Getting information about an error with EventSource

Question

I'm trying to get information about an error when using EventSource in NodeJs, I think you could understand me better with the following example:

var url = 'http://api.example.com/resource'
var EventSource = require('eventsource');

var es = new EventSource(url);
es.onmessage = function(e) {
   console.log(e.data);
};

es.onerror = function(event) {
   console.log(event);
};

In the onerror function I would like to get information about the error but the event is empty or undefined as well as the es object (well, this object just cames with a pair of curly brackets {}). I would like to read the response header in case of error, something like:

es.onerror = function(e) {
   console.log(e.header.location);
};

Is this possible? What I'm missing? I think the answer should be very easy but I'm a king of new in NodeJs.

Uchida

Yes its possible but first let us know how you are calling the Eventsource? – Haerle

@RahilWazir I don't understand what is exactly the question, in the code you can see that I'm calling the EventSource when I create a new instance and then I'm subscribing me to the event onmessage and onerror. – Uchida

Answer 1

Well, I have been looking a solutions for a couple of days and I solved my problem. First of all my code was wrong (the documentation of the EventSource is not updated), so my code should look like this:

var url = 'http://api.example.com/resource'
var es = new EventSource(url);

es.on('status', function(e) {
    console.log(e.data);
  }).on('result', function(e) {
    console.log(e.data);
  }).on('error', function() {
   console.log('ERROR!');
   es.close()
  });
}); 

So, the asynchronous responses from the server are located in the e.data object, an example should look like this:

var url = 'http://api.example.com/resource'
var es = new EventSource(url);

es.on('status', function(e) {
    console.log(e.data);
  }).on('result', function(e) {
    var jsonData = JSON.parse(e.data);
    console.log(e.data, jsonData.url);
  }).on('error', function() {
   console.log('ERROR!');
   es.close()
  });
}); 

Note that we don't have yet information about the error but that is because the way the EventSource works. They don't send back the error from the server, they just rise and error string. They have this on their code:

if (!res.headers.location) {
    // Server sent redirect response without Location header.
    _emit('error', new Event('error'));
    return;
}

Uchida

Q: "Getting information about an error with EventSource". A: "They don't send back the error from the server, they just rise an error string." - So there is obviously never an information about the error. Not easy for debugging. --- But check your server side error log, that could give a clue. – Gunpowder

@Gunpowder we have this error. As you state, there's no information about the error on the client side. However, when we look at the server side logs, we don't see any errors. Any additional tips? – Laevorotatory

Then set error_log() at different positions in your code and see where it stops/breaks. Then analyse the logic of your code. – Also avoid common SSE mistakes in PHP, like relying on the server to detect when the user/browser is gone etc. – Gunpowder