How do URLs work under the hood?


Since it is impossible to go from user space to ring 0 in a typed manner, we have to use some weakly typed representation (that is, we can't use an enum, unless we want to do transmutations and friends). Therefore, we use a string-like representation when moving to kernel space. This is basically just a raw pointer to a C-like, null-terminated string. To avoid further overhead, we use more efficient representations:


The first of the three representations is the simplest one. It consists of a struct containing two fat pointers, representing the scheme and the reference respectively.


This is a struct containing two Strings (that is, growable, heap-allocated UTF-8 string), being the scheme and the reference respectively.


This is a Copy-on-Write (CoW) URL, which, when mutated, gets cloned to heap. This way, you get efficient conditional allocation of the URL.

Not much fanciness here.

Opening a URL

Opening URLs happens through the OPEN system call. OPEN takes a C-like, null-terminated string, and two pointer-sized integers, keeping the open flags and the file mode, respectively.

The path argument of OPEN does not have to be an URL. For compatibility reasons, it will default to the file: scheme. If otherwise specified, the scheme will be resolved by the registrar (see The root scheme), and then opened.