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From Luca Toscano <toscano.l...@gmail.com>
Subject Re: [users@httpd] Last-Modified header overridden
Date Thu, 09 Jun 2016 14:07:05 GMT
2016-06-08 13:42 GMT+02:00 Luca Toscano <toscano.luca@gmail.com>:

> [+devs]
>
> 2016-06-07 23:02 GMT+02:00 Luca Toscano <toscano.luca@gmail.com>:
>
>>
>>
>> 2016-06-07 10:55 GMT+02:00 Vacelet, Manuel <manuel.vacelet@enalean.com>:
>>
>>>
>>>
>>> On Mon, Jun 6, 2016 at 5:32 PM, Vacelet, Manuel <
>>> manuel.vacelet@enalean.com> wrote:
>>>
>>>> dOn Mon, Jun 6, 2016 at 5:00 PM, Vacelet, Manuel <
>>>> manuel.vacelet@enalean.com> wrote:
>>>>
>>>>> On Mon, Jun 6, 2016 at 4:09 PM, Luca Toscano <toscano.luca@gmail.com>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>> I was able to repro building httpd from 2.4.x branch and following
>>>>>> your configuration files on github. I am almost sure that somewhere
httpd
>>>>>> sets the Last-Modified header translating "foo" to the first Jan
1970 date.
>>>>>> I realized though that I didn't recall the real issue, since passing
value
>>>>>> not following the RFC can lead to inconsistencies, so I went back
and
>>>>>> checked the correspondence. Quoting:
>>>>>>
>>>>>> "Actually I wrote this snippet to highlight the behaviour (the
>>>>>> original code sent the date in iso8601 instead of rfc1123) because
it was
>>>>>> more obvious.
>>>>>> During my tests (this is extracted from an automated test suite),
>>>>>> even after having converted dates to rfc1123, I continued to get
some
>>>>>> sparse errors. What I got is that the value I sent was sometimes
slightly
>>>>>> modified (a second or 2) depending on the machine load."
>>>>>>
>>>>>> So my understanding is that you would like to know why a
>>>>>> Last-Modified header with a legitimate date/time set by a PHP app
gets
>>>>>> "delayed" by a couple of seconds from httpd, right?
>>>>>>
>>>>>
>>>>> Yes for sure, this is the primary issue.
>>>>> However, the (undocumented) difference of behavior from one version to
>>>>> another (2.2 -> 2.4 and more surprisingly from between two 2.4 versions)
is
>>>>> also in question here.
>>>>> Even more strange, 2.4 built for other distrib doesn't highlight the
>>>>> behaviour !
>>>>>
>>>>>
>>>>
>>>> I made another series of test and it seems to be linked to fastcgi.
>>>>
>>>> I took the stock apache (2.4.6 plus tons of patches)  & php-fpm (5.4.16
>>>> + tons of patches) from RHEL7 and I get the exact same behaviour (headers
>>>> rewritten to EPOCH)
>>>> However, if I server the very same php script from mod_php (instead of
>>>> fcgi) it "works" (the headers are not modified).
>>>>
>>>>
>>> For the record, I also have the same behaviour (headers rewritten when
>>> using php-fpm + fastcgi) on alpine linux 3.4 that ships apache2-2.4.20.
>>> So AFAICT, it doesn't seem distro specific.
>>>
>>> On the root of the problem, from my point of view:
>>> - the difference between mod_php vs. php-fpm + fcgi is understandable
>>> (even if not desired and not documented).
>>> - the fact that fcgi handler parse & rewrite headers seems to lead to
>>> inconsistencies (I'll try to build a test case for that).
>>> - however, even if the headers are wrong, I think apache default (use
>>> EPOCH) is wrong as it leads to very inconsistent behaviour (the resource
>>> will never expire). I would prefer either:
>>> -- do not touch the header
>>> -- raise a warning and discard the header
>>>
>>> What do you think ?
>>>
>>
>>
>> From my tests the following snippet of code should be responsible for the
>> switch from 'foo' to unix epoch:
>>
>> *https://github.com/apache/httpd/blob/2.4.x/server/util_script.c#L663
>> <https://github.com/apache/httpd/blob/2.4.x/server/util_script.c#L663>*
>>
>> The function that contains the code, ap_scan_script_header_err_core_ex,
>> is wrapped by a lot of other functions eventually called by modules like
>> mod-proxy-fcgi. A more verbose description of the function in:
>>
>> https://github.com/apache/httpd/blob/2.4.x/include/util_script.h#L200
>>
>> Not sure what would be the best thing to do, but probably we could follow
>> up in a official apache bugzilla task?
>> https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2
>>
>> Any thoughts by other readers of the email list?
>>
>
> More specifically, the following patch let the "foo" Last-Modified header
> to be returned instead of unix epoch:
>
> --- server/util_script.c (revision 1747375)
> +++ server/util_script.c (working copy)
> @@ -665,8 +665,13 @@
>           * pass it on blindly because of restrictions on future values.
>           */
>          else if (!strcasecmp(w, "Last-Modified")) {
> -            ap_update_mtime(r, apr_date_parse_http(l));
> -            ap_set_last_modified(r);
> +            apr_time_t last_modified_date = apr_date_parse_http(l);
> +            if (last_modified_date) {
> +                ap_update_mtime(r, last_modified_date);
> +                ap_set_last_modified(r);
> +            } else {
> +                apr_table_set(r->headers_out, w, l);
> +            }
>          }
>          else if (!strcasecmp(w, "Set-Cookie")) {
>              apr_table_add(cookie_table, w, l);
>
> Omitting the "else" branch will force httpd to drop anything that is not a
> date in Last-Modified (like 'foo'). Of course this patch is only a proof of
> concept, it is not meant to be the final solution :)
>
> Reading https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html I am not
> sure what would be the best course of action.
>
> I added the httpd-dev mailing list to get some opinion. Steps to repro are
> contained in https://bugs.centos.org/view.php?id=10940
>
>
More specific:

ap_scan_script_header_err_core_ex in server/utils.c (that should be used by
mod-proxy-fcgi) checks headers returned from fcgi scripts and translates
non RFC compliant Last-Modified header values to unix epoch. For example,
Last-Modified: foo is returned to the client as Last-Modified: Thu, 01 Jan
1970 00:00:00 GMT.

What would be the correct behavior in this case? Not returning any
Last-Modified to the client (and maybe logging an error/warning?),
returning the non compliant value as it is, returning Last-Modified: now(),
other?

Any help would really be appreciated :)

Thanks!

Regards,

Luca

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