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//! Convenient downcasting from Packets to Packet Bodies.
use crate::packet::{
Packet,
Unknown,
Signature,
OnePassSig,
key::{
PublicKey,
PublicSubkey,
SecretKey,
SecretSubkey,
},
Marker,
Trust,
UserID,
UserAttribute,
Literal,
CompressedData,
PKESK,
SKESK,
SEIP,
MDC,
AED,
};
/// Convenient downcasting from Packets to Packet Bodies.
///
/// This trait offers functionality similar to [`std::any::Any`],
/// hence the name.
///
/// # Sealed trait
///
/// This trait is [sealed] and cannot be implemented for types outside
/// this crate. Therefore it can be extended in a non-breaking way.
///
/// [sealed]: https://rust-lang.github.io/api-guidelines/future-proofing.html#sealed-traits-protect-against-downstream-implementations-c-sealed
pub trait Any<T>: crate::seal::Sealed {
/// Attempts to downcast to `T`, returning the packet if it fails.
///
/// # Examples
///
/// ```rust
/// # use sequoia_openpgp::packet::prelude::*;
/// let p: Packet = Marker::default().into();
/// let m: Marker = p.downcast().unwrap();
/// # let _ = m;
/// ```
fn downcast(self) -> std::result::Result<T, Packet>;
/// Attempts to downcast to `&T`, returning `None` if it fails.
///
/// # Examples
///
/// ```rust
/// # use sequoia_openpgp::packet::prelude::*;
/// let p: Packet = Marker::default().into();
/// let m: &Marker = p.downcast_ref().unwrap();
/// # let _ = m;
/// ```
fn downcast_ref(&self) -> Option<&T>;
/// Attempts to downcast to `&mut T`, returning `None` if it fails.
///
/// # Examples
///
/// ```rust
/// # use sequoia_openpgp::packet::prelude::*;
/// let mut p: Packet = Marker::default().into();
/// let m: &mut Marker = p.downcast_mut().unwrap();
/// # let _ = m;
/// ```
fn downcast_mut(&mut self) -> Option<&mut T>;
}
macro_rules! impl_downcast_for {
($typ: tt) => {
#[allow(deprecated)]
impl Any<$typ> for Packet {
fn downcast(self) -> std::result::Result<$typ, Packet> {
match self {
Packet::$typ(v) => Ok(v),
p => Err(p),
}
}
fn downcast_ref(&self) -> Option<&$typ> {
match self {
Packet::$typ(v) => Some(v),
_ => None,
}
}
fn downcast_mut(&mut self) -> Option<&mut $typ> {
match self {
Packet::$typ(v) => Some(v),
_ => None,
}
}
}
};
}
macro_rules! impl_downcasts {
($($typ:ident, )*) => {
$(impl_downcast_for!($typ);)*
/// Checks that all packet types have implementations of `Any`.
///
/// Not visible outside this module, isn't supposed to be
/// called, this is a compile-time check.
#[allow(unused, deprecated)]
fn check_exhaustion(p: Packet) {
match p {
$(Packet::$typ(_) => (),)*
}
}
}
}
impl_downcasts!(
Unknown,
Signature,
OnePassSig,
PublicKey,
PublicSubkey,
SecretKey,
SecretSubkey,
Marker,
Trust,
UserID,
UserAttribute,
Literal,
CompressedData,
PKESK,
SKESK,
SEIP,
MDC,
AED,
);
#[cfg(test)]
mod test {
use super::*;
#[test]
fn downcast() {
let p: Packet = Marker::default().into();
let mut p = Any::<UserID>::downcast(p).unwrap_err();
let r: Option<&UserID> = p.downcast_ref();
assert!(r.is_none());
let r: Option<&mut UserID> = p.downcast_mut();
assert!(r.is_none());
let _: &Marker = p.downcast_ref().unwrap();
let _: &mut Marker = p.downcast_mut().unwrap();
let _: Marker = p.downcast().unwrap();
}
}