Add support for PostgreSQL data type macaddr8

[daniele-solutiontech]

Diesel now supports PostgreSQL data type macaddr (EUI-48), it would be awesome to support also the macaddr8 (EUI-64)

[weiznich]

We are happy to accept a PR that adds support for this type.

[daniele-solutiontech]

I’m currently working on adding macaddr8 support for a pull request, but I’m not entirely clear on the purpose of the ByteArrayProxy code. I’ve been reviewing the implementation for macaddr6 and came across the following:

#[allow(dead_code)]
mod foreign_derives {
    use super::*;
    use crate::deserialize::FromSqlRow;
    use crate::expression::AsExpression;

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[diesel(sql_type = MacAddr)]
    struct ByteArrayProxy([u8; 6]);
}

Apologies—I’m still relatively new to the Diesel library and could use some guidance.

[weiznich]

That's one part of the necessary trait setup to convert a MacAddr to/from a [u8;6] on rust side. We likely want something similar for the new MacAddr8 type. The other parts are the FromSql/ToSql impls below.

I think it should be possible to essentially just copy all of that + change the array size to 8 + use the MacAddr8 type there (needs to be created).

[daniele-solutiontech]

I was considering implementing something like this:

#[allow(dead_code)]
mod foreign_derives {
    use super::*;
    use crate::deserialize::FromSqlRow;
    use crate::expression::AsExpression;

    #[derive(AsExpression, FromSqlRow)]
    #[diesel(foreign_derive)]
    #[diesel(sql_type = MacAddr)]
    struct MacAddressProxy(MacAddress);

    #[derive(Debug, PartialEq)]
    enum MacAddress {
        MacAddr6([u8; 6]),
        MacAddr8([u8; 8]),
    }
}

Afterward, I would simply replicate the ToSql and FromSql implementations. What do you think about it?

[weiznich]

That would be a breaking change for the old impl. Just replicating everything for the new type, including the byte wrapper.

Also to just write that out explicitly: We also need a distinct MacAddr8 type for representing the SQL side type. You also can copy the definition of the existing type there, but you need to adjust the oids.

[daniele-solutiontech]

I’ve just submitted a PR. Please let me know if anything is incorrect or missing.