20.20. http.server — HTTP servers
This module defines classes for implementing HTTP servers (Web servers).
One 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=HTTPServer, handler_class=BaseHTTPRequestHandler):
server_address = ('', 8000)
httpd = server_class(server_address, handler_class)
httpd.serve_forever()
-
class http.server.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.
The HTTPServer must be given a RequestHandlerClass on instantiation,
of which this module provides three different variants:
-
class http.server.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.
-
server
- Contains the server instance.
-
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.
-
error_content_type
- Specifies the Content-Type HTTP header of error responses sent to the
client. The default value is 'text/html'.
-
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 an email.message.Message-like class to parse HTTP
headers. Typically, this is not overridden, and it defaults to
http.client.HTTPMessage.
-
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=None)
- 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=None)
- 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(timestamp=None)
Returns the date and time given by timestamp (which must be None or in
the format returned by time.time()), formatted for a message
header. If timestamp is omitted, it uses the current date and time.
The result looks like 'Sun, 06 Nov 1994 08:49:37 GMT'.
-
log_date_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.
-
class http.server.SimpleHTTPRequestHandler(request, client_address, server)
This class serves files from the current directory and below, directly
mapping the directory structure to HTTP requests.
A lot of the work, such as parsing the request, is done by the base class
BaseHTTPRequestHandler. This class implements the do_GET()
and do_HEAD() functions.
The following are defined as class-level attributes of
SimpleHTTPRequestHandler:
-
server_version
- This will be "SimpleHTTP/" + __version__, where __version__ is
defined at the module level.
-
extensions_map
- A dictionary mapping suffixes into MIME types. The default is
signified by an empty string, and is considered to be
application/octet-stream. The mapping is used case-insensitively,
and so should contain only lower-cased keys.
The SimpleHTTPRequestHandler class defines the following methods:
-
do_HEAD()
- This method serves the 'HEAD' request type: it sends the headers it
would send for the equivalent GET request. See the do_GET()
method for a more complete explanation of the possible headers.
-
do_GET()
The request is mapped to a local file by interpreting the request as a
path relative to the current working directory.
If the request was mapped to a directory, the directory is checked for a
file named index.html or index.htm (in that order). If found, the
file’s contents are returned; otherwise a directory listing is generated
by calling the list_directory() method. This method uses
os.listdir() to scan the directory, and returns a 404 error
response if the listdir() fails.
If the request was mapped to a file, it is opened and the contents are
returned. Any IOError exception in opening the requested file is
mapped to a 404, 'File not found' error. Otherwise, the content
type is guessed by calling the guess_type() method, which in turn
uses the extensions_map variable.
A 'Content-type:' header with the guessed content type is output,
followed by a 'Content-Length:' header with the file’s size and a
'Last-Modified:' header with the file’s modification time.
Then follows a blank line signifying the end of the headers, and then the
contents of the file are output. If the file’s MIME type starts with
text/ the file is opened in text mode; otherwise binary mode is used.
For example usage, see the implementation of the test() function
invocation in the http.server module.
The SimpleHTTPRequestHandler class can be invoked the following manner
with the http.server to create a very basic webserver serving files
relative to the current directory.:
import http.server
import socketserver
PORT = 8000
Handler = http.server.SimpleHTTPRequestHandler
httpd = socketserver.TCPServer(("", PORT), Handler)
print("serving at port", PORT)
httpd.serve_forever()
http.server can also be invoked directly using the -m switch of
interpreter a with port number argument which uses
SimpleHTTPRequestHandler as the default request Handler. Similar to
the previous example, even this serves files relative to the current
directory.:
python -m http.server 8000
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class http.server.CGIHTTPRequestHandler(request, client_address, server)
This class is used to serve either files or output of CGI scripts from the
current directory and below. Note that mapping HTTP hierarchic structure to
local directory structure is exactly as in SimpleHTTPRequestHandler.
Note
CGI scripts run by the CGIHTTPRequestHandler class cannot execute
redirects (HTTP code 302), because code 200 (script output follows) is
sent prior to execution of the CGI script. This pre-empts the status
code.
The class will however, run the CGI script, instead of serving it as a file,
if it guesses it to be a CGI script. Only directory-based CGI are used —
the other common server configuration is to treat special extensions as
denoting CGI scripts.
The do_GET() and do_HEAD() functions are modified to run CGI scripts
and serve the output, instead of serving files, if the request leads to
somewhere below the cgi_directories path.
The CGIHTTPRequestHandler defines the following data member:
-
cgi_directories
- This defaults to ['/cgi-bin', '/htbin'] and describes directories to
treat as containing CGI scripts.
The CGIHTTPRequestHandler defines the following method:
-
do_POST()
- This method serves the 'POST' request type, only allowed for CGI
scripts. Error 501, “Can only POST to CGI scripts”, is output when trying
to POST to a non-CGI url.
Note that CGI scripts will be run with UID of user nobody, for security
reasons. Problems with the CGI script will be translated to error 403.