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Issue #15608: Merge socketserver doc from 3.5

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Martin Panter 2016-02-19 03:35:00 +00:00
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Doc/library/socketserver.rst
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@ -10,16 +10,34 @@
The :mod:`socketserver` module simplifies the task of writing network servers. The :mod:`socketserver` module simplifies the task of writing network servers.
There are four basic server classes: :class:`TCPServer` uses the Internet TCP There are four basic concrete server classes:
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 .. class:: TCPServer(server_address, RequestHandlerClass, bind_and_activate=True)
infrequently used :class:`UnixStreamServer` and :class:`UnixDatagramServer`
classes are similar, but use Unix domain sockets; they're not available on This uses the Internet TCP protocol, which provides for
non-Unix platforms. For more details on network programming, consult a book continuous streams of data between the client and server.
such as If *bind_and_activate* is true, the constructor automatically attempts to
W. Richard Steven's UNIX Network Programming or Ralph Davis's Win32 Network invoke :meth:`~BaseServer.server_bind` and
Programming. :meth:`~BaseServer.server_activate`. The other parameters are passed to
the :class:`BaseServer` base class.
.. class:: UDPServer(server_address, RequestHandlerClass, bind_and_activate=True)
This uses datagrams, which are discrete packets of information that may
arrive out of order or be lost while in transit. The parameters are
the same as for :class:`TCPServer`.
.. class:: UnixStreamServer(server_address, RequestHandlerClass, bind_and_activate=True)
UnixDatagramServer(server_address, RequestHandlerClass, bind_and_activate=True)
These more infrequently used classes are similar to the TCP and
UDP classes, but use Unix domain sockets; they're not available on
non-Unix platforms. The parameters are the same as for
:class:`TCPServer`.
These four classes process requests :dfn:`synchronously`; each request must be 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 completed before the next request can be started. This isn't suitable if each
@ -31,10 +49,12 @@ support asynchronous behaviour.
Creating a server requires several steps. First, you must create a request Creating a server requires several steps. First, you must create a request
handler class by subclassing the :class:`BaseRequestHandler` class and handler class by subclassing the :class:`BaseRequestHandler` class and
overriding its :meth:`handle` method; this method will process incoming overriding its :meth:`~BaseRequestHandler.handle` method;
this method will process incoming
requests. Second, you must instantiate one of the server classes, passing it requests. Second, you must instantiate one of the server classes, passing it
the server's address and the request handler class. Then call the the server's address and the request handler class. Then call the
:meth:`handle_request` or :meth:`serve_forever` method of the server object to :meth:`~BaseServer.handle_request` or
:meth:`~BaseServer.serve_forever` method of the server object to
process one or many requests. Finally, call :meth:`~BaseServer.server_close` process one or many requests. Finally, call :meth:`~BaseServer.server_close`
to close the socket. to close the socket.
@ -76,18 +96,33 @@ Note that :class:`UnixDatagramServer` derives from :class:`UDPServer`, not from
stream server is the address family, which is simply repeated in both Unix stream server is the address family, which is simply repeated in both Unix
server classes. 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 .. class:: ForkingMixIn
ThreadingMixIn
Forking and threading versions of each type of server can be created
using these mix-in classes. For instance, :class:`ThreadingUDPServer`
is created as follows::
class ThreadingUDPServer(ThreadingMixIn, UDPServer):
pass
The mix-in class comes first, since it overrides a method defined in
:class:`UDPServer`. Setting the various attributes also changes the
behavior of the underlying server mechanism.
.. class:: ForkingTCPServer
ForkingUDPServer
ThreadingTCPServer
ThreadingUDPServer
These classes are pre-defined using the mix-in classes.
The mix-in class must come first, since it overrides a method defined in
:class:`UDPServer`. Setting the various attributes also change the
behavior of the underlying server mechanism.
To implement a service, you must derive a class from :class:`BaseRequestHandler` 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 and redefine its :meth:`~BaseRequestHandler.handle` method.
You can then run various versions of
the service by combining one of the server classes with your request handler 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 class. The request handler class must be different for datagram or stream
services. This can be hidden by using the handler subclasses services. This can be hidden by using the handler subclasses
@ -109,7 +144,7 @@ has requested. Here a threading or forking server is appropriate.
In some cases, it may be appropriate to process part of a request synchronously, 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 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 can be implemented by using a synchronous server and doing an explicit fork in
the request handler class :meth:`handle` method. the request handler class :meth:`~BaseRequestHandler.handle` method.
Another approach to handling multiple simultaneous requests in an environment Another approach to handling multiple simultaneous requests in an environment
that supports neither threads nor :func:`~os.fork` (or where these are too that supports neither threads nor :func:`~os.fork` (or where these are too
@ -127,227 +162,240 @@ connected for a long time (if threads or subprocesses cannot be used). See
Server Objects Server Objects
-------------- --------------
.. class:: BaseServer .. class:: BaseServer(server_address, RequestHandlerClass)
This is the superclass of all Server objects in the module. It defines the This is the superclass of all Server objects in the module. It defines the
interface, given below, but does not implement most of the methods, which is interface, given below, but does not implement most of the methods, which is
done in subclasses. done in subclasses. The two parameters are stored in the respective
:attr:`server_address` and :attr:`RequestHandlerClass` attributes.
.. method:: BaseServer.fileno() .. method:: fileno()
Return an integer file descriptor for the socket on which the server is Return an integer file descriptor for the socket on which the server is
listening. This function is most commonly passed to :mod:`selectors`, to listening. This function is most commonly passed to :mod:`selectors`, to
allow monitoring multiple servers in the same process. allow monitoring multiple servers in the same process.
.. method:: BaseServer.handle_request() .. method:: handle_request()
Process a single request. This function calls the following methods in Process a single request. This function calls the following methods in
order: :meth:`get_request`, :meth:`verify_request`, and order: :meth:`get_request`, :meth:`verify_request`, and
:meth:`process_request`. If the user-provided :meth:`handle` method of the :meth:`process_request`. If the user-provided
handler class raises an exception, the server's :meth:`handle_error` method :meth:`~BaseRequestHandler.handle` method of the
will be called. If no request is received within :attr:`self.timeout` handler class raises an exception, the server's :meth:`handle_error` method
seconds, :meth:`handle_timeout` will be called and :meth:`handle_request` will be called. If no request is received within :attr:`timeout`
will return. seconds, :meth:`handle_timeout` will be called and :meth:`handle_request`
will return.
.. method:: BaseServer.serve_forever(poll_interval=0.5) .. method:: serve_forever(poll_interval=0.5)
Handle requests until an explicit :meth:`shutdown` request. Poll for Handle requests until an explicit :meth:`shutdown` request. Poll for
shutdown every *poll_interval* seconds. Ignores :attr:`self.timeout`. It shutdown every *poll_interval* seconds.
also calls :meth:`service_actions`, which may be used by a subclass or mixin Ignores the :attr:`timeout` attribute. It
to provide actions specific to a given service. For example, the also calls :meth:`service_actions`, which may be used by a subclass or mixin
:class:`ForkingMixIn` class uses :meth:`service_actions` to clean up zombie to provide actions specific to a given service. For example, the
child processes. :class:`ForkingMixIn` class uses :meth:`service_actions` to clean up zombie
child processes.
.. versionchanged:: 3.3 .. versionchanged:: 3.3
Added ``service_actions`` call to the ``serve_forever`` method. Added ``service_actions`` call to the ``serve_forever`` method.
.. method:: BaseServer.service_actions() .. method:: service_actions()
This is called in the :meth:`serve_forever` loop. This method can be This is called in the :meth:`serve_forever` loop. This method can be
overridden by subclasses or mixin classes to perform actions specific to overridden by subclasses or mixin classes to perform actions specific to
a given service, such as cleanup actions. a given service, such as cleanup actions.
.. versionadded:: 3.3 .. versionadded:: 3.3
.. method:: BaseServer.shutdown() .. method:: shutdown()
Tell the :meth:`serve_forever` loop to stop and wait until it does. Tell the :meth:`serve_forever` loop to stop and wait until it does.
.. method:: BaseServer.server_close() .. method:: server_close()
Clean up the server. May be overridden. Clean up the server. May be overridden.
.. versionadded:: 2.6
.. attribute:: address_family
.. attribute:: BaseServer.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`.
The family of protocols to which the server's socket belongs.
Common examples are :const:`socket.AF_INET` and :const:`socket.AF_UNIX`.
.. attribute:: RequestHandlerClass
.. attribute:: BaseServer.RequestHandlerClass The user-provided request handler class; an instance of this class is created
for each request.
The user-provided request handler class; an instance of this class is created
for each request.
.. attribute:: server_address
.. attribute:: BaseServer.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 :mod:`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.
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.
.. attribute:: socket
.. attribute:: BaseServer.socket The socket object on which the server will listen for incoming requests.
The socket object on which the server will listen for incoming requests.
The server classes support the following class variables:
The server classes support the following class variables: .. XXX should class variables be covered before instance variables, or vice versa?
.. XXX should class variables be covered before instance variables, or vice versa? .. attribute:: allow_reuse_address
.. attribute:: BaseServer.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.
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.
.. attribute:: request_queue_size
.. attribute:: BaseServer.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.
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.
.. attribute:: socket_type
.. attribute:: BaseServer.socket_type The type of socket used by the server; :const:`socket.SOCK_STREAM` and
:const:`socket.SOCK_DGRAM` are two common values.
The type of socket used by the server; :const:`socket.SOCK_STREAM` and
:const:`socket.SOCK_DGRAM` are two common values.
.. attribute:: timeout
.. attribute:: BaseServer.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.
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.
There are various server methods that can be overridden by subclasses of base .. XXX should the default implementations of these be documented, or should
server classes like :class:`TCPServer`; these methods aren't useful to external it be assumed that the user will look at socketserver.py?
users of the server object.
.. XXX should the default implementations of these be documented, or should .. method:: finish_request()
it be assumed that the user will look at socketserver.py?
.. method:: BaseServer.finish_request() Actually processes the request by instantiating :attr:`RequestHandlerClass` and
calling its :meth:`~BaseRequestHandler.handle` method.
Actually processes the request by instantiating :attr:`RequestHandlerClass` and
calling its :meth:`handle` method.
.. method:: get_request()
.. method:: BaseServer.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.
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.
.. method:: handle_error(request, client_address)
.. method:: BaseServer.handle_error(request, client_address) This function is called if the :meth:`~BaseRequestHandler.handle`
method of a :attr:`RequestHandlerClass` instance raises
an exception. The default action is to print the traceback to
standard output and continue handling further requests.
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.
.. method:: handle_timeout()
.. method:: BaseServer.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.
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.
.. method:: process_request(request, client_address)
.. method:: BaseServer.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.
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?
.. Is there any point in documenting the following two functions? .. method:: server_activate()
What would the purpose of overriding them be: initializing server
instance variables, adding new network families?
.. method:: BaseServer.server_activate() Called by the server's constructor to activate the server. The default behavior
for a TCP server just invokes :meth:`~socket.socket.listen`
on the server's socket. May be overridden.
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.
.. method:: server_bind()
.. method:: BaseServer.server_bind() Called by the server's constructor to bind the socket to the desired address.
May be overridden.
Called by the server's constructor to bind the socket to the desired address.
May be overridden.
.. method:: verify_request(request, client_address)
.. method:: BaseServer.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`.
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`.
Request Handler Objects
-----------------------
RequestHandler Objects .. class:: BaseRequestHandler
----------------------
The request handler class must define a new :meth:`handle` method, and can This is the superclass of all request handler objects. It defines
override any of the following methods. A new instance is created for each the interface, given below. A concrete request handler subclass must
request. define a new :meth:`handle` method, and can override any of
the other methods. A new instance of the subclass is created for each
request.
.. method:: RequestHandler.finish() .. method:: setup()
Called after the :meth:`handle` method to perform any clean-up actions Called before the :meth:`handle` method to perform any initialization actions
required. The default implementation does nothing. If :meth:`setup` required. The default implementation does nothing.
raises an exception, this function will not be called.
.. method:: RequestHandler.handle() .. method:: handle()
This function must do all the work required to service a request. The This function must do all the work required to service a request. The
default implementation does nothing. Several instance attributes are default implementation does nothing. Several instance attributes are
available to it; the request is available as :attr:`self.request`; the client available to it; the request is available as :attr:`self.request`; the client
address as :attr:`self.client_address`; and the server instance as address as :attr:`self.client_address`; and the server instance as
:attr:`self.server`, in case it needs access to per-server information. :attr:`self.server`, in case it needs access to per-server information.
The type of :attr:`self.request` is different for datagram or stream The type of :attr:`self.request` is different for datagram or stream
services. For stream services, :attr:`self.request` is a socket object; for services. For stream services, :attr:`self.request` is a socket object; for
datagram services, :attr:`self.request` is a pair of string and socket. 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.
.. method:: RequestHandler.setup() .. method:: finish()
Called before the :meth:`handle` method to perform any initialization actions Called after the :meth:`handle` method to perform any clean-up actions
required. The default implementation does nothing. required. The default implementation does nothing. If :meth:`setup`
raises an exception, this function will not be called.
.. class:: StreamRequestHandler
DatagramRequestHandler
These :class:`BaseRequestHandler` subclasses override the
:meth:`~BaseRequestHandler.setup` and :meth:`~BaseRequestHandler.finish`
methods, and provide :attr:`self.rfile` and :attr:`self.wfile` attributes.
The :attr:`self.rfile` and :attr:`self.wfile` attributes can be
read or written, respectively, to get the request data or return data
to the client.
Examples Examples
@ -362,7 +410,7 @@ This is the server side::
class MyTCPHandler(socketserver.BaseRequestHandler): class MyTCPHandler(socketserver.BaseRequestHandler):
""" """
The RequestHandler class for our server. The request handler class for our server.
It is instantiated once per connection to the server, and must It is instantiated once per connection to the server, and must
override the handle() method to implement communication to the override the handle() method to implement communication to the