190 lines
6.7 KiB
Python
190 lines
6.7 KiB
Python
# Routing demux: forwards datagrams from the root socket to connected
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# sockets bound to ephemeral ports.
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# Copyright 2012 Ray Brown
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# The License is also distributed with this work in the file named "LICENSE."
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Routing UDP Demux
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This module implements an explicitly routing UDP demux. New connections create
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datagram sockets bound to ephemeral ports on the loopback interface and
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connected to a forwarding socket. The demux services incoming datagrams by
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receiving them from the root socket and sending them to the socket belonging to
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the connection that is associated with the sending peer.
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A routing UDP demux can be used on any platform.
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Classes:
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UDPDemux -- an explicitly routing UDP demux
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Exceptions:
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InvalidSocketError -- exception raised for improper socket objects
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KeyError -- raised for unknown peer addresses
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"""
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import socket
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from logging import getLogger
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from weakref import WeakValueDictionary
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from ..err import InvalidSocketError
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_logger = getLogger(__name__)
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UDP_MAX_DGRAM_LENGTH = 65527
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class UDPDemux(object):
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"""Explicitly routing UDP demux
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This class implements a demux that forwards packets from the root
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socket to sockets belonging to connections. It does this whenever its
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service method is invoked.
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Methods:
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remove_connection -- remove an existing connection
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service -- distribute datagrams from the root socket to connections
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forward -- forward a stored datagram to a connection
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"""
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_forwarding_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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_forwarding_socket.bind(('127.0.0.1', 0))
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def __init__(self, datagram_socket):
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"""Constructor
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Arguments:
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datagram_socket -- the root socket; this must be a bound, unconnected
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datagram socket
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"""
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if datagram_socket.type != socket.SOCK_DGRAM:
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raise InvalidSocketError("datagram_socket is not of " +
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"type SOCK_DGRAM")
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try:
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datagram_socket.getsockname()
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except:
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raise InvalidSocketError("datagram_socket is unbound")
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try:
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datagram_socket.getpeername()
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except:
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pass
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else:
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raise InvalidSocketError("datagram_socket is connected")
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self.datagram_socket = datagram_socket
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self.payload = ""
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self.payload_peer_address = None
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self.connections = WeakValueDictionary()
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def get_connection(self, address):
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"""Create or retrieve a muxed connection
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Arguments:
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address -- a peer endpoint in IPv4/v6 address format; None refers
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to the connection for unknown peers
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Return:
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a bound, connected datagram socket instance
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"""
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if self.connections.has_key(address):
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return self.connections[address]
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# We need a new datagram socket on a dynamically assigned ephemeral port
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conn = socket.socket(self._forwarding_socket.family,
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self._forwarding_socket.type,
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self._forwarding_socket.proto)
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conn.bind((self._forwarding_socket.getsockname()[0], 0))
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conn.connect(self._forwarding_socket.getsockname())
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if not address:
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conn.setblocking(0)
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self.connections[address] = conn
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_logger.debug("Created new connection for address: %s", address)
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return conn
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def remove_connection(self, address):
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"""Remove a muxed connection
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Arguments:
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address -- an address that was previously returned by the service
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method and whose connection has not yet been removed
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Return:
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the socket object whose connection has been removed
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"""
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return self.connections.pop(address)
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def service(self):
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"""Service the root socket
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Read from the root socket and forward one datagram to a
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connection. The call will return without forwarding data
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if any of the following occurs:
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* An error is encountered while reading from the root socket
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* Reading from the root socket times out
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* The root socket is non-blocking and has no data available
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* An empty payload is received
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* A non-empty payload is received from an unknown peer (a peer
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for which get_connection has not yet been called); in this case,
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the payload is held by this instance and will be forwarded when
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the forward method is called
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Return:
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if the datagram received was from a new peer, then the peer's
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address; otherwise None
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"""
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self.payload, self.payload_peer_address = \
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self.datagram_socket.recvfrom(UDP_MAX_DGRAM_LENGTH)
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_logger.debug("Received datagram from peer: %s",
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self.payload_peer_address)
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if not self.payload:
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self.payload_peer_address = None
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return
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if self.connections.has_key(self.payload_peer_address):
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self.forward()
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else:
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return self.payload_peer_address
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def forward(self):
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"""Forward a stored datagram
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When the service method returns the address of a new peer, it holds
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the datagram from that peer in this instance. In this case, this
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method will perform the forwarding step. The target connection is the
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one associated with address None if get_connection has not been called
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since the service method returned the new peer's address, and the
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connection associated with the new peer's address if it has.
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"""
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assert self.payload
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assert self.payload_peer_address
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if self.connections.has_key(self.payload_peer_address):
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conn = self.connections[self.payload_peer_address]
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default = False
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else:
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conn = self.connections[None] # propagate exception if not created
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default = True
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_logger.debug("Forwarding datagram from peer: %s, default: %s",
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self.payload_peer_address, default)
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self._forwarding_socket.sendto(self.payload, conn.getsockname())
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self.payload = ""
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self.payload_peer_address = None
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