code: private HandshakeResponse build400Response(WebSocketConnection conn) throws WebSocketException {
          if (log.isDebugEnabled()) {
              log.debug("build400Response: {}", conn);
          }
          // make up reply data...
          IoBuffer buf = IoBuffer.allocate(32);
          buf.setAutoExpand(true);
          buf.put("HTTP/1.1 400 Bad Request".getBytes());
          buf.put(Constants.CRLF);
          buf.put("Sec-WebSocket-Version-Server: 13".getBytes());
          buf.put(Constants.CRLF);
          buf.put(Constants.CRLF);
          if (log.isTraceEnabled()) {
              log.trace("Handshake error response size: {}", buf.limit());
          }
          return new HandshakeResponse(buf);
      }
docs: Build an HTTP 400 "Bad Request" response.
  
  @return response
  @throws WebSocketException