[Web-SIG] Web Container Interface
ianb at colorstudy.com
Sat Jan 24 14:05:30 EST 2004
On Jan 23, 2004, at 6:36 PM, Phillip J. Eby wrote:
> At 03:31 PM 1/23/04 -0600, Ian Bicking wrote:
>> Well, I was thinking of the "parsed" representation of headers being
>> a dictionary, or a list of two-tuples. Systems that speak HTTP
>> directly will want access to these, so they can do all the CGI-ish
>> stuff necessary (translate the Status header to the response code,
>> look at Location). They can re-parse the headers on the way out, or
>> they could be provided with the headers directly. Seeing as most
>> frameworks collect the headers directly, it might be nice to save the
>> trouble of serializing the headers and then parsing them, at least
>> when possible.
> Maybe it would help if I rephrase one of my goals for WCI 1.0: *no
> existing app may be left behind*. There are *plenty* of existing apps
> and frameworks that expect to send headers over the output stream for
> external parsing. Making the interface used pre-parsed headers or
> no-parse headers would strand those applications in the pre-WCI world,
> or force everybody to write header parsers. In my view, that simply
> voids the point of having the interface in the first place.
I'm not proposing that applications be required to implement a richer
interface than what WCI 1.0 currently requires. Rather, that
applications be given the opportunity to implement a richer interface,
even if we don't give any indication (in the PEP) of what that
interface would be.
>> Well, the application may want to share configuration with other
>> applications (even if it's where-do-I-find-my-configuration-file
>> configuration). This could be container-wide, so the application
>> could query the container for that information.
> That seems to me like straying into general component framework
> territory. PEAK and Zope X3, for example, (and no doubt many more
> systems) have their own notions of how to share that kind of
> information. WCI should be agnostic about that.
These are use cases, not things I think need to be in WCI 1.0. We
should work towards making these things possible -- which means we
should leave room for WCI implementations to define their own
interfaces that work in this direction.
>> Or, the application may want to know something about the URL layout.
>> Mmm... which makes me think that PATH_INFO and SCRIPT_NAME need to be
>> well defined for runCGI, or alternate variables need to be
>> considered. Does SCRIPT_NAME (and several associated CGI variables,
>> PATH_INFO included) point to the application, or the container, or
> An excellent point. That *should* be added to the spec. I simply
> assumed they point to the object that is receiving the runCGI() call.
> It should be made explicit, though. Thanks!
Hmm... that might not be backward compatible. In both Webware and I
believe Zope (and probably several others) these point to the container
root, not the resource root. I would propose that these variables
remain undefined, and that additional variables be added with better
>> The application may want to know if there are any shared services it
>> can use, like a persistent storage for sessions, or a cron-type
>> service. Scheduling tasks particularly comes to mind -- it has to be
>> done very differently depending on the environment. In a
>> long-running threaded environment you could probably do it yourself.
>> In an async environment there's a specific callback that's part of
>> the control loop. In a process-based environment you may have to
>> talk to some parent process. In a CGI environment... well, you just
>> don't get one there.
> Again, this is totally the job of an application framework, and will
> result in an instant religious war to try and put it in what ought to
> be a nice narrowly defined interface. It should be more like a power
> outlet, and less like an ethernet jack. :)
Again, I'm not proposing we set out a standard that covers these, but
that we leave room for implementations to extend the standard to cover
>> Maybe I'm not entirely sure either. Something's bothering me,
>> though. I'm having a hard time picturing the use of this proposal to
>> do things we can't do now, i.e., hooking up things that weren't built
>> with each other specifically in mind.
> I have applications that run on ancient versions of ZPublisher that
> run as happily under my WCI containers as they do under straight CGI
> or in ZServer. I imagine I could run them under a Webware container
> if there was one, or a mod_python container, or whatever else.
> If that's not "things that weren't built with each other specifically
> in mind", I don't know what is.
> Granted, in each case a few lines of glue code are required, to create
> the container and create the app. And if a library doesn't already
> have a WCI container or app wrapper available, you have to write those
I remain skeptical. I can't really see how you'll run a Zope
application under plain CGI, or how both a Zope application and a
Twisted application could successfully run with the same interface. I
still can see that this is a step in the right direction -- not a big
step, but it's still the right direction.
> But that's a *lot* better than having to figure out from scratch how
> to connect two things today, if you can connect them at all. And, if
> somebody writes a WCI router, you should be able to use multiple apps
> in the same process. Indeed, people can write many different WCI
> routers, allowing them to use different mechanisms to find apps.
>> That's what I was conceding. We aren't ready to define what those
>> interfaces will be, but we need to keep in mind that there *will* be
>> other interfaces, and that the growth of those interfaces is
>> important to the utility of the WCI. Simply passing in the container
>> as an argument to runCGI is probably sufficient.
> Actually, I think it's more likely that a WCI 2.0 would grow another
> method, similar to the Java servlet 'init()' method, to tell the app
> that it's being "used by" a particular container. However, at that
> point we'll also want to know something about what people actually
> want to get from a container, if anything.
I think WCI 1.0 needs an init(), or something equivalent (like simply
passing the container in to runCGI()). I think it is useful to provide
that hook, even if we give implementors no specification beyond that.
A portable application might even go as far as doing:
if container.__class__.__name__ == 'AppServer':
# Probably Webware, we'll do X
elif container.__class__.__name__ == 'ZPublisher':
# Zope, we do Y
If that's what it takes for the author of the application to get things
to work, so be it. Portable applications in Python typically require
some special cases as issues arise -- it's better to enable developers
than to enforce agnosticism. This is the distinction I would make
between Python's approach to portability and Java's -- and I think
Python is more successful in its approach. Hopefully experience with
these special cases can be used to specify container interfaces for WCI
Ian Bicking | ianb at colorstudy.com | http://blog.ianbicking.org
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