lua client uses two write() calls per framed message send

1) realize thrift server with TNonblockingServer via c++;

2) realize thrift client via lua lib and choose frame transport.

3) call remote interface failed with "TTransportException:0: Default (unknown)" print, and the server show "TConnection::workSocket(): THRIFT_EAGAIN (unavailable resources)" error.

4)investigate this fault with tcpdump tool, attachment 9090.pcap show the frame msg doesnot contains frame size field, the rifht situation of attachment 9090_1.pcap show the frame msg contains 4 bytes (00 00 00 25) before protocol id field.

5) dig into the fault and tried to find root cause, then i found there is an fault in TFramedTransport:flush function in TFramedTransport.lua file. the original realization is:

function TFramedTransport:flush()
  if self.doWrite == false then
    return self.trans:flush()
  end

  – If the write fails we still want wBuf to be clear
  local tmp = self.wBuf
  self.wBuf = ''
  local frame_len_buf = libluabpack.bpack("i", string.len(tmp))
  self.trans:write(frame_len_buf)
  self.trans:write(tmp)
  self.trans:flush()
end

which send frame size file and reset msg content independently.