Cannot read properties of undefined (reading 'transfer-encoding')错误求助

核心问题：multer中间件参数顺序颠倒 #

你在调用multer的upload函数时，把res和req的参数顺序写反了。multer的处理函数要求第一个参数是请求对象req，第二个是响应对象res，顺序错误会导致multer内部无法正确读取请求头，从而抛出transfer-encoding相关的未定义错误。

修正后的路由代码片段：

express.post('/', (req, res) => {
    // 修正参数顺序：req在前，res在后
    upload(req, res, async (error) => {
        // validate request
        if (!req.file) {
            return res.json({ error: "Files are not valid :(" })
        }
        if (error) {
            return res.status(500).send({ error: error.message })
        }

        // store into database 
        const file = new File({
            filename: req.file.filename,
            uuid: uuid4(),
            path: req.file.path,
            size: req.file.size
        })

        const response = await file.save();
        return res.json({ file: `${process.env.APP_BASE_URL}/files/${response.uuid}` })
    })
})

其他潜在问题修正 #

• 目录拼写错误：存储路径'uplods/'应为'uploads/'，避免文件存储时找不到目录
• multer配置项错误：limit需改为复数limits，否则文件大小限制不生效
• 确保目录存在：multer不会自动创建uploads目录，需手动创建该目录，或在代码中添加目录检查逻辑

修正后的完整代码：

require('dotenv').config()
const express = require('express').Router();
const multer = require('multer');
const path = require('path');
const fs = require('fs');
const File = require('../models/file');
const { v4: uuid4 } = require('uuid');

// 确保uploads目录存在
const uploadDir = 'uploads/';
if (!fs.existsSync(uploadDir)) {
    fs.mkdirSync(uploadDir);
}

let storage = multer.diskStorage({
    destination: (req, file, cb) => cb(null, uploadDir),
    filename: (req, file, cb) => {
        const uniqueName = `${Date.now()}-${Math.round(Math.random() * 1E9)}${path.extname(file.originalname)}`;
        cb(null, uniqueName)
    },
})

let upload = multer({
    storage,
    limits: { fileSize: 1000000 * 100 }, // 修正为limits
}).single('myfile');

express.post('/', (req, res) => {
    upload(req, res, async (error) => {
        if (!req.file) {
            return res.json({ error: "Files are not valid :(" })
        }
        if (error) {
            return res.status(500).send({ error: error.message })
        }

        const file = new File({
            filename: req.file.filename,
            uuid: uuid4(),
            path: req.file.path,
            size: req.file.size
        })

        const response = await file.save();
        return res.json({ file: `${process.env.APP_BASE_URL}/files/${response.uuid}` })
    })
})

module.exports = express;

错误截图：

内容的提问来源于stack exchange，提问作者Yashwant Gurjar