Express request is called twice

Question

To learn node.js I'm creating a small app that get some rss feeds stored in mongoDB, process them and create a single feed (ordered by date) from these ones.

It parses a list of ~50 rss feeds, with ~1000 blog items, so it's quite long to parse the whole, so I put the following req.connection.setTimeout(60*1000); to get a long enough time out to fetch and parse all the feeds.

Everything runs quite fine, but the request is called twice. (I checked with wireshark, I don't think it's about favicon here).

I really don't get it.

You can test yourself here : http://mighty-springs-9162.herokuapp.com/feed/mde/20 (it should create a rss feed with the last 20 articles about "mde").

The code is here: https://github.com/xseignard/rss-unify

And if we focus on the interesting bits :

I have a route defined like this : app.get('/feed/:name/:size?', topics.getFeed);

And the topics.getFeed is like this :

function getFeed(req, res) {
  // 1 minute timeout to get enough time for the request to be processed
  req.connection.setTimeout(60*1000);   

  var name = req.params.name;
  var callback = function(err, topic) {
  // if the topic has been found
  if (topic) {
    // aggregate the corresponding feeds
    rssAggregator.aggregate(topic, function(err, rssFeed) {
      if (err) {
        res.status(500).send({error: 'Error while creating feed'});
      }
      else {
        res.send(rssFeed);
      }
    },
    req);
  }
  else {
    res.status(404).send({error: 'Topic not found'});
  }};
  // look for the topic in the db
  findTopicByName(name, callback);
}

So nothing fancy, but still, this getFeed function is called twice.

What's wrong there? Any idea?

Answer 1

This annoyed me for a long time. It's most likely the Firebug extension which is sending a duplicate of each GET request in the background. Try turning off Firebug to make sure that's not the issue.

Answer 2

I faced the same issue while using Google Cloud Functions Framework (which uses express to handle requests) on my local machine. Each fetch request (in browser console and within web page) made resulted in two requests to the server. The issue was related to CORS (because I was using different ports), Chrome made a OPTIONS method call before the actual call. Since OPTIONS method was not necessary in my code, I used an if-statement to return an empty response.

if(req.method == "OPTIONS"){
    res.set('Access-Control-Allow-Origin', '*');
    res.set('Access-Control-Allow-Headers', 'Content-Type');
    res.status(204).send('');
}

Spent nearly 3hrs banging my head. Thanks to user105279's answer for hinting this.