[tbnl-devel] Handling HTTP errors

[Stefan Scholl]

On 2004-08-03 07:34:48, Edi Weitz wrote:
> On Sat, 31 Jul 2004 02:10:11 +0200, Stefan Scholl <stesch at no-spoon.de> wrote:
> > There could be different approaches:
> >
> > * Simple hash
> >   A hash with error code as key and handler as value.
> >
> >   + Easy to implement
> >   + Can handle all errors (thrown by handlers _and_ when no
> >     dispatcher is found)
> >   - Not very flexible. Just checks for the code and not for
> >     any request data.
> >
> > * Error dispatcher
> >   Like the normal dispatcher, but checking for the right error
> >   output handler.
> >
> >   + Can handle all errors (thrown by handlers _and_ when no
> >     dispatcher is found)
> >   + Flexible. Can check the code _and_ request data.
> >   - A bit big. The same effort like handling normal requests.
> >
> > * Handler outputs itself and signals that
> >   A handler wants to return a 404. It constructs the output
> >   string and signals the fact that there's no need for TBNL to
> >   build the HTML for the output.
> >
> >   + Easy to implement(? clean?)
> >   + Flexible
> >   - Can't handle all errors. (No handler found? Then the code
> >     won't be executed.)

* Generic function
  Make a specialized method if you want to catch a certain
  error. 
  E. g. (defmethod error-handler ((code (eql #.+http-not-found+)) ...

  + Easy to implement
  + Can handle all errors (thrown by handlers _and_ when no
    dispatcher is found)
  + Let CLOS to the "lookup" work
  + CLOS: You can add :before, :around, :after, ... methods
  - Not very flexible. Just checks for the code and not for any
    request data.


> I agree that this would generally be a good idea. I'm not sure yet
> which of the above-mentioned alternatives I like most or if there's
> another one that would even be better.

Do we need all the features (and more) of Apache's ErrorDocument?
<http://httpd.apache.org/docs/mod/core.html#errordocument>

A function can call the redirect itself.

If you don't need someting similar to the contexts (server
config, virtual host, directory, .htaccess) of ErrorDocument then
a hash table or generic function is enough.

The contexts can be simulated with error dispatcher which checks
the request, too.

But how often would someone need this together with mod_lisp? If
someone wants to emit different error messages for the same error
code but different request data (host, uri, ...) then he could
handle this himself.



Regards,
Stefan