Fixing (and making easier) Apache mod_proxy_fcgi with PHP-FPM

Hi everyone (already discussed this a bit off-list with Julien),

Ilia and I sat down last week at International PHP Conference to discuss https://bugs.php.net/bug.php?id=65641.

This is a pretty critical issue with Apache 2.4, since it leads to an incorrect SCRIPT_NAME (and thus also PHP_SELF) value if PATH_INFO is given, and frameworks such as CodeIgniter (I know…) break under these circumstances. Ilia has remarked that the emalloc() that never gets free()d might not be ideal with debug on, but it's hard to do in this case, so not sure how critical the patch is. It may need some comments though explaining that if SCRIPT_NAME contains PATH_INFO, the latter is stripped from it again.

More importantly:

We also looked at a related thing together: support for a new way of proxying requests to PHP-FPM in Apache trunk (and the feature will now be backported to Apache 2.4.x, so it'll be in the next release).

This is very big news for PHP-FPM, because the current two options for using mod_proxy_fcgi (which is the future-proof way of connecting Apache and FPM) are both far from ideal:

1. ProxyPassMatch: skips all .htaccess rewrites etc
2. Default mod_rewrite rules on VirtualHost level: will always have to take precedence over certain user-land rewrites, so there's always conflicts, redirect loops and so forth (I've tried, it's messy).

The new approach, which can also be built as a standalone module for older versions of Apache (https://gist.github.com/progandy/6ed4eeea60f6277c3e39), works like this:

<FilesMatch .php$>
SetHandler proxy:fcgi://localhost:9000
</FilesMatch>

It's very simple, and very similar to how mod_php is used in Apache, so that'll make it very easy and convenient for users to use FPM with Apache 2.4.10+

It works very well, except in one situation: when rewriting to PATH INFO like this (common case with many frameworks):

RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.+)$ index.php/$1 [L]

In this situation this really old code, apparently copied from the CGI handling into FPM (see https://bugs.php.net/bug.php?id=47042 for instance), will break stuff:

if (env_path_translated != NULL && env_redirect_url != NULL &&
env_path_translated != script_path_translated &&
strcmp(env_path_translated, script_path_translated) != 0) {
/*
* pretty much apache specific. If we have a redirect_url
* then our script_filename and script_name point to the
* php executable
/
script_path_translated = env_path_translated;
/ we correct SCRIPT_NAME now in case we don't have PATH_INFO */
env_script_name = env_redirect_url;
}

The PHP executable obviously never will be in SCRIPT_FILENAME because we're dealing with FCGI here, so the entire bit is redundant.

It doesn't trigger with /index.php/a:

env_script_name='/index.php'"
env_path_translated='redirect:/index.php/a'";
env_redirect_url='(null)'"
script_path_translated='/Users/dzuelke/Code/heroku/php-test/hello_heroku_php2/index.php'"

But breaks stuff when using the above rewrite and requesting /a, because in this situation:

env_script_name='/index.php'"
env_path_translated='redirect:/index.php/a'
env_redirect_url='/a'"
script_path_translated='/Users/dzuelke/Code/heroku/php-test/hello_heroku_php2/index.php'

Here, the if will trigger, and env_script_name will be changed from the correct '/index.php' to the incorrect '/a', so FPM will report file not found.

With cgi.fix_pathinfo 0, it doesn't work either; script_filename='redirect:/index.php/a' at the end.

Just removing the segment above will lead to a missing PATH_INFO though. There is a related segment further down in the /* make sure path_info/translated are empty */ bit (which should be reworded "remember original values in the request"). Remember, it clears PATH_INFO because with Apache and pure CGI, SCRIPT_FILENAME is the path to the PHP executable, and PATH_INFO has the .php file that was requested:

if (env_redirect_url) {
if (orig_path_info) {
_sapi_cgibin_putenv("ORIG_PATH_INFO", orig_path_info TSRMLS_CC);
_sapi_cgibin_putenv("PATH_INFO", NULL TSRMLS_CC);
}
if (orig_path_translated) {
_sapi_cgibin_putenv("ORIG_PATH_TRANSLATED", orig_path_translated TSRMLS_CC);
_sapi_cgibin_putenv("PATH_TRANSLATED", NULL TSRMLS_CC);
}
}

Once that bit is removed as well, everything works as expected.

To reproduce, use any Apache 2.4+ (Ubuntu 14.04 has 2.4.7) and build and configure the module from the gist.

Could we still squeeze this fix into 5.2.14? I know you just rolled RC1 (while I was fiddling with this stuff), but it would be so, so huge to have this in… or at least in 5.2.15.

I should mention that when using the new SetHandler approach, the https://bugs.php.net/bug.php?id=65641 ticket isn't strictly necessary as the error condition covered there doesn't occur anymore, but for people using the (very inferior) ProxyPassMatch or mod_rewrite solutions, it'd still solve a lot of problems.

Pull request here: https://github.com/php/php-src/pull/694

Thanks,

David