pkcs8: provide PrivateKeyInfoRef/PrivateKeyInfoOwned

[baloo]

see #1117

[tarcieri]

Why are you exposing BytesRef/BytesOwned?

Why not OctetString/OctetStringRef ala spki (i.e. the ASN.1 type, though it's BIT STRING there), or if not that then &'a [u8] and Vec<u8>?

Really BytesRef and BytesOwned exist for one reason: because they pre-check that the Length is valid and thus permit operations which would otherwise be fallible. Otherwise they're just analogues for &'a [u8] and Vec<u8>.

[baloo]

I was actually looking for a &'a [u8]/Box<[u8]> tuple. But the BytesRef/BytesOwned was looking like the closest to that.

I don't think I'm too comfortable with OctetString, went with just the &'a [u8]/Box<[u8]> and implement RefToOwned there.

[dishmaker]

Why not OctetString/OctetStringRef

Why not merge OctetString and OctetStringRef into something like Cow<[u8]> ?
With minor CPU overhead an enum would be easier to maintain.

Regular OctetString would just contain Cow<'static, [u8]> which is Vec<u8>
Ref OctetString would contain &'a [u8]

https://doc.rust-lang.org/std/vec/struct.Vec.html#impl-From%3CCow%3C'a,+%5BT%5D%3E%3E-for-Vec%3CT%3E

Also, conversions from/to owned would just swap an enum.

[tarcieri]

@dishmaker this crate is designed to support heapless targets that don’t have alloc available, which OctetStringRef is capable of working on

[dishmaker]

Ohhh so such Cow feature needs a kill switch 😢

struct BytesRef<'a> {

    pub length: Length,

    #[cfg(feature = "alloc")]
    pub inner: Cow<'a, [u8]>,

    #[cfg(not(feature = "alloc"))]
    pub inner: &'a [u8],
}

[tarcieri]

But then you haven't actually gotten rid of the *Ref type, and since it's immutable anyway, there's no "write" case to worry about, so Cow doesn't buy you anything.

Anyway, if you'd like to keep discussing this, it would probably be better to open a separate issue.

[tarcieri]

@baloo are you going to redo this? I think it would be great to get in before the next stable release series

[baloo]

I guess I could, I honestly lost track.

[tarcieri]

Aah ok, I'm down to take it then. Seems like it will be a bit of a mess but worth it.

[baloo]

The rebase looks like it's a mess indeed.

I can give it a shot, you have a fair amount of things on your hand.

[tarcieri]

Sure!