact(128);
+    assert_eq!(buffer.chunks_vectored(&mut [IoSlice::new(&[])]), 0);
+
+    buffer.extend(0..64);
+    buffer.drain(..32);
+    buffer.extend(64..160);
+
+    assert_eq!(buffer.chunks_vectored(&mut []), 0);
+
+    let mut chunks = [IoSlice::new(&[]); 1];
+    assert_eq!(buffer.chunks_vectored(&mut chunks), 1);
+    assert!(!chunks[0].is_empty());
+    let combined = chunks[0].iter().copied().collect::<Vec<u8>>();
+    let expected = (32..160).take(chunks[0].len()).collect::<Vec<_>>();
+    assert_eq!(combined, expected);
+
+    let mut chunks = [IoSlice::new(&[]); 2];
+    assert_eq!(buffer.chunks_vectored(&mut chunks), 2);
+    assert!(!chunks[0].is_empty());
+    assert!(!chunks[1].is_empty());
+    let combined = chunks
+        .iter()
+        .flat_map(|chunk| chunk.iter())
+        .copied()
+        .collect::<Vec<u8>>();
+    let expected = (32..160).collect::<Vec<u8>>();
+    assert_eq!(combined, expected);
+
+    assert_eq!(buffer.chunks_vectored(&mut [IoSlice::new(&[]); 8]), 2);
+}
+
 #[allow(unused_allocation)] // This is intentional.
 #[test]
 fn test_deref_buf_forwards() {