Hey there! Let's tackle these two Node.js PDF handling scenarios step by step—they're super common when working with document-based services.

If you've got a byte array (usually a Uint8Array in JavaScript) and want to save it as a PDF file on your filesystem, Node.js's built-in fs module is all you need. The key here is converting the byte array to a Node.js Buffer first, since fs works seamlessly with Buffers for binary data.

Here's a practical example:

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

// 假设这是你的输入字节数组（比如从数据库或另一个服务获取的）
const pdfByteArray = new Uint8Array([/* 你的字节数据 */]);

// 将Uint8Array转换为Node.js Buffer
const pdfBuffer = Buffer.from(pdfByteArray);

// 写入到本地PDF文件
fs.writeFile(path.join(__dirname, 'generated.pdf'), pdfBuffer, (err) => {
  if (err) {
    console.error('Failed to write PDF file:', err);
    return;
  }
  console.log('PDF file saved successfully!');
});

// 如果你更喜欢同步写法（适合脚本，不推荐在服务端请求处理中使用）：
// fs.writeFileSync(path.join(__dirname, 'generated.pdf'), pdfBuffer);

Quick note: If your byte array is already a Buffer (common in Node.js), you can skip the Buffer.from() step and write it directly to the file.

When you call an external service that returns a PDF as a byte stream, you need to ensure you capture the raw binary data first, then convert it to a byte array (or pass it directly as a response to your own clients).

Let's use axios for the external request (a popular HTTP client) and Express for our own service:

const express = require('express');
const axios = require('axios');
const app = express();

app.get('/get-proxied-pdf', async (req, res) => {
  try {
    // 调用外部服务时，必须设置responseType为'arraybuffer'以获取原始字节数据
    const externalServiceResponse = await axios.get('https://your-external-service.com/pdf-endpoint', {
      responseType: 'arraybuffer'
    });

    // 将返回的二进制数据转换为字节数组（Uint8Array）
    const pdfByteArray = new Uint8Array(externalServiceResponse.data);

    // 设置响应头，让客户端识别这是PDF文件
    res.setHeader('Content-Type', 'application/pdf');
    res.setHeader('Content-Disposition', 'inline; filename="proxied.pdf"'); // 或者用'attachment'让浏览器下载

    // 将字节数组作为响应发送——Express会自动处理为Buffer
    res.send(pdfByteArray);

    // 替代方案：如果不需要显式转成Uint8Array，直接发送Buffer也可以：
    // res.send(externalServiceResponse.data);
  } catch (error) {
    console.error('Error fetching PDF from external service:', error);
    res.status(500).send('Failed to retrieve PDF');
  }
});

app.listen(3000, () => {
  console.log('Service running on port 3000');
});

Key point: Setting responseType: 'arraybuffer' is critical here. Without it, axios will try to parse the response as a UTF-8 string, which will corrupt the PDF binary data.

内容的提问来源于stack exchange，提问作者Sowmya Poovannan