wsgiref — WSGI Utilities and Reference Implementation (original) (raw)

Source code: Lib/wsgiref

The Web Server Gateway Interface (WSGI) is a standard interface between web server software and web applications written in Python. Having a standard interface makes it easy to use an application that supports WSGI with a number of different web servers.

Only authors of web servers and programming frameworks need to know every detail and corner case of the WSGI design. You don’t need to understand every detail of WSGI just to install a WSGI application or to write a web application using an existing framework.

wsgiref is a reference implementation of the WSGI specification that can be used to add WSGI support to a web server or framework. It provides utilities for manipulating WSGI environment variables and response headers, base classes for implementing WSGI servers, a demo HTTP server that serves WSGI applications, types for static type checking, and a validation tool that checks WSGI servers and applications for conformance to the WSGI specification (PEP 3333).

See wsgi.readthedocs.io for more information about WSGI, and links to tutorials and other resources.

wsgiref.util – WSGI environment utilities¶

This module provides a variety of utility functions for working with WSGI environments. A WSGI environment is a dictionary containing HTTP request variables as described in PEP 3333. All of the functions taking an _environ_parameter expect a WSGI-compliant dictionary to be supplied; please seePEP 3333 for a detailed specification andWSGIEnvironment for a type alias that can be used in type annotations.

wsgiref.util.guess_scheme(environ)¶

Return a guess for whether wsgi.url_scheme should be “http” or “https”, by checking for a HTTPS environment variable in the environ dictionary. The return value is a string.

This function is useful when creating a gateway that wraps CGI or a CGI-like protocol such as FastCGI. Typically, servers providing such protocols will include a HTTPS variable with a value of “1”, “yes”, or “on” when a request is received via SSL. So, this function returns “https” if such a value is found, and “http” otherwise.

wsgiref.util.request_uri(environ, include_query=True)¶

Return the full request URI, optionally including the query string, using the algorithm found in the “URL Reconstruction” section of PEP 3333. If_include_query_ is false, the query string is not included in the resulting URI.

wsgiref.util.application_uri(environ)¶

Similar to request_uri(), except that the PATH_INFO andQUERY_STRING variables are ignored. The result is the base URI of the application object addressed by the request.

wsgiref.util.shift_path_info(environ)¶

Shift a single name from PATH_INFO to SCRIPT_NAME and return the name. The environ dictionary is modified in-place; use a copy if you need to keep the original PATH_INFO or SCRIPT_NAME intact.

If there are no remaining path segments in PATH_INFO, None is returned.

Typically, this routine is used to process each portion of a request URI path, for example to treat the path as a series of dictionary keys. This routine modifies the passed-in environment to make it suitable for invoking another WSGI application that is located at the target URI. For example, if there is a WSGI application at /foo, and the request URI path is /foo/bar/baz, and the WSGI application at /foo calls shift_path_info(), it will receive the string “bar”, and the environment will be updated to be suitable for passing to a WSGI application at /foo/bar. That is, SCRIPT_NAME will change from/foo to /foo/bar, and PATH_INFO will change from /bar/baz to/baz.

When PATH_INFO is just a “/”, this routine returns an empty string and appends a trailing slash to SCRIPT_NAME, even though empty path segments are normally ignored, and SCRIPT_NAME doesn’t normally end in a slash. This is intentional behavior, to ensure that an application can tell the difference between URIs ending in /x from ones ending in /x/ when using this routine to do object traversal.

wsgiref.util.setup_testing_defaults(environ)¶

Update environ with trivial defaults for testing purposes.

This routine adds various parameters required for WSGI, including HTTP_HOST,SERVER_NAME, SERVER_PORT, REQUEST_METHOD, SCRIPT_NAME,PATH_INFO, and all of the PEP 3333-defined wsgi.* variables. It only supplies default values, and does not replace any existing settings for these variables.

This routine is intended to make it easier for unit tests of WSGI servers and applications to set up dummy environments. It should NOT be used by actual WSGI servers or applications, since the data is fake!

Example usage (see also demo_app()for another example):

from wsgiref.util import setup_testing_defaults from wsgiref.simple_server import make_server

A relatively simple WSGI application. It's going to print out the

environment dictionary after being updated by setup_testing_defaults

def simple_app(environ, start_response): setup_testing_defaults(environ)

status = '200 OK'
headers = [('Content-type', 'text/plain; charset=utf-8')]

start_response(status, headers)

ret = [("%s: %s\n" % (key, value)).encode("utf-8")
       for key, value in environ.items()]
return ret

with make_server('', 8000, simple_app) as httpd: print("Serving on port 8000...") httpd.serve_forever()

In addition to the environment functions above, the wsgiref.util module also provides these miscellaneous utilities:

wsgiref.util.is_hop_by_hop(header_name)¶

Return True if ‘header_name’ is an HTTP/1.1 “Hop-by-Hop” header, as defined byRFC 2616.

class wsgiref.util.FileWrapper(filelike, blksize=8192)¶

A concrete implementation of the wsgiref.types.FileWrapperprotocol used to convert a file-like object to an iterator. The resulting objects are iterables. As the object is iterated over, the optional blksize parameter will be repeatedly passed to the _filelike_object’s read() method to obtain bytestrings to yield. When read()returns an empty bytestring, iteration is ended and is not resumable.

If filelike has a close() method, the returned object will also have aclose() method, and it will invoke the filelike object’s close()method when called.

Example usage:

from io import StringIO from wsgiref.util import FileWrapper

We're using a StringIO-buffer for as the file-like object

filelike = StringIO("This is an example file-like object"*10) wrapper = FileWrapper(filelike, blksize=5)

for chunk in wrapper: print(chunk)

Changed in version 3.11: Support for __getitem__() method has been removed.

wsgiref.simple_server – a simple WSGI HTTP server¶

This module implements a simple HTTP server (based on http.server) that serves WSGI applications. Each server instance serves a single WSGI application on a given host and port. If you want to serve multiple applications on a single host and port, you should create a WSGI application that parses PATH_INFO to select which application to invoke for each request. (E.g., using the shift_path_info() function fromwsgiref.util.)

wsgiref.simple_server.make_server(host, port, app, server_class=WSGIServer, handler_class=WSGIRequestHandler)¶

Create a new WSGI server listening on host and port, accepting connections for app. The return value is an instance of the supplied server_class, and will process requests using the specified handler_class. app must be a WSGI application object, as defined by PEP 3333.

Example usage:

from wsgiref.simple_server import make_server, demo_app

with make_server('', 8000, demo_app) as httpd: print("Serving HTTP on port 8000...")

# Respond to requests until process is killed
httpd.serve_forever()

# Alternative: serve one request, then exit
httpd.handle_request()

wsgiref.simple_server.demo_app(environ, start_response)¶

This function is a small but complete WSGI application that returns a text page containing the message “Hello world!” and a list of the key/value pairs provided in the environ parameter. It’s useful for verifying that a WSGI server (such as wsgiref.simple_server) is able to run a simple WSGI application correctly.

The start_response callable should follow the StartResponse protocol.

class wsgiref.simple_server.WSGIServer(server_address, RequestHandlerClass)¶

Create a WSGIServer instance. server_address should be a(host,port) tuple, and RequestHandlerClass should be the subclass ofhttp.server.BaseHTTPRequestHandler that will be used to process requests.

You do not normally need to call this constructor, as the make_server()function can handle all the details for you.

WSGIServer is a subclass of http.server.HTTPServer, so all of its methods (such as serve_forever() and handle_request()) are available. WSGIServer also provides these WSGI-specific methods:

set_app(application)¶

Sets the callable application as the WSGI application that will receive requests.

get_app()¶

Returns the currently set application callable.

Normally, however, you do not need to use these additional methods, asset_app() is normally called by make_server(), and theget_app() exists mainly for the benefit of request handler instances.

class wsgiref.simple_server.WSGIRequestHandler(request, client_address, server)¶

Create an HTTP handler for the given request (i.e. a socket), client_address(a (host,port) tuple), and server (WSGIServer instance).

You do not need to create instances of this class directly; they are automatically created as needed by WSGIServer objects. You can, however, subclass this class and supply it as a handler_class to themake_server() function. Some possibly relevant methods for overriding in subclasses:

get_environ()¶

Return a WSGIEnvironment dictionary for a request. The default implementation copies the contents of the WSGIServer object’sbase_environ dictionary attribute and then adds various headers derived from the HTTP request. Each call to this method should return a new dictionary containing all of the relevant CGI environment variables as specified inPEP 3333.

get_stderr()¶

Return the object that should be used as the wsgi.errors stream. The default implementation just returns sys.stderr.

handle()¶

Process the HTTP request. The default implementation creates a handler instance using a wsgiref.handlers class to implement the actual WSGI application interface.

wsgiref.validate — WSGI conformance checker¶

When creating new WSGI application objects, frameworks, servers, or middleware, it can be useful to validate the new code’s conformance usingwsgiref.validate. This module provides a function that creates WSGI application objects that validate communications between a WSGI server or gateway and a WSGI application object, to check both sides for protocol conformance.

Note that this utility does not guarantee complete PEP 3333 compliance; an absence of errors from this module does not necessarily mean that errors do not exist. However, if this module does produce an error, then it is virtually certain that either the server or application is not 100% compliant.

This module is based on the paste.lint module from Ian Bicking’s “Python Paste” library.

wsgiref.validate.validator(application)¶

Wrap application and return a new WSGI application object. The returned application will forward all requests to the original application, and will check that both the application and the server invoking it are conforming to the WSGI specification and to RFC 2616.

Any detected nonconformance results in an AssertionError being raised; note, however, that how these errors are handled is server-dependent. For example, wsgiref.simple_server and other servers based onwsgiref.handlers (that don’t override the error handling methods to do something else) will simply output a message that an error has occurred, and dump the traceback to sys.stderr or some other error stream.

This wrapper may also generate output using the warnings module to indicate behaviors that are questionable but which may not actually be prohibited by PEP 3333. Unless they are suppressed using Python command-line options or the warnings API, any such warnings will be written tosys.stderr (not wsgi.errors, unless they happen to be the same object).

Example usage:

from wsgiref.validate import validator from wsgiref.simple_server import make_server

Our callable object which is intentionally not compliant to the

standard, so the validator is going to break

def simple_app(environ, start_response): status = '200 OK' # HTTP Status headers = [('Content-type', 'text/plain')] # HTTP Headers start_response(status, headers)

# This is going to break because we need to return a list, and
# the validator is going to inform us
return b"Hello World"

This is the application wrapped in a validator

validator_app = validator(simple_app)

with make_server('', 8000, validator_app) as httpd: print("Listening on port 8000....") httpd.serve_forever()

wsgiref.handlers – server/gateway base classes¶

This module provides base handler classes for implementing WSGI servers and gateways. These base classes handle most of the work of communicating with a WSGI application, as long as they are given a CGI-like environment, along with input, output, and error streams.

class wsgiref.handlers.CGIHandler¶

CGI-based invocation via sys.stdin, sys.stdout, sys.stderr andos.environ. This is useful when you have a WSGI application and want to run it as a CGI script. Simply invoke CGIHandler().run(app), where app is the WSGI application object you wish to invoke.

This class is a subclass of BaseCGIHandler that sets wsgi.run_onceto true, wsgi.multithread to false, and wsgi.multiprocess to true, and always uses sys and os to obtain the necessary CGI streams and environment.

class wsgiref.handlers.IISCGIHandler¶

A specialized alternative to CGIHandler, for use when deploying on Microsoft’s IIS web server, without having set the config allowPathInfo option (IIS>=7) or metabase allowPathInfoForScriptMappings (IIS<7).

By default, IIS gives a PATH_INFO that duplicates the SCRIPT_NAME at the front, causing problems for WSGI applications that wish to implement routing. This handler strips any such duplicated path.

IIS can be configured to pass the correct PATH_INFO, but this causes another bug where PATH_TRANSLATED is wrong. Luckily this variable is rarely used and is not guaranteed by WSGI. On IIS<7, though, the setting can only be made on a vhost level, affecting all other script mappings, many of which break when exposed to the PATH_TRANSLATED bug. For this reason IIS<7 is almost never deployed with the fix (Even IIS7 rarely uses it because there is still no UI for it.).

There is no way for CGI code to tell whether the option was set, so a separate handler class is provided. It is used in the same way asCGIHandler, i.e., by calling IISCGIHandler().run(app), whereapp is the WSGI application object you wish to invoke.

Added in version 3.2.

class wsgiref.handlers.BaseCGIHandler(stdin, stdout, stderr, environ, multithread=True, multiprocess=False)¶

Similar to CGIHandler, but instead of using the sys andos modules, the CGI environment and I/O streams are specified explicitly. The multithread and multiprocess values are used to set thewsgi.multithread and wsgi.multiprocess flags for any applications run by the handler instance.

This class is a subclass of SimpleHandler intended for use with software other than HTTP “origin servers”. If you are writing a gateway protocol implementation (such as CGI, FastCGI, SCGI, etc.) that uses aStatus: header to send an HTTP status, you probably want to subclass this instead of SimpleHandler.

class wsgiref.handlers.SimpleHandler(stdin, stdout, stderr, environ, multithread=True, multiprocess=False)¶

Similar to BaseCGIHandler, but designed for use with HTTP origin servers. If you are writing an HTTP server implementation, you will probably want to subclass this instead of BaseCGIHandler.

This class is a subclass of BaseHandler. It overrides the__init__(), get_stdin(),get_stderr(), add_cgi_vars(),_write(), and _flush() methods to support explicitly setting the environment and streams via the constructor. The supplied environment and streams are stored in the stdin, stdout, stderr, andenviron attributes.

The write() method of stdout should write each chunk in full, like io.BufferedIOBase.

class wsgiref.handlers.BaseHandler¶

This is an abstract base class for running WSGI applications. Each instance will handle a single HTTP request, although in principle you could create a subclass that was reusable for multiple requests.

BaseHandler instances have only one method intended for external use:

run(app)¶

Run the specified WSGI application, app.

All of the other BaseHandler methods are invoked by this method in the process of running the application, and thus exist primarily to allow customizing the process.

The following methods MUST be overridden in a subclass:

_write(data)¶

Buffer the bytes data for transmission to the client. It’s okay if this method actually transmits the data; BaseHandler just separates write and flush operations for greater efficiency when the underlying system actually has such a distinction.

_flush()¶

Force buffered data to be transmitted to the client. It’s okay if this method is a no-op (i.e., if _write() actually sends the data).

get_stdin()¶

Return an object compatible with InputStreamsuitable for use as the wsgi.input of the request currently being processed.

get_stderr()¶

Return an object compatible with ErrorStreamsuitable for use as the wsgi.errors of the request currently being processed.

add_cgi_vars()¶

Insert CGI variables for the current request into the environ attribute.

Here are some other methods and attributes you may wish to override. This list is only a summary, however, and does not include every method that can be overridden. You should consult the docstrings and source code for additional information before attempting to create a customized BaseHandlersubclass.

Attributes and methods for customizing the WSGI environment:

wsgi_multithread¶

The value to be used for the wsgi.multithread environment variable. It defaults to true in BaseHandler, but may have a different default (or be set by the constructor) in the other subclasses.

wsgi_multiprocess¶

The value to be used for the wsgi.multiprocess environment variable. It defaults to true in BaseHandler, but may have a different default (or be set by the constructor) in the other subclasses.

wsgi_run_once¶

The value to be used for the wsgi.run_once environment variable. It defaults to false in BaseHandler, but CGIHandler sets it to true by default.

os_environ¶

The default environment variables to be included in every request’s WSGI environment. By default, this is a copy of os.environ at the time thatwsgiref.handlers was imported, but subclasses can either create their own at the class or instance level. Note that the dictionary should be considered read-only, since the default value is shared between multiple classes and instances.

server_software¶

If the origin_server attribute is set, this attribute’s value is used to set the default SERVER_SOFTWARE WSGI environment variable, and also to set a default Server: header in HTTP responses. It is ignored for handlers (such as BaseCGIHandler and CGIHandler) that are not HTTP origin servers.

Changed in version 3.3: The term “Python” is replaced with implementation specific term like “CPython”, “Jython” etc.

get_scheme()¶

Return the URL scheme being used for the current request. The default implementation uses the guess_scheme() function from wsgiref.utilto guess whether the scheme should be “http” or “https”, based on the current request’s environ variables.

setup_environ()¶

Set the environ attribute to a fully populated WSGI environment. The default implementation uses all of the above methods and attributes, plus theget_stdin(), get_stderr(), and add_cgi_vars() methods and thewsgi_file_wrapper attribute. It also inserts a SERVER_SOFTWARE key if not present, as long as the origin_server attribute is a true value and the server_software attribute is set.

Methods and attributes for customizing exception handling:

log_exception(exc_info)¶

Log the exc_info tuple in the server log. exc_info is a (type, value, traceback) tuple. The default implementation simply writes the traceback to the request’s wsgi.errors stream and flushes it. Subclasses can override this method to change the format or retarget the output, mail the traceback to an administrator, or whatever other action may be deemed suitable.

traceback_limit¶

The maximum number of frames to include in tracebacks output by the defaultlog_exception() method. If None, all frames are included.

error_output(environ, start_response)¶

This method is a WSGI application to generate an error page for the user. It is only invoked if an error occurs before headers are sent to the client.

This method can access the current error using sys.exception(), and should pass that information to start_response when calling it (as described in the “Error Handling” section of PEP 3333). In particular, the start_response callable should follow the StartResponseprotocol.

The default implementation just uses the error_status,error_headers, and error_body attributes to generate an output page. Subclasses can override this to produce more dynamic error output.

Note, however, that it’s not recommended from a security perspective to spit out diagnostics to any old user; ideally, you should have to do something special to enable diagnostic output, which is why the default implementation doesn’t include any.

error_status¶

The HTTP status used for error responses. This should be a status string as defined in PEP 3333; it defaults to a 500 code and message.

error_headers¶

The HTTP headers used for error responses. This should be a list of WSGI response headers ((name, value) tuples), as described in PEP 3333. The default list just sets the content type to text/plain.

error_body¶

The error response body. This should be an HTTP response body bytestring. It defaults to the plain text, “A server error occurred. Please contact the administrator.”

Methods and attributes for PEP 3333’s “Optional Platform-Specific File Handling” feature:

wsgi_file_wrapper¶

A wsgi.file_wrapper factory, compatible withwsgiref.types.FileWrapper, or None. The default value of this attribute is the wsgiref.util.FileWrapper class.

sendfile()¶

Override to implement platform-specific file transmission. This method is called only if the application’s return value is an instance of the class specified by the wsgi_file_wrapper attribute. It should return a true value if it was able to successfully transmit the file, so that the default transmission code will not be executed. The default implementation of this method just returns a false value.

Miscellaneous methods and attributes:

origin_server¶

This attribute should be set to a true value if the handler’s _write() and_flush() are being used to communicate directly to the client, rather than via a CGI-like gateway protocol that wants the HTTP status in a specialStatus: header.

This attribute’s default value is true in BaseHandler, but false inBaseCGIHandler and CGIHandler.

http_version¶

If origin_server is true, this string attribute is used to set the HTTP version of the response set to the client. It defaults to "1.0".

wsgiref.handlers.read_environ()¶

Transcode CGI variables from os.environ to PEP 3333 “bytes in unicode” strings, returning a new dictionary. This function is used byCGIHandler and IISCGIHandler in place of directly usingos.environ, which is not necessarily WSGI-compliant on all platforms and web servers using Python 3 – specifically, ones where the OS’s actual environment is Unicode (i.e. Windows), or ones where the environment is bytes, but the system encoding used by Python to decode it is anything other than ISO-8859-1 (e.g. Unix systems using UTF-8).

If you are implementing a CGI-based handler of your own, you probably want to use this routine instead of just copying values out of os.environdirectly.

Added in version 3.2.

wsgiref.types – WSGI types for static type checking¶

This module provides various types for static type checking as described in PEP 3333.

Added in version 3.11.

class wsgiref.types.StartResponse¶

A typing.Protocol describing start_response()callables (PEP 3333).

wsgiref.types.WSGIEnvironment¶

A type alias describing a WSGI environment dictionary.

wsgiref.types.WSGIApplication¶

A type alias describing a WSGI application callable.

class wsgiref.types.InputStream¶

A typing.Protocol describing a WSGI Input Stream.

class wsgiref.types.ErrorStream¶

A typing.Protocol describing a WSGI Error Stream.

class wsgiref.types.FileWrapper¶

A typing.Protocol describing a file wrapper. See wsgiref.util.FileWrapper for a concrete implementation of this protocol.

Examples¶

This is a working “Hello World” WSGI application, where the _start_response_callable should follow the StartResponse protocol:

""" Every WSGI application must have an application object - a callable object that accepts two arguments. For that purpose, we're going to use a function (note that you're not limited to a function, you can use a class for example). The first argument passed to the function is a dictionary containing CGI-style environment variables and the second variable is the callable object. """ from wsgiref.simple_server import make_server

def hello_world_app(environ, start_response): status = "200 OK" # HTTP Status headers = [("Content-type", "text/plain; charset=utf-8")] # HTTP Headers start_response(status, headers)

# The returned object is going to be printed
return [b"Hello World"]

with make_server("", 8000, hello_world_app) as httpd: print("Serving on port 8000...")

# Serve until process is killed
httpd.serve_forever()

Example of a WSGI application serving the current directory, accept optional directory and port number (default: 8000) on the command line:

""" Small wsgiref based web server. Takes a path to serve from and an optional port number (defaults to 8000), then tries to serve files. MIME types are guessed from the file names, 404 errors are raised if the file is not found. """ import mimetypes import os import sys from wsgiref import simple_server, util

def app(environ, respond): # Get the file name and MIME type fn = os.path.join(path, environ["PATH_INFO"][1:]) if "." not in fn.split(os.path.sep)[-1]: fn = os.path.join(fn, "index.html") mime_type = mimetypes.guess_file_type(fn)[0]

# Return 200 OK if file exists, otherwise 404 Not Found
if os.path.exists(fn):
    respond("200 OK", [("Content-Type", mime_type)])
    return util.FileWrapper(open(fn, "rb"))
else:
    respond("404 Not Found", [("Content-Type", "text/plain")])
    return [b"not found"]

if name == "main": # Get the path and port from command-line arguments path = sys.argv[1] if len(sys.argv) > 1 else os.getcwd() port = int(sys.argv[2]) if len(sys.argv) > 2 else 8000

# Make and start the server until control-c
httpd = simple_server.make_server("", port, app)
print(f"Serving {path} on port {port}, control-C to stop")
try:
    httpd.serve_forever()
except KeyboardInterrupt:
    print("Shutting down.")
    httpd.server_close()