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391 lines
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ReStructuredText
391 lines
15 KiB
ReStructuredText
:mod:`http.server` --- HTTP servers
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===================================
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.. module:: http.server
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:synopsis: HTTP server and request handlers.
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.. index::
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pair: WWW; server
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pair: HTTP; protocol
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single: URL
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single: httpd
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**Source code:** :source:`Lib/http/server.py`
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--------------
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This module defines classes for implementing HTTP servers (Web servers).
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One class, :class:`HTTPServer`, is a :class:`socketserver.TCPServer` subclass.
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It creates and listens at the HTTP socket, dispatching the requests to a
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handler. Code to create and run the server looks like this::
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def run(server_class=HTTPServer, handler_class=BaseHTTPRequestHandler):
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server_address = ('', 8000)
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httpd = server_class(server_address, handler_class)
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httpd.serve_forever()
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.. class:: HTTPServer(server_address, RequestHandlerClass)
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This class builds on the :class:`TCPServer` class by storing the server
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address as instance variables named :attr:`server_name` and
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:attr:`server_port`. The server is accessible by the handler, typically
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through the handler's :attr:`server` instance variable.
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The :class:`HTTPServer` must be given a *RequestHandlerClass* on instantiation,
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of which this module provides three different variants:
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.. class:: BaseHTTPRequestHandler(request, client_address, server)
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This class is used to handle the HTTP requests that arrive at the server. By
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itself, it cannot respond to any actual HTTP requests; it must be subclassed
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to handle each request method (e.g. GET or POST).
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:class:`BaseHTTPRequestHandler` provides a number of class and instance
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variables, and methods for use by subclasses.
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The handler will parse the request and the headers, then call a method
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specific to the request type. The method name is constructed from the
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request. For example, for the request method ``SPAM``, the :meth:`do_SPAM`
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method will be called with no arguments. All of the relevant information is
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stored in instance variables of the handler. Subclasses should not need to
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override or extend the :meth:`__init__` method.
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:class:`BaseHTTPRequestHandler` has the following instance variables:
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.. attribute:: client_address
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Contains a tuple of the form ``(host, port)`` referring to the client's
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address.
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.. attribute:: server
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Contains the server instance.
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.. attribute:: command
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Contains the command (request type). For example, ``'GET'``.
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.. attribute:: path
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Contains the request path.
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.. attribute:: request_version
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Contains the version string from the request. For example, ``'HTTP/1.0'``.
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.. attribute:: headers
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Holds an instance of the class specified by the :attr:`MessageClass` class
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variable. This instance parses and manages the headers in the HTTP
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request.
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.. attribute:: rfile
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Contains an input stream, positioned at the start of the optional input
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data.
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.. attribute:: wfile
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Contains the output stream for writing a response back to the
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client. Proper adherence to the HTTP protocol must be used when writing to
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this stream.
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:class:`BaseHTTPRequestHandler` has the following class variables:
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.. attribute:: server_version
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Specifies the server software version. You may want to override this. The
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format is multiple whitespace-separated strings, where each string is of
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the form name[/version]. For example, ``'BaseHTTP/0.2'``.
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.. attribute:: sys_version
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Contains the Python system version, in a form usable by the
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:attr:`version_string` method and the :attr:`server_version` class
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variable. For example, ``'Python/1.4'``.
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.. attribute:: error_message_format
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Specifies a format string for building an error response to the client. It
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uses parenthesized, keyed format specifiers, so the format operand must be
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a dictionary. The *code* key should be an integer, specifying the numeric
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HTTP error code value. *message* should be a string containing a
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(detailed) error message of what occurred, and *explain* should be an
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explanation of the error code number. Default *message* and *explain*
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values can found in the *responses* class variable.
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.. attribute:: error_content_type
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Specifies the Content-Type HTTP header of error responses sent to the
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client. The default value is ``'text/html'``.
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.. attribute:: protocol_version
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This specifies the HTTP protocol version used in responses. If set to
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``'HTTP/1.1'``, the server will permit HTTP persistent connections;
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however, your server *must* then include an accurate ``Content-Length``
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header (using :meth:`send_header`) in all of its responses to clients.
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For backwards compatibility, the setting defaults to ``'HTTP/1.0'``.
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.. attribute:: MessageClass
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Specifies an :class:`email.message.Message`\ -like class to parse HTTP
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headers. Typically, this is not overridden, and it defaults to
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:class:`http.client.HTTPMessage`.
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.. attribute:: responses
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This variable contains a mapping of error code integers to two-element tuples
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containing a short and long message. For example, ``{code: (shortmessage,
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longmessage)}``. The *shortmessage* is usually used as the *message* key in an
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error response, and *longmessage* as the *explain* key (see the
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:attr:`error_message_format` class variable).
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A :class:`BaseHTTPRequestHandler` instance has the following methods:
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.. method:: handle()
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Calls :meth:`handle_one_request` once (or, if persistent connections are
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enabled, multiple times) to handle incoming HTTP requests. You should
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never need to override it; instead, implement appropriate :meth:`do_\*`
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methods.
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.. method:: handle_one_request()
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This method will parse and dispatch the request to the appropriate
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:meth:`do_\*` method. You should never need to override it.
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.. method:: handle_expect_100()
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When a HTTP/1.1 compliant server receives a ``Expect: 100-continue``
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request header it responds back with a ``100 Continue`` followed by ``200
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OK`` headers.
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This method can be overridden to raise an error if the server does not
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want the client to continue. For e.g. server can chose to send ``417
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Expectation Failed`` as a response header and ``return False``.
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.. versionadded:: 3.2
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.. method:: send_error(code, message=None)
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Sends and logs a complete error reply to the client. The numeric *code*
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specifies the HTTP error code, with *message* as optional, more specific text. A
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complete set of headers is sent, followed by text composed using the
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:attr:`error_message_format` class variable.
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.. method:: send_response(code, message=None)
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Adds a response header to the headers buffer and logs the accepted
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request. The HTTP response line is sent, followed by *Server* and
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*Date* headers. The values for these two headers are picked up from
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the :meth:`version_string` and :meth:`date_time_string` methods,
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respectively.
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.. method:: send_header(keyword, value)
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Adds the HTTP header to an internal buffer which will be written to the
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output stream when either :meth:`end_headers` or :meth:`flush_headers` is
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invoked. *keyword* should specify the header keyword, with *value*
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specifying its value. Note that, after the send_header calls are done,
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:meth:`end_headers` MUST BE called in order to complete the operation.
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.. versionchanged:: 3.2 Storing the headers in an internal buffer
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.. method:: send_response_only(code, message=None)
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Sends the reponse header only, used for the purposes when ``100
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Continue`` response is sent by the server to the client. The headers not
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buffered and sent directly the output stream.If the *message* is not
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specified, the HTTP message corresponding the response *code* is sent.
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.. versionadded:: 3.2
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.. method:: end_headers()
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Adds a blank line
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(indicating the end of the HTTP headers in the response)
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to the headers buffer and calls :meth:`flush_headers()`
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.. versionchanged:: 3.2 Writing the buffered headers to the output stream.
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.. method:: flush_headers()
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Finally send the headers to the output stream and flush the internal
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headers buffer.
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.. versionadded:: 3.3
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.. method:: log_request(code='-', size='-')
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Logs an accepted (successful) request. *code* should specify the numeric
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HTTP code associated with the response. If a size of the response is
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available, then it should be passed as the *size* parameter.
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.. method:: log_error(...)
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Logs an error when a request cannot be fulfilled. By default, it passes
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the message to :meth:`log_message`, so it takes the same arguments
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(*format* and additional values).
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.. method:: log_message(format, ...)
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Logs an arbitrary message to ``sys.stderr``. This is typically overridden
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to create custom error logging mechanisms. The *format* argument is a
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standard printf-style format string, where the additional arguments to
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:meth:`log_message` are applied as inputs to the formatting. The client
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address and current date and time are prefixed to every message logged.
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.. method:: version_string()
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Returns the server software's version string. This is a combination of the
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:attr:`server_version` and :attr:`sys_version` class variables.
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.. method:: date_time_string(timestamp=None)
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Returns the date and time given by *timestamp* (which must be None or in
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the format returned by :func:`time.time`), formatted for a message
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header. If *timestamp* is omitted, it uses the current date and time.
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The result looks like ``'Sun, 06 Nov 1994 08:49:37 GMT'``.
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.. method:: log_date_time_string()
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Returns the current date and time, formatted for logging.
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.. method:: address_string()
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Returns the client address, formatted for logging. A name lookup is
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performed on the client's IP address.
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.. class:: SimpleHTTPRequestHandler(request, client_address, server)
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This class serves files from the current directory and below, directly
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mapping the directory structure to HTTP requests.
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A lot of the work, such as parsing the request, is done by the base class
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:class:`BaseHTTPRequestHandler`. This class implements the :func:`do_GET`
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and :func:`do_HEAD` functions.
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The following are defined as class-level attributes of
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:class:`SimpleHTTPRequestHandler`:
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.. attribute:: server_version
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This will be ``"SimpleHTTP/" + __version__``, where ``__version__`` is
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defined at the module level.
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.. attribute:: extensions_map
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A dictionary mapping suffixes into MIME types. The default is
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signified by an empty string, and is considered to be
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``application/octet-stream``. The mapping is used case-insensitively,
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and so should contain only lower-cased keys.
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The :class:`SimpleHTTPRequestHandler` class defines the following methods:
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.. method:: do_HEAD()
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This method serves the ``'HEAD'`` request type: it sends the headers it
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would send for the equivalent ``GET`` request. See the :meth:`do_GET`
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method for a more complete explanation of the possible headers.
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.. method:: do_GET()
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The request is mapped to a local file by interpreting the request as a
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path relative to the current working directory.
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If the request was mapped to a directory, the directory is checked for a
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file named ``index.html`` or ``index.htm`` (in that order). If found, the
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file's contents are returned; otherwise a directory listing is generated
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by calling the :meth:`list_directory` method. This method uses
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:func:`os.listdir` to scan the directory, and returns a ``404`` error
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response if the :func:`listdir` fails.
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If the request was mapped to a file, it is opened and the contents are
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returned. Any :exc:`IOError` exception in opening the requested file is
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mapped to a ``404``, ``'File not found'`` error. Otherwise, the content
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type is guessed by calling the :meth:`guess_type` method, which in turn
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uses the *extensions_map* variable.
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A ``'Content-type:'`` header with the guessed content type is output,
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followed by a ``'Content-Length:'`` header with the file's size and a
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``'Last-Modified:'`` header with the file's modification time.
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Then follows a blank line signifying the end of the headers, and then the
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contents of the file are output. If the file's MIME type starts with
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``text/`` the file is opened in text mode; otherwise binary mode is used.
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For example usage, see the implementation of the :func:`test` function
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invocation in the :mod:`http.server` module.
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The :class:`SimpleHTTPRequestHandler` class can be used in the following
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manner in order to create a very basic webserver serving files relative to
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the current directory. ::
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import http.server
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import socketserver
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PORT = 8000
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Handler = http.server.SimpleHTTPRequestHandler
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httpd = socketserver.TCPServer(("", PORT), Handler)
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print("serving at port", PORT)
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httpd.serve_forever()
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:mod:`http.server` can also be invoked directly using the :option:`-m`
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switch of the interpreter a with ``port number`` argument. Similar to
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the previous example, this serves files relative to the current directory. ::
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python -m http.server 8000
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.. class:: CGIHTTPRequestHandler(request, client_address, server)
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This class is used to serve either files or output of CGI scripts from the
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current directory and below. Note that mapping HTTP hierarchic structure to
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local directory structure is exactly as in :class:`SimpleHTTPRequestHandler`.
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.. note::
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CGI scripts run by the :class:`CGIHTTPRequestHandler` class cannot execute
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redirects (HTTP code 302), because code 200 (script output follows) is
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sent prior to execution of the CGI script. This pre-empts the status
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code.
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The class will however, run the CGI script, instead of serving it as a file,
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if it guesses it to be a CGI script. Only directory-based CGI are used ---
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the other common server configuration is to treat special extensions as
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denoting CGI scripts.
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The :func:`do_GET` and :func:`do_HEAD` functions are modified to run CGI scripts
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and serve the output, instead of serving files, if the request leads to
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somewhere below the ``cgi_directories`` path.
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The :class:`CGIHTTPRequestHandler` defines the following data member:
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.. attribute:: cgi_directories
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This defaults to ``['/cgi-bin', '/htbin']`` and describes directories to
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treat as containing CGI scripts.
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The :class:`CGIHTTPRequestHandler` defines the following method:
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.. method:: do_POST()
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This method serves the ``'POST'`` request type, only allowed for CGI
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scripts. Error 501, "Can only POST to CGI scripts", is output when trying
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to POST to a non-CGI url.
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Note that CGI scripts will be run with UID of user nobody, for security
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reasons. Problems with the CGI script will be translated to error 403.
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