This allows stateful or configurable codecs without having to express
all configuration in the type name itself. For example, we could have a
Base64 type with configurable Base64 engines without having to duplicate
the Base64 type itself.
(Note that the different engines in the Base64 crate are values, not
types.)
Let’s continue reexporting jid and minidom, but not their inner pub
items, users of this crate can go one level deeper if they need that.
Only xso::error::Error is still useful to reexport, as this is part of
the public API of all of our parsers.
This is a large change and as such, it needs good motivation. Let me
remind you of the ultimate goal: we want a derive macro which allows us
to FromXml/IntoXml, and that derive macro should be usable from
`xmpp_parsers` and other crates.
For that, any code generated by the derive macro mustn't depend on any
code in the `xmpp_parsers` crate, because you cannot name the crate you
are in portably (`xmpp_parsers::..` wouldn't resolve within
`xmpp_parsers`, and `crate::..` would point at other crates if the macro
was used in other crates).
We also want to interoperate with code already implementing
`TryFrom<Element>` and `Into<Element>` on structs. This ultimately
requires that we have an error type which is shared by the two
implementations and that error type must be declared in the `xso` crate
to be usable by the macros.
Thus, we port the error type over to use the type declared in `xso`.
This changes the structure of the error type greatly; I do not think
that `xso` should have to know about all the different types we are
parsing there and they don't deserve special treatment. Wrapping them in
a `Box<dyn ..>` seems more appropriate.
[RFC 2426][1] says:
> The binary data MUST be encoded using the "B" encoding format.
> Long lines of encoded binary data SHOULD BE folded to 75 characters
> using the folding method defined in [MIME-DIR].
That implies that whitespace may occur in binval data and we thus must
be able to parse this correctly.
[1]: https://datatracker.ietf.org/doc/html/rfc2426#section-2.4.1
