How to Download Files with Correct Filenames and Extensions from Express.js Servers?

Download Files from Express.js Servers with Complete Filename and Extension

In Node.js, serving a file for download is straightforward, but ensuring it has the correct name and file extension can be a bit trickier.

Old Approach:

When writing a file download route using Express.js, you'll need to explicitly set the Content-Disposition header to provide the file name and file extension. Additionally, you may want to include the Content-Length and Content-Type headers for better handling:

app.get('/download', function(req, res) {
  const file = `${__dirname}/upload-folder/dramaticpenguin.MOV`;
  res.setHeader('Content-disposition', 'attachment; filename=dramaticpenguin.MOV');
  res.write(fs.readFileSync(file, 'binary'));
  res.end();
});

Express.js Helper:

Express.js now includes a helper method called download that simplifies the file download process:

app.get('/download', function(req, res) {
  const file = `${__dirname}/upload-folder/dramaticpenguin.MOV`;
  res.download(file); // Sets 'Content-Disposition' and sends the file
});

Enhancements:

For more advanced functionality, you can utilize third-party libraries like path and mime to automatically determine the filename, file extension, and mime type:

const path = require('path');
const mime = require('mime');

app.get('/download', function(req, res) {
  const file = `${__dirname}/upload-folder/dramaticpenguin.MOV`;
  const filename = path.basename(file);
  const mimetype = mime.getType(file);

  res.setHeader('Content-disposition', 'attachment; filename=' + filename);
  res.setHeader('Content-Type', mimetype);
  res.download(file);
});

This approach ensures that your downloaded file always has the correct name and file extension, regardless of its location on the server.

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