Nginx try_files gotcha

Question

Ok - i've been using this rule for a while

location ~* /(?:abc12345|12abcdef)/(.*\.(jpe?g|gif|png)) {
    alias /usr/local/image/$1;
    error_page 404 /handler.php;
}

where if the image file exists, it is served - if the file doesn't exist, a custom 404 error_page named /handler.php works to deliver the goods. if the image was unchanged, it would return a 304 - new images returned a 200. Almost perfect.

Problem is, returning a 404 with the image isn't the proper thing to do - I should accept the request, determine if the file exists, and if not run handler and return the image - and not show a 404.

I've tried to replace error_page with try_files, but am not getting the desired result:

 location ~* /(?:abc12345|12abcdef)/(.*\.(jpe?g|gif|png)) {
     alias /usr/local/image/$1;
     try_files $uri $uri/ /handler.php;
 }

Nothing seems to match in try_files so all requests fall through to handler.php. I understand that alias is a special match pattern, but if I try to enter in

try_files "" /handler.php;

Which works, but the "" returns the incorrect content-type (Content-Type:·application/octet-stream) while handler.php returns the correct one (Content-Type:·image/jpeg)

sure, I could add in "default_type image/jpeg;" to force the default, but I run the risk of returning a jpeg content-type when the actual image could be gif or png.

I'm running debian 6 - nginx-1.0.6-1~dotdeb.2

Any ideas on how to make this work?

Alexander Azarov · Accepted Answer · 2011-10-04T13:48:39.247

5

The first of all, you could force Nginx to return the status code from your script when using error_page:

location ~* /(?:abc12345|12abcdef)/(.*\.(jpe?g|gif|png)) {
    alias /usr/local/image/$1;
    error_page 404 = /handler.php;
}

That equal sign tells Nginx to return the status code from handler.php instead of 404.

As of try_files, try this config:

location ~* /(?:abc12345|12abcdef)/(.*\.(jpe?g|gif|png)) {
    root /usr/local/image;
    try_files /$1 /handler.php;
}

edited Oct 04 '11 at 13:48

answered Oct 04 '11 at 08:50

Alexander Azarov

3,550
21
19

Any benefit of using the first approach over the other? Is root / try_files more efficient than alias / error_page? – jimg Oct 04 '11 at 19:04
In terms of performance they are more or less equivalent in your case. `error_page` is more generic, it's possible to intercept other status codes. `try_files` was designed specifically for this kind of problems, when there is a need to search for a file – Alexander Azarov Oct 04 '11 at 20:01
ok - using try_files / root then. Thanks for your insight. – jimg Oct 04 '11 at 20:13

Nginx try_files gotcha

1 Answers1