code: public void writeHeader(Writer writer) throws IOException
      {
          if (_state != __MSG_EDITABLE) throw new IllegalStateException("Not MSG_EDITABLE");
  
          _state = __MSG_BAD;
          writeRequestLine(writer);
          writer.write(HttpFields.__CRLF);
          _header.write(writer);
          _state = __MSG_SENDING;
      }
docs: Write the request header. Places the message in __MSG_SENDING state.
  
  @param writer Http output stream
  @exception IOException IO problem