websocket_server.py

# Author: Johan Hanssen Seferidis
# License: MIT

import re, sys
import struct
from base64 import b64encode
from hashlib import sha1

if sys.version_info[0] < 3 :
	from SocketServer import ThreadingMixIn, TCPServer, StreamRequestHandler
else:
	from socketserver import ThreadingMixIn, TCPServer, StreamRequestHandler




'''
+-+-+-+-+-------+-+-------------+-------------------------------+
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-------+-+-------------+-------------------------------+
|F|R|R|R| opcode|M| Payload len |    Extended payload length    |
|I|S|S|S|  (4)  |A|     (7)     |             (16/64)           |
|N|V|V|V|       |S|             |   (if payload len==126/127)   |
| |1|2|3|       |K|             |                               |
+-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
|     Extended payload length continued, if payload len == 127  |
+ - - - - - - - - - - - - - - - +-------------------------------+
|                     Payload Data continued ...                |
+---------------------------------------------------------------+
'''

FIN    = 0x80
OPCODE = 0x0f
MASKED = 0x80
PAYLOAD_LEN = 0x7f
PAYLOAD_LEN_EXT16 = 0x7e
PAYLOAD_LEN_EXT64 = 0x7f

OPCODE_TEXT = 0x01
CLOSE_CONN  = 0x8



# -------------------------------- API ---------------------------------

class API():
	def run_forever(self):
		try:
			print("Listening on port %d for clients.." % self.port)
			self.serve_forever()
		except KeyboardInterrupt:
			self.server_close()
			print("Server terminated.")
		except Exception as e:
			print("ERROR: WebSocketsServer: "+str(e))
			exit(1)
	def new_client(self, client, server):
		pass
	def client_left(self, client, server):
		pass
	def message_received(self, client, server, message):
		pass
	def set_fn_new_client(self, fn):
		self.new_client=fn
	def set_fn_client_left(self, fn):
		self.client_left=fn
	def set_fn_message_received(self, fn):
		self.message_received=fn
	def send_message(self, client, msg):
		self._unicast_(client, msg)
	def send_message_to_all(self, msg):
		self._multicast_(msg)



# ------------------------- Implementation -----------------------------

class WebsocketServer(ThreadingMixIn, TCPServer, API):

	allow_reuse_address = True
	daemon_threads = True # comment to keep threads alive until finished

	'''
	clients is a list of dict:
	    {
	     'id'      : id,
	     'handler' : handler,
	     'address' : (addr, port)
	    }
	'''
	clients=[]
	id_counter=0

	def __init__(self, port, host='127.0.0.1'):
		self.port=port
		TCPServer.__init__(self, (host, port), WebSocketHandler)

	def _message_received_(self, handler, msg):
		self.message_received(self.handler_to_client(handler), self, msg)

	def _new_client_(self, handler):
		self.id_counter += 1
		client={
			'id'      : self.id_counter,
			'handler' : handler,
			'address' : handler.client_address
		}
		self.clients.append(client)
		self.new_client(client, self)

	def _client_left_(self, handler):
		client=self.handler_to_client(handler)
		self.client_left(client, self)
		if client in self.clients:
			self.clients.remove(client)
	
	def _unicast_(self, to_client, msg):
		to_client['handler'].send_message(msg)

	def _multicast_(self, msg):
		for client in self.clients:
			self._unicast_(client, msg)
		
	def handler_to_client(self, handler):
		for client in self.clients:
			if client['handler'] == handler:
				return client



class WebSocketHandler(StreamRequestHandler):

	def __init__(self, socket, addr, server):
		self.server=server
		StreamRequestHandler.__init__(self, socket, addr, server)

	def setup(self):
		StreamRequestHandler.setup(self)
		self.keep_alive = True
		self.handshake_done = False
		self.valid_client = False

	def handle(self):
		while self.keep_alive:
			if not self.handshake_done:
				self.handshake()
			elif self.valid_client:
				self.read_next_message()

	def read_bytes(self, num):
		# python3 gives ordinal of byte directly
		bytes = self.rfile.read(num)
		if sys.version_info[0] < 3:
			return map(ord, bytes)
		else:
			return bytes

	def read_next_message(self):

		b1, b2 = self.read_bytes(2)

		fin    = b1 & FIN
		opcode = b1 & OPCODE
		masked = b2 & MASKED
		payload_length = b2 & PAYLOAD_LEN

		if not b1:
			print("Client closed connection.")
			self.keep_alive = 0
			return
		if opcode == CLOSE_CONN:
			print("Client asked to close connection.")
			self.keep_alive = 0
			return
		if not masked:
			print("Client must always be masked.")
			self.keep_alive = 0
			return

		if payload_length == 126:
			payload_length = struct.unpack(">H", self.rfile.read(2))[0]
		elif payload_length == 127:
			payload_length = struct.unpack(">Q", self.rfile.read(8))[0]

		masks = self.read_bytes(4)
		decoded = ""
		for char in self.read_bytes(payload_length):
			char ^= masks[len(decoded) % 4]
			decoded += chr(char)
		self.server._message_received_(self, decoded)

	def send_message(self, message):
		self.send_text(message)

	def send_text(self, message):
		'''
		NOTES
		Fragmented(=continuation) messages are not being used since their usage
		is needed in very limited cases - when we don't know the payload length.
		'''
	
		# Validate message
		if isinstance(message, bytes):
			message = try_decode_UTF8(message) # this is slower but assures we have UTF-8
			if not message:
				print("Can\'t send message, message is not valid UTF-8")
				return False
		elif isinstance(message, str) or isinstance(message, unicode):
			pass
		else:
			print('Can\'t send message, message has to be a string or bytes. Given type is %s' % type(message))
			return False

		header  = bytearray()
		payload = encode_to_UTF8(message)
		payload_length = len(payload)

		# Normal payload
		if payload_length <= 125:
			header.append(FIN | OPCODE_TEXT)
			header.append(payload_length)

		# Extended payload
		elif payload_length >= 126 and payload_length <= 65535:
			header.append(FIN | OPCODE_TEXT)
			header.append(PAYLOAD_LEN_EXT16)
			header.extend(struct.pack(">H", payload_length))

		# Huge extended payload
		elif payload_length < 18446744073709551616:
			header.append(FIN | OPCODE_TEXT)
			header.append(PAYLOAD_LEN_EXT64)
			header.extend(struct.pack(">Q", payload_length))
			
		else:
			raise Exception("Message is too big. Consider breaking it into chunks.")
			return

		self.request.send(header + payload)

	def handshake(self):
		message = self.request.recv(1024).decode().strip()
		upgrade = re.search('\nupgrade[\s]*:[\s]*websocket', message.lower())
		if not upgrade:
			self.keep_alive = False
			return
		key = re.search('\n[sS]ec-[wW]eb[sS]ocket-[kK]ey[\s]*:[\s]*(.*)\r\n', message)
		if key:
			key = key.group(1)
		else:
			print("Client tried to connect but was missing a key")
			self.keep_alive = False
			return
		response = self.make_handshake_response(key)
		self.handshake_done = self.request.send(response.encode())
		self.valid_client = True
		self.server._new_client_(self)
		
	def make_handshake_response(self, key):
		return \
		  'HTTP/1.1 101 Switching Protocols\r\n'\
		  'Upgrade: websocket\r\n'              \
		  'Connection: Upgrade\r\n'             \
		  'Sec-WebSocket-Accept: %s\r\n'        \
		  '\r\n' % self.calculate_response_key(key)
		
	def calculate_response_key(self, key):
		GUID = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11'
		hash = sha1(key.encode() + GUID.encode())
		response_key = b64encode(hash.digest()).strip()
		return response_key.decode('ASCII')

	def finish(self):
		self.server._client_left_(self)



def encode_to_UTF8(data):
	try:
		return data.encode('UTF-8')
	except UnicodeEncodeError as e:
		print("Could not encode data to UTF-8 -- %s" % e)
		return False
	except Exception as e:
		raise(e)
		return False



def try_decode_UTF8(data):
	try:
		return data.decode('utf-8')
	except UnicodeDecodeError:
		return False
	except Exception as e:
		raise(e)
		


# This is only for testing purposes
class DummyWebsocketHandler(WebSocketHandler):
    def __init__(self, *_):
        pass