Replace `IpNumber` & `EtherType` with structs

[JulianSchmid]

Task

Rewrite EtherType & IpNumber to be single value structs. E.g.:

struct EtherType(pub u16);

Also add implementations of the From & Into traits for simply converting from u8/u16 into the struct type and from the struct type into u8/u16. Also manually implement the Debug and Display to also display the human readable name if available (e.g. IPv4(0x0800) for EtherType(0x0800)).

Why

Both EtherType and IpNumber are currently implemented as simple enums. E.g.:

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum EtherType {
    Ipv4 = 0x0800,
    Ipv6 = 0x86dd,
    // ...
}

Originally the plan was to use the enums in the headers. But this approach was discarded in early versions of the library as it would limit the values to only the ones present in the enums. Additionally adding an Unknown(u8)value to the enums would disabled the ability to simply cast the values to their underlying type and added unneeded computation when converting from and into the enum type. So the headers were switched back to the underlying types u8 & u16 to support all valid IP & Ethernet headers.

But some time ago I noticed that that the pcap crate had implemented the Linktype as struct with a simple value ( https://docs.rs/pcap/1.0.0/pcap/struct.Linktype.html ). To me this seems the more sensible approach for EtherType & IpNumber as well, as it comes with the following advantages:

• Allows all possible values without any need for re-mapping values when converting the underlying types (u8/u16) from and to the struct type.
• Gives some type safety when assigning values.
• Allows for printing of the underlying meaning of the value (e.g. UDP) when printing with Debug or Display.

[0xcrust]

Hello! I noticed that a major refactor is in the works as per PR #47. Would it be fine for me to work on this now or is is it advisable to wait so that this PR(which comes with a lot of changes) lands.

[JulianSchmid]

Hi @0xcrust

I would wait until I at least have merged it to master. I will try to at least merge a partial state this weekend.

Greets Julian

[JulianSchmid]

Hi @0xcrust ,

I merged https://github.com/JulianSchmid/etherparse/pull/47 to master. There will be additional changes, but no where near to the same extend.

Greets Julian

[0xcrust]

Great! I'd like to go ahead with this then if that's fine

[JulianSchmid]

That would be great 😀