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import asyncio
import inspect
def is_double_callable(application):
Tests to see if an application is a legacy-style (double-callable) application.
# Look for a hint on the object first
if getattr(application, "_asgi_single_callable", False):
return False
if getattr(application, "_asgi_double_callable", False):
return True
# Uninstanted classes are double-callable
if inspect.isclass(application):
return True
# Instanted classes depend on their __call__
if hasattr(application, "__call__"):
# We only check to see if its __call__ is a coroutine function -
# if it's not, it still might be a coroutine function itself.
if asyncio.iscoroutinefunction(application.__call__):
return False
# Non-classes we just check directly
return not asyncio.iscoroutinefunction(application)
def double_to_single_callable(application):
Transforms a double-callable ASGI application into a single-callable one.
async def new_application(scope, receive, send):
instance = application(scope)
return await instance(receive, send)
return new_application
def guarantee_single_callable(application):
Takes either a single- or double-callable application and always returns it
in single-callable style. Use this to add backwards compatibility for ASGI
2.0 applications to your server/test harness/etc.
if is_double_callable(application):
application = double_to_single_callable(application)
return application
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