How can I force a Save-As dialog box without leaving the page in php?

I have an anchor tag:

<a href="file.pdf">Download Me</a>

I would like for the user to click on it and then have a Save-As dialog box appear with a new filename I determine.

I found this(http://www.w3schools.com/php/func_http_header.asp):

header("Content-type:application/pdf");

// It will be called downloaded.pdf
header("Content-Disposition:attachment;filename='downloaded.pdf'");
                                
// The PDF source is in file.pdf
readfile("file.pdf");

I don't understand where to开发者_JAVA百科 put those headers. At the top of the page? When I try to place those 3 lines directly above my link I receive the following errors:

Warning: Cannot modify header information - headers already sent by (output started at /home5/ideapale/public_html/amatorders_basic/admin/download.php:38) in /home5/ideapale/public_html/amatorders_basic/admin/download.php on line 118

I got the same error for both of the header lines I just added. Right after that, there are thousands lines of ASCII letters. How can I get the Save-As dialog box to appear using either jQuery or PHP(whatever is easier)?

Please be careful when using Stijn Van Bael's code, it opens you up to some serious security exploits.

Try something like:

--- download.php ---
$allowed_files = array('file.pdf', 'otherfile.pdf');

if (isset($_REQUEST['file']) && in_array($_REQUEST['file'], $allowed_files))
{
  $filename = $_REQUEST['file'];

  header("Content-type:application/pdf");
  header("Content-Disposition:attachment;filename='$filename'");

  // The PDF source is in file.pdf
  readfile($filename);

  exit();
}
else
{
  // error
}


--- linkpage.php ---
<a href="download.php?file=file.pdf">Download PDF</a>
<a href="download.php?file=otherfile.pdf">Download PDF</a>

Probabaly a better way to do this is at the web server level (this can go in .htaccess) This will force all PDF's to be treated as a binary file (forcing the browser to download them) in and below the directory you put this in.

<FilesMatch "\.(?i:pdf)$">
 Header set Content-Disposition attachment
 ForceType application/octet-stream
</FilesMatch>

Create a new page with the headers and the readfile, then make the download link refer to the page, which will return the PDF file.

For example:

<a href="download.php?file=file.pdf">Download Me</a>

Source for download.php:

$filename = $_REQUEST['file'];
header("Content-type:application/pdf");
// It will be called downloaded.pdf
header("Content-Disposition:attachment;filename='$filename'");

// The PDF source is in file.pdf
readfile($filename);

Or you could just use the new HTML5 property download in the anchor tag of your html.

The code will look something like

<a download href="path/to/the/download/file"> Clicking on this link will force download the file</a>