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From Graham Leggett <minf...@sharp.fm>
Subject ap_directory_walk() marking non existent files as APR_DIR
Date Tue, 31 Mar 2015 22:36:23 GMT
Hi all,

I am picking apart some strange behaviour where use of the Alias directive inside a Location
along with a file path that doesn’t exist (/_thumbs/i/dont/exist.jpg) triggers a loop of
redirects to …/index.html/index.html/index.html/…

The loop of redirects is caused by mod_dir being told that the non existent file is actually
a directory (r->finfo.filetype == APR_DIR) instead of a nonexistent file (r->finfo.filetype
== APR_NOFILE). Working backwards to find where a non existent file is being mislabelled as
a directory, it leads me to ap_directory_walk(), specifically these lines:

        do {
[snip]

            if (*seg_name == '/')
                ++seg_name;

            /* If nothing remained but a '/' string, we are finished
             * XXX: NO WE ARE NOT!!!  Now process this puppy!!! */
            if (!*seg_name) {
                break;
            }

[snip]
        } while (thisinfo.filetype == APR_DIR);

What is happening is that we are reaching the break, which aborts the loop but leaves the
value thisinfo.filetype == APR_DIR, thus triggering the downstream mod_dir mayhem.

Further down in the loop, we have some code that looks like this that explicitly sets the
file to APR_NOFILE before breaking:

            if (APR_STATUS_IS_ENOENT(rv)) {
                /* Nothing?  That could be nice.  But our directory
                 * walk is done.
                 */
                thisinfo.filetype = APR_NOFILE;
                break;
            }

In theory following the pattern above, we might change the code above to:

            if (!*seg_name) {
+                thisinfo.filetype = APR_NOFILE;
                break;
            }

However I don’t fully understand what the comment "XXX: NO WE ARE NOT!!!  Now process this
puppy!!!” actually means.

Can anyone confirm?

Regards,
Graham
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