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//! Object type for our RPC system.
pub(crate) mod cast;
use derive_deftly::define_derive_deftly;
use downcast_rs::DowncastSync;
use serde::{Deserialize, Serialize};
use self::cast::CastTable;
/// An object in our RPC system to which methods can be addressed.
///
/// You shouldn't implement this trait yourself; instead, use the
/// [`derive_deftly(Object)`].
///
/// See the documentation for [`derive_deftly(Object)`]
/// for examples of how to declare and
/// downcast `Object`s.
///
/// [`derive_deftly(Object)`]: crate::templates::derive_deftly_template_Object
pub trait Object: DowncastSync + Send + Sync + 'static {
/// Return true if this object should be given an identifier that allows it
/// to be used outside of the session that generated it.
///
/// Currently, the only use for such IDs in arti is identifying stream
/// contexts in when opening a SOCKS connection: When an application opens a
/// stream, it needs to declare what RPC context (like a `TorClient`) it's
/// using, which requires that some identifier for that context exist
/// outside of the RPC session that owns it.
//
// TODO RPC: It would be neat if this were automatically set to true if and
// only if there were any "out-of-session psuedomethods" defined on the
// object.
fn expose_outside_of_session(&self) -> bool {
false
}
/// Return a [`CastTable`] that can be used to downcast a `dyn Object` of
/// this type into various kinds of `dyn Trait` references.
///
/// The default implementation of this method declares that the `Object`
/// can't be downcast into any traits.
///
/// You should not implement this method yourself; instead use
/// [`derive_deftly(Object)`](crate::templates::derive_deftly_template_Object).
fn get_cast_table(&self) -> &CastTable {
&cast::EMPTY_CAST_TABLE
}
}
downcast_rs::impl_downcast!(sync Object);
/// An identifier for an Object within the context of a Session.
///
/// These are opaque from the client's perspective.
#[derive(Debug, Eq, PartialEq, Hash, Clone, Serialize, Deserialize)]
#[serde(transparent)]
pub struct ObjectId(
// (We use Box<str> to save a word here, since these don't have to be
// mutable ever.)
Box<str>,
);
impl AsRef<str> for ObjectId {
fn as_ref(&self) -> &str {
self.0.as_ref()
}
}
impl<T> From<T> for ObjectId
where
T: Into<Box<str>>,
{
fn from(value: T) -> Self {
Self(value.into())
}
}
/// Extension trait for `dyn Object` and similar to support convenient
/// downcasting to `dyn Trait`.
///
/// You don't need to use this for downcasting to an object's concrete
/// type; for that, use [`downcast_rs::DowncastSync`].
///
/// # Examples
///
/// ```
/// use tor_rpcbase::{Object, ObjectRefExt, templates::*};
/// use derive_deftly::Deftly;
/// use std::sync::Arc;
///
/// #[derive(Deftly)]
/// #[derive_deftly(Object)]
/// #[deftly(rpc(downcastable_to = "HasFeet"))]
/// pub struct Frog {}
/// pub trait HasFeet {
/// fn num_feet(&self) -> usize;
/// }
/// impl HasFeet for Frog {
/// fn num_feet(&self) -> usize { 4 }
/// }
///
/// /// If `obj` is a HasFeet, return how many feet it has.
/// /// Otherwise, return 0.
/// fn check_feet(obj: Arc<dyn Object>) -> usize {
/// let maybe_has_feet: Option<&dyn HasFeet> = obj.cast_to_trait();
/// match maybe_has_feet {
/// Some(foot_haver) => foot_haver.num_feet(),
/// None => 0,
/// }
/// }
///
/// assert_eq!(check_feet(Arc::new(Frog{})), 4);
/// ```
pub trait ObjectRefExt {
/// Try to cast this `Object` to a `T`. On success, return a reference to
/// T; on failure, return None.
fn cast_to_trait<T: ?Sized + 'static>(&self) -> Option<&T>;
}
impl ObjectRefExt for dyn Object {
fn cast_to_trait<T: ?Sized + 'static>(&self) -> Option<&T> {
let table = self.get_cast_table();
table.cast_object_to(self)
}
}
impl ObjectRefExt for std::sync::Arc<dyn Object> {
fn cast_to_trait<T: ?Sized + 'static>(&self) -> Option<&T> {
self.as_ref().cast_to_trait()
}
}
define_derive_deftly! {
/// Allow a type to participate as an Object in the RPC system.
///
/// This template implements `Object` for the
/// target type, and can be used to cause objects to participate in the trait
/// downcasting system.
///
/// # Examples
///
/// ## Simple case, just implements `Object`.
///
/// ```
/// use tor_rpcbase::{self as rpc, templates::*};
/// use derive_deftly::Deftly;
///
/// #[derive(Default, Deftly)]
/// #[derive_deftly(Object)]
/// struct Houseplant {
/// oxygen_per_sec: f64,
/// benign_neglect: u8
/// }
///
/// // You can downcast an Object to a concrete type.
/// use downcast_rs::DowncastSync;
/// use std::sync::Arc;
/// let plant_obj: Arc<dyn rpc::Object> = Arc::new(Houseplant::default());
/// let as_plant: Arc<Houseplant> = plant_obj.downcast_arc().ok().unwrap();
/// ```
///
/// ## With trait downcasting
///
/// By default, you can use [`downcast_rs`] to downcast a `dyn Object` to its
/// concrete type. If you also need to be able to downcast a `dyn Object` to a given
/// trait that it implements, you can use the `downcastable_to` attributes for `Object` to have
/// it participate in trait downcasting:
///
/// ```
/// use tor_rpcbase::{self as rpc, templates::*};
/// use derive_deftly::Deftly;
///
/// #[derive(Deftly)]
/// #[derive_deftly(Object)]
/// #[deftly(rpc(downcastable_to = "Gizmo, Doodad"))]
/// struct Frobnitz {}
///
/// trait Gizmo {}
/// trait Doodad {}
/// impl Gizmo for Frobnitz {}
/// impl Doodad for Frobnitz {}
///
/// use std::sync::Arc;
/// use rpc::ObjectRefExt; // for the cast_to method.
/// let frob_obj: Arc<dyn rpc::Object> = Arc::new(Frobnitz {});
/// let gizmo: &dyn Gizmo = frob_obj.cast_to_trait().unwrap();
/// let doodad: &dyn Doodad = frob_obj.cast_to_trait().unwrap();
/// ```
///
/// ## With generic objects
///
/// Right now, a generic object can't participate in our method lookup system,
/// but it _can_ participate in trait downcasting. We'll try to remove this
/// limitation in the future.
///
/// ```
/// use tor_rpcbase::{self as rpc, templates::*};
/// use derive_deftly::Deftly;
///
/// #[derive(Deftly)]
/// #[derive_deftly(Object)]
/// #[deftly(rpc(downcastable_to = "ExampleTrait"))]
/// struct Generic<T,U> where T:Clone, U:PartialEq {
/// t: T,
/// u: U,
/// }
///
/// trait ExampleTrait {}
/// impl<T:Clone,U:PartialEq> ExampleTrait for Generic<T,U> {}
///
/// use std::sync::Arc;
/// use rpc::ObjectRefExt; // for the cast_to method.
/// let obj: Arc<dyn rpc::Object> = Arc::new(Generic { t: 42_u8, u: 42_u8 });
/// let tr: &dyn ExampleTrait = obj.cast_to_trait().unwrap();
/// ```
///
/// ## Making an object "exposed outside of the session"
///
/// You flag any kind of Object so that its identifiers will be exported
/// outside of the local RPC session. (Arti uses this for Objects whose
/// ObjectId needs to be used as a SOCKS identifier.) To do so,
/// use the `expose_outside_session` attribute:
///
/// ```
/// use tor_rpcbase::{self as rpc, templates::*};
/// use derive_deftly::Deftly;
///
/// #[derive(Deftly)]
/// #[derive_deftly(Object)]
/// #[deftly(rpc(expose_outside_of_session))]
/// struct Visible {}
/// ```
pub Object expect items =
impl<$tgens> $ttype where
// We need this restriction in case there are generics
// that might not impl these traits.
$ttype: Send + Sync + 'static,
$twheres
{
/// Construct a new `CastTable` for this type.
///
/// This is a function so that we can call it multiple times as
/// needed if the type is generic.
///
/// Don't invoke this yourself; instead use `decl_object!`.
#[doc(hidden)]
fn make_cast_table() -> $crate::CastTable {
${if tmeta(rpc(downcastable_to)) {
$crate::cast_table_deftness_helper!{ ${tmeta(rpc(downcastable_to)) } }
} else {
$crate::CastTable::default()
}}
}
}
impl<$tgens> $crate::Object for $ttype where
// We need this restriction in case there are generics
// that might not impl these traits.
$ttype: Send + Sync + 'static,
$twheres
{
${if tmeta(rpc(expose_outside_of_session)) {
fn expose_outside_of_session(&self) -> bool {
true
}
}}
fn get_cast_table(&self) -> &$crate::CastTable {
// TODO RPC: Is there a better way to check "is this a generic type"?
// See derive-deftly#37
${if not(approx_equal({$tgens}, {})) {
// For generic types, we have a potentially unbounded number
// of CastTables: one for each instantiation of the type.
// Therefore we keep a mutable add-only HashMap of CastTables.
use $crate::once_cell::sync::Lazy;
use std::sync::RwLock;
use std::collections::HashMap;
use std::any::TypeId;
// Map from concrete type to CastTable.
//
// Note that we use `&'static CastTable` here, not
// `Box<CastTable>`: If we used Box<>, the borrow checker would
// worry that our `CastTable`s might get freed after we returned
// a reference to them. Using `&'static` guarantees that the CastTable
// references are safe to return.
//
// In order to get a `&'static`, we need to use Box::leak().
// That's fine, since we only create one CastTable per
// instantiation of the type.
static TABLES: Lazy<RwLock<HashMap<TypeId, &'static $crate::CastTable>>> =
Lazy::new(|| RwLock::new(HashMap::new()));
{
let tables_r = TABLES.read().expect("poisoned lock");
if let Some(table) = tables_r.get(&TypeId::of::<Self>()) {
// Fast case: we already had a CastTable for this instantiation.
table
} else {
// We didn't find a CastTable.
drop(tables_r); // prevent deadlock.
TABLES
.write()
.expect("poisoned lock")
.entry(TypeId::of::<Self>())
// We use `or_insert_with` here to avoid a race
// condition: we only want to call make_cast_table if
// one didn't already exist.
.or_insert_with(|| Box::leak(Box::new(Self::make_cast_table())))
}
}
} else {
// For non-generic types, we only ever have a single CastTable,
// so we can just construct it once and return it.
use $crate::once_cell::sync::Lazy;
static TABLE: Lazy<$crate::CastTable> = Lazy::new(|| $ttype::make_cast_table());
&TABLE
}}
}
}
}
pub use derive_deftly_template_Object;
#[cfg(test)]
mod test {
// @@ begin test lint list maintained by maint/add_warning @@
#![allow(clippy::bool_assert_comparison)]
#![allow(clippy::clone_on_copy)]
#![allow(clippy::dbg_macro)]
#![allow(clippy::mixed_attributes_style)]
#![allow(clippy::print_stderr)]
#![allow(clippy::print_stdout)]
#![allow(clippy::single_char_pattern)]
#![allow(clippy::unwrap_used)]
#![allow(clippy::unchecked_duration_subtraction)]
#![allow(clippy::useless_vec)]
#![allow(clippy::needless_pass_by_value)]
//! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
use super::*;
use derive_deftly::Deftly;
#[derive(Deftly)]
#[derive_deftly(Object)]
#[deftly(rpc(downcastable_to = "HasWheels"))]
struct Bicycle {}
trait HasWheels {
fn num_wheels(&self) -> usize;
}
impl HasWheels for Bicycle {
fn num_wheels(&self) -> usize {
2
}
}
#[test]
fn standard_cast() {
let bike = Bicycle {};
let erased_bike: &dyn Object = &bike;
let has_wheels: &dyn HasWheels = erased_bike.cast_to_trait().unwrap();
assert_eq!(has_wheels.num_wheels(), 2);
}
#[derive(Deftly)]
#[derive_deftly(Object)]
#[deftly(rpc(downcastable_to = "HasWheels"))]
struct Crowd<T: HasWheels + Send + Sync + 'static> {
members: Vec<T>,
}
impl<T: HasWheels + Send + Sync> HasWheels for Crowd<T> {
fn num_wheels(&self) -> usize {
self.members.iter().map(T::num_wheels).sum()
}
}
#[test]
fn generic_cast() {
let bikes = Crowd {
members: vec![Bicycle {}, Bicycle {}],
};
let erased_bikes: &dyn Object = &bikes;
let has_wheels: &dyn HasWheels = erased_bikes.cast_to_trait().unwrap();
assert_eq!(has_wheels.num_wheels(), 4);
}
}