Difficult to work with `Dname` and `ParsedDname` due to `Octets`

[Jerome Gravel-Niquet]

I might be missing something, but we're having to write a lot more code than I think necessary in our tests to fashion an impl ToDname.

In our app, we have a function that takes a ParsedDname<&Bytes> because that's what we get from a Question::qname() call from a Message<Bytes>.

Now, to get an impl ToDname from scratch (without manually writing out the bytes with the length of each label, which is tedious), there are 2 options as far as I can see:

1. Dname::bytes_from_str(&str) -> Result<Dname<Bytes>, FromStrError>
   This would be the easiest! Except that's not what the function we want to test expects. There's Dname::into that can return a ParsedDname<Bytes>, but we need a ParsedDname<&Bytes>.

2. Doing the above, but re-parsing the bytes:

        let dname = Dname::bytes_from_str("example.com").unwrap();
        let mut parser = Parser::from_ref(dname.as_octets());
        let question = Question::new_in(ParsedDname::parse(&mut parser).unwrap(), Rtype::A);

Is there a better way to do this?

This is not a big deal, we can abstract this out. This is only used in our tests, but I feel like it could be better ergonomically.

[Martin Hoffmann]

I think Dname::for_ref and impl From<Dname<Ref>> for ParsedDname<Ref> should do the trick:

    let dname = Dname::bytes_from_str("example.com").unwrap();
    let question = Question::new_in(ParsedDname::from(dname.for_ref()), Rtype::A);

[Jerome Gravel-Niquet]

Thank you, I missed that!

[Hugo]

An example of this would be very handy in domain::base::Dname. Having a &str, my first instinct was to try and use from_str, which I didn't work for me and I couldn't really figure out what I was doing wrong.

[Martin Hoffmann]

Fair point. We will have to go over the documentation for all the changes in 0.8, anyways. Better explanations on how to deal with those octets generics will be a point of that.

We might also provide a convenience module that provides types aliases for the types you are most likely to instantiate manually.