What in the world of facebook is rsrc.php? - php

Question

http://static.ak.fbcdn.net/rsrc.php/117600/css/base.css
http://static.ak.fbcdn.net/rsrc.php/z4HBM/hash/3krgnmig.swf
http://b.static.ak.fbcdn.net/rsrc.php/z23ZQ/hash/3ls2fki5.xml
http://static.ak.fbcdn.net/rsrc.php/z7O0P/hash/4hw14aet.png
What does rsrc.php really does? I know that rsrc stands for resource and rsrc.php/z[random]/hash or css/file.extenstion loads a file from somehwere.
Assuming /hash/ or /css/ is a folder which keeps the files like .xml .png .swf but whats with z[random] thing and why they want to load a file from a php? Is it for something like version control for the file or what? If so how to do it (in a simpler way)?

Answer 1

rsrc.php is used by Facebook for version control of all static files, especially images, javascript, and stylesheets. This allows Facebook to apply changes to the main application stack including changes to static content files without breaking functionality for users who are running off an old cached version. It is built into the Facebook architecture as part of the Haste system.
Reference To Code Function Identification By Original Developer
Recommended Process For Managing Static Resources (phabricator.com)

Answer 2

I think that these files are stored in a database. Anything after the SELF (script name, in this case the script is rsrc.php) is passed to the script as a param for the database. I use myself on image files, you base64 the image, store it in the database and usually with a bit of mod_rewrite magic your can get the url of the image to be youtsite.com/images/fish-with-wings when it is really doing this: yoursite.com/some-script.php/fish-with-wings which is really telling the database to look look for get the image from the database where title is = fish-with-wings, and it spits out the base64 for that file.
The advantages of having everything in the database are that for content writers its easier to reference a file and you can delete or purge, or even modify with some cool AJAX and it's also useful to stop hotlinking, which facebook hasn't done here but you could say, if the url is the the full path the redirect to a hotlink warning.

Answer 3

There is a my version of rsrc.php
$request = basename($_SERVER[REQUEST_URI]);
$dotIndex = strrpos($request, ".");
$extension = substr($request, $dotIndex+1);
switch ($extension):
case 'js': $content_type="application/javascript"; break;
default: $content_type="text/css"; break;
endswitch;
$file = Gdecode($request);
$script_file = dirname(__FILE__)."/".$extension."/".$file.".".$extension;
$fp = #fopen($script_file, "r");
if($fp):
fclose($fp);
header('Content-type: '.$content_type);
echo file_get_contents($script_file);
endif;

Answer 4

Don't think it's related to CDN purposes, woulden't make sense running it through an "static" service to serve up dynamic generated content.
I do think however this might be used to hold an open connection, and push data through for facebook updates, ( that's where the xml would make sense for me ).

Answer 5

All of script/css files of Facebook are stored in database and Facebook uses rsrc.php to get them.
rsrc.php code may look like this:
$request = basename($_SERVER["REQUEST_URI"])
if($request != " ") {
$sql = "SELECT * FROM scripts";
$result = mysqli_query($conn, $sql);
if (mysqli_num_rows($result) > 0) {
while($row = mysqli_fetch_assoc($result)) {
header('Content-type: '.$row["type"]);
echo $row["script"];
}
}
}