Concurrency issues with 0.7

I’m observing a strange behavior with concurrent requests. I have read all the issues on that matter and I think I’m using the library (0.7) properly (i.e. not using global i18n.setLocale()).

app.js

var app = express();

// Add helpers to handlebars
app.use(function(req, res, next) {
  handlebars.registerHelper('i18n', function() {
    return i18n.__.apply(req, arguments);
  });
  next();
});

// Configure i18n
i18n.configure({
  objectNotation: true,
  locales: ['en', 'fr'],
  defaultLocale: 'en',
  directory: path.join(__dirname, '/locales/server')
});

app.use(i18n.init);

routes/foo.js

var sendEmail = function(req, res, next) {
  var locale = req.user.preferredLocale; // can be 'fr' or 'en'
  req.setLocale(locale);
  handlebars.render('email.hbs', { firstName: 'John' });
}

views/email.hbs

{{i18n 'common.hello' firstName}}

When I render one email at a time, either in english or french, it works fine. But if I send 2+ emails in a for loop I’m starting to get emails in random languages. It seems that each time I run the loop I get different languages.

To your knowledge, is the configuration above correct? I read the code of setLocale and I don’t see where the locale could leak from a req to another. But how can you explain that the issue only occurs when sending multiple requests in a short amount of time?

[gzurbach]

Sorry for the noise I just figured out what the issue was. Long story short, the app is sharing a single instance of Handlebars. Therefore its helper was getting overridden each time a request was initiated.

The solution simply consists in using the data.root.locale from the last argument of the helper.

app.use(function(req, res, next) {
  handlebars.registerHelper('i18n', function() {
    var args = Array.prototype.slice.call(arguments);
    var options = args.pop();
    return i18n.__.apply(options.data.root, args);
  });
  next();
});

I had tried this solution a while ago but because emails are rendered outside of a req/res context the locale was not present in data.root. I had to pass it manually. That was one of the most painful debugging I had to do in a while 😃

Thanks for your help!

[gzurbach]

I use espress-handlebars as well. Here is the relevant code in my app:

In the app.js

expressHandlebars = require('express-handlebars');

var hbs = expressHandlebars.create({
  extname: '.hbs'
});

hbs.handlebars.registerHelper('i18n', function() {
  var args = Array.prototype.slice.call(arguments);
  var options = args.pop();
  return i18n.__.apply(options.data.root, args);
});

Then when I send an email, I have to pass the desired locale as a “context”:

sendEmail({
  from: '[e-mail]',
  to: '[e-mail]',
  subject
}, {
  message: message,
  locale
});

In the handlebars view I do not have to pass the locale when using the i18n helper:

{{i18n 'myKey' someOtionalParam}}

This is the only way for options.data.root to contain the right locale. Let me know if you need further details.