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How to Force a File Download Using PHP
How to Force a File Download Using PHP

A common usage and requirement of a lot of blogger, developers and programmers is a technique of "Force a File Download". As a PHP programmer, i will like to share a built-in mechanism of PHP which will do this job efficiently.

Before going to explain in detail, i would like to break-up some important parts of this logic as i do in my previous post "PHP random password generator"

1. File Name

It is self-explanatory - as we require a file name to download. Make sure it is on the server. Otherwise i can bet, Very very perfect PHP script cannot offer to download this file ;). It is easy, yes very easy to ensure the validity of file, that will be discussed in the later section.

$file = "logo.jpg";

Waoo, we are successful in the completion of our first step.

2. File Path

We will require a "Valid Absolute Path" to the file directory. Example can be, "E:/wamp/www/download/ " and by combining our File Name, it will be,

$file_path = "E:/wamp/www/download/" . $file; /* E:/wamp/www/download/logo.jpg */

The path is an example of Windows environment. Now it is time to validate this path and file name. Again, it is easy by using the built-in methods of PHP.

if( empty( $file ) || !file_exists( $file_path ) ) {

exit("File not found or inaccessible!");

}

If our script fails to find the exact path, execution will be halt, and will said "File not found or inaccessible!" at its last breath.

But i am sure, you are smart to fix it by giving the correct path. and i am happy as we have completed our second variable as well.

3. Content Type (Mimi Type) of a File

It is very important to know about the mimi-type of a file which we are going to offer to download, yes of course Force Download. Every file has a specific mimi-type which helps the browser to offer download in a correct way. Example of mimi-type can be,

pdf: application/pdf

txt: text/plain

exe: application/octet-stream

zip: application/zip

gif: image/gif

png: image/png

jpg: image/jpg

jpeg: image/jpeg

Don't worry, it is not important to learn every mimi-type. PHP has very smart solutions to get the mimi-type of a file automatically, that's why "I Love PHP". You can use any of below method to determine the mimi-type by using $file_path variable.

a. By mimi_content_type

if( function_exists( 'mime_content_type' ) ) {

$file_mime_type = @mime_content_type( $file_path );

}

b. By finfo_file

if( function_exists( 'finfo_file' ) ) {

$finfo = @finfo_open(FILEINFO_MIME);

$file_mime_type = @finfo_file($finfo, $file_path);

finfo_close($finfo);

}

:( - You have not any of above function enabled on your PHP server. Friend, consider to change your hosting, No, really not - you still want to stick with that, Okay don't worry, we can try a standard mimi-type that will help in force downloading a file.

if( empty( $file_mime_type ) ) {

$file_mime_type = "application/force-download";

}

Great, our third step is completed. We have assigned a proper value to $file_mime_type.

4. File Size

I promise, it is last step - as we have to require to determine the file size before executing our final algorithm. Let's arrange some weighing scale to do this. Yes, PHP has a built-in weight scale to accomplish this task.

$file_size = filesize($file_path);

All in One

We have prepared our four inputs. and we are ready to write final algorithm.

$file = "logo.jpg";

$file_path = "E:/wamp/www/download/logo.jpg";

$file_mime_type = "image/jpg"; // Auto / Default Detection

$file_size = filesize($file_path);

Ready to offer Force Download - readfile()

I will use readfile(), built-in method of PHP, which is very powerful to this job. Following is tested algorithm which i am using in my "Free PHP Download File Script".

header('Content-Description: File Transfer');

header('Content-Type: ' . $file_mime_type);

header('Content-Disposition: attachment; filename=' . $file);

header('Content-Transfer-Encoding: binary');

header('Expires: 0');

header('Cache-Control: must-revalidate, post-check=0, pre-check=0');

header('Pragma: public');

header('Content-Length: ' . $file_size);

ob_clean();

flush();

readfile($file_path);

exit;

I hope, this tutorial has helped you a lot in undertanding the concept of Forde File download using PHP.

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