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POWebsocket implementation in Python 3
 

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    <p>Trying to create a web-front end for a Python3 backed application. The application will require bi-directional streaming which sounded like a good opportunity to look into websockets.</p> <p>My first inclination was to use something already existing, and the example applications from <em>mod-pywebsocket</em> have proved valuable. Unfortunately their API doesn't appear to easily lend itself to extension, and it is Python2.</p> <p>Looking around the blogosphere many people have written their own websocket server for earlier versions of the websocket protocol, most don't implement the security key hash so dont' work.</p> <p>Reading <a href="http://tools.ietf.org/html/rfc6455">RFC 6455</a> I decided to take a stab at it myself and came up with the following:</p> <pre><code>#!/usr/bin/env python3 """ A partial implementation of RFC 6455 http://tools.ietf.org/pdf/rfc6455.pdf Brian Thorne 2012 """ import socket import threading import time import base64 import hashlib def calculate_websocket_hash(key): magic_websocket_string = b"258EAFA5-E914-47DA-95CA-C5AB0DC85B11" result_string = key + magic_websocket_string sha1_digest = hashlib.sha1(result_string).digest() response_data = base64.encodestring(sha1_digest) response_string = response_data.decode('utf8') return response_string def is_bit_set(int_type, offset): mask = 1 &lt;&lt; offset return not 0 == (int_type &amp; mask) def set_bit(int_type, offset): return int_type | (1 &lt;&lt; offset) def bytes_to_int(data): # note big-endian is the standard network byte order return int.from_bytes(data, byteorder='big') def pack(data): """pack bytes for sending to client""" frame_head = bytearray(2) # set final fragment frame_head[0] = set_bit(frame_head[0], 7) # set opcode 1 = text frame_head[0] = set_bit(frame_head[0], 0) # payload length assert len(data) &lt; 126, "haven't implemented that yet" frame_head[1] = len(data) # add data frame = frame_head + data.encode('utf-8') print(list(hex(b) for b in frame)) return frame def receive(s): """receive data from client""" # read the first two bytes frame_head = s.recv(2) # very first bit indicates if this is the final fragment print("final fragment: ", is_bit_set(frame_head[0], 7)) # bits 4-7 are the opcode (0x01 -&gt; text) print("opcode: ", frame_head[0] &amp; 0x0f) # mask bit, from client will ALWAYS be 1 assert is_bit_set(frame_head[1], 7) # length of payload # 7 bits, or 7 bits + 16 bits, or 7 bits + 64 bits payload_length = frame_head[1] &amp; 0x7F if payload_length == 126: raw = s.recv(2) payload_length = bytes_to_int(raw) elif payload_length == 127: raw = s.recv(8) payload_length = bytes_to_int(raw) print('Payload is {} bytes'.format(payload_length)) """masking key All frames sent from the client to the server are masked by a 32-bit nounce value that is contained within the frame """ masking_key = s.recv(4) print("mask: ", masking_key, bytes_to_int(masking_key)) # finally get the payload data: masked_data_in = s.recv(payload_length) data = bytearray(payload_length) # The ith byte is the XOR of byte i of the data with # masking_key[i % 4] for i, b in enumerate(masked_data_in): data[i] = b ^ masking_key[i%4] return data def handle(s): client_request = s.recv(4096) # get to the key for line in client_request.splitlines(): if b'Sec-WebSocket-Key:' in line: key = line.split(b': ')[1] break response_string = calculate_websocket_hash(key) header = '''HTTP/1.1 101 Switching Protocols\r Upgrade: websocket\r Connection: Upgrade\r Sec-WebSocket-Accept: {}\r \r '''.format(response_string) s.send(header.encode()) # this works print(receive(s)) # this doesn't s.send(pack('Hello')) s.close() s = socket.socket( socket.AF_INET, socket.SOCK_STREAM) s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) s.bind(('', 9876)) s.listen(1) while True: t,_ = s.accept() threading.Thread(target=handle, args = (t,)).start() </code></pre> <p>Using this basic test page (which works with mod-pywebsocket):</p> <pre><code>&lt;!DOCTYPE html&gt; &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt; &lt;head&gt; &lt;title&gt;Web Socket Example&lt;/title&gt; &lt;meta charset="UTF-8"&gt; &lt;/head&gt; &lt;body&gt; &lt;div id="serveroutput"&gt;&lt;/div&gt; &lt;form id="form"&gt; &lt;input type="text" value="Hello World!" id="msg" /&gt; &lt;input type="submit" value="Send" onclick="sendMsg()" /&gt; &lt;/form&gt; &lt;script&gt; var form = document.getElementById('form'); var msg = document.getElementById('msg'); var output = document.getElementById('serveroutput'); var s = new WebSocket("ws://"+window.location.hostname+":9876"); s.onopen = function(e) { console.log("opened"); out('Connected.'); } s.onclose = function(e) { console.log("closed"); out('Connection closed.'); } s.onmessage = function(e) { console.log("got: " + e.data); out(e.data); } form.onsubmit = function(e) { e.preventDefault(); msg.value = ''; window.scrollTop = window.scrollHeight; } function sendMsg() { s.send(msg.value); } function out(text) { var el = document.createElement('p'); el.innerHTML = text; output.appendChild(el); } msg.focus(); &lt;/script&gt; &lt;/body&gt; &lt;/html&gt; </code></pre> <p>This receives data and demasks it correctly, but I can't get the transmit path to work.</p> <p>As a test to write "Hello" to the socket, the program above calculates the bytes to be written to the socket as:</p> <pre><code>['0x81', '0x5', '0x48', '0x65', '0x6c', '0x6c', '0x6f'] </code></pre> <p>Which match the hex values given in <a href="http://tools.ietf.org/html/rfc6455#section-5.7">section 5.7</a> of the RFC. Unfortunately the frame never shows up in Chrome's Developer Tools.</p> <p>Any idea what I'm missing? Or a currently working Python3 websocket example?</p>
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    1. COTornado supports both websockets and Python 3. http://www.tornadoweb.org/documentation/websocket.html
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    2. COThanks Thomas. I'd like to have a standalone implementation first though - this is as much about understanding the protocol as solving a problem for me. Taking a look at the [tornado source code](https://github.com/facebook/tornado/blob/master/tornado/websocket.py) I see one header **Sec-WebSocket-Protocol** being sent from the server to the client, but the [spec](http://tools.ietf.org/html/rfc6455#section-4.2.2) says that is optional.
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    3. COIf a client requests a sub-protocol, the server is expected to echo it (always assuming it supports the sub-protocol). Failure to do so would cause a handshake error so this probably isn't related to your message sending problems.
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