docs and test

1 files changed, 143 insertions, 0 deletions

diff --git a/docs/narr/subrequest.rst b/docs/narr/subrequest.rst
new file mode 100644
index 000000000..6ed679579
--- /dev/null
+++ b/docs/narr/subrequest.rst
@@ -0,0 +1,143 @@
+.. index::
+   single: subrequest
+
+.. _subrequest_chapter:
+
+Invoking a Subrequest
+=====================
+
+.. warning:: 
+
+   This feature was added in Pyramid 1.4a1.
+
+:app:`Pyramid` allows you to invoke a subrequest at any point during the
+processing of a request.  Invoking a subrequest allows you to obtain a
+:term:`response` object from a view callable within your :app:`Pyramid`
+application while you're executing a different view callable within the same
+application.
+
+Here's an example application which uses a subrequest:
+
+.. code-block:: python
+
+   from wsgiref.simple_server import make_server
+   from pyramid.config import Configurator
+   from pyramid.request import Request
+
+   def view_one(request):
+       subreq = Request.blank('/view_two')
+       response = request.subrequest(subreq)
+       return response
+
+   def view_two(request):
+       request.response.body = 'This came from view_two'
+       return request.response
+
+   if __name__ == '__main__':
+       config = Configurator()
+       config.add_route('one', '/view_one')
+       config.add_route('two', '/view_two')
+       config.add_view(view_one, route_name='one')
+       config.add_view(view_two, route_name='two')
+       app = config.make_wsgi_app()
+       server = make_server('0.0.0.0', 8080, app)
+       server.serve_forever()
+
+When ``/view_one`` is visted in a browser, the text printed in the browser
+pane will be ``This came from view_two``.  The ``view_one`` view used the
+:meth:`pyramid.request.Request.subrequest` API to obtain a response from
+another view (``view_two``) within the same application when it executed.  It
+did so by constructing a new request that had a URL that it knew would match
+the ``view_two`` view registration, and passed that new request along to
+:meth:`pyramid.request.Request.subrequest`.  The ``view_two`` view callable
+was invoked, and it returned a response.  The ``view_one`` view callable then
+simply returned the response it obtained from the ``view_two`` view callable.
+
+Note that it doesn't matter if the view callable invoked via a subrequest
+actually returns a literal Response object.  Any view callable that uses a
+renderer or which returns an object that can be interpreted by a response
+adapter will work too:
+
+.. code-block:: python
+
+   from wsgiref.simple_server import make_server
+   from pyramid.config import Configurator
+   from pyramid.request import Request
+
+   def view_one(request):
+       subreq = Request.blank('/view_two')
+       response = request.subrequest(subreq)
+       return response
+
+   def view_two(request):
+       return 'This came from view_two'
+
+   if __name__ == '__main__':
+       config = Configurator()
+       config.add_route('one', '/view_one')
+       config.add_route('two', '/view_two')
+       config.add_view(view_one, route_name='one')
+       config.add_view(view_two, route_name='two', renderer='string')
+       app = config.make_wsgi_app()
+       server = make_server('0.0.0.0', 8080, app)
+       server.serve_forever()
+
+Being able to unconditionally obtain a response object by invoking a view
+callable indirectly is the main advantage to using
+:meth:`pyramid.request.Request.subrequest` instead of simply importing it and
+executing it directly.  Note that there's not much advantage to invoking a
+view using a subrequest if you *can* invoke a view callable directly.  It's
+much slower to use a subrequest.
+
+The :meth:`pyramid.request.Request.subrequest` API accepts two arguments: a
+positional argument ``request`` that must be provided, and and ``use_tweens``
+keyword argument that is optional; it defaults to ``False``.
+
+The ``request`` object passed to the API must be an object that implements
+the Pyramid request interface (such as a :class:`pyramid.request.Request`
+instance).  If ``use_tweens`` is ``True``, the request will be sent to the
+:term:`tween` in the tween stack closest to the request ingress.  If
+``use_tweens`` is ``False``, the request will be sent to the main router
+handler, and no tweens will be invoked.  It's usually best to not invoke any
+tweens when executing a subrequest, because the original request will invoke
+any tween logic as necessary.  The :meth:`pyramid.request.Request.subrequest`
+function also:
+        
+- manages the threadlocal stack so that
+  :func:`~pyramid.threadlocal.get_current_request` and
+  :func:`~pyramid.threadlocal.get_current_registry` work during a request 
+  (they will return the subrequest instead of the original request)
+
+- Adds a ``registry`` attribute and a ``subrequest`` attribute to the request
+  object it's handed.
+
+- sets request extensions (such as those added via
+  :meth:`~pyramid.config.Configurator.add_request_method` or
+  :meth:`~pyramid.config.Configurator.set_request_property`) on the subrequest
+  object passed as ``request``
+
+- causes a :class:`~pyramid.event.NewRequest` event to be sent at the
+  beginning of request processing.
+
+- causes a :class:`~pyramid.event.ContextFound` event to be sent when a
+  context resource is found.
+  
+- causes a :class:`~pyramid.event.NewResponse` event to be sent when the
+  Pyramid application returns a response.
+
+- Calls any :term:`response callback` functions defined within the subrequest's
+  lifetime if a response is obtained from the Pyramid application.
+
+- Calls any :term:`finished callback` functions defined within the subrequest's
+  lifetime.
+
+It's a poor idea to use the original ``request`` object as an argument to
+:meth:`~pyramid.request.Request.subrequest`.  You should construct a new
+request instead as demonstrated in the above example, using
+:meth:`pyramid.request.Request.blank`.  Once you've constructed a request
+object, you'll need to massage the it to match the view callable you'd like
+to be executed during the subrequest.  This can be done by adjusting the
+subrequest's URL, its headers, its request method, and other attributes.  See
+the documentation for :class:`pyramid.request.Request` to understand how to
+massage your new request object into something that will match the view you'd
+like to call via a subrequest.