Dispatch to multiple ASGI applications

It is often useful serve multiple ASGI applications at once, under differing root paths. Hypercorn does not support this directly, but the DispatcherMiddleware included with Hypercorn can. This middleware allows multiple applications to be served on different mounts.

The DispatcherMiddleware takes a dictionary of applications keyed by the root path. The order of entry in this dictionary is important, as the root paths will be checked in this order. Hence it is important to add /a/b before /a or the latter will match everything first. Also note that the root path should not include the trailing slash.

An example usage is to to serve a graphql application alongside a static file serving application. Using the graphql app is called graphql_app serving everything with the root path /graphql and a static file app called static_app serving everything else i.e. a root path of / the DispatcherMiddleware can be setup as,

from hypercorn.middleware import DispatcherMiddleware

dispatcher_app = DispatcherMiddleware({
    "/graphql": graphql_app,
    "/": static_app,
})

which can then be served by hypercorn,

$ hypercorn module:dispatcher_app