Overly aggressive AutoLocation rootURL assertion

[tomdale]

There are two invariants maintained by AutoLocation via assertions that have caused a regression in Skylight. I don't know exactly what change caused this to break, and I'm trying to untangle the thread, but the bottom line is I believe AutoLocation is too aggressive and should handle this case more gracefully.

The two invariants causing problems are:

1. AutoLocation enforces that rootURL must always end with a slash /. So, for example, if we set the rootURL to /app, it will raise an exception unless we change it to /app/.
2. AutoLocation verifies that the rootURL is contained in the URL inside _getHistoryPath(), and raises an exception if not (https://github.com/emberjs/ember.js/blob/master/packages/ember-routing/lib/location/auto_location.js#L240)

This is problematic because our Ember app is served by our Rails app, and links generated by Rails link to, you guessed it, /app (no trailing slash).

At some point, our app started throwing exceptions when hitting localhost:4200/app directly instead of /app/. Perversely, everything works fine if I comment out the above-linked assertion, so it seems like it's not doing much. (In that case, Ember automatically redirects to /app/ from /app.)

I don't know the most robust way to handle this case, but it seems like we should loosen the constraints on rootURL and automatically do the normalization in code, rather than pushing complexity to the user.

cc/ @cibernox @jayphelps

[jayphelps]

@tomdale I'll dig up all the old convos explaining why these choices were made.

[jayphelps]

@tomdale

#4717 (comment)
#4751
#4793

The tl;dr is that both history/hash location classes assume /app and /app/ are different paths (cause they are) so extra history states are created and several users reported redirect issues. This is because /app/ is an index path, but /app is a path to app, not an index inside app.

When you comment out the assertions and try it, you noted that it redirected to /app/. Did you try this on a non-history supported browser like IE9? On many servers, this will be cause an infinite redirect battle, where the visitor lands on /app, ember redirects to /app/ via window.location.replace (no pushState support) then the server redirects back to /app, etc, etc.

[tomdale]

@jayphelps I did not try it on IE9 (we only support browsers with pushState). I naively had not considered carefully the case with hash routes and, in particular, the index state. Given that, it probably makes sense for us in our app to either mandate the trailing slash in Rails (which seems pretty easy via http://stackoverflow.com/questions/16218670/enforce-trailing-slash-in-rails-routing) or, more likely, just always use the history location.

Thanks again for the info!

[jayphelps]

@tomdale no problem! It's a very complex situation we've had to explain to many..wish there was an easy way to support it.

btw, I would guess you don't want to serve all routes with trailing slashes (via default_url_options), only the /app/ one:

get 'app/' => 'app#index', :trailing_slash => true

Otherwise your normal ember-route URLs will get the trailing slash too, incorrectly. /app/users/123 => /app/users/123/ (wrong)

[rwjblue]

I did not try it on IE9 (we only support browsers with pushState).

Then why use AutoLocation at all?