Broken If-Match handling and mod_dav

[Justin Erenkrantz]

http://nagoya.apache.org/bugzilla/show_bug.cgi?id=16593

This bug states that a PUT with an If-Match condition to a mod_dav resource always fails.

The problem is that the set_headers mod_dav hook isn't necessarily called for dav_method_{put, post, etc, etc, etc}. It is called for GET though when the special GET handling is enabled (see dav_method_get). When we call ap_meets_condition in dav_validate_request for the PUT, we don't have an ETag header to satisfy the conditional request. Therefore, PUT with If-Match always return a 412.

Calling the set_headers hook seems a bit bogus to me when that has nothing to do with the actual response. I imagine we could fudge r->headers_out for the duration of ap_meets_condition and add the output of set_headers (which should contain ETag from the provider). (Hmm, the fact that mod_dav_fs doesn't implement set_headers may be harmful here.)

The problem here is that the output of set_headers indicates the original state of the resource, but by the time the request is over, we should probably have new resource state. That leads me to a temporary r->headers_out, but it just seems wrong.

Another solution would be to set the ETag if it isn't there right before the ap_meets_conditions() call in dav_validate_resource using the getetag hook, and unset it if we set it temporarily. But, ouch. (This does solve the mod_dav_fs problem though.)

Thoughts? Is there another way? -- justin