11.17 BaseHTTPServer -- Basic HTTP server

Python 2.2

previous page next page

11.17 `BaseHTTPServer` -- Basic HTTP server

This module defines two classes for implementing HTTP servers (Web servers). Usually, this module isn't used directly, but is used as a basis for building functioning Web servers. See the SimpleHTTPServer and CGIHTTPServer modules.

The first class, HTTPServer, is a SocketServer.TCPServer subclass. It creates and listens at the HTTP socket, dispatching the requests to a handler. Code to create and run the server looks like this:

def run(server_class=BaseHTTPServer.HTTPServer,
        handler_class=BaseHTTPServer.BaseHTTPRequestHandler):
    server_address = ('', 8000)
    httpd = server_class(server_address, handler_class)
    httpd.serve_forever()

class HTTPServer( server_address, RequestHandlerClass): This class builds on the TCPServer class by storing the server address as instance variables named server_name and server_port. The server is accessible by the handler, typically through the handler's server instance variable.

class BaseHTTPRequestHandler( request, client_address, server): This class is used to handle the HTTP requests that arrive at the server. By itself, it cannot respond to any actual HTTP requests; it must be subclassed to handle each request method (e.g. GET or POST). BaseHTTPRequestHandler provides a number of class and instance variables, and methods for use by subclasses.
The handler will parse the request and the headers, then call a method specific to the request type. The method name is constructed from the request. For example, for the request method "SPAM", the do_SPAM() method will be called with no arguments. All of the relevant information is stored in instance variables of the handler. Subclasses should not need to override or extend the __init__() method.

BaseHTTPRequestHandler has the following instance variables:

client_address: Contains a tuple of the form (host, port) referring to the client's address.

command: Contains the command (request type). For example, 'GET'.

path: Contains the request path.

request_version: Contains the version string from the request. For example, 'HTTP/1.0'.

headers: Holds an instance of the class specified by the MessageClass class variable. This instance parses and manages the headers in the HTTP request.

rfile: Contains an input stream, positioned at the start of the optional input data.

wfile: Contains the output stream for writing a response back to the client. Proper adherence to the HTTP protocol must be used when writing to this stream.

BaseHTTPRequestHandler has the following class variables:

server_version: Specifies the server software version. You may want to override this. The format is multiple whitespace-separated strings, where each string is of the form name[/version]. For example, 'BaseHTTP/0.2'.

sys_version: Contains the Python system version, in a form usable by the version_string method and the server_version class variable. For example, 'Python/1.4'.

error_message_format: Specifies a format string for building an error response to the client. It uses parenthesized, keyed format specifiers, so the format operand must be a dictionary. The code key should be an integer, specifying the numeric HTTP error code value. message should be a string containing a (detailed) error message of what occurred, and explain should be an explanation of the error code number. Default message and explain values can found in the responses class variable.

protocol_version: This specifies the HTTP protocol version used in responses. If set to 'HTTP/1.1', the server will permit HTTP persistent connections; however, your server must then include an accurate Content-Length header (using send_header()) in all of its responses to clients. For backwards compatibility, the setting defaults to 'HTTP/1.0'.

MessageClass: Specifies a rfc822.Message-like class to parse HTTP headers. Typically, this is not overridden, and it defaults to mimetools.Message.

responses: This variable contains a mapping of error code integers to two-element tuples containing a short and long message. For example, {code: (shortmessage, longmessage)}. The shortmessage is usually used as the message key in an error response, and longmessage as the explain key (see the error_message_format class variable).

A BaseHTTPRequestHandler instance has the following methods:

handle( ): Calls handle_one_request() once (or, if persistent connections are enabled, multiple times) to handle incoming HTTP requests. You should never need to override it; instead, implement appropriate do_*() methods.

handle_one_request( ): This method will parse and dispatch the request to the appropriate do_*() method. You should never need to override it.

send_error( code[, message]): Sends and logs a complete error reply to the client. The numeric code specifies the HTTP error code, with message as optional, more specific text. A complete set of headers is sent, followed by text composed using the error_message_format class variable.

send_response( code[, message]): Sends a response header and logs the accepted request. The HTTP response line is sent, followed by Server and Date headers. The values for these two headers are picked up from the version_string() and date_time_string() methods, respectively.

send_header( keyword, value): Writes a specific HTTP header to the output stream. keyword should specify the header keyword, with value specifying its value.

end_headers( ): Sends a blank line, indicating the end of the HTTP headers in the response.

log_request( [code[, size]]): Logs an accepted (successful) request. code should specify the numeric HTTP code associated with the response. If a size of the response is available, then it should be passed as the size parameter.

log_error( ...): Logs an error when a request cannot be fulfilled. By default, it passes the message to log_message(), so it takes the same arguments (format and additional values).

log_message( format, ...): Logs an arbitrary message to sys.stderr. This is typically overridden to create custom error logging mechanisms. The format argument is a standard printf-style format string, where the additional arguments to log_message() are applied as inputs to the formatting. The client address and current date and time are prefixed to every message logged.

version_string( ): Returns the server software's version string. This is a combination of the server_version and sys_version class variables.

date_time_string( ): Returns the current date and time, formatted for a message header.

log_data_time_string( ): Returns the current date and time, formatted for logging.

address_string( ): Returns the client address, formatted for logging. A name lookup is performed on the client's IP address.