mirror of https://github.com/python/cpython.git
200 lines
8.0 KiB
TeX
200 lines
8.0 KiB
TeX
\section{\module{SocketServer} ---
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A framework for network servers}
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\declaremodule{standard}{SocketServer}
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\modulesynopsis{A framework for network servers.}
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The \module{SocketServer} module simplifies the task of writing network
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servers.
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There are four basic server classes: \class{TCPServer} uses the
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Internet TCP protocol, which provides for continuous streams of data
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between the client and server. \class{UDPServer} uses datagrams, which
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are discrete packets of information that may arrive out of order or be
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lost while in transit. The more infrequently used
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\class{UnixStreamServer} and \class{UnixDatagramServer} classes are
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similar, but use \UNIX{} domain sockets; they're not available on
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non-\UNIX{} platforms. For more details on network programming, consult
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a book such as W. Richard Steven's \citetitle{UNIX Network Programming}
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or Ralph Davis's \citetitle{Win32 Network Programming}.
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These four classes process requests \dfn{synchronously}; each request
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must be completed before the next request can be started. This isn't
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suitable if each request takes a long time to complete, because it
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requires a lot of computation, or because it returns a lot of data
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which the client is slow to process. The solution is to create a
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separate process or thread to handle each request; the
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\class{ForkingMixIn} and \class{ThreadingMixIn} mix-in classes can be
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used to support asynchronous behaviour.
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Creating a server requires several steps. First, you must create a
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request handler class by subclassing the \class{BaseRequestHandler}
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class and overriding its \method{handle()} method; this method will
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process incoming requests. Second, you must instantiate one of the
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server classes, passing it the server's address and the request
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handler class. Finally, call the \method{handle_request()} or
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\method{serve_forever()} method of the server object to process one or
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many requests.
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Server classes have the same external methods and attributes, no
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matter what network protocol they use:
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\setindexsubitem{(SocketServer protocol)}
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%XXX should data and methods be intermingled, or separate?
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% how should the distinction between class and instance variables be
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% drawn?
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\begin{funcdesc}{fileno}{}
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Return an integer file descriptor for the socket on which the server
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is listening. This function is most commonly passed to
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\function{select.select()}, to allow monitoring multiple servers in the
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same process.
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\end{funcdesc}
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\begin{funcdesc}{handle_request}{}
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Process a single request. This function calls the following methods
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in order: \method{get_request()}, \method{verify_request()}, and
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\method{process_request()}. If the user-provided \method{handle()}
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method of the handler class raises an exception, the server's
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\method{handle_error()} method will be called.
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\end{funcdesc}
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\begin{funcdesc}{serve_forever}{}
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Handle an infinite number of requests. This simply calls
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\method{handle_request()} inside an infinite loop.
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\end{funcdesc}
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\begin{datadesc}{address_family}
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The family of protocols to which the server's socket belongs.
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\constant{socket.AF_INET} and \constant{socket.AF_UNIX} are two
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possible values.
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\end{datadesc}
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\begin{datadesc}{RequestHandlerClass}
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The user-provided request handler class; an instance of this class is
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created for each request.
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\end{datadesc}
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\begin{datadesc}{server_address}
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The address on which the server is listening. The format of addresses
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varies depending on the protocol family; see the documentation for the
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socket module for details. For Internet protocols, this is a tuple
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containing a string giving the address, and an integer port number:
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\code{('127.0.0.1', 80)}, for example.
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\end{datadesc}
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\begin{datadesc}{socket}
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The socket object on which the server will listen for incoming requests.
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\end{datadesc}
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% XXX should class variables be covered before instance variables, or
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% vice versa?
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The server classes support the following class variables:
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\begin{datadesc}{request_queue_size}
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The size of the request queue. If it takes a long time to process a
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single request, any requests that arrive while the server is busy are
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placed into a queue, up to \member{request_queue_size} requests. Once
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the queue is full, further requests from clients will get a
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``Connection denied'' error. The default value is usually 5, but this
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can be overridden by subclasses.
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\end{datadesc}
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\begin{datadesc}{socket_type}
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The type of socket used by the server; \constant{socket.SOCK_STREAM}
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and \constant{socket.SOCK_DGRAM} are two possible values.
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\end{datadesc}
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There are various server methods that can be overridden by subclasses
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of base server classes like \class{TCPServer}; these methods aren't
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useful to external users of the server object.
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% should the default implementations of these be documented, or should
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% it be assumed that the user will look at SocketServer.py?
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\begin{funcdesc}{finish_request}{}
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Actually processes the request by instantiating
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\member{RequestHandlerClass} and calling its \method{handle()} method.
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\end{funcdesc}
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\begin{funcdesc}{get_request}{}
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Must accept a request from the socket, and return a 2-tuple containing
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the \emph{new} socket object to be used to communicate with the
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client, and the client's address.
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\end{funcdesc}
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\begin{funcdesc}{handle_error}{request, client_address}
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This function is called if the \member{RequestHandlerClass}'s
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\method{handle()} method raises an exception. The default action is
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to print the traceback to standard output and continue handling
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further requests.
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\end{funcdesc}
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\begin{funcdesc}{process_request}{request, client_address}
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Calls \method{finish_request()} to create an instance of the
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\member{RequestHandlerClass}. If desired, this function can create a
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new process or thread to handle the request; the \class{ForkingMixIn}
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and \class{ThreadingMixIn} classes do this.
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\end{funcdesc}
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% Is there any point in documenting the following two functions?
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% What would the purpose of overriding them be: initializing server
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% instance variables, adding new network families?
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\begin{funcdesc}{server_activate}{}
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Called by the server's constructor to activate the server.
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May be overridden.
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\end{funcdesc}
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\begin{funcdesc}{server_bind}{}
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Called by the server's constructor to bind the socket to the desired
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address. May be overridden.
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\end{funcdesc}
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\begin{funcdesc}{verify_request}{request, client_address}
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Must return a Boolean value; if the value is true, the request will be
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processed, and if it's false, the request will be denied.
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This function can be overridden to implement access controls for a server.
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The default implementation always return true.
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\end{funcdesc}
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The request handler class must define a new \method{handle()} method,
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and can override any of the following methods. A new instance is
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created for each request.
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\begin{funcdesc}{finish}{}
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Called after the \method{handle()} method to perform any clean-up
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actions required. The default implementation does nothing. If
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\method{setup()} or \method{handle()} raise an exception, this
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function will not be called.
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\end{funcdesc}
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\begin{funcdesc}{handle}{}
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This function must do all the work required to service a request.
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Several instance attributes are available to it; the request is
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available as \member{self.request}; the client address as
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\member{self.client_address}; and the server instance as
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\member{self.server}, in case it needs access to per-server
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information.
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The type of \member{self.request} is different for datagram or stream
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services. For stream services, \member{self.request} is a socket
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object; for datagram services, \member{self.request} is a string.
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However, this can be hidden by using the mix-in request handler
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classes
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\class{StreamRequestHandler} or \class{DatagramRequestHandler}, which
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override the \method{setup()} and \method{finish()} methods, and
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provides \member{self.rfile} and \member{self.wfile} attributes.
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\member{self.rfile} and \member{self.wfile} can be read or written,
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respectively, to get the request data or return data to the client.
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\end{funcdesc}
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\begin{funcdesc}{setup}{}
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Called before the \method{handle()} method to perform any
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initialization actions required. The default implementation does
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nothing.
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\end{funcdesc}
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