the "if" directive have problems in location context

[s "hr" berder]

To start, I'm doing tricky stuff so please don't point out at the weird things and stay focused on the issue at hand.
I'm mixing a configuration with userdir and symfony2 (​http://wiki.nginx.org/Symfony) for a development environment, php is using php-fpm and a unix socket.
The userdir configuration is classic, all your files in ~user/public_html/ will be accessible through http://server/~user/.
I add to this the fact that if you create a folder ~user/public_html/symfony/ and put a symfony project in it (~user/public_html/symfony/project/) it will have the usual symfony configuration applied (rewrites and fastcgi path split).

Here you go for the configuration :

    # match 1:username, 2:project name, 3:the rest
    location ~ ^/~(.+?)/symfony/(.+?)/(.+)$ {
        alias /home/$1/public_html/symfony/$2/web/$3;
        if (-f $request_filename) {
            break;
        }
        # if no app.php or app_dev.php, redirect to app.php (prod)
        rewrite ^/~(.+?)/symfony(/.+?)/(.+)$ /~$1/symfony/$2/app.php/$3 last;
    }

    # match 1:username, 2:project name, 3:env (prod/dev), 4:trailing ('/' or
    # end)
    location ~ ^/~(.+?)/symfony(/.+)/(app|app_dev)\.php(/|$) {
        root /home/$1/public_html/symfony$2/web;
        # fake $request_filename
        set $req_filename /home/$1/public_html/symfony$2/web/$3.php;
        include fastcgi_params;
        fastcgi_split_path_info ^((?U).+\.php)(/?.+)$;
        fastcgi_param PATH_INFO $fastcgi_path_info;
        fastcgi_param PATH_TRANSLATED $document_root$fastcgi_path_info;
        fastcgi_param SCRIPT_FILENAME $req_filename;
        fastcgi_pass unix:/tmp/php-fpm.sock;
    }

The second block (PHP backend) works on its own. The first block (files direct access) works on its own.

You can see that I already had a problem with PHP but went around it with creating my own variable.

To help understand, here is a sample of a symfony project layout (I removed some folders to help the comprehension):

project/
    src/
        [... my php code ...]
    web/
        app_dev.php
        app.php
        favicon.ico

If I try to access http://server/~user/symfony/project/favicon.ico I see this in the logs :

2012/01/17 16:36:25 [error] 27736#0: *1 open() "/home/user/public_html/symfony/project/web/favicon.icoavicon.ico" failed (2: No such file or directory), client: 10.11.60.36, server: server, request: "HEAD /~user/symfony/project/favicon.ico HTTP/1.1", host: "server"

If I remove the block that tests $request_filename, it works but I have to remove the rewrite as well.

The server is a CentOS 5.7 and the nginx is coming from the EPEL repository.

Unfortunately my C skills are down the floor so I can't really provide a better understanding of the problem. I tried to poke around the code but with not much luck.

[Maxim Dounin]

This is one of the known problems with the "if" directive used in a location context, see ​http://wiki.nginx.org/IfIsEvil. Reduced test case is as follows (copied from the wiki page in question):

        # alias with captures isn't correcly inherited into implicit nested
        # location created by if
 
        location ~* ^/if-and-alias/(?<file>.*) {
            alias /tmp/$file;
 
            set $true 1;
 
            if ($true) {
                # nothing
            }
        }

Workaround is not to use if, or use it in a safe way, see the wiki page in question.

[Maxim Dounin]

A particular case with regex location + alias + if is resolved by c985d90a8d1f.

Leaving the ticket open as there are other cases which still need to be fixed, see ​​http://wiki.nginx.org/IfIsEvil.

[Maxim Dounin <mdounin@…>]

In aeea0522332f4007b30683ad2a8c77a9a4bd2371/nginx:

Proxy: fixed incorrect URI change due to if (ticket #86).

In the following configuration request was sent to a backend without
URI changed to '/' due to if:

location /proxy-pass-uri {

proxy_pass ​http://127.0.0.1:8080/;

set $true 1;

if ($true) {

# nothing

}

}

Fix is to inherit conf->location from the location where proxy_pass was
configured, much like it's done with conf->vars.

[Maxim Dounin]

See also #633, which is basically identical to the same problem with if:

# try_files wont work due to if

location /if-try-files {
     try_files  /file  @fallback;

     set $true 1;

     if ($true) {
         # nothing
     }
}

In both cases try_files is not inherited into an implicit location created with if / limit_except and this results in unexpected behaviour.

[Maxim Dounin]

See also #1383.

[Maxim Dounin]

See also #1434.

[Maxim Dounin]

See also #1507.

[Maxim Dounin]

See also #1707.

[Maxim Dounin]

See also #2511.