Text codecs allow to customize the conversion of data from/to XML,
in particular in two scenarios:
1. When the type for which the behaviour is to be defined comes from a
foreign crate, preventing the implementation of
FromXmlText/IntoXmlText.
2. When there is not one obvious, or more than one sensible, way to
convert a value to XML text and back.
This specification defines a token-based method to streamline
authentication in XMPP, allowing fully authenticated stream
establishment within a single round-trip.
This is more in line with how we handle closely coupled specifications
already. While there are subdirectories for "large" specifications (such
as MUC and PubSub), those only refer to a single XEP document. When
there are multiple separate XEP documents, we have separate modules for
that.
There is at least one branch of the FromStr implementation which passes
user input right into the error struct, so we cannot assume that `'` is
not part of that value.
The previous code didn't build with 1.78:
```
error[E0716]: temporary value dropped while borrowed
--> parsers/src/data_forms/validate.rs:394:46
|
380 | let value = match self {
| ----- borrow later stored here
...
394 | Datatype::UserDefined(value) => &format!("x:{value}"),
| ^^^^^^^^^^^^^^^^^^^-
| | |
| | temporary value is freed at the end of this statement
| creates a temporary value which is freed while still in use
|
= note: consider using a `let` binding to create a longer lived value
= note: this error originates in the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)
error[E0716]: temporary value dropped while borrowed
--> parsers/src/data_forms/validate.rs:395:51
|
380 | let value = match self {
| ----- borrow later stored here
...
395 | Datatype::Other { prefix, value } => &format!("{prefix}:{value}"),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^-
| | |
| | temporary value is freed at the end of this statement
| creates a temporary value which is freed while still in use
|
= note: consider using a `let` binding to create a longer lived value
= note: this error originates in the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)
For more information about this error, try `rustc --explain E0716`.
```
This seems like a silly reason to pull up the compiler version
requirements, so I fixed it with a trivial modification.
This is bare-bones and is missing many features which we intend to add
in future commits, such as parsing from attributes whose names differ
from the field names and parsing into non-String types.
Well, not really, of course. All of this will make sense once we start
adding support for fields and non-struct types. Refactoring the code now
before we start to add actual member field parsing is much easier.
How do I know that this will work out? Well, my crystal ball knows it.
Don't believe me? Okay, ChatGPT told me ... Alright alright, I went
through the entire process of implementing this feature *twice* at this
point and have a pretty good idea of where to draw the abstraction lines
so that everything falls neatly into place. You'll have to trust me on
this one.
(Or, you know, check out old branches in my xmpp-rs repo. That might
work, too. `feature/derive-macro-streaming-full` might be a name to look
for if you dare.)
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.
From [XEP-0004: Data Forms](https://xmpp.org/extensions/xep-0004.html#protocol-field):
> ...
> The <field/> element MAY contain any of the following child elements:
>
> <desc/>
> The XML character data of this element provides a natural-language
> description of the field, intended for presentation in a
> user-agent (e.g., as a "tool-tip", help button, or explanatory text
> provided near the field). The <desc/> element SHOULD NOT contain
> newlines (the \n and \r characters), since layout is the
> responsibility of a user agent, and any handling of
> newlines (e.g., presentation in a user interface) is unspecified
> herein. (Note: To provide a description of a field, it
> is RECOMMENDED to use a <desc/> element rather than
> a separate <field/> element of type "fixed".)
> ...
This adds shims which provide FromXml and IntoXml implementations to
*all* macro-generated types in `xmpp_parsers`. Mind that this does not
cover all types in `xmpp_parsers`, but a good share of them.
This is another first step toward real, fully streamed parsing.
[gone](https://datatracker.ietf.org/doc/html/rfc6120#section-8.3.3.5) and [redirect](https://datatracker.ietf.org/doc/html/rfc6120#section-8.3.3.14) errors may include an alternative address.
> gone
>
> The recipient or server can no longer be contacted at this address,
> typically on a permanent basis (as opposed to the <redirect/> error
> condition, which is used for temporary addressing failures); the
> associated error type SHOULD be "cancel" and the error stanza SHOULD
> include a new address (if available) as the XML character data of the
> <gone/> element (which MUST be a Uniform Resource Identifier [URI] or
> Internationalized Resource Identifier [IRI] at which the entity can
> be contacted, typically an XMPP IRI as specified in [XMPP-URI]).
—
> redirect
>
> The recipient or server is redirecting requests for this information
> to another entity, typically in a temporary fashion (as opposed to
> the <gone/> error condition, which is used for permanent addressing
> failures); the associated error type SHOULD be "modify" and the error
> stanza SHOULD contain the alternate address in the XML character data
> of the <redirect/> element (which MUST be a URI or IRI with which the
> sender can communicate, typically an XMPP IRI as specified in
> [XMPP-URI](https://datatracker.ietf.org/doc/html/rfc6120#ref-XMPP-URI)).
Looking at [the spec](https://xmpp.org/extensions/xep-0004.html#protocol-field)
it seems valid not to have a `var` attribute set, at least for fields of type
`fixed` that is:
> If the element type is anything other than "fixed" (see below), it MUST
> possess a 'var' attribute that uniquely identifies the field in the context
> of the form (if it is "fixed", it MAY possess a 'var' attribute). The element
> MAY possess a 'label' attribute that defines a human-readable name for the field.
Nightly rust complains about `cfg(..)` tests against undeclared
features and other unknown cfgs. They need to be explicitly declared
now.
The nightly/stable features don't exist, so I removed them and
substitutes the currently correct number for the single test where they
were used.
The `xmpprs_doc_build` cfg flag is now declared as expectable.
