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(Continued from previous part...)
Sending Files for Downloading
In the previous section, the requested file is delivered to the browser for opening immediately.
HTTP does also support another header line called "Content-Disposition" which tells the browser to not
open the file immediately, but prepare for downloading the entity body. The following script
will show you how to do this:
<?php #GetFile.php
# Copyright (c) 2005 by Dr. Herong Yang, http://www.herongyang.com/
#
$ok = array_key_exists('QUERY_STRING', $_SERVER);
if ($ok) {
$p = $_SERVER['QUERY_STRING'];
$ok = strlen($p)>0 && file_exists($p);
}
if ($ok) {
if (strpos($p,".html")!=false) {
header("Content-Type: text/html");
} else if (strpos($p,".gif")!=false) {
header("Content-Type: image/gif");
} else if (strpos($p,".pdf")!=false) {
header("Content-Type: application/pdf");
} else if (strpos($p,".doc")!=false) {
header("Content-Type: application/msword");
} else {
$ok = false;
}
}
if ($ok) {
header("Content-Length: ".filesize($p));
header("Content-disposition: attachment; filename=".$p);
readfile($p);
} else {
print("<html><body>Bad request.</body></html>");
}
?>
In this page, anther header line, "Content-Disposition", is added to the response,
in which I am telling the client program that the entity data is an attachment,
with file name specified.
Now try to use IE to request http://localhost/Download.php?hello.pdf, you
will see IE prompting you to save the attachment instead of calling Adobe Reader
to display the data.
Try to use IE to request http://localhost/Download.php?other_existing_file, you
will see IE prompting you to save the attachment. The script is working correctly.
Conclusions
- Setting header lines in PHP is simple, one function, header(), all cases.
- "Location" is a interesting header line. It tells the browser to redirect itself to
a new URL.
- "Content-disposition" tells the browser to prepare for downloading the entity body.
- I like the powerful function, readfile(), reading the content of a file and sending it
to the HTTP response directly.
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