best way to encode whitespace in URL passed via 'mailto' HREF link

I wrote a PHP based web front end for file upload & download a few years ago.

Outside our firewall, people connect to it via a browser or via WebDAV.  They can download files, navigate thru nested directories, and upload files as well.  Authentication is required to browse client directories, auth is tied to an Open LDAP directory.

Inside of our firewall, people connect to via SMB/CIFS or AFP file sharing.

Our external user population like the convenience of having a direct link to a file for download.

Our internal user population lacks the technical savvy to construct such direct links for delivery via email.

I am trying to code up a link/form that does the following -

1. shows up only for internal web connections (using HTTP_PC_REMOTE_ADDR in $_SERVER allows for this it appears)
2. addresses an email message with a URL to the file in the body of the message

Early tests showed this was quite possible using PHP/HTML.

Further coding to allow for files/folders with whitespace in the name have proved more challenging.

I've tried a variety of methods to accomplish this...

- php eregreplace " " with "%20"
- php urlencode
- now javascript document.write with either escape() or encodeURI()

When the source code for the web page generates, the URL is formatted properly - " " prints out as "%20".  As soon as the mail client launches though, the URL loses the proper encoding.

My next attempt will involve setting the MIME type specifically I think.

The other option is to 'tell' my local users *NOT* to use spaces in file/folder names.  Thing is I've been trying to get cooperation with such a policy for years...sigh.

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if (ereg('^192.168.', $_SERVER['HTTP_PC_REMOTE_ADDR']) || $_SERVER['HTTP_PC_REMOTE_ADDR'] == '72.214.10.199') {
     print '<tr>';
     print '<td valign="top" align="right" bgcolor="#999999" colspan="3" class="mail_text">';
     print '<script language="JavaScript" type="text/javascript">';
     print 'document.write("<a href=\"mailto:?subject=file download from vitrorobertson?body=http://ftp.vitrorobertson.com" + encodeURI("'.$_GET['dir_to_list'].'/'.$item.'") + "\">Email direct link to client</a>")';
     print '</script>';
     print '</td>';
     print '</tr>';
};
 
$_GET['dir_to_list'] is, obviously, passed from the last posting of the self-posting page/form.  I am obviously not using CSS for table generation.