538 lines
19 KiB
ReStructuredText
538 lines
19 KiB
ReStructuredText
:mod:`socketserver` --- A framework for network servers
|
|
=======================================================
|
|
|
|
.. module:: SocketServer
|
|
:synopsis: Old name for the socketserver module.
|
|
|
|
.. module:: socketserver
|
|
:synopsis: A framework for network servers.
|
|
|
|
.. note::
|
|
The :mod:`SocketServer` module has been renamed to :mod:`socketserver` in
|
|
Python 3.0. It is importable under both names in Python 2.6 and the rest of
|
|
the 2.x series.
|
|
|
|
|
|
The :mod:`socketserver` module simplifies the task of writing network servers.
|
|
|
|
There are four basic server classes: :class:`TCPServer` uses the Internet TCP
|
|
protocol, which provides for continuous streams of data between the client and
|
|
server. :class:`UDPServer` uses datagrams, which are discrete packets of
|
|
information that may arrive out of order or be lost while in transit. The more
|
|
infrequently used :class:`UnixStreamServer` and :class:`UnixDatagramServer`
|
|
classes are similar, but use Unix domain sockets; they're not available on
|
|
non-Unix platforms. For more details on network programming, consult a book
|
|
such as
|
|
W. Richard Steven's UNIX Network Programming or Ralph Davis's Win32 Network
|
|
Programming.
|
|
|
|
These four classes process requests :dfn:`synchronously`; each request must be
|
|
completed before the next request can be started. This isn't suitable if each
|
|
request takes a long time to complete, because it requires a lot of computation,
|
|
or because it returns a lot of data which the client is slow to process. The
|
|
solution is to create a separate process or thread to handle each request; the
|
|
:class:`ForkingMixIn` and :class:`ThreadingMixIn` mix-in classes can be used to
|
|
support asynchronous behaviour.
|
|
|
|
Creating a server requires several steps. First, you must create a request
|
|
handler class by subclassing the :class:`BaseRequestHandler` class and
|
|
overriding its :meth:`handle` method; this method will process incoming
|
|
requests. Second, you must instantiate one of the server classes, passing it
|
|
the server's address and the request handler class. Finally, call the
|
|
:meth:`handle_request` or :meth:`serve_forever` method of the server object to
|
|
process one or many requests.
|
|
|
|
When inheriting from :class:`ThreadingMixIn` for threaded connection behavior,
|
|
you should explicitly declare how you want your threads to behave on an abrupt
|
|
shutdown. The :class:`ThreadingMixIn` class defines an attribute
|
|
*daemon_threads*, which indicates whether or not the server should wait for
|
|
thread termination. You should set the flag explicitly if you would like threads
|
|
to behave autonomously; the default is :const:`False`, meaning that Python will
|
|
not exit until all threads created by :class:`ThreadingMixIn` have exited.
|
|
|
|
Server classes have the same external methods and attributes, no matter what
|
|
network protocol they use.
|
|
|
|
|
|
Server Creation Notes
|
|
---------------------
|
|
|
|
There are five classes in an inheritance diagram, four of which represent
|
|
synchronous servers of four types::
|
|
|
|
+------------+
|
|
| BaseServer |
|
|
+------------+
|
|
|
|
|
v
|
|
+-----------+ +------------------+
|
|
| TCPServer |------->| UnixStreamServer |
|
|
+-----------+ +------------------+
|
|
|
|
|
v
|
|
+-----------+ +--------------------+
|
|
| UDPServer |------->| UnixDatagramServer |
|
|
+-----------+ +--------------------+
|
|
|
|
Note that :class:`UnixDatagramServer` derives from :class:`UDPServer`, not from
|
|
:class:`UnixStreamServer` --- the only difference between an IP and a Unix
|
|
stream server is the address family, which is simply repeated in both Unix
|
|
server classes.
|
|
|
|
Forking and threading versions of each type of server can be created using the
|
|
:class:`ForkingMixIn` and :class:`ThreadingMixIn` mix-in classes. For instance,
|
|
a threading UDP server class is created as follows::
|
|
|
|
class ThreadingUDPServer(ThreadingMixIn, UDPServer): pass
|
|
|
|
The mix-in class must come first, since it overrides a method defined in
|
|
:class:`UDPServer`. Setting the various member variables also changes the
|
|
behavior of the underlying server mechanism.
|
|
|
|
To implement a service, you must derive a class from :class:`BaseRequestHandler`
|
|
and redefine its :meth:`handle` method. You can then run various versions of
|
|
the service by combining one of the server classes with your request handler
|
|
class. The request handler class must be different for datagram or stream
|
|
services. This can be hidden by using the handler subclasses
|
|
:class:`StreamRequestHandler` or :class:`DatagramRequestHandler`.
|
|
|
|
Of course, you still have to use your head! For instance, it makes no sense to
|
|
use a forking server if the service contains state in memory that can be
|
|
modified by different requests, since the modifications in the child process
|
|
would never reach the initial state kept in the parent process and passed to
|
|
each child. In this case, you can use a threading server, but you will probably
|
|
have to use locks to protect the integrity of the shared data.
|
|
|
|
On the other hand, if you are building an HTTP server where all data is stored
|
|
externally (for instance, in the file system), a synchronous class will
|
|
essentially render the service "deaf" while one request is being handled --
|
|
which may be for a very long time if a client is slow to receive all the data it
|
|
has requested. Here a threading or forking server is appropriate.
|
|
|
|
In some cases, it may be appropriate to process part of a request synchronously,
|
|
but to finish processing in a forked child depending on the request data. This
|
|
can be implemented by using a synchronous server and doing an explicit fork in
|
|
the request handler class :meth:`handle` method.
|
|
|
|
Another approach to handling multiple simultaneous requests in an environment
|
|
that supports neither threads nor :func:`fork` (or where these are too expensive
|
|
or inappropriate for the service) is to maintain an explicit table of partially
|
|
finished requests and to use :func:`select` to decide which request to work on
|
|
next (or whether to handle a new incoming request). This is particularly
|
|
important for stream services where each client can potentially be connected for
|
|
a long time (if threads or subprocesses cannot be used). See :mod:`asyncore` for
|
|
another way to manage this.
|
|
|
|
.. XXX should data and methods be intermingled, or separate?
|
|
how should the distinction between class and instance variables be drawn?
|
|
|
|
|
|
Server Objects
|
|
--------------
|
|
|
|
|
|
.. function:: fileno()
|
|
|
|
Return an integer file descriptor for the socket on which the server is
|
|
listening. This function is most commonly passed to :func:`select.select`, to
|
|
allow monitoring multiple servers in the same process.
|
|
|
|
|
|
.. function:: handle_request()
|
|
|
|
Process a single request. This function calls the following methods in
|
|
order: :meth:`get_request`, :meth:`verify_request`, and
|
|
:meth:`process_request`. If the user-provided :meth:`handle` method of the
|
|
handler class raises an exception, the server's :meth:`handle_error` method
|
|
will be called. If no request is received within :attr:`self.timeout`
|
|
seconds, :meth:`handle_timeout` will be called and :meth:`handle_request`
|
|
will return.
|
|
|
|
|
|
.. function:: serve_forever(poll_interval=0.5)
|
|
|
|
Handle requests until an explicit :meth:`shutdown` request. Polls for
|
|
shutdown every *poll_interval* seconds.
|
|
|
|
|
|
.. function:: shutdown()
|
|
|
|
Tells the :meth:`serve_forever` loop to stop and waits until it does.
|
|
|
|
|
|
.. data:: address_family
|
|
|
|
The family of protocols to which the server's socket belongs.
|
|
Common examples are :const:`socket.AF_INET` and :const:`socket.AF_UNIX`.
|
|
|
|
|
|
.. data:: RequestHandlerClass
|
|
|
|
The user-provided request handler class; an instance of this class is created
|
|
for each request.
|
|
|
|
|
|
.. data:: server_address
|
|
|
|
The address on which the server is listening. The format of addresses varies
|
|
depending on the protocol family; see the documentation for the socket module
|
|
for details. For Internet protocols, this is a tuple containing a string giving
|
|
the address, and an integer port number: ``('127.0.0.1', 80)``, for example.
|
|
|
|
|
|
.. data:: socket
|
|
|
|
The socket object on which the server will listen for incoming requests.
|
|
|
|
The server classes support the following class variables:
|
|
|
|
.. XXX should class variables be covered before instance variables, or vice versa?
|
|
|
|
|
|
.. data:: allow_reuse_address
|
|
|
|
Whether the server will allow the reuse of an address. This defaults to
|
|
:const:`False`, and can be set in subclasses to change the policy.
|
|
|
|
|
|
.. data:: request_queue_size
|
|
|
|
The size of the request queue. If it takes a long time to process a single
|
|
request, any requests that arrive while the server is busy are placed into a
|
|
queue, up to :attr:`request_queue_size` requests. Once the queue is full,
|
|
further requests from clients will get a "Connection denied" error. The default
|
|
value is usually 5, but this can be overridden by subclasses.
|
|
|
|
|
|
.. data:: socket_type
|
|
|
|
The type of socket used by the server; :const:`socket.SOCK_STREAM` and
|
|
:const:`socket.SOCK_DGRAM` are two common values.
|
|
|
|
.. data:: timeout
|
|
|
|
Timeout duration, measured in seconds, or :const:`None` if no timeout is
|
|
desired. If :meth:`handle_request` receives no incoming requests within the
|
|
timeout period, the :meth:`handle_timeout` method is called.
|
|
|
|
There are various server methods that can be overridden by subclasses of base
|
|
server classes like :class:`TCPServer`; these methods aren't useful to external
|
|
users of the server object.
|
|
|
|
.. XXX should the default implementations of these be documented, or should
|
|
it be assumed that the user will look at socketserver.py?
|
|
|
|
|
|
.. function:: finish_request()
|
|
|
|
Actually processes the request by instantiating :attr:`RequestHandlerClass` and
|
|
calling its :meth:`handle` method.
|
|
|
|
|
|
.. function:: get_request()
|
|
|
|
Must accept a request from the socket, and return a 2-tuple containing the *new*
|
|
socket object to be used to communicate with the client, and the client's
|
|
address.
|
|
|
|
|
|
.. function:: handle_error(request, client_address)
|
|
|
|
This function is called if the :attr:`RequestHandlerClass`'s :meth:`handle`
|
|
method raises an exception. The default action is to print the traceback to
|
|
standard output and continue handling further requests.
|
|
|
|
.. function:: handle_timeout()
|
|
|
|
This function is called when the :attr:`timeout` attribute has been set to a
|
|
value other than :const:`None` and the timeout period has passed with no
|
|
requests being received. The default action for forking servers is
|
|
to collect the status of any child processes that have exited, while
|
|
in threading servers this method does nothing.
|
|
|
|
.. function:: process_request(request, client_address)
|
|
|
|
Calls :meth:`finish_request` to create an instance of the
|
|
:attr:`RequestHandlerClass`. If desired, this function can create a new process
|
|
or thread to handle the request; the :class:`ForkingMixIn` and
|
|
:class:`ThreadingMixIn` classes do this.
|
|
|
|
.. Is there any point in documenting the following two functions?
|
|
What would the purpose of overriding them be: initializing server
|
|
instance variables, adding new network families?
|
|
|
|
|
|
.. function:: server_activate()
|
|
|
|
Called by the server's constructor to activate the server. The default behavior
|
|
just :meth:`listen`\ s to the server's socket. May be overridden.
|
|
|
|
|
|
.. function:: server_bind()
|
|
|
|
Called by the server's constructor to bind the socket to the desired address.
|
|
May be overridden.
|
|
|
|
|
|
.. function:: verify_request(request, client_address)
|
|
|
|
Must return a Boolean value; if the value is :const:`True`, the request will be
|
|
processed, and if it's :const:`False`, the request will be denied. This function
|
|
can be overridden to implement access controls for a server. The default
|
|
implementation always returns :const:`True`.
|
|
|
|
|
|
RequestHandler Objects
|
|
----------------------
|
|
|
|
The request handler class must define a new :meth:`handle` method, and can
|
|
override any of the following methods. A new instance is created for each
|
|
request.
|
|
|
|
|
|
.. function:: finish()
|
|
|
|
Called after the :meth:`handle` method to perform any clean-up actions
|
|
required. The default implementation does nothing. If :meth:`setup` or
|
|
:meth:`handle` raise an exception, this function will not be called.
|
|
|
|
|
|
.. function:: handle()
|
|
|
|
This function must do all the work required to service a request. The
|
|
default implementation does nothing. Several instance attributes are
|
|
available to it; the request is available as :attr:`self.request`; the client
|
|
address as :attr:`self.client_address`; and the server instance as
|
|
:attr:`self.server`, in case it needs access to per-server information.
|
|
|
|
The type of :attr:`self.request` is different for datagram or stream
|
|
services. For stream services, :attr:`self.request` is a socket object; for
|
|
datagram services, :attr:`self.request` is a pair of string and socket.
|
|
However, this can be hidden by using the request handler subclasses
|
|
:class:`StreamRequestHandler` or :class:`DatagramRequestHandler`, which
|
|
override the :meth:`setup` and :meth:`finish` methods, and provide
|
|
:attr:`self.rfile` and :attr:`self.wfile` attributes. :attr:`self.rfile` and
|
|
:attr:`self.wfile` can be read or written, respectively, to get the request
|
|
data or return data to the client.
|
|
|
|
|
|
.. function:: setup()
|
|
|
|
Called before the :meth:`handle` method to perform any initialization actions
|
|
required. The default implementation does nothing.
|
|
|
|
|
|
Examples
|
|
--------
|
|
|
|
:class:`socketserver.TCPServer` Example
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
This is the server side::
|
|
|
|
import socketserver
|
|
|
|
class MyTCPHandler(socketserver.BaseRequestHandler):
|
|
"""
|
|
The RequestHandler class for our server.
|
|
|
|
It is instantiated once per connection to the server, and must
|
|
override the handle() method to implement communication to the
|
|
client.
|
|
"""
|
|
|
|
def handle(self):
|
|
# self.request is the TCP socket connected to the client
|
|
self.data = self.request.recv(1024).strip()
|
|
print "%s wrote:" % self.client_address[0]
|
|
print self.data
|
|
# just send back the same data, but upper-cased
|
|
self.request.send(self.data.upper())
|
|
|
|
if __name__ == "__main__":
|
|
HOST, PORT = "localhost", 9999
|
|
|
|
# Create the server, binding to localhost on port 9999
|
|
server = socketserver.TCPServer((HOST, PORT), MyTCPHandler)
|
|
|
|
# Activate the server; this will keep running until you
|
|
# interrupt the program with Ctrl-C
|
|
server.serve_forever()
|
|
|
|
An alternative request handler class that makes use of streams (file-like
|
|
objects that simplify communication by providing the standard file interface)::
|
|
|
|
class MyTCPHandler(socketserver.StreamRequestHandler):
|
|
|
|
def handle(self):
|
|
# self.rfile is a file-like object created by the handler;
|
|
# we can now use e.g. readline() instead of raw recv() calls
|
|
self.data = self.rfile.readline().strip()
|
|
print "%s wrote:" % self.client_address[0]
|
|
print self.data
|
|
# Likewise, self.wfile is a file-like object used to write back
|
|
# to the client
|
|
self.wfile.write(self.data.upper())
|
|
|
|
The difference is that the ``readline()`` call in the second handler will call
|
|
``recv()`` multiple times until it encounters a newline character, while the
|
|
single ``recv()`` call in the first handler will just return what has been sent
|
|
from the client in one ``send()`` call.
|
|
|
|
|
|
This is the client side::
|
|
|
|
import socket
|
|
import sys
|
|
|
|
HOST, PORT = "localhost", 9999
|
|
data = " ".join(sys.argv[1:])
|
|
|
|
# Create a socket (SOCK_STREAM means a TCP socket)
|
|
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
|
|
|
|
# Connect to server and send data
|
|
sock.connect((HOST, PORT))
|
|
sock.send(data + "\n")
|
|
|
|
# Receive data from the server and shut down
|
|
received = sock.recv(1024)
|
|
sock.close()
|
|
|
|
print "Sent: %s" % data
|
|
print "Received: %s" % received
|
|
|
|
|
|
The output of the example should look something like this:
|
|
|
|
Server::
|
|
|
|
$ python TCPServer.py
|
|
127.0.0.1 wrote:
|
|
hello world with TCP
|
|
127.0.0.1 wrote:
|
|
python is nice
|
|
|
|
Client::
|
|
|
|
$ python TCPClient.py hello world with TCP
|
|
Sent: hello world with TCP
|
|
Received: HELLO WORLD WITH TCP
|
|
$ python TCPClient.py python is nice
|
|
Sent: python is nice
|
|
Received: PYTHON IS NICE
|
|
|
|
|
|
:class:`socketserver.UDPServer` Example
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
This is the server side::
|
|
|
|
import socketserver
|
|
|
|
class MyUDPHandler(socketserver.BaseRequestHandler):
|
|
"""
|
|
This class works similar to the TCP handler class, except that
|
|
self.request consists of a pair of data and client socket, and since
|
|
there is no connection the client address must be given explicitly
|
|
when sending data back via sendto().
|
|
"""
|
|
|
|
def handle(self):
|
|
data = self.request[0].strip()
|
|
socket = self.request[1]
|
|
print "%s wrote:" % self.client_address[0]
|
|
print data
|
|
socket.sendto(data.upper(), self.client_address)
|
|
|
|
if __name__ == "__main__":
|
|
HOST, PORT = "localhost", 9999
|
|
server = socketserver.UDPServer((HOST, PORT), BaseUDPRequestHandler)
|
|
server.serve_forever()
|
|
|
|
This is the client side::
|
|
|
|
import socket
|
|
import sys
|
|
|
|
HOST, PORT = "localhost"
|
|
data = " ".join(sys.argv[1:])
|
|
|
|
# SOCK_DGRAM is the socket type to use for UDP sockets
|
|
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
|
|
|
|
# As you can see, there is no connect() call; UDP has no connections.
|
|
# Instead, data is directly sent to the recipient via sendto().
|
|
sock.sendto(data + "\n", (HOST, PORT))
|
|
received = sock.recv(1024)
|
|
|
|
print "Sent: %s" % data
|
|
print "Received: %s" % received
|
|
|
|
The output of the example should look exactly like for the TCP server example.
|
|
|
|
|
|
Asynchronous Mixins
|
|
~~~~~~~~~~~~~~~~~~~
|
|
|
|
To build asynchronous handlers, use the :class:`ThreadingMixIn` and
|
|
:class:`ForkingMixIn` classes.
|
|
|
|
An example for the :class:`ThreadingMixIn` class::
|
|
|
|
import socket
|
|
import threading
|
|
import socketserver
|
|
|
|
class ThreadedTCPRequestHandler(socketserver.BaseRequestHandler):
|
|
|
|
def handle(self):
|
|
data = self.request.recv(1024)
|
|
cur_thread = threading.currentThread()
|
|
response = "%s: %s" % (cur_thread.getName(), data)
|
|
self.request.send(response)
|
|
|
|
class ThreadedTCPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
|
|
pass
|
|
|
|
def client(ip, port, message):
|
|
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
|
|
sock.connect((ip, port))
|
|
sock.send(message)
|
|
response = sock.recv(1024)
|
|
print "Received: %s" % response
|
|
sock.close()
|
|
|
|
if __name__ == "__main__":
|
|
# Port 0 means to select an arbitrary unused port
|
|
HOST, PORT = "localhost", 0
|
|
|
|
server = ThreadedTCPServer((HOST, PORT), ThreadedTCPRequestHandler)
|
|
ip, port = server.server_address
|
|
|
|
# Start a thread with the server -- that thread will then start one
|
|
# more thread for each request
|
|
server_thread = threading.Thread(target=server.serve_forever)
|
|
# Exit the server thread when the main thread terminates
|
|
server_thread.setDaemon(True)
|
|
server_thread.start()
|
|
print "Server loop running in thread:", t.getName()
|
|
|
|
client(ip, port, "Hello World 1")
|
|
client(ip, port, "Hello World 2")
|
|
client(ip, port, "Hello World 3")
|
|
|
|
server.shutdown()
|
|
|
|
The output of the example should look something like this::
|
|
|
|
$ python ThreadedTCPServer.py
|
|
Server loop running in thread: Thread-1
|
|
Received: Thread-2: Hello World 1
|
|
Received: Thread-3: Hello World 2
|
|
Received: Thread-4: Hello World 3
|
|
|
|
|
|
The :class:`ForkingMixIn` class is used in the same way, except that the server
|
|
will spawn a new process for each request.
|