Internal Redirect

Web server internal redirect via backend response header, aka X-Sendfile or X-Accel-Redirect, is a feature used by some web backend developers and popularized by Ruby on Rails. LSWS and OLS use a simple header “Location” or X-LiteSpeed-Location to achieve the same goal.

What is This Internal Redirect via Response Header?

The backend process, instead of returning a full HTTP page response back, returns only a pointer to a local path.

When the web server receives this special url location pointer via a header variable, the web server will output the content of the specified path, rather than the response from the backend process.

The end user is not aware of this internal redirection and the data appears to be returned from the original url.

Implementing Internal Redirect on LiteSpeed Through the Header

To get this to work on LiteSpeed, just use a simple X-LiteSpeed-Location header in your PHP script.

Method 1: Set "Location" Header

In a PHP script, set a Location header pointing to a URI without the http://domain.com part. Do not set a Status header in response. Make sure no Status header is returned. PHP always adds a Status header automatically when a Location header is set.

<?php
header('Location: /php-icon.png');
?>

Method 2: Set "X-LiteSpeed-Location" Header

Add a special X-LiteSpeed-Location header (in LSWS v3.0.2 and above) in exactly the same way as the Location header was added in Method 1 above. X-LiteSpeed-Location is the recommended way to implement an Internal Redirect on LSWS.

For example, add a line like this to the PHP script:

header('X-LiteSpeed-Location: /path/to/file_to_be_redirected');

Note: /path/to/file_to_be_redirected should be a URI without http://domain.com, but with the preceding /, such as can be seen in the test.php script in your document root. LSWS only supports “URI” instead of “file path”.

<?php
header('X-LiteSpeed-Location: /img/php-icon.png');
?>   

That's it, folks. LiteSpeed will take over the rest, perform an internal redirect, and send the file back with sendfile() support if the URL points to a static file.

Run a test through http://yourdomain.com/test.php and you will see it return the php-icon.png image.

Downloading the File Instead of Displaying

If you want to download the file instead of showing it in the browser, you can add an extra header, Content-Disposition, like so:

<?php
header('Content-Disposition: attachment; filename = php-icon.png');
header('X-LiteSpeed-Location: /img/php-icon.png');
?>   

Save the above to http://yourdomain.com/test.php and run it. The script will download php-icon.png instead of displaying it in the browser.

Redirecting via URL vs. File Path

Unlike the X-Sendfile or X-Accel-Redirect implementations in other web servers, LiteSpeed uses a URI instead of a file path for security reasons. In this way, only a file under the document root of a virtual host or a context can be returned. Otherwise, you could have a huge security issue. Imagine if, for some reason, either accidentally or maliciously, the script sends back a header X-Sendfile: /../etc/./passwd%00, or something like that. The user accounts on your server would no longer be a secret!

Protection from Direct Access

If you want to prevent a user from accessing a file directly, just use a hard-to-guess URI like /you_never_know/where_file_is_stored/…. Or you can use a rewrite rule (in httpd.conf) to deny direct access to the directory holding the files, like so:

RewriteCond %{ORG_REQ_URI} ^/blocked/uri/
RewriteRule ^/blocked/uri/ - [R=403,F]

Here is a version in .htaccess (notice the difference between ^/blocked… and ^blocked…)

RewriteCond %{ORG_REQ_URI} ^/blocked/uri/
RewriteRule ^blocked/uri/ - [R=403,F]

%{ORG_REQ_URI} is a LiteSpeed-specific rewrite variable, which refers to the URI in the original request header.

Another advantage of our internal redirect implementation is that it does not limit you to sending static files. It can be used to pass the request to another script for further processing.

Ruby-on-Rails

Here is a short example of how to use Internal Redirect for sending files within a RoR Controller. Below is a sendfile function that can be attached to any action.

def sendfile
  @name = session[:filename]                 # a session variable set in a view or other function
  filename = "public/download/" + @name      # create the URI, must be under /public     
  headers["Location"] = filename             # set the 'Location header
  redirect_to(filename)                      # redirect
end
 
litespeed_wiki/config/internal-redirect.txt · Last modified: 2018/09/28 15:42 by Lisa Clarke