Sort by precedence in Accept header if priorities are equal

[jonathanong]

is this a spec? i think order doesn't matter in the spec, but the q value does. i'd personally rather have the values be returned in the user-provided values than by the client-provided values.

[federomero]

I'm pretty sure there's nothing on the specs that says that the order of appearance matters. It would be nice to know if this is expected in practice.

Do you have any specific need for this?

[madbence]

This is definitely a problem:

var express = require('express');

var app = express();

app
  .route('/')
  .get(function(req, res) {
    res.format({
      json: function() { res.send('json'); },
      html: function() { res.send('html'); }
    });
  });

app.listen(8000);

Chrome sends Accept: text/html, application/xhtml+xml, */*;q=0.8, and the response has correct type:

HTTP/1.1 200 OK
X-Powered-By: Express
Vary: Accept
Content-Type: text/html; charset=utf-8
Content-Length: 4
ETag: W/"4-410646757"
Date: Wed, 11 Jun 2014 11:22:58 GMTConnection: keep-alive

IE (9, 10) sends Accept: text/html, application/xhtml+xml, */*, and the response type is definitely wrong.

neg-tmp λ curl -I -H "Accept: text/html, application/xhtml+xml, */*" localhost:8000
HTTP/1.1 200 OK
X-Powered-By: Express
Vary: Accept
Content-Type: application/json; charset=utf-8
Content-Length: 4
ETag: W/"4-1795630405"
Date: Wed, 11 Jun 2014 11:23:11 GMT
Connection: keep-alive

So res.format is currently broken in express.

According to the spec, the order of appearance doesn't matter, but more specific types should have higher precedence (see RFC2616 section 14.1).

var n = require('negotiator/lib/mediaType')
n('text/html, application/xhtml+xml, */*', ['application/json', 'text/html']);
// [ 'application/json', 'text/html' ]
// but it should be
// [ 'text/html', 'application/json' ]

A temporary workaround is to order res.format entries by precedence.

[federomero]

Hi @madbence, thank you for reporting this.

I agree this is not working correctly but I don't think it's the same issue that was originally submitted, this has nothing to do with the order that items appear on the accept header.

[madbence]

Sure, you're right, I've created a new issue for this

[dougwilson]

@madbence I saw this change and the new version of this module is making it way up the dep chain right now for an express destination ;)