Getting ERROR: uncaughtException: source.on is not a function, when using request and multiparty for multipart/form-data

Question

I am trying to send data from my node application to a 3rd party HTTP endpoint.

I am parsing the data on the request object coming from the client using the multiparty module and sending the data through the request module. I am getting the error

error: uncaughtException: source.on is not a function

var request = require('request');
const multiparty = require('multiparty');

function addAttachment(req, res) {
  let form = new multiparty.Form();
  let parsedFile = {};
  const formData = {};
  form.parse(req, function(err, fields, files){
    Object.keys(fields).forEach(function(name) {
      formData[name] = fields[name][0];
    });

    Object.keys(files).forEach(function(name) {
      logger.debug(name);
      parsedFile[name] = files[name][0];
    });
    formData.uploadFile = parsedFile.uploadFile;
    logger.debug('formData ', formData);

    reqOptions.url = imageURL;
    reqOptions.formData = formData;

    logger.debug('REQ_OPTIONS ', reqOptions);

    request.post(reqOptions, function (err, response, body) {
      if (err) {
        logger.warn(req, ' Error sending attachment', err);
        res.status(400);
        res.json({ "msg": "Error sending attachment" });
      } else {
        res.status(201);
        logger.debug('BODY ', body);
        res.send(body);
      }
    });
  });
}

The reqOptions obj contains the headers, url, auth obj, we then add the form data to it.

When I log the form data it looks to be in the correct format

{
"meta": {
    "prop1": "xxxxxx",
    "prop2": "xxxxxxxxxxxxx",
    "uploadFile": {
        "fieldName": "uploadFile",
        "originalFilename": "test.PNG",
        "path": "/tmp/W1IppPiK04JpkPrnZWEhzkmV.PNG",
        "headers": {
            "content-disposition": "form-data; name=\"uploadFile\"; filename=\"test.PNG\"",
            "content-type": "image/png"
        },
        "size": 42786
    }
}

}

Answer 1

This error is probably one of the best examples how error message can be perfectly misleading. Therefore. it's very frustrating to do RCA of the issue:

ERROR: uncaught Exception: source.on is not a function

Actually there is nothing about any function here. In my case, I spent hours scratching my head and finally only to find it is JSON under another JSON which was causing this error:

  let subJson = 
  {
      field1: "value1",
      field2: "value2"
  }

  let myJson = 
  {
      field1: "value1",
      field2: "value2",
      field3: subJson
  }

  createFormData(myJson);

This is it! When you call createFormData with myJson as parameter, you will see exception source.on is not a function! And we keep thinking where is that function?

Solution is JSON.stringify

   field3: JSON.stringify(subJson)

Will solve this issue.

javascript!