message: perf(http): reduce a copy when not using Chunked encoding
diff: @@ -242,10 +242,14 @@ impl<T: Write + ::vecio::Writev> AtomicWrite for T {
  */
  impl<T: Write> AtomicWrite for T {
  fn write_atomic(&mut self, bufs: &[&[u8]]) -> io::Result<usize> {
  + if bufs.len() == 1 {
  + self.write(bufs[0])
  + } else {
  let vec = bufs.concat();
  self.write(&vec)
  }
  }
  +}
  //}
  // an internal buffer to collect writes before flushes
  