message: no flush before copy all
diff: @@ -238,7 +238,7 @@ impl<R, W> Future for CopyExactEncrypted<R, W>
  // If our buffer has some data, let's write it out!
  while *pos < *cap {
  - let i = try_nb!(writer.write(&enc_buf[*pos..*cap]).and_then(|x| writer.flush().map(|_| x)));
  + let i = try_nb!(writer.write(&enc_buf[*pos..*cap]));
  *pos += i;
  }
  