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"""
Application Dispatcher
======================
This middleware creates a single WSGI application that dispatches to
multiple other WSGI applications mounted at different URL paths.
A common example is writing a Single Page Application, where you have a
backend API and a frontend written in JavaScript that does the routing
in the browser rather than requesting different pages from the server.
The frontend is a single HTML and JS file that should be served for any
path besides "/api".
This example dispatches to an API app under "/api", an admin app
under "/admin", and an app that serves frontend files for all other
requests::
app = DispatcherMiddleware(serve_frontend, {
'/api': api_app,
'/admin': admin_app,
})
In production, you might instead handle this at the HTTP server level,
serving files or proxying to application servers based on location. The
API and admin apps would each be deployed with a separate WSGI server,
and the static files would be served directly by the HTTP server.
.. autoclass:: DispatcherMiddleware
:copyright: 2007 Pallets
:license: BSD-3-Clause
"""
import typing as t
if t.TYPE_CHECKING:
from _typeshed.wsgi import StartResponse
from _typeshed.wsgi import WSGIApplication
from _typeshed.wsgi import WSGIEnvironment
class DispatcherMiddleware:
"""Combine multiple applications as a single WSGI application.
Requests are dispatched to an application based on the path it is
mounted under.
:param app: The WSGI application to dispatch to if the request
doesn't match a mounted path.
:param mounts: Maps path prefixes to applications for dispatching.
"""
def __init__(
self,
app: "WSGIApplication",
mounts: t.Optional[t.Dict[str, "WSGIApplication"]] = None,
) -> None:
self.app = app
self.mounts = mounts or {}
def __call__(
self, environ: "WSGIEnvironment", start_response: "StartResponse"
) -> t.Iterable[bytes]:
script = environ.get("PATH_INFO", "")
path_info = ""
while "/" in script:
if script in self.mounts:
app = self.mounts[script]
break
script, last_item = script.rsplit("/", 1)
path_info = f"/{last_item}{path_info}"
else:
app = self.mounts.get(script, self.app)
original_script_name = environ.get("SCRIPT_NAME", "")
environ["SCRIPT_NAME"] = original_script_name + script
environ["PATH_INFO"] = path_info
return app(environ, start_response)
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