python CGI : upload error

I use Python version 3.4

and this is server source code in python

import io
from socket import *
import threading
import cgi

serverPort = 8181
serverSocket = socket(AF_INET, SOCK_STREAM)
serverSocket.bind(('', serverPort))
serverSocket.listen(5)


def serverHandle(connectionSocket, addr):     
    try:
        message = connectionSocket.recv(1024)

        if not message:
            return

        path = message.split()[1].decode('utf-8')

        if path == '/':
            connectionSocket.send(b'HTTP/1.1 200 OK\r\n')
            connectionSocket.send(b'Content-type: text/html\r\n\r\n')
            with open('upload.html', 'rb') as f:
                connectionSocket.send(f.read())

        elif path == '/upload':
            header = message.split(b'\r\n\r\n')[0]
            query = message.split(b'\r\n\r\n')[-1]

            if not query:
                return

            fp = io.BytesIO(query)

            form = cgi.FieldStorage(fp, environ={'REQUEST_METHOD':'POST', 'CONTENT_TYPE': 'multipart/form-data'})

            f = open(form.filename, 'w')
            f.write(form.file)
            f.close()

        connectionSocket.close()

    except IOError:
        connectionSocket.send('404 File Not Found\r\n\r\n'.encode('utf_8'))
        connectionSocket.close()

while True:
    connectionSocket, addr = serverSocket.accept();
    threading._start_new_thread(serverHandle, (connectionSocket, addr))
serverSocket.close()

and upload HTML source is here

<HTML>
    <BODY>
        <FORM ENCTYPE="multipart/form-data" ACTION="http://127.0.0.1:8181/upload" METHOD=POST>
        File to process: <INPUT NAME="file" TYPE="file">
        <INPUT TYPE="submit" VALUE="Send File">
        </FORM>
    </BODY>
</HTML>

I try upload file to server and save file in directory but error is occurred like this

Unhandled exception in thread started by <function serverHandle at 0x000000000240CBF8>
Traceback (most recent call last):
  File "C:\Users\Inwoo\Eclipse\workspace\WebServer\src\webserver1.py", line 36, in serverHandle
    form = cgi.FieldStorage(fp, environ={'REQUEST_METHOD':'POST', 'CONTENT_TYPE': 'multipart/form-data'})
  File "C:\Python34\lib\cgi.py", line 559, in __init__
    self.read_multi(environ, keep_blank_values, strict_parsing)
  File "C:\Python34\lib\cgi.py", line 681, in read_multi
    raise ValueError('Invalid boundary in multipart form: %r' % (ib,))
ValueError: Invalid boundary in multipart form: b''

I cant understand this problem?

and sometimes query of message is empty!

so I wrote if not query: return, is it correct?

and how can I receive uploaded file and save them in server?

You need to not split the query on as many newlines as you do; there can be embedded newlines in it. Use str.partition() instead here:

header, _, query = message.partition(b'\r\n\r\n')

You'll have to parse the headers; the Content-Type header contains the multipart boundary; the FieldStorage instance needs this to determine where the fields begin and end.

import re

content_type = re.search(br'content-type:\s+(.*?)\r\n', header, flags=re.I).group(1)

form = cgi.FieldStorage(fp, environ={'REQUEST_METHOD':'POST', 'CONTENT_TYPE': content_type})

Take into account that a HTTP message with a file upload can easily contain much more that 1024 bytes; you only ever read that little. Just the headers can easily make up most of the message; my browser sends 819 bytes for the header and keeps that in one packet. Your connectionSocket.recv(1024) call will then contain just those headers and you'll need to read more data still.