Please help write a regular code

Ask a master to help write a regular code
Get the content of the Web page by following the code

$conn =file_get_contents ("http://ygtc.tmall.com");

Then, all of the URLs with HTTP.///are processed by the Foo () function, put back in place, and finally output the Web page
The Foo () function is as follows

function foo ($url)}
$url for incoming URLs
return MD5 ($URL);//Here is simply a simple way to write down the function, in fact, the processing method is not so simple, just as an example;
}

------Solution--------------------
$conn = file_get_contents ("http://ygtc.tmall.com");
echo Preg_replace_callback ('/(
function foo ($url) {
return $url [1]. MD5 ($url [2]);//Here is simply a simple way to write down the function, in fact, the processing method is not so simple, just as an example;
}

