How to Use Content-disposition for force a file to download

When a user clicks on a link to a file, the web browser usually decides how to handle it. Some file types, such as images, videos, or PDFs, are often displayed directly in the browser instead of being downloaded. To force the browser to download a file instead of opening it, the Content-Disposition HTTP header can be utilized.

Understanding the Content-Disposition Header

The Content-Disposition header tells the browser how to handle the response. It has two main values:

inline – The file is displayed within the browser if possible.
attachment – The file is downloaded instead of being displayed.

How to Use Content-Disposition to Force Download

To ensure a file is downloaded, the server must send the correct HTTP headers. Below is an example of how to use this header:

  
Content-Disposition: attachment; filename="example.pdf"

This instructs the browser to present a download option for example.pdf rather than displaying it. The filename parameter suggests a default name for the downloaded file.

Example Implementation in Various Languages

PHP

In a PHP script, the headers can be set as follows:

  
header('Content-Type: application/pdf');  
header('Content-Disposition: attachment; filename="example.pdf"');  
readfile('example.pdf');

This script ensures that example.pdf is downloaded instead of being opened in the browser.

Apache .htaccess

Apache users can force file downloads using .htaccess:

  
  
    Header set Content-Disposition attachment

This forces the download of files with specified extensions.

Node.js with Express

In a Node.js application using Express, a similar effect can be achieved:

  
app.get('/download', function(req, res) {  
    res.setHeader('Content-Disposition', 'attachment; filename="file.txt"');  
    res.sendFile(__dirname + '/file.txt');  
});

This approach ensures that file.txt is downloaded when accessed.

Best Practices for Using Content-Disposition

Ensure the correct MIME type is set using Content-Type.
Use the filename attribute responsibly to suggest a reasonable file name.
Validate and sanitize file names before sending them in headers.
Test across different browsers to ensure expected behavior.

Common Issues and Troubleshooting

Despite setting Content-Disposition: attachment, the behavior may vary depending on browser settings. Some users may have configured their browsers to open certain file types automatically. In such cases: