The information on this page is obsolete, incomplete or incorrect and left here only for reference and has not been ported to the new documentation wiki.
Please refer to the TurboGears documentation wiki for up-to-date documentation.
Paste & Turbogears Basic Flow
The following shows the default wsgi stack when running TurboGears with Paste. Note that the particular middleware might change depending on config values (right now, these are in the [app:main] section of the config file. Does that change?)
Here's the default wsgi call stack:
paste.httpserver basically just python's BaseHTTPServer. It gets the request in and calls the top of the wsgi stack.
paste.deploy.config adds paste.config (copy of config data) to the wsgi environment.
Note: there are several debug related middlewares which may be inserted here by config parameters. See: rhubarbtart/paste_templates/rhubarbtart/docs/devel_config.ini_tmpl
paste.recursive this allows "internal redirects" and "include" calling. Adds paste.recursive.forward and paste.recursive.include to the wsgi environment. (enabled in conf with 'use_recursive')
paste.httpexceptions Handles basic http exceptions. If downstream wsgi apps throws (for instance) an HTTPMovedPermanently exception, then this module handles the exception and fills out the headers appropriate for the exception.
rhubarbtart.__init__ Create cherry-py-like request and response objects, then call the approprite method based on the url.
The RhubarbTart object that gets called is really the root TurboGears controller. The _run_app method matches the url from PATH_INFO, to nodes in the root TurboGears controller. When it hits a node which is a wsgi app (for instance, if a sub-controller under TurboGears is a RootController rather than a Controller), then it moves the "swollowed" part of PATH_INFO to SCRIPT_NAME and immediately calls the root controller.
If it doesn't find any wsgi_application controllers at all, then it calls the node furthest down on the path that has the "expose" property set.
So, if our nodes look like:
Note that boxes are "root" controllers, ovals are regular controllers and diamonds are methods.
Processing the url /tg_blog/index/blah/boom will match the tg_blog and index nodes (neither of which is a wsgi application), so it ends up calling the index method.
Processing the url /members/member_list/get_member will first get to members which is a wsgi application, so it's immediately called. Note that SCRIPT_NAME environment now has /members in it and PATH_INFO has /member_list/get_member. Now members happens to also be a TurboGears RootController so the same RhubarbTart call happens all over again, this time with members as the root. This time, the url matches down to the get_member method and it is called.
Just as a note, this low-level flow seems to be changing...