How to upload File with node and form data POST

 Hello, this is a simple project for testing my app in Android, but is very useful for work in other app. In this case is using for upload a CSV file, but is very simple change the type of file

This code is available on GitHub

Requirement:

• Node JS >= 12 
• Nodemon 

First the node app is created:

npm init (Change the main to app.js)

Second, install dependencie:

npm i ---save express
npm i ---save multer
npm i ---save cors

The magic or helper is multer, with this library we can upload different files. Express is a simple web server and the cors is to avoid problems.

Initialize all const for work

const multer = require('multer');
const express = require('express');
const cors = require('cors');
const path = require('path');
const fs = require('fs');
const app = express();
const port = 3000;

Now is necessary to create a folder for upload all CSV, in this case is called "uploads"

let uploads = __dirname + '/uploads';
if (!fs.existsSync(uploads)) {
    console.log('trying for create the directory "upload"');
    fs.mkdirSync(uploads);
}

The nextstep is create the function for storage, filter and initialize the multer:

global.__basedir = __dirname;

const storage = multer.diskStorage({
    destination: (req, file, callback) => {
        callback(null, __basedir + '/uploads/');
    },
    filename: (req, file, callback) => {
        callback(null, file.fieldname + "-" + Date.now() + "-" + file.originalname);
    }
});

const filterCSV = (req, file, callback) => {
    let ext = path.extname(file.originalname);
    if(ext === '.csv') {
        callback(null, true);
    } else {
        callback('File format is not a CSV', false);
    }
}

const upload = multer({
    storage: storage,
    fileFilter: filterCSV
});

For work with other type of file is necesary change the value on:

const filterCSV = (req, file, callback) => {
    let ext = path.extname(file.originalname);
    if(ext === '.csv') {
        callback(null, true);
    } else {
        callback('File format is not a CSV', false);
    }
}

for example, is necessary to evaluate ext == '.pdf' or another extension for work with your code. Rename the function to make it look better.

Then we all declare all function for work with express:

app.use(cors())

app.post('/upload/', upload.single('uploadFile'), (req, res) => {
    try{
        if(req.file == undefined) {
            res.status(400).send({
                message: "Please upload a CSV file: "
            });
        } else {
            res.status(200).send({
                message: "File Upload: "
            });
        }
    } catch(error) {
        res.status(500).send({
            message: "Could not upload the file: " + req.file.originalname
        });
    }
});

app.get('/upload/', (req, res) => {
    res.send("Hello from Node") ;
});


app.listen(port, '0.0.0.0', () => {
    console.log(`App listening port ${port}`);
});

On the line in the method POST is declare an argument for the callback "upload.single('uploadFile')", the "uploadFile" is the name of the input file.

Testing:

For run the app

nodemon dev or node app (for this case, if the app is crashed, is necessary back to run the app)

That's all folks