unsafe impl<'a> BufMut for ReadBuf<'a>

tokio/src/io/read_buf.rs

@@ -270,6 +270,26 @@ impl<'a> ReadBuf<'a> {
     }
 }
 
+#[cfg(feature = "io-util")]
+#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+unsafe impl<'a> bytes::BufMut for ReadBuf<'a> {
+    fn remaining_mut(&self) -> usize {
+        self.remaining()
+    }
+
+    unsafe fn advance_mut(&mut self, cnt: usize) {
+        self.advance(cnt);
+    }
+
+    fn chunk_mut(&mut self) -> &mut bytes::buf::UninitSlice {
+        unsafe {
+            let len = self.unfilled_mut().len();
+            let ptr = self.unfilled_mut().as_mut_ptr();
+            bytes::buf::UninitSlice::from_raw_parts_mut(ptr as *mut u8, len)
+        }
+    }
+}
+
 impl fmt::Debug for ReadBuf<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("ReadBuf")

tokio/tests/io_read_buf.rs

@@ -34,3 +34,41 @@ async fn read_buf() {
     assert_eq!(n, 11);
     assert_eq!(buf[..], b"hello world"[..]);
 }
+
+#[tokio::test]
+#[cfg(feature = "io-util")]
+async fn issue_5588() {
+    use bytes::BufMut;
+
+    // steps to zero
+    let mut buf = [0; 8];
+    let mut read_buf = ReadBuf::new(&mut buf);
+    assert_eq!(read_buf.remaining_mut(), 8);
+    assert_eq!(read_buf.remaining_mut(), 8);
+    unsafe {
+        read_buf.advance_mut(1);
+    }
+    assert_eq!(read_buf.remaining_mut(), 7);
+    assert_eq!(read_buf.remaining_mut(), 7);
+    unsafe {
+        read_buf.advance_mut(5);
+    }
+    assert_eq!(read_buf.remaining_mut(), 2);
+    assert_eq!(read_buf.remaining_mut(), 2);
+    unsafe {
+        read_buf.advance_mut(2);
+    }
+    assert_eq!(read_buf.remaining_mut(), 0);
+    assert_eq!(read_buf.remaining_mut(), 0);
+
+    // directly to zero
+    let mut buf = [0; 8];
+    let mut read_buf = ReadBuf::new(&mut buf);
+    assert_eq!(read_buf.remaining_mut(), 8);
+    assert_eq!(read_buf.chunk_mut().len(), 8);
+    unsafe {
+        read_buf.advance_mut(8);
+    }
+    assert_eq!(read_buf.remaining_mut(), 0);
+    assert_eq!(read_buf.chunk_mut().len(), 0);
+}