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Posted to embperl@perl.apache.org by Scott Chapman <sc...@mischko.com> on 2001/11/14 17:30:00 UTC
Modular web sites - is this possible? (was Re: Modular web site not behaving as expected.)
Gerald,
I've been giving a lot of thought to the idea of modular web pages
and "exit" functionality is not nearly as nice as what I think you
could build into embperl.
The problem is one of trying to create very modular web sites with
resuable chuncks of code embodied in a web page that calls itself
for data validation, etc. As an example, I have a page that presents
some instructions and asks for the user to input their userid,
password, and email address to create a new userid on the site. It
calls upon itself to do the data validation. When the data is
validated, it adds the userid to the .htpasswd file.
This userid/password page is a module that I'd like to be able to
drop into any project that needs this functionality. Problem with
exit functionality:
When PageA executes this userid/password page (PageB) and it
EXIT's at the bottom of the page, it does not return to PageA. [So
far so good. I don't want PageA to be returned to until after the
validation is done and the userid added.] Next the user submits
the data back to PageB. The conditionals in PageB make it so it
checks the data rather than putting out the form again. It is
validated and the user is added to the .htpasswd file. Now the
problem. How do I get PageB to return to the line just following the
calling line from PageA? This should be just like calling a
subroutine in Perl it should return to the next line when it's done.
It would be very nice to have Execute handle this with a parameter
saying "Don't return here until you're told to by the page I'm
calling". PageB executes and at the end of PageB it automatically
stops (like "exit" would do) but it keeps track of where it's
supposed to return to internally like a regular subroutine would in a
modular programming language. When PageB finally executes a
"return to calling page" command (perhaps passing parameters
back like perls "return" statement), then and only then would
PageB actually drop out the bottom and return to PageA.
I realize this is a stateless arena and implementing this would
require some magic but think Embperl (and you) are able to make
that kind of magic. Is this possible or does the stateless nature of
this make it impossible? More modularity would be SO nice in this
environment!
Cordially,
Scott
On 12 Nov 2001, at 10:06, Gerald Richter wrote:
> Scott,
>
> Andrew have already given an excelent explanation, so there is not much to
> add...
>
> >
> > Gerald, you want to build this functionality? :-)
> >
>
> I am not sure which functionality you want to see here ? Just something like
> exit, that does not only exit the current file, but end the whole request ?
> In this case that's something what's on my todo list for 2.0. If you intent
> a more sophisticated thing, please try to explain it again, at the moment I
> understand your problem, but I don't see what EMbperl can do for you in this
> case ?
>
> Gerald
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Re: Modular web sites - is this possible? (was Re: Modular web site not behaving as expected.)
Posted by Andrew O'Brien <an...@switchonline.com.au>.
On Thu, Nov 15, 2001 at 03:05:24PM -0800, Scott Chapman wrote:
To summarise your summary:
You want Embperl to implement an Execution state machine for you.
I've just implemented a largish, completely forms based site using
just that code snippet I posted earlier for progression. There were a
few extra things for moving backwards and jumping around the execution
tree but thats was basically it.
I agree completely with you that it would be nice to be able to
conceptually program like you wish .... but with a small wrapper in
place you can do it yourself and not have to wait for Gerald to muck
around in Embperl internals to get the same thing :)
> I posted a very similar question on the ModPerl list and someone
> else summarized my request very nicely. This may help:
>
> > On 15 Nov 2001, at 15:33, Perrin Harkins wrote:
> >
> > The original e-mail was confusing, but I think what he's after is not
> > so much the ability to call pages as subs but rather the ability to
> > abstract away the fact that a sub might actually involve multiple user
> > interactions (present a form, get a response, present another form,
> > etc.) with breaks in actual execution. In other words, he wants to
> > think of program execution in terms of a linear user session (as you
> > would with a GUI app) rather than a series of separate requests.
--
Andrew O'Brien
Product Engineer email: andrewo@switchonline.com.au.
Switch Online Group Pty Limited phone: +61 2 9299 1133
ABN 89 092 286 327 fax: +61 2 9299 1134
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Re: Modular web sites - is this possible? (was Re: Modular web site not behaving as expected.)
Posted by Gerald Richter <ri...@ecos.de>.
I think I got now what you want...
>
> Do you still think this is possible?
>
It's possible, but not easy to do in a common and abstract way on the other
side it's not hard to do it for a concret problem, like Andrew said.
I will think about this and maybe come up with an idea, but at the moment I
can't say how a concrete implementaion could look like, so it's more a long
term perspective...
> > Gerald wrote:
> > Yes, this is possible and especially for form validation I have some
plans
> > in mind, which I can hopefully release before the end of the year, which
> > will allows you to specify validation rules and what should happen if
the
> > validation fails.
>
> Typically, I just have a form call itself for validation with appropriate
> conditionals. What do you have in mind here?
>
1.) Give you an extentable library of "conditionals", so you don't have to
code them every time
2.) Let Embperl verify these conditional for you and take an action (e.g.
call different pages), depending on the result
So basicly it does the same as you also do, just do it for you, so you don't
have to do everytime the same.
Gerald
-------------------------------------------------------------
Gerald Richter ecos electronic communication services gmbh
Internetconnect * Webserver/-design/-datenbanken * Consulting
Post: Tulpenstrasse 5 D-55276 Dienheim b. Mainz
E-Mail: richter@ecos.de Voice: +49 6133 925131
WWW: http://www.ecos.de Fax: +49 6133 925152
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Re: Modular web sites - is this possible? (was Re: Modular web site not behaving as expected.)
Posted by Scott Chapman <sc...@mischko.com>.
On 15 Nov 2001, at 21:26, Gerald Richter wrote:
> There are many nice ideas (and I have a lot of them too), but it takes also
> a lot of time to implementing them and as long as nobody pays me for that
> (which is fortunately sometimes the case :-), I have to do things that I
> need for my projects first and keep the other nice features for the time
> that is left. I says this here, because I could imagine that implementing
> something like you have in mind, would be really cool, but also would be a
> lot of work. Haveing this said, I really like to hear your ideas and discuss
> them and as far as we come up with good solutions try to integrate them into
> Embperl!
I appreciate the busy problem and all the great stuff you've done
with Embperl! I think it is part of the human condition to be too
busy to get it all done in one lifetime. Let me know how difficult it
looks after you read the rest of this.
[- snipped -]
I posted a very similar question on the ModPerl list and someone
else summarized my request very nicely. This may help:
> On 15 Nov 2001, at 15:33, Perrin Harkins wrote:
>
> The original e-mail was confusing, but I think what he's after is not
> so much the ability to call pages as subs but rather the ability to
> abstract away the fact that a sub might actually involve multiple user
> interactions (present a form, get a response, present another form,
> etc.) with breaks in actual execution. In other words, he wants to
> think of program execution in terms of a linear user session (as you
> would with a GUI app) rather than a series of separate requests.
He summarized it just right. I'd like to have an abstraction that
effectively removes the stateless nature of this. HTML was not
made as a 2-way thing so using it is painful some times. Can it be
made more like a typical programming scenario?
A typical example:
1) Top level page calls another page to present a form. Execution of the calling page is stopped (actually suspended) waiting for the return to happen.
2) The form is presented to the user and processing stops while waiting for the reply.
3) The user submits the page either to the calling page or to another one (doesn't matter). Validation happens.
4) Other pages could be called either as modules (like step 1) or like they are called now.
5) Final page executes a "return" statement and processing returns to the top level calling page and continues where it left off.
In order to implement this:
The calling page needs to be able to continue execution when the call is returned.
Pages that are called need to know that they are not to drop out
the bottom and return to the calling page but to stop instead.
The called page needs to pass on the return-to information or a
"stack" needs to be implemented for the session so that the
eventual return causes execution to go back to the top-level calling
page like you would expect.
> Is your idea, chaining these pages together, so that one page would only be
> displayed if the previous one is done ? Or is a module as see it only a
> part of a page, so you can have lets say a user add form and a mail form or
> what ever on the same page ?
The idea is that a group of pages become a module, with a single
entry point and a single return point. Flow of control among the
pages in a module would be done normally (as done right now),
including the possibility of calling other modules.
> Is your idea mainly for input forms or do you have other sort of
> objects in mind ? If yes, what ?
Not form specific at all. Just a generic control structure that
makes a group of stateless transactions behave like a regular
subroutine in a modular language. Generic is more useful.
> > Scott wrote:
> > I realize this is a stateless arena and implementing this would
> > require some magic but think Embperl (and you) are able to
> > make that kind of magic. Is this possible or does the stateless
> > nature of this make it impossible? More modularity would be
> > SO nice in this environment!
Do you still think this is possible?
> Gerald wrote:
> Yes, this is possible and especially for form validation I have some plans
> in mind, which I can hopefully release before the end of the year, which
> will allows you to specify validation rules and what should happen if the
> validation fails.
Typically, I just have a form call itself for validation with appropriate
conditionals. What do you have in mind here?
Cordially,
Scott
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Re: Modular web sites - is this possible? (was Re: Modular web site not behaving as expected.)
Posted by Gerald Richter <ri...@ecos.de>.
Hi,
>
> I've been giving a lot of thought to the idea of modular web pages
> and "exit" functionality is not nearly as nice as what I think you
> could build into embperl.
>
There are many nice ideas (and I have a lot of them too), but it takes also
a lot of time to implementing them and as long as nobody pays me for that
(which is fortunately sometimes the case :-), I have to do things that I
need for my projects first and keep the other nice features for the time
that is left. I says this here, because I could imagine that implementing
something like you have in mind, would be really cool, but also would be a
lot of work. Haveing this said, I really like to hear your ideas and discuss
them and as far as we come up with good solutions try to integrate them into
Embperl!
> ....
> It would be very nice to have Execute handle this with a parameter
> saying "Don't return here until you're told to by the page I'm
> calling". PageB executes and at the end of PageB it automatically
> stops (like "exit" would do) but it keeps track of where it's
> supposed to return to internally like a regular subroutine would in a
> modular programming language. When PageB finally executes a
> "return to calling page" command (perhaps passing parameters
> back like perls "return" statement), then and only then would
> PageB actually drop out the bottom and return to PageA.
>
Is your idea, chaining these pages together, so that one page would only be
displayed if the previous one is done ? Or is a module as see it only a
part of a page, so you can have lets say a user add form and a mail form or
what ever on the same page ?
Is your idea mainly for input forms or do you have other sort of objects in
mind ? If yes, what ?
> I realize this is a stateless arena and implementing this would
> require some magic but think Embperl (and you) are able to make
> that kind of magic. Is this possible or does the stateless nature of
> this make it impossible? More modularity would be SO nice in this
> environment!
>
Yes, this is possible and especially for form validation I have some plans
in mind, which I can hopefully release before the end of the year, which
will allows you to specify validation rules and what should happen if the
validation fails.
Gerald
-------------------------------------------------------------
Gerald Richter ecos electronic communication services gmbh
Internetconnect * Webserver/-design/-datenbanken * Consulting
Post: Tulpenstrasse 5 D-55276 Dienheim b. Mainz
E-Mail: richter@ecos.de Voice: +49 6133 925131
WWW: http://www.ecos.de Fax: +49 6133 925152
-------------------------------------------------------------
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Re: Modular web sites - is this possible? (was Re: Modular web site not behaving as expected.)
Posted by Scott Chapman <sc...@mischko.com>.
Wim,
It may be possible with more complex coding but the idea is
transparent abstraction layer here to make things behave just like
calling a regular subroutine with a return statement at the end. I'm
hoping to hear from Gerald on the possibility of implementing this
into Embperl. It would be a serious improvment in the way we can
make web sites where we don't have to spend as much time
thinking about the problem and more time thinking in terms of the
solution. That's the promise of object oriented programming! :-)
Cordially,
Scott
On 15 Nov 2001, at 10:44, Wim Kerkhoff wrote:
> Hi Scott,
>
> I think I understand your point better now. I'm still convinced that it
> is possible to do what you have described using EmbperlObject.
>
> Wim
>
> Scott Chapman wrote:
> >
> > Wim,
> > I think you missed the point of our discussion. This isn't about
> > authentication at all. It's about modular site design. The web page
> > I was talking about is just for getting a userid, password and email
> > address to CREATE a new user in the .htpasswd file, not
> > authenticate 'em. (After they create a userid they'll be asked to
> > login using regular HTTP authentication). It was just a sample of a
> > modular design I'd like to see added to Embperl. Read the
> > previous discussion again for details. Maybe I wasn't clear.
> >
> > This modular idea is useful for any instance where you need to get
> > form input from a person and validate it.
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Re: Modular web sites - is this possible? (was Re: Modular web site
not behaving as expected.)
Posted by Wim Kerkhoff <wi...@merilus.com>.
Hi Scott,
I think I understand your point better now. I'm still convinced that it
is possible to do what you have described using EmbperlObject.
Wim
Scott Chapman wrote:
>
> Wim,
> I think you missed the point of our discussion. This isn't about
> authentication at all. It's about modular site design. The web page
> I was talking about is just for getting a userid, password and email
> address to CREATE a new user in the .htpasswd file, not
> authenticate 'em. (After they create a userid they'll be asked to
> login using regular HTTP authentication). It was just a sample of a
> modular design I'd like to see added to Embperl. Read the
> previous discussion again for details. Maybe I wasn't clear.
>
> This modular idea is useful for any instance where you need to get
> form input from a person and validate it.
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Re: Modular web sites - is this possible? (was Re: Modular web site not behaving as expected.)
Posted by Scott Chapman <sc...@mischko.com>.
Wim,
I think you missed the point of our discussion. This isn't about
authentication at all. It's about modular site design. The web page
I was talking about is just for getting a userid, password and email
address to CREATE a new user in the .htpasswd file, not
authenticate 'em. (After they create a userid they'll be asked to
login using regular HTTP authentication). It was just a sample of a
modular design I'd like to see added to Embperl. Read the
previous discussion again for details. Maybe I wasn't clear.
This modular idea is useful for any instance where you need to get
form input from a person and validate it.
Cordially,
Scott
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Re: Modular web sites - is this possible? (was Re: Modular web site not
behaving as expected.)
Posted by Wim Kerkhoff <wi...@merilus.com>.
Scott Chapman wrote:
>
> Neil,
> Thanks for the tip.
Aye! That's a nice way of doing it.
> I'm already using Embperl Object quite a bit
> and intend to use it more. Putting things in subs.epl is an option
> I'm using for some things but I don't want to put basically my entire
> modular site into subs.epl files.
He wasn't suggest that you do this -- only put your authentications
stuff into subs.epl.
> You hit it right on the head when you said I want it to be
> transparent. This stateless environment is a continued amazement
> to me. It's a wonder so much is being done with it when it has
> such design flaws. Clearly, it is being used in ways it was not
> designed for. The more modular it can be made the better for
> everyone involved (in development anway!).
>
> Cordially,
> Scott
>
> Neil wrote:
> > Of course what you are looking for is a way to make all this
> > transparent, which I can understand. But just throwing an idea out
> > there.
There is another alternative to transparent authentication and
authorization that we use all the time.
Follow Chapter 6 [1] of the mod_perl book [2], and write a
Apache::MyAuth handler that does the authentication/authorization. This
module would be written in pure perl. If they user is not logged in, use
HTML::Embperl::Execute to call your
header.html/loginform.html/footer.html, and return OK. If they are
logged in, return DECLINED so that the page can be loaded. This mod_perl
would be compiled at server startup time, and run *before* every request
that you specify. Ie, add it into httpd.conf/.htaccess via:
PerlAccessHandler Apache::MyAuth
While the EmbperlObject solution is nice way of doing it if you don't
feel like writing a mod_perl handler, I prefer this method. The handler
can be run before any request: plain CGI scripts, static HTML, images,
other handlers, whatever. If they login fails, the page isn't executed.
I find it a lot more reliable as well -- it's easier to add a bug in the
individual base.epl or subs.epl.
If you want to get fancy, you can use PerlSetVar, so that you can
control the authentication system (on/off, which users/groups, etc) on a
per directory/per file basis.
My last version of this used Apache::Session to store whether they were
logged in or not... this means that the auth handler can use the same
sessioning system as Embperl for maintaining state.
Just some more ideas... my $0.03 CDN.
1. http://www.modperl.com/book/chapters/ch6.html
2. http://www.modperl.com
--
Regards,
Wim Kerkhoff, Software Engineer
Merilus, Inc. -|- http://www.merilus.com
Email: wim@merilus.com
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Re: Modular web sites - is this possible? (was Re: Modular web site not behaving as expected.)
Posted by Scott Chapman <sc...@mischko.com>.
Neil,
Thanks for the tip. I'm already using Embperl Object quite a bit
and intend to use it more. Putting things in subs.epl is an option
I'm using for some things but I don't want to put basically my entire
modular site into subs.epl files.
You hit it right on the head when you said I want it to be
transparent. This stateless environment is a continued amazement
to me. It's a wonder so much is being done with it when it has
such design flaws. Clearly, it is being used in ways it was not
designed for. The more modular it can be made the better for
everyone involved (in development anway!).
Cordially,
Scott
Neil wrote:
> Of course what you are looking for is a way to make all this
> transparent, which I can understand. But just throwing an idea out
> there.
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Re: Modular web sites - is this possible? (was Re: Modular web site not
behaving as expected.)
Posted by Neil Gunton <ne...@nilspace.com>.
Scott Chapman wrote:
> This userid/password page is a module that I'd like to be able to
> drop into any project that needs this functionality.
Scott,
Just my two cents on your scenario...
You can achieve a high degree of modularity using EmbperlObject as it
stands. For instance, let's say you have a module which performs user
validation, as in your example. You can put this into a common library
area, say /www/lib/perl/. You then put some code in your base.epl file
(EMBPERL_OBJECT_BASE): (omitting obvious code)
/base.epl
[-
$subs = Execute ({object => 'subs.epl'});
if (!$subs->handle())
{
Execute ({inputfile => '*', package => __PACKAGE__});
}
-]
/subs.epl
[!
sub handle
{
my ($self) = @_;
return 0;
}
!]
So, by default the behavior is for handle() to return 0, which means
that the requested page ('*') will be called. Now, in a subdirectory
where you want to have your page handled by the module, you put a
subs.epl something like this:
/subdir/subs.epl
[! Execute ({isa => '/www/lib/perl/Auth.epl'}) !]
You can then redefine the subroutine handle() in Auth.epl, so that it
does something (i.e. handles the request) and then returns 1. This gets
rid of the need for exit() in the way that you are describing, I think -
whenever you want to use a module, you simply make a subdirectory as a
'stub' for that module, and place a subs.epl like the one above there.
Then, you direct the browser to that location, and it will automatically
be handled by your module. For finer control, you could pass in as a
parameter to handle() the uri of the calling page. The handle() module
could then use this to construct the final destination, using a
redirect. An additional parameter could be passed to indicate a finer
level of granularity within the calling module. This parameter could
then be passed back to the original module from Auth.epl in a CGI
parameter, so that it's available in %fdat. This could then be used to
determine the current state.
Of course what you are looking for is a way to make all this
transparent, which I can understand. But just throwing an idea out
there.
HTH
-Neil
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