如何将input type="file"多文件转为Resend要求的string/buffer格式？

前端处理：将文件转为Base64字符串（适配JSON传输） #

因为JSON无法直接传输File对象，需要把文件转成Base64字符串（属于Resend支持的string格式范畴），再和其他表单数据一起打包成JSON发送：

document.getElementById('contact-form').addEventListener('submit', async (e) => {
  e.preventDefault();
  
  // 收集基础表单数据
  const payload = {
    from: 'Acme <onboarding@resend.dev>',
    to: ['delivered@resend.dev'],
    subject: document.getElementById('subject').value,
    text: document.getElementById('message').value,
    attachments: []
  };

  // 获取多文件选择的结果
  const fileInput = document.getElementById('file-attachments');
  const files = fileInput.files;

  // 遍历文件，转成Base64字符串
  for (let i = 0; i < files.length; i++) {
    const file = files[i];
    const base64Content = await new Promise((resolve) => {
      const reader = new FileReader();
      reader.onloadend = () => {
        // 去掉dataURL前缀，只保留纯Base64字符串
        resolve(reader.result.split(',')[1]);
      };
      reader.readAsDataURL(file);
    });
    payload.attachments.push({
      filename: file.name,
      content: base64Content
    });
  }

  // 发送JSON格式的POST请求到后端
  await fetch('/api/send-email', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(payload)
  });
});

后端处理：将Base64转为Buffer（适配Resend要求） #

后端接收JSON后，把Base64字符串转成Resend需要的Buffer格式，再调用API发送邮件：

const express = require('express');
const { Resend } = require('resend');
const app = express();

app.use(express.json());

const resend = new Resend('你的Resend API密钥');

app.post('/api/send-email', async (req, res) => {
  try {
    // 处理附件：Base64字符串转Buffer
    const processedAttachments = req.body.attachments.map(att => ({
      filename: att.filename,
      content: Buffer.from(att.content, 'base64')
    }));

    // 调用Resend发送邮件
    const data = await resend.emails.send({
      from: req.body.from,
      to: req.body.to,
      subject: req.body.subject,
      text: req.body.text,
      attachments: processedAttachments
    });

    res.status(200).json(data);
  } catch (error) {
    res.status(400).json({ error: error.message });
  }
});

app.listen(3000, () => console.log('服务运行在3000端口'));

关键注意点 #

1. 前端转Base64时必须去掉data:xxx;base64,前缀，否则后端转Buffer会失败
2. 后端通过Buffer.from(base64Str, 'base64')完成格式转换，完全符合Resend的参数要求
3. 整个流程保持JSON传输方式，和你现有代码逻辑兼容

内容的提问来源于stack exchange，提问作者Aspiring Dev 23000