Forward uploaded file in POST request - express

Question

I want my web server to have a file POSTed, then forward it in a POST request to another server.

const pug = require('pug');
var cloudinary = require('cloudinary');
var express = require('express');
var multer  = require('multer');
var upload = multer({ dest: 'uploads/' });
var request = require('request');
var bodyParser = require('body-parser');
var JSON = require('JSON');
var https = require('https');
var fs = require('fs');
var request = require('request');
var upload = multer({ dest: 'uploads/' });
process.env.NODE_TLS_REJECT_UNAUTHORIZED = "0"; // We are OK with self-signed

var serverURL = 'https://ec2-54-202-139-197.us-west-2.compute.amazonaws.com:443';

var app = express();
var parser = bodyParser.raw();
var result = null;
app.use(parser);

app.set('view engine', 'pug');

app.get('/',upload.single('avatar'), function (req, res) {
    return res.render('index.pug', {results: [], result_pics: {}});
});

app.post('/makeRequest*', upload.single('uploadPicture'), function(req, res) {
    console.log("Files:");
    console.log(req.file);
    console.log(req.body);

    var r = request.post({url: serverURL, headers: {'User-Agent': 'Client Webserver'}}, function (err, httpResponse, body) {
        console.log('got response');
        console.log(err);
        console.log(body);
        body = JSON.parse(body);
        content = body['content'];
        console.log(content);
        message_type = body.message_type;
        result_pics = [];
        result = [];
        if (message_type == "error") {
            result = ["ERROR: " + body.content];
        }
        else if (message_type == "student created") {
            result = ["Student created."];
        }
        else if (message_type == "student deleted") {
            result = ["Student deleted."]
        }
        else if (message_type == "picture inserted") {
            result = ["Picture inserted."];
        }
        else if (message_type == "viewed pictures") {
            pics = body.pictures;
            for (key in pics) {
                result_pics.push(cloudinary.image(pics[key], {width: 300, height: 200, crop: "crop"}));
            }
        }
        else if (message_type == "listing information") {
            student_table = body.content["student_table"];
            student_to_pic_table = body.content["student_to_pic_table"];

            for (i in student_table) {
                student = student_table[i];
                result.push("Student ID: " + student["student_id"] + " Nickname: " + student["nickname"]);
            }
            for (i in student_to_pic_table) {
                student_pic = student_to_pic_table[i];
                result.push("Student ID: " + student_pic["student_id"] + " Pic ID: " + student_pic["image_id"]);
            }
        }
        else {
            result = ["ERROR: returned message is not of valid type"];
        }

        res.render('index.pug', {results: result, result_pics: result_pics});
        res.end();
    });
    var form = r.form();
    if (req.file) {
        form.append('uploadPicture', req.file);
    }
    form.append('content', JSON.stringify(req.body));


});

app.listen(3000, function() { console.log('listening'); });

So, I get the following error when req.file is true:

TypeError: source.on is not a function
    at Function.DelayedStream.create (/home/daniel/node_modules/delayed-stream/lib/delayed_stream.js:33:10)
    at FormData.CombinedStream.append (/home/daniel/node_modules/combined-stream/lib/combined_stream.js:43:37)
    at FormData.append (/home/daniel/node_modules/form-data/lib/form_data.js:68:3)
    at /home/daniel/WebstormProjects/CloudA3 Client/CloudA3/skrpt.js:95:18
    at Layer.handle [as handle_request] (/home/daniel/node_modules/express/lib/router/layer.js:95:5)
    at next (/home/daniel/node_modules/express/lib/router/route.js:131:13)
    at Immediate.<anonymous> (/home/daniel/node_modules/multer/lib/make-middleware.js:53:37)
    at Immediate.immediate._onImmediate (timers.js:440:18)
    at processImmediate [as _immediateCallback] (timers.js:383:17)
got response
{ [Error: socket hang up] code: 'ECONNRESET' }

I am guessing that I need to convert req.file to some other type in order to transfer it, but I cannot find any information about this anywhere, nor any examples, nor can I find out what the type of req.file even is!

How can I solve this problem?

Answer 1

Since you're using multer and DiskStorage the req.file object has the full path where the file content is stored locally in the req.file.path property. You can use this to create a stream.Readable via fs.createReadStream() and pass that directly to the form. So very easily you can do something like this.

form.append('uploadPicture', fs.createReadStream(req.file.path))

Answer 2

I am working on uploading a file to another server through a backend. I'm currently using multer with MemoryStorage and req.file.buffer for the form data, where I also had to include the filename, which also caused the content type to be set correctly.

form.append('uploadPicture', req.file.buffer, { filename: req.file.originalname });

It is also possible to copy the content type from the request:

form.append('uploadPicture', req.file.buffer, { contentType: req.file.mimetype, filename: req.file.originalname });

I'm expecting low usage for the service, so for me MemoryStorage should be fine, but DiskStorage may be better for your use case.