Merge pull request #54 from Chandler/websockets

Netlib WebSockets take 1

netlib/utils.py

@@ -8,6 +8,9 @@ def isascii(s):
         return False
     return True
 
+# best way to do it in python 2.x
+def bytes_to_int(i):
+  return int(i.encode('hex'), 16)
 
 def cleanBin(s, fixspacing=False):
     """

netlib/websockets/__init__.py

@@ -0,0 +1 @@
+from __future__ import (absolute_import, print_function, division)

netlib/websockets/implementations.py

@@ -0,0 +1,80 @@
+from netlib import tcp
+from base64 import b64encode
+from StringIO import StringIO
+from . import websockets as ws
+import struct
+import SocketServer
+import os
+
+# Simple websocket client and servers that are used to exercise the functionality in websockets.py
+# These are *not* fully RFC6455 compliant
+
+class WebSocketsEchoHandler(tcp.BaseHandler): 
+    def __init__(self, connection, address, server):
+        super(WebSocketsEchoHandler, self).__init__(connection, address, server)
+        self.handshake_done = False
+
+    def handle(self):
+       while True:
+          if not self.handshake_done:
+              self.handshake()
+          else:
+              self.read_next_message()
+
+    def read_next_message(self):
+        decoded = ws.WebSocketsFrame.from_byte_stream(self.rfile.read).decoded_payload
+        self.on_message(decoded)
+
+    def send_message(self, message):
+        frame = ws.WebSocketsFrame.default(message, from_client = False)
+        self.wfile.write(frame.safe_to_bytes())
+        self.wfile.flush()
+ 
+    def handshake(self):
+        client_hs = ws.read_handshake(self.rfile.read, 1)
+        key       = ws.process_handshake_from_client(client_hs)
+        response  = ws.create_server_handshake(key)
+        self.wfile.write(response)
+        self.wfile.flush()
+        self.handshake_done = True
+
+    def on_message(self, message):
+        if message is not None:
+            self.send_message(message)
+
+
+class WebSocketsClient(tcp.TCPClient):
+    def __init__(self, address, source_address=None):
+        super(WebSocketsClient, self).__init__(address, source_address)
+        self.version       = "13"
+        self.client_nounce = ws.create_client_nounce()
+        self.resource      = "/"
+
+    def connect(self):
+        super(WebSocketsClient, self).connect()
+
+        handshake = ws.create_client_handshake(
+            self.address.host,
+            self.address.port,
+            self.client_nounce,
+            self.version,
+            self.resource
+        )
+
+        self.wfile.write(handshake)
+        self.wfile.flush()
+
+        server_handshake = ws.read_handshake(self.rfile.read, 1)
+
+        server_nounce = ws.process_handshake_from_server(server_handshake, self.client_nounce)
+
+        if not server_nounce == ws.create_server_nounce(self.client_nounce):
+            self.close()
+
+    def read_next_message(self):
+        return ws.WebSocketsFrame.from_byte_stream(self.rfile.read).payload
+
+    def send_message(self, message):
+        frame = ws.WebSocketsFrame.default(message, from_client = True)
+        self.wfile.write(frame.safe_to_bytes())
+        self.wfile.flush()

netlib/websockets/websockets.py

@@ -0,0 +1,389 @@
+from __future__ import absolute_import
+
+from base64 import b64encode
+from hashlib import sha1
+from mimetools import Message
+from netlib import tcp
+from netlib import utils
+from StringIO import StringIO
+import os
+import SocketServer
+import struct
+import io
+
+# Colleciton of utility functions that implement small portions of the RFC6455 WebSockets Protocol
+# Useful for building WebSocket clients and servers. 
+#
+# Emphassis is on readabilty, simplicity and modularity, not performance or completeness
+#
+# This is a work in progress and does not yet contain all the utilites need to create fully complient client/servers
+#
+# Spec: https://tools.ietf.org/html/rfc6455
+
+# The magic sha that websocket servers must know to prove they understand RFC6455
+websockets_magic = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11'
+
+class WebSocketFrameValidationException(Exception):
+    pass
+
+class WebSocketsFrame(object):
+    """
+        Represents one websockets frame.
+        Constructor takes human readable forms of the frame components
+        from_bytes() is also avaliable.
+
+        WebSockets Frame as defined in RFC6455
+       
+          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  |
+         + - - - - - - - - - - - - - - - +-------------------------------+
+         |                               |Masking-key, if MASK set to 1  |
+         +-------------------------------+-------------------------------+
+         | Masking-key (continued)       |          Payload Data         |
+         +-------------------------------- - - - - - - - - - - - - - - - +
+         :                     Payload Data continued ...                :
+         + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
+         |                     Payload Data continued ...                |
+         +---------------------------------------------------------------+
+    """
+    def __init__(
+        self,
+        fin,                          # decmial integer 1 or 0
+        opcode,                       # decmial integer 1 - 4
+        mask_bit,                     # decimal integer 1 or 0
+        payload_length_code,          # decimal integer 1 - 127
+        decoded_payload,              # bytestring
+        rsv1                  = 0,    # decimal integer 1 or 0
+        rsv2                  = 0,    # decimal integer 1 or 0
+        rsv3                  = 0,    # decimal integer 1 or 0
+        payload               = None, # bytestring 
+        masking_key           = None, # 32 bit byte string
+        actual_payload_length = None, # any decimal integer
+    ):
+        self.fin                   = fin
+        self.rsv1                  = rsv1
+        self.rsv2                  = rsv2
+        self.rsv3                  = rsv3
+        self.opcode                = opcode
+        self.mask_bit              = mask_bit
+        self.payload_length_code   = payload_length_code
+        self.masking_key           = masking_key
+        self.payload               = payload
+        self.decoded_payload       = decoded_payload
+        self.actual_payload_length = actual_payload_length
+
+    @classmethod
+    def from_bytes(cls, bytestring):
+        """
+          Construct a websocket frame from an in-memory bytestring
+          to construct a frame from a stream of bytes, use from_byte_stream() directly
+        """ 
+        return cls.from_byte_stream(io.BytesIO(bytestring).read)
+
+
+    @classmethod
+    def default(cls, message, from_client = False):
+        """
+          Construct a basic websocket frame from some default values. 
+          Creates a non-fragmented text frame.
+        """ 
+        length_code, actual_length = get_payload_length_pair(message)
+
+        if from_client:
+            mask_bit    = 1
+            masking_key = random_masking_key()
+            payload     = apply_mask(message, masking_key)
+        else:
+            mask_bit    = 0
+            masking_key = None
+            payload     = message
+        
+        return cls(
+            fin                   = 1, # final frame
+            opcode                = 1, # text
+            mask_bit              = mask_bit,
+            payload_length_code   = length_code,
+            payload               = payload,
+            masking_key           = masking_key,
+            decoded_payload       = message,
+            actual_payload_length = actual_length
+        )
+
+    def is_valid(self):
+        """
+         Validate websocket frame invariants, call at anytime to ensure the WebSocketsFrame
+         has not been corrupted.
+        """ 
+        try: 
+            assert 0 <= self.fin <= 1
+            assert 0 <= self.rsv1 <= 1
+            assert 0 <= self.rsv2 <= 1
+            assert 0 <= self.rsv3 <= 1
+            assert 1 <= self.opcode <= 4
+            assert 0 <= self.mask_bit <= 1
+            assert 1 <= self.payload_length_code <= 127
+            
+            if self.mask_bit == 1:
+                assert 1 <= len(self.masking_key) <= 4
+            else:
+                assert self.masking_key == None
+            
+            assert self.actual_payload_length == len(self.payload)
+
+            if self.payload is not None and self.masking_key is not None:
+                assert apply_mask(self.payload, self.masking_key) == self.decoded_payload
+
+            return True 
+        except AssertionError:
+            return False
+
+    def human_readable(self):
+        return "\n".join([
+          ("fin                   - " + str(self.fin)),
+          ("rsv1                  - " + str(self.rsv1)),
+          ("rsv2                  - " + str(self.rsv2)),
+          ("rsv3                  - " + str(self.rsv3)),
+          ("opcode                - " + str(self.opcode)),
+          ("mask_bit              - " + str(self.mask_bit)),
+          ("payload_length_code   - " + str(self.payload_length_code)),
+          ("masking_key           - " + str(self.masking_key)),
+          ("payload               - " + str(self.payload)),
+          ("decoded_payload       - " + str(self.decoded_payload)),
+          ("actual_payload_length - " + str(self.actual_payload_length))])
+
+    def safe_to_bytes(self):
+        if self.is_valid():
+            return self.to_bytes()
+        else:
+            raise WebSocketFrameValidationException()
+
+    def to_bytes(self):
+        """
+          Serialize the frame back into the wire format, returns a bytestring
+          If you haven't checked is_valid_frame() then there's no guarentees that the
+          serialized bytes will be correct. see safe_to_bytes()
+        """ 
+
+        max_16_bit_int = (1 << 16)
+        max_64_bit_int = (1 << 63)
+
+        # break down of the bit-math used to construct the first byte from the frame's integer values
+        # first shift the significant bit into the correct position  
+        # 00000001 << 7 = 10000000
+        # ...
+        # then combine:
+        # 
+        # 10000000 fin
+        # 01000000 res1
+        # 00100000 res2
+        # 00010000 res3
+        # 00000001 opcode
+        # -------- OR 
+        # 11110001   = first_byte
+
+        first_byte  = (self.fin << 7) | (self.rsv1 << 6) | (self.rsv2 << 4) | (self.rsv3 << 4) | self.opcode
+        
+        second_byte = (self.mask_bit << 7) | self.payload_length_code
+
+        bytes = chr(first_byte) + chr(second_byte)
+
+        if self.actual_payload_length < 126:
+            pass
+
+        elif self.actual_payload_length < max_16_bit_int:
+
+            # '!H' pack as 16 bit unsigned short
+            bytes += struct.pack('!H', self.actual_payload_length) # add 2 byte extended payload length
+        
+        elif self.actual_payload_length < max_64_bit_int:
+            # '!Q' = pack as 64 bit unsigned long long
+            bytes += struct.pack('!Q', self.actual_payload_length) # add 8 bytes extended payload length
+
+        if self.masking_key is not None:
+            bytes += self.masking_key
+
+        bytes += self.payload # already will be encoded if neccessary
+
+        return bytes
+
+
+    @classmethod
+    def from_byte_stream(cls, read_bytes):
+        """
+          read a websockets frame sent by a server or client
+      
+          read_bytes is a function that can be backed
+          by sockets or by any byte reader. So this 
+          function may be used to read frames from disk/wire/memory
+        """ 
+        first_byte  = utils.bytes_to_int(read_bytes(1))
+        second_byte = utils.bytes_to_int(read_bytes(1))
+        
+        fin            = first_byte  >> 7  # grab the left most bit
+        opcode         = first_byte  & 15  # grab right most 4 bits by and-ing with 00001111
+        mask_bit       = second_byte >> 7  # grab left most bit
+        payload_length = second_byte & 127 # grab the next 7 bits
+
+        # payload_lengthy > 125 indicates you need to read more bytes
+        # to get the actual payload length
+        if payload_length <= 125:
+           actual_payload_length = payload_length
+
+        elif payload_length == 126:
+           actual_payload_length = utils.bytes_to_int(read_bytes(2))
+
+        elif payload_length == 127: 
+           actual_payload_length = utils.bytes_to_int(read_bytes(8))
+
+        # masking key only present if mask bit set
+        if mask_bit == 1:
+            masking_key = read_bytes(4)
+        else:
+            masking_key = None
+        
+        payload = read_bytes(actual_payload_length)
+        
+        if mask_bit == 1:
+            decoded_payload = apply_mask(payload, masking_key)
+        else:
+            decoded_payload = payload
+
+        return cls(
+            fin                   = fin,
+            opcode                = opcode,
+            mask_bit              = mask_bit,
+            payload_length_code   = payload_length,
+            payload               = payload,
+            masking_key           = masking_key,
+            decoded_payload       = decoded_payload,
+            actual_payload_length = actual_payload_length
+        )
+
+    def __eq__(self, other):
+        return (
+         self.fin                   == other.fin and
+         self.rsv1                  == other.rsv1 and
+         self.rsv2                  == other.rsv2 and
+         self.rsv3                  == other.rsv3 and
+         self.opcode                == other.opcode and
+         self.mask_bit              == other.mask_bit and
+         self.payload_length_code   == other.payload_length_code and
+         self.masking_key           == other.masking_key and
+         self.payload               == other.payload and
+         self.decoded_payload       == other.decoded_payload and
+         self.actual_payload_length == other.actual_payload_length)
+
+def apply_mask(message, masking_key):
+    """
+    Data sent from the server must be masked to prevent malicious clients
+    from sending data over the wire in predictable patterns
+
+    This method both encodes and decodes strings with the provided mask
+
+    Servers do not have to mask data they send to the client.
+    https://tools.ietf.org/html/rfc6455#section-5.3
+    """
+    masks = [utils.bytes_to_int(byte) for byte in masking_key]
+    result = ""
+    for char in message:
+        result += chr(ord(char) ^ masks[len(result) % 4])
+    return result
+
+def random_masking_key():
+    return os.urandom(4)
+
+def create_client_handshake(host, port, key, version, resource):
+    """
+      WebSockets connections are intiated by the client with a valid HTTP upgrade request
+    """
+    headers = [
+        ('Host', '%s:%s' % (host, port)),
+        ('Connection', 'Upgrade'),
+        ('Upgrade', 'websocket'),
+        ('Sec-WebSocket-Key', key),
+        ('Sec-WebSocket-Version', version)
+    ]
+    request = "GET %s HTTP/1.1" % resource
+    return build_handshake(headers, request)
+
+def create_server_handshake(key):
+    """
+      The server response is a valid HTTP 101 response. 
+    """ 
+    headers = [
+        ('Connection', 'Upgrade'),
+        ('Upgrade', 'websocket'),
+        ('Sec-WebSocket-Accept', create_server_nounce(key))
+    ]
+    request = "HTTP/1.1 101 Switching Protocols"
+    return build_handshake(headers, request)
+
+
+def build_handshake(headers, request):
+    handshake = [request.encode('utf-8')]
+    for header, value in headers:
+        handshake.append(("%s: %s" % (header, value)).encode('utf-8'))
+    handshake.append(b'\r\n')
+    return b'\r\n'.join(handshake)
+
+def read_handshake(read_bytes, num_bytes_per_read):
+    """
+      From provided function that reads bytes, read in a 
+      complete HTTP request, which terminates with a CLRF
+    """ 
+    response   = b''
+    doubleCLRF = b'\r\n\r\n'
+    while True:
+        bytes = read_bytes(num_bytes_per_read)
+        if not bytes:
+            break
+        response += bytes
+        if doubleCLRF in response:
+            break
+    return response
+
+def get_payload_length_pair(payload_bytestring):
+    """
+     A websockets frame contains an initial length_code, and an optional
+     extended length code to represent the actual length if length code is larger
+     than 125
+    """ 
+    actual_length = len(payload_bytestring)
+  
+    if actual_length <= 125:
+        length_code = actual_length
+    elif actual_length >= 126 and actual_length <= 65535:
+        length_code = 126
+    else:
+        length_code = 127
+    return (length_code, actual_length)
+
+def process_handshake_from_client(handshake):
+    headers = headers_from_http_message(handshake)
+    if headers.get("Upgrade", None) != "websocket":
+        return
+    key = headers['Sec-WebSocket-Key']
+    return key
+
+def process_handshake_from_server(handshake, client_nounce):
+    headers = headers_from_http_message(handshake)
+    if headers.get("Upgrade", None) != "websocket":
+        return
+    key = headers['Sec-WebSocket-Accept']
+    return key
+
+def headers_from_http_message(http_message):
+    return Message(StringIO(http_message.split('\r\n', 1)[1]))
+
+def create_server_nounce(client_nounce):
+    return b64encode(sha1(client_nounce + websockets_magic).hexdigest().decode('hex'))
+
+def create_client_nounce():
+    return b64encode(os.urandom(16)).decode('utf-8')
+

test/test_websockets.py

@@ -0,0 +1,83 @@
+from netlib import tcp
+from netlib import test
+from netlib.websockets import implementations as impl
+from netlib.websockets import websockets as ws
+import os
+from nose.tools import raises
+
+class TestWebSockets(test.ServerTestBase):
+    handler = impl.WebSocketsEchoHandler
+
+    def random_bytes(self, n = 100):
+        return os.urandom(n)
+
+    def echo(self, msg):
+        client = impl.WebSocketsClient(("127.0.0.1", self.port))
+        client.connect()
+        client.send_message(msg)
+        response = client.read_next_message()
+        assert response == msg
+
+    def test_simple_echo(self):
+        self.echo("hello I'm the client")
+
+    def test_frame_sizes(self):
+        small_msg  = self.random_bytes(100)    # length can fit in the the 7 bit payload length 
+        medium_msg = self.random_bytes(50000)  # 50kb, sligthly larger than can fit in a 7 bit int
+        large_msg  = self.random_bytes(150000) # 150kb, slightly larger than can fit in a 16 bit int
+
+        self.echo(small_msg)
+        self.echo(medium_msg)
+        self.echo(large_msg)
+
+    def test_default_builder(self):
+        """
+          default builder should always generate valid frames
+        """ 
+        msg = self.random_bytes()
+        client_frame = ws.WebSocketsFrame.default(msg, from_client = True)
+        assert client_frame.is_valid()
+
+        server_frame = ws.WebSocketsFrame.default(msg, from_client = False)
+        assert server_frame.is_valid()
+
+    def test_serialization_bijection(self):
+        """
+          Ensure that various frame types can be serialized/deserialized back and forth
+          between to_bytes() and from_bytes()
+        """ 
+        for is_client in [True, False]:
+          for num_bytes in [100, 50000, 150000]:
+            frame = ws.WebSocketsFrame.default(self.random_bytes(num_bytes), is_client)
+            assert frame == ws.WebSocketsFrame.from_bytes(frame.to_bytes())
+
+        bytes = b'\x81\x11cba'
+        assert ws.WebSocketsFrame.from_bytes(bytes).to_bytes() == bytes
+
+    @raises(ws.WebSocketFrameValidationException)
+    def test_safe_to_bytes(self):
+        frame = ws.WebSocketsFrame.default(self.random_bytes(8))
+        frame.actual_payload_length = 1 #corrupt the frame
+        frame.safe_to_bytes()
+
+
+class BadHandshakeHandler(impl.WebSocketsEchoHandler):
+    def handshake(self):
+        client_hs = ws.read_handshake(self.rfile.read, 1)
+        key       = ws.process_handshake_from_client(client_hs)
+        response  = ws.create_server_handshake("malformed_key")
+        self.wfile.write(response)
+        self.wfile.flush()
+        self.handshake_done = True
+
+class TestBadHandshake(test.ServerTestBase):
+    """
+      Ensure that the client disconnects if the server handshake is malformed
+    """ 
+    handler = BadHandshakeHandler
+
+    @raises(tcp.NetLibDisconnect)
+    def test(self):
+        client = impl.WebSocketsClient(("127.0.0.1", self.port))
+        client.connect()
+        client.send_message("hello")