NodeJS - 如何在不将文件保存在服务器上的情况下从 Base64 返回 PDF？

Question

Here is my scenario:

• I have an application built in Node with Express;
• I have an external API that returns a Base64 PDF file;
• I have to get this Base64 and open the file for the user;
• I am unable to save the PDF on server.

I've tried many ways and I can't open the file to the user.

Ways I've tried:

const buff = Buffer.from(myBase64, 'base64');
const file = fs.writeFileSync('boleto.pdf', buff, { encoding: 'base64' });

try {
  res.setHeader('Content-Length', file.size);
  res.setHeader('Content-Type', 'application/pdf');
  res.setHeader('Content-Disposition', 'attachment; filename=boleto.pdf');
} catch (e) {
  return res.status(404).send({ error: e, message: 'File does not exist.', statusCode: 404 });
}

const buff = Buffer.from(myBase64, 'base64');
const file = fs.writeFileSync('boleto.pdf', buff, { encoding: 'base64' });

try {
  res.contentType('application/pdf');
  return res.status(200).sendFile('boleto');
} catch (e) {
  return res.status(404).send({ error: e, message: 'File does not exist.', statusCode: 404 });
}

const buff = Buffer.from(myBase64, 'base64');
const file = fs.readFileSync(buff, { encoding: 'base64' });

try {
  res.contentType('application/pdf');
  return res.status(200).sendFile(file);
} catch (e) {
  return res.status(404).send({ error: e, message: 'File does not exist.', statusCode: 404 });
}

Can someone help me?

Answer 1

The proper way to do this here would be to call the service and direct the base64 string response to a decoding stream, then pipe that to the response output. That would save you having to wait for files to download or for the string -> byte translation to finish.

However if you are only dealing with small files (<1MB) or you dont have to handle traffic from thousands of concurrent requests its probably fine to just download the base64 string and use Buffer.from(base64str, 'base64') to decode it before passing it onwards.

This "minimal implementation" approach goes something like this:

const axios = require('axios'); // or any other similar library (request, got, http...)

const express = require('express');
const router = express.Router();

router.get('/invoice/:id.pdf', async (req, res) => {
  // Here is the call to my external API to get a base64 string.
  const id = req.params.id;
  const base64str = await axios.get('https://myfileapi.domain.com/file/?id=' + id);

  // Here is how I get user to download it nicely as PDF bytes instead of base64 string.
  res.type('application/pdf');
  res.header('Content-Disposition', `attachment; filename="${id}.pdf"`);
  res.send(Buffer.from(base64str, 'base64'));
});

module.exports = router;

Note that there is no authentication here to block other users accessing this file, if you want authentication you'll have to handle that separately.