PHP实现从远程下载文件的方法

<?php
if ($_get[xfer]) {
if ($_post[from] == "") {
print "you forgot to enter a url.";
} else {
copy("$_post[from]", "$_post[to]");
$size = round((filesize($_post[to])/1000000), 3);
print "transfer complete.<br>
<a><a href=\"$_post[from]\">$_post[from]</a><br>
<a><a href=\"$_post[to]\">$_post[to]</a> : $size mb";
}
} else {
print "<form action=\"$php_self?xfer=true\" method=post>
from(http://): <input name=from><br>
to(filename): <input name=to><br>
<input type=submit value=\"transload\">";
}
?>