Websocket handshake problem using Python server

Question

This is a question regarding handshaking in Websocket Protocol 76.

I have written a client and server, but am having trouble getting the client to accept the handshake. I can see that it is being returned, but the client immediately closes the connection. I'm guessing that my md5sum response must be incorrect.

As far as I can tell, I'm following the proper procedure, can anyone tell me what I am doing wrong?

def create_handshake_resp(handshake):

  # parse request
  final_line = ""
  lines = handshake.splitlines()
  for line in lines:
    parts = line.partition(":")
    if parts[0] == "Sec-WebSocket-Key1":
      key1 = parts[2]
    elif parts[0] == "Sec-WebSocket-Key2":
      key2 = parts[2]
    final_line = line

  #concat the keys and encrypt
  e = hashlib.md5()
  e.update(parse_key(key1))
  e.update(parse_key(key2))
  e.update(final_line)
  return "HTTP/1.1 101 WebSocket Protocol Handshake\r\nUpgrade: WebSocket\r\nConnection:     Upgrade\r\nWebSocket-Origin: http://%s\r\nWebSocket-Location: ws://%s/\r\nWebSocket-Protocol: sample\r\n\r\n%s" % (httphost, sockethost, e.digest())



def parse_key(key):

  spaces = -1
  digits = ""
  for c in key:
    if c == " ":
      spaces += 1
    if is_number(c):
      digits = digits + c


  new_key = int(digits) / spaces
  return str(new_key)

As you can see, I am performing what I think to be the correct operations on the keys (divide numbers by space count, concat results and the last line of the request and then MD5) and a 16 byte response is definitely being returned.

Any help would be much appreciated, and as soon as I have a working copy I will post it here.

Thanks.

EDIT:

Changed the headers to comply with kanaka's response. Handshake is still not being accepted by the client. I found out how to display the requests in Chromium, and this is the request and response being given:

(P) t=1291739663323 [st=3101]     WEB_SOCKET_SEND_REQUEST_HEADERS  
                              --> GET / HTTP/1.1   
                                  Upgrade: WebSocket
                                  Connection: Upgrade
                                  Host: ---
                                  Origin: http://---
                                  Sec-WebSocket-Key1: 3E 203C 220 642;
                                  Sec-WebSocket-Key2: Lg 590 ~5 703O G7  =%t 9
                                                   
                                  \x74\x66\xef\xab\x50\x60\x35\xc6\x0a
(P) t=1291739663324 [st=3102]     SOCKET_STREAM_SENT     
(P) t=1291739663348 [st=3126]     SOCKET_STREAM_RECEIVED  
(P) t=1291739663348 [st=3126]     WEB_SOCKET_READ_RESPONSE_HEADERS  
                              --> HTTP/1.1 101 WebSocket Protocol Handshake
                                  Upgrade: WebSocket
                                  Connection: Upgrade
                                  Sec-WebSocket-Origin: http://---
                                  Sec-WebSocket-Location: ws://---/
                                  Sec-WebSocket-Protocol: sample
                                                   
                                  \xe7\x6f\xb9\xcf\xae\x70\x57\x43\xc6\x20\x85\xe7\x39\x2e\x83\xec\x0

Ad verbatim, except I've removed the IP address for obvious reasons.

Your indentation doesn't make sense. I presume the lines #concat..return are meant to be in create_handshake_resp? — Chris Morgan
– Chris Morgan, Commented Dec 7, 2010 at 1:42
You needed the spaces = -1 because you are not ignoring the first space after : in the header (e.g Sec-WebSocket-Key1: a b only contains one space, as far as the response is concerned). Doing line.partition(": ") prevents this — dbr
– dbr, Commented Mar 12, 2011 at 10:50

kanaka · Accepted Answer · 2010-12-07 16:12:49Z

5

You have a couple problems that immediately jump out at me:

You aren't counting spaces properly. You counter should start at 0 not -1.
Your response headers are still v75 style. Any header starting with "WebSocket-" (WebSocket-Origin, WebSocket-Location, WebSocket-Protocol) should instead start with "Sec-WebSocket-" in v76.

Here is how I calculate the response chksum in wsproxy (part of noVNC an HTML5 VNC client):

import struct, md5
...
spaces1 = key1.count(" ")
spaces2 = key2.count(" ")
num1 = int("".join([c for c in key1 if c.isdigit()])) / spaces1
num2 = int("".join([c for c in key2 if c.isdigit()])) / spaces2

return md5(struct.pack('>II8s', num1, num2, key3)).digest()

answered Dec 7, 2010 at 16:12

kanaka

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3 Comments

Jivings Over a year ago

The space count starting at -1 is because when the string is split there is a space in between the : and the key, which shouldn't be counted. I'll try changing the headers to 76, I didn't notice that they had changed. Thanks for your help, I'll let you know the outcome.

Jivings Over a year ago

Still no luck, but I've updated the question to show the request and response.

Jivings Over a year ago

Whahey! I changed my code to your response code and it works :) though I had to include the -1 on spaces.Not sure what was wrong with mine but thanks anyway!

dbr · Accepted Answer · 2011-03-12 11:28:09Z

Here is a working example of a WebSocket client/server (client in Javascript, server in Python 2.6)

It used examples from various places (including kanaka's answer/noVNC, and this page and this page)

Works with Chrome 10.0.648.127, Safari 5.0.3 and MobileSafari on iPad from iOS 4.3

It's by no means well written code (the example HTML page is especially terrible) - use at your own risk and so on..

#!/usr/bin/env python

import socket
import threading
import struct
import hashlib

PORT = 9876


def create_handshake_resp(handshake):
    final_line = ""
    lines = handshake.splitlines()
    for line in lines:
        parts = line.partition(": ")
        if parts[0] == "Sec-WebSocket-Key1":
            key1 = parts[2]
        elif parts[0] == "Sec-WebSocket-Key2":
            key2 = parts[2]
        elif parts[0] == "Host":
            host = parts[2]
        elif parts[0] == "Origin":
            origin = parts[2]
        final_line = line

    spaces1 = key1.count(" ")
    spaces2 = key2.count(" ")
    num1 = int("".join([c for c in key1 if c.isdigit()])) / spaces1
    num2 = int("".join([c for c in key2 if c.isdigit()])) / spaces2

    token = hashlib.md5(struct.pack('>II8s', num1, num2, final_line)).digest()

    return (
        "HTTP/1.1 101 WebSocket Protocol Handshake\r\n"
        "Upgrade: WebSocket\r\n"
        "Connection: Upgrade\r\n"
        "Sec-WebSocket-Origin: %s\r\n"
        "Sec-WebSocket-Location: ws://%s/\r\n"
        "\r\n"
        "%s") % (
        origin, host, token)


def handle(s, addr):
    data = s.recv(1024)
    s.send(create_handshake_resp(data))
    lock = threading.Lock()

    while 1:
        print "Waiting for data from", s, addr
        data = s.recv(1024)
        print "Done"
        if not data:
            print "No data"
            break

        print 'Data from', addr, ':', data

        # Broadcast received data to all clients
        lock.acquire()
        [conn.send(data) for conn in clients]
        lock.release()

    print 'Client closed:', addr
    lock.acquire()
    clients.remove(s)
    lock.release()
    s.close()

def start_server():
    s = socket.socket()
    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    s.bind(('', PORT))
    s.listen(1)
    while 1:
        conn, addr = s.accept()
        print 'Connected by', addr
        clients.append(conn)
        threading.Thread(target = handle, args = (conn, addr)).start()

clients = []
start_server()

Also, a crappy example HTML page to show it working:

<!DOCTYPE html>
<html lang="en">
    <head>
        <title>Test</title>
        <script type="application/javascript">
            var ws;

            function init() {
                var servermsg = document.getElementById("servermsg");

                ws = new WebSocket("ws://localhost:9876/");
                ws.onopen = function(){
                    servermsg.innerHTML = servermsg.innerHTML + "<br>Server connected";
                    servermsg.innerHTML = servermsg.innerHTML + "<br>Sending message to server";
                    ws.send("Hello Mr. Server!");
                };
                ws.onmessage = function(e){
                    servermsg.innerHTML = servermsg.innerHTML + "<br>Recieved data: " + e.data;
                };
                ws.onclose = function(){
                    console.log("Server disconnected");
                    servermsg.innerHTML = servermsg.innerHTML + "<br>Connected";
                };
            }
            function postmsg(){
                var text = document.getElementById("message").value;
                ws.send(text);
                servermsg.innerHTML = servermsg.innerHTML + "<br>Sent: " + text;
                return false;
            }
        </script>
    </head>
    <body onload="init();">
        <form action="" onSubmit="postmsg()">
            <input type="text" name="message" value="" id="message">
            <input type="submit" name="submit" value="" id="submit">
        </form>
        <div id="servermsg"><h1>Message log:</h1></div>
    </body>
</html>

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