The following code:

$size = filesize($userfile);
$fp=fopen($userfile,"r");

header("Pragma: no-cache");// HTTP/1.0
header("Cache-Control: no-cache, must-revalidate");// HTTP/1.1
header("Content-Type: application/octet-stream");
if(preg_match("/MSIE 5.5/", $HTTP_USER_AGENT))
	header("Content-Disposition: filename=$userfile");  
else
	header("Content-Disposition: attachment; filename=$userfile"); 
header("Content-Length:	$size");
header("Content-Transfer-Encoding: binary\n");
fpassthru($fp);

when run under Linux/Apache results in a zero length file on MS IE 5.5 when connecting via an ISP or proxy. I have tried various ISPs all with the same result. All is fine with Netscape, or with a direct LAN connection.

Also, if the same PHP script is run under Windows NT 4.0 / IIS 5.0 all is well. 

By removing the line: header("Content-Length: $size"); the download is successful, but we lose any progress bar so this workaround is far from ideal.

Is the $size correct for the file?

Yes.

In the script,

$size=filesize($file);

Where $file is the filename and path.

To prove that it's correct, I have printed the value. Also, both NS and IE (when it works, ie. not through a proxy), display the correct file size and bytes remaining, etc.

I would guess this has something to do with proxy being 
in between..is there one?

--Jani

No feedback. Closing.

As stated in my original submission, EITHER going through a proxy, OR simply dialling up through an ISP, you get the problem.

Connecting directly over a LAN, you do not.

Please re-open.

Are you sure there isn't some transparent proxy involved?

Not tham I am specifically aware of, but it is highly possible that my ISP (BT Internet) has some kind of proxy.

Incidentally, I have tried a couple of different ISPs with the same result.

I would guess that this IS a proxying-related issue.

Here is your code, altered slightly

$userfile = "file.xls";

$size = filesize($userfile);
$fp=fopen($userfile,"r");

header("Pragma: no-cache");// HTTP/1.0
header("Cache-Control: no-cache, must-revalidate");// HTTP/1.1
header("Content-Type: application/octet-stream");
if(preg_match("/MSIE 5.5/", $HTTP_USER_AGENT)) {
        $header = "Content-Disposition: filename=".$userfile;
        //header("Content-Disposition: filename=$userfile");
}else {
        $header = "Content-Disposition: attachment; filename=".$userfile;
        //header("Content-Disposition: attachment; filename=$userfile");
}

header($header);
$header_str = "Content-Length: ".$size;
header($header_str);
header("Content-Transfer-Encoding: binary\n");
fpassthru($fp);


Hope this works.