implementing a simple language switch using rocket in rust

Let's look how easy it is to implement a simple cookie based language switch in the rocket web framework for the rust programming language. Defining the language type:

In this case there will be support for Dutch and English. PartialEq is derived to be able to compare Lang items with ==.

The Default trait is implemented to define the default language:

The FromStr trait is implemented to allow creating a Lang item from a string.

The Into<&'static str> trait is added to allow the conversion in the other direction.

Finally the FromRequest trait is implemented to allow extracting the "lang" cookie from the request.

It always succeeds and falls back to the default when no cookie or an unknown language is is found. How to use the Lang constraint on a request:

And the language switch page:

And as a cherry on the pie, let's have the language switch page automatically redirect to the referrer. First let's implement a FromRequest trait for our own Referer type:

When it finds a Referer header it uses the content, else the request is forwarded to the next handler. This means that if the request has no Referer header it is not handled, and a 404 will be returned.
Finally let's update the language switch request handler:

Pretty elegant. A recap with all code combined and adding the missing glue: