Using PHP Headers to Force Download

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Introduction

Sometimes, when creating a website, you may encounter a situation in which you would like to allow your users to download one or more files.

Probably most of us think that we simply need to create a link to the file itself on our server. The problem in this simplistic method works different for every browser and platform.

For instance, let's suppose that we have a pdf file and you want to let users to download this file. You can link to this file by simply creating a link:

<a href="myfile.pdf">Download pdf</a>

The problem with this method is that most browsers have the capability to open your pdf files. So, they will automatically load up their Adobe Reader plug-in and in short time will display your pdf content in your browser.

The good way to force the download is to use the php header function. header() is used to send a raw HTTP header and must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP. It is a very common error to read code with include(), or require(), functions, or another file access function, and have spaces or empty lines that are output before header() is called. The same problem exists when using a single PHP/HTML file.

The source code

First off all we need to declare an array with the mime types for all the file extensions that we need to download. If you download the article attachment you will find this array with the mimes types for the most used file extensions.

<?php class DownloadManager { var $mimes = array('hqx' => 'application/mac-binhex40', 'cpt' => 'application/mac-compactpro', 'csv' => 'text/x-comma-separated-values', 'bin' => 'application/macbinary', 'dms' => 'application/octet-stream', 'lha' => 'application/octet-stream', 'lzh' => 'application/octet-stream', 'exe' => 'application/octet-stream' //for more mime types download the article attachement ); function DownloadManager() { } function DownloadFile($file) { //First, see if the file exists if (!is_file($file)) return false; //takes the file informations $len = filesize($file); $filename = basename($file); if (FALSE === strpos($file, '.')) return FALSE; // Grab the file extension $ext = explode('.', $filename); $file_extension = end($ext); //set the Content-Type if ( ! isset($mimes[$file_extension])) { $mime = 'application/octet-stream'; } else { $mime = $mimes[$extension]; } //write headers header("Pragma: public"); header("Expires: 0"); header("Cache-Control: must-revalidate, post-check=0, pre-check=0"); header("Cache-Control: public"); header("Content-Description: File Transfer"); header("Content-Type: $mime"); //force download $header="Content-Disposition: attachment; filename=".$filename.";"; header($header ); header("Content-Transfer-Encoding: binary"); header("Content-Length: ".$len); readfile($file); exit; } } ?>

The DownloadFile get the file path as parameter, we check to make sure that it actually exists before going any further. If the file doesn't exist we return FALSE.

After that we get some information's about the specified file like: file size, file name, the extension and the mime type,we display the headers and the file content.

You can use the class described above in the following manner:

$down = new DownloadManager(); $down->DownloadFile('c:\\s.bmp');

License

This article, along with any associated source code and files, is licensed under The Intelliproject Open License (IPOL)

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