On Mar 30, 2006, at 10:30 PM, James M Snell wrote:
Antone Roundy wrote:
[snip]
2) If you're consuming Atom and you encounter a relative URI, how
should
you choose the appropriate base URI with which to resolve it?
I think there are only three remotely possible answers to #2:
xml:base
(including the URI from which the feed was retrieved if xml:base
isn't
explicitly defined), the URI of the self link, and the URI of the
alternate link. Given that Atom explicitly supports xml:base, if
it's
explicitly defined, it's difficult to justify ignoring it in favor of
anything else.
There is no basis in any of the specs for using the URI of the self or
alternate link as a base uri for resolving relative references in the
content. The process for resolving relative references is very
clearly
defined.
Right--my point is:
1) If the original publisher made the mistake of using relative
references without explicitly setting xml:base (figuring that
consumers could resolve the references relative to the location of
the feed), and then the feed got moved or mirrored, one would
certainly fail at finding the things the publisher intended to point
to if the URI from which the feed was retrieved was used as the base
URI, but might succeed by using the self link as the base URI. (I do
not advocate doing this as default behavior, as stated below).
2) If the original publisher made the mistake of not even thinking
about relative references in the content and therefore didn't set
xml:base, the relative references may very well be relative to the
location pointed to by the alternate link. For example, the person
generating the content may have been thinking "my blog entry will
appear at http://example.org/blog/2006/03/foo.html, so I can use the
relative URL "../../../img/button.gif" to point to the image at
http://example.org/img/button.gif";. If the alternate link points to
http://example.org/blog/2006/03/foo.html, then the consumer that
wants to find the image will only succeed by using the alternate link
as the base URI. (I do not advocate doing this as default behavior,
as stated below).
Moral of this story: failing to explicitly set xml:base is bad
because it tempts consumers to ignore the spec in order to get what
they want. I do not advocate ignoring the spec as default behavior.
But honestly, I might give the user of a consuming application the
option of overriding the default behavior on specific feeds if they
know that the publisher makes the mistake of publishing links
relative to the self or alternate link without setting xml:base. I'd
LIKE to be able to hold the publisher's feet to the fire and make
them fix the feed, but sometimes my users hold MY feet to the fire
and make me give them usable workarounds.
Antone
![http://example.org/img/button.gif"](http://example.org/img/button.gif"){kind=link}