Merge branch 'feature.subrequest'

5 files changed, 253 insertions, 0 deletions

diff --git a/docs/api/request.rst b/docs/api/request.rst
index 1112ea069..1718d0743 100644
--- a/docs/api/request.rst
+++ b/docs/api/request.rst
@@ -161,6 +161,55 @@
       request, the value of this attribute will be ``None``. See
       :ref:`matched_route`.
 
+   .. method:: invoke_subrequest(request, use_tweens=False)
+
+      .. warning:: 
+
+         This API was added in Pyramid 1.4a1.
+
+      Obtain a response object from the Pyramid application based on
+      information in the ``request`` object provided.  The ``request`` object
+      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.  This isn't *actually* a method of the Request object; it's
+      a callable added when the Pyramid router is invoked, or when a
+      subrequest is invoked.  This 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)
+
+      - Adds a ``registry`` attribute (the current Pyramid registry) and a
+        ``invoke_subrequest`` attribute (a callable) 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
+        request it's passed.
+
+      - 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
+        request's lifetime if a response is obtained from the Pyramid
+        application.
+
+      - Calls any :term:`finished callback` functions defined within the
+        request's lifetime.
+
+      See also :ref:`subrequest_chapter`.
+
    .. automethod:: add_response_callback
 
    .. automethod:: add_finished_callback
diff --git a/docs/index.rst b/docs/index.rst
index 4a9b3951b..faf8258c1 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -83,6 +83,7 @@ Narrative documentation in chapter form explaining how to use
    narr/traversal
    narr/security
    narr/hybrid
+   narr/subrequest
    narr/hooks
    narr/introspector
    narr/extending
diff --git a/docs/latexindex.rst b/docs/latexindex.rst
index 604e6e7c6..6bb875f73 100644
--- a/docs/latexindex.rst
+++ b/docs/latexindex.rst
@@ -54,6 +54,7 @@ Narrative Documentation
    narr/traversal
    narr/security
    narr/hybrid
+   narr/subrequest
    narr/hooks
    narr/introspector
    narr/extending
diff --git a/docs/narr/subrequest.rst b/docs/narr/subrequest.rst
new file mode 100644
index 000000000..bd50b6053
--- /dev/null
+++ b/docs/narr/subrequest.rst
@@ -0,0 +1,186 @@
+.. 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.invoke_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.invoke_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.invoke_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.invoke_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()
+
+Even though the ``view_two`` view callable returned a string, it was invoked
+in such a way that the ``string`` renderer associated with the view
+registration that was found turned it into a "real" response object for
+consumption by ``view_one``.
+
+Being able to unconditionally obtain a response object by invoking a view
+callable indirectly is the main advantage to using
+:meth:`pyramid.request.Request.invoke_subrequest` instead of simply importing
+the view callable 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.  Subrequests are slower and are less convenient if you
+actually do want just the literal information returned by a function that
+happens to be a view callable.
+
+Note that if a view callable invoked by a subrequest raises an exception, the
+exception will usually bubble up to the invoking code:
+
+.. 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.invoke_subrequest(subreq)
+       return response
+
+   def view_two(request):
+       raise ValueError('foo')
+
+   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()
+
+In the above application, the call to ``request.invoke_subrequest(subreq)``
+will actually raise a :exc:`ValueError` exception instead of retrieving a
+"500" response from the attempted invocation of ``view_two``.
+
+The :meth:`pyramid.request.Request.invoke_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.invoke_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 ``invoke_subrequest`` attribute (a
+  callable) 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.invoke_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.
+
+We've demonstrated use of a subrequest from within a view callable, but you
+can use the :meth:`~pyramid.request.Request.invoke_subrequest` API from
+within a tween or an event handler as well.
diff --git a/docs/whatsnew-1.4.rst b/docs/whatsnew-1.4.rst
index 58a44202c..8e333bf5d 100644
--- a/docs/whatsnew-1.4.rst
+++ b/docs/whatsnew-1.4.rst
@@ -65,6 +65,14 @@ Partial Mako and Chameleon Template Renderings
   defined as ``macroname`` within the ``template.pt`` template instead of the
   entire templae.
 
+Subrequest Support
+~~~~~~~~~~~~~~~~~~
+
+- Developers may invoke a subrequest by using the
+  :meth:`pyramid.request.Request.invoke_subrequest` API.  This allows a
+  developer to obtain a response from one view callable by issuing a subrequest
+  from within a different view callable.
+
 Minor Feature Additions
 -----------------------
 
@@ -222,6 +230,12 @@ Backwards Incompatibilities
   * ``registerSettings``, use 
     :meth:`pyramid.config.Configurator.add_settings` instead.
 
+- In Pyramid 1.3 and previous, the ``__call__`` method of a Response object
+  returned by a view was invoked before any finished callbacks were executed.
+  As of this release, the ``__call__`` method of a Response object is invoked
+  *after* finished callbacks are executed.  This is in support of the
+  :meth:`pyramid.request.Request.invoke_subrequest` feature.
+
 Deprecations
 ------------
 
@@ -239,6 +253,8 @@ Documentation Enhancements
   how to show Pyramid-generated deprecation warnings while running tests and
   while running a server.
 
+- Added a :ref:`subrequest_chapter` chapter to the narrative documentation.
+
 - Many cleanups and improvements to narrative and API docs.
 
 Dependency Changes