multer – req.file always undefined

In case of postman, try following:

1. Close the postman tab for the API
2. Open a new tab again
3. Rebuild the API request and then send.

This may fix the problem. Every time you restart the server you need to do above steps for calling the API again. The reason being multer sends back some cookies called connect.sid to the client which it may require in further communication. Using old cookies will not upload the file.

I put MY (there are many I imagine and surely better) solution to help many people like me because I have searched during 1 entire day ;-(

//JS file on node side

var express = require('express');
var fileUpload = require('express-fileupload');
var fs = require("fs");
var app = express();
console.log('étape 0');
app.use(express.static('mesStatic'));
app.use(fileUpload());
console.log('étape 1');
app.get('/indexFileUpload.htm', function (req, res) {
   res.sendFile( __dirname + "https://stackoverflow.com/" + "indexFileUpload.htm" );
})
console.log('étape 2');
app.post('/file_upload', function (req, res) {

   console.log('étape 3');
   console.log('req.files:' , req.files);
   if (!req.files) {
       res.send('No files to upload.');
       return;
   }

   console.log('req.files.file.data:' , req.files.file.data);
   var bufDataFile = new Buffer(req.files.file.data, "utf-8");
   console.log('étape 3.1');
   console.log('__dirname : ' + __dirname);
   fs.writeFile(__dirname + '/file_upload/output.txt', bufDataFile,  function(err) {
      if (err) {
         return console.error(err);
      }
      else {
         console.log("Data written successfully !");
      }      
      console.log('étape 4');
      res.end('Fin OK !!!');  
   })
})
var server = app.listen(8081, function () {
   var host = server.address().address
   var port = server.address().port

   console.log("Example app listening at http://%s:%s", host, port);
})

Yes, your enctype is wrong and that is the only problem. Make sure that you correct your enctype otherwise you are likely to get undefined in req.file or req.files.

Hello Guys I have also wasted 24 hours and was getting same error i.e req.file is undefined. Now you can refer below code to check your solution. This is single file demo code for uploading file using multer in Node and postman. In POSTMAN Select POST method and select form-data and Key name should be ‘profile’.

var express = require('express');
const app = express();
const port = 3000;
var multer = require('multer');
var upload = multer({dest:'uploads/'});
var storage = multer.diskStorage({
    destination: function(req, file, cb) {
        cb(null, './uploads');
     },
    filename: function (req, file, cb) {
        cb(null , file.originalname);
    }
});
var upload = multer({ storage: storage })

app.post('/single', upload.single('profile'), (req, res, error) => {
    try {
      console.log(req.file);
      res.send(req.file);
    }catch(err) {
      res.send(400);
    }
  });
app.get("https://stackoverflow.com/", (req, res) => {
    res.send('hello Guys');
});
app.listen(port, () => {
    console.log('listening to the port: ' + port);
});

If you are using error handling as mentioned in the document, then req.file will be undefined.

An alternative way to use both error handling and to check if the file exists is to make use of express error handling:

index.js

const express = require("express");
const bodyParser = require("body-parser");
const upload = require("./upload");
const multer = require("multer");

const app = express();

app.use(bodyParser.urlencoded({ extended: true }));

app.get("/", function (req, res) {
  res.send("Hello World");
});

app.post("/upload_file", upload.single("file"), function (req, res) {
  if (!req.file) {
    throw Error("FILE_MISSING");
  } else {
    res.send("success");
  }
});

//Express Error Handling
app.use(function (err, req, res, next) {
  if (err instanceof multer.MulterError) {
    res.statusCode = 400;
    res.send(err.code);
  } else if (err) {
    if (err.message === "FILE_MISSING") {
      res.statusCode = 400;
      res.send("FILE_MISSING");
    } else {
      res.statusCode = 500;
      res.send("GENERIC_ERROR");
    }
  }
});

const server = app.listen(8081, function () {
  const port = server.address().port;

  console.log("App started at http://localhost:%s", port);
});

upload.js

const multer = require("multer");
const storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, "./uploads");
  },
  filename: function (req, file, cb) {
    cb(null, Date.now() + "_" + file.originalname);
  },
});

const upload = multer({
  storage: storage,
  //   limits: { fileSize: 10 },
});

module.exports = upload;

HTML File,

<form class="uploadForm" action="/upload" method="post" enctype="multipart/form-data">
    <label class="control-label">Select File</label>
    <input name="upl" id="input-1" type="file" class="file">
    <input type="submit" value="submit" />
</form>

app.js

var express=require("express");
var multer=require("multer");
var app=express();
var upload=multer({dest:"uploads/"});
app.post("/upload",upload.single("upl"),function(req,res){
console.log("Uploaded Successfull with filename : "+req.upl.filename);
});

For us this was because we were using express-http-proxy to proxy the call before multer, and we needed to use the parseReqBody: false option to properly send over the file.

ie.

app.post('file/upload', proxy(process.env.API_URL, {
  parseReqBody: false,
}))

Use:

formdata.append('file',document.getElementById("input-file").files[0]);

Instead of:

formdata.append('file',document.getElementById("input-file").files);

This is where I have done the mistake.