From c1736849971a4ca2f9a855c1840d5ff1fcabcb45 Mon Sep 17 00:00:00 2001
From: Alice Ryhl <aliceryhl@google.com>
Date: Tue, 23 Nov 2021 12:38:51 +0000
Subject: rust: add conversion between sync and async interfaces

Test: add new test
Bug: 207463587
Change-Id: Ib01ffb737c15b1e919d9d87e89a1c47e40723b92
---
 libs/binder/rust/src/binder.rs        | 57 +++++++++++++++++++++++++++++++++++
 libs/binder/rust/src/lib.rs           |  4 +--
 libs/binder/rust/tests/integration.rs | 26 ++++++++++++++++
 3 files changed, 85 insertions(+), 2 deletions(-)

diff --git a/libs/binder/rust/src/binder.rs b/libs/binder/rust/src/binder.rs
index 3d2eddf611..4d6b294000 100644
--- a/libs/binder/rust/src/binder.rs
+++ b/libs/binder/rust/src/binder.rs
@@ -66,6 +66,35 @@ pub trait Interface: Send + Sync {
     }
 }
 
+/// Implemented by sync interfaces to specify what the associated async interface is.
+/// Generic to handle the fact that async interfaces are generic over a thread pool.
+///
+/// The binder in any object implementing this trait should be compatible with the
+/// `Target` associated type, and using `FromIBinder` to convert it to the target
+/// should not fail.
+pub trait ToAsyncInterface<P>
+where
+    Self: Interface,
+    Self::Target: FromIBinder,
+{
+    /// The async interface associated with this sync interface.
+    type Target: ?Sized;
+}
+
+/// Implemented by async interfaces to specify what the associated sync interface is.
+///
+/// The binder in any object implementing this trait should be compatible with the
+/// `Target` associated type, and using `FromIBinder` to convert it to the target
+/// should not fail.
+pub trait ToSyncInterface
+where
+    Self: Interface,
+    Self::Target: FromIBinder,
+{
+    /// The sync interface associated with this async interface.
+    type Target: ?Sized;
+}
+
 /// Interface stability promise
 ///
 /// An interface can promise to be a stable vendor interface ([`Vintf`]), or
@@ -337,6 +366,26 @@ impl<I: FromIBinder + ?Sized> Strong<I> {
     pub fn downgrade(this: &Strong<I>) -> Weak<I> {
         Weak::new(this)
     }
+
+    /// Convert this synchronous binder handle into an asynchronous one.
+    pub fn into_async<P>(self) -> Strong<<I as ToAsyncInterface<P>>::Target>
+    where
+        I: ToAsyncInterface<P>,
+    {
+        // By implementing the ToAsyncInterface trait, it is guaranteed that the binder
+        // object is also valid for the target type.
+        FromIBinder::try_from(self.0.as_binder()).unwrap()
+    }
+
+    /// Convert this asynchronous binder handle into a synchronous one.
+    pub fn into_sync(self) -> Strong<<I as ToSyncInterface>::Target>
+    where
+        I: ToSyncInterface,
+    {
+        // By implementing the ToSyncInterface trait, it is guaranteed that the binder
+        // object is also valid for the target type.
+        FromIBinder::try_from(self.0.as_binder()).unwrap()
+    }
 }
 
 impl<I: FromIBinder + ?Sized> Clone for Strong<I> {
@@ -1017,6 +1066,14 @@ macro_rules! declare_binder_interface {
                     .expect(concat!("Error cloning interface ", stringify!($async_interface)))
             }
         }
+
+        impl<P: $crate::BinderAsyncPool> $crate::ToAsyncInterface<P> for dyn $interface {
+            type Target = dyn $async_interface<P>;
+        }
+
+        impl<P: $crate::BinderAsyncPool> $crate::ToSyncInterface for dyn $async_interface<P> {
+            type Target = dyn $interface;
+        }
         )?
     };
 }
diff --git a/libs/binder/rust/src/lib.rs b/libs/binder/rust/src/lib.rs
index b94dfa137e..7c04a7207b 100644
--- a/libs/binder/rust/src/lib.rs
+++ b/libs/binder/rust/src/lib.rs
@@ -109,8 +109,8 @@ pub mod parcel;
 
 pub use crate::binder::{
     BinderFeatures, FromIBinder, IBinder, IBinderInternal, Interface, InterfaceClass, Remotable,
-    Stability, Strong, TransactionCode, TransactionFlags, Weak, FIRST_CALL_TRANSACTION,
-    FLAG_CLEAR_BUF, FLAG_ONEWAY, FLAG_PRIVATE_LOCAL, LAST_CALL_TRANSACTION,
+    Stability, Strong, ToAsyncInterface, ToSyncInterface, TransactionCode, TransactionFlags, Weak,
+    FIRST_CALL_TRANSACTION, FLAG_CLEAR_BUF, FLAG_ONEWAY, FLAG_PRIVATE_LOCAL, LAST_CALL_TRANSACTION,
 };
 pub use crate::binder_async::{BoxFuture, BinderAsyncPool};
 pub use error::{status_t, ExceptionCode, Result, Status, StatusCode};
diff --git a/libs/binder/rust/tests/integration.rs b/libs/binder/rust/tests/integration.rs
index 40359b4749..f8bc5acd4f 100644
--- a/libs/binder/rust/tests/integration.rs
+++ b/libs/binder/rust/tests/integration.rs
@@ -510,6 +510,32 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn get_selinux_context_sync_to_async() {
+        let service_name = "get_selinux_context";
+        let _process = ScopedServiceProcess::new(service_name);
+        let test_client: Strong<dyn ITest> =
+            binder::get_interface(service_name).expect("Did not get manager binder service");
+        let test_client = test_client.into_async::<Tokio>();
+        assert_eq!(
+            test_client.get_selinux_context().await.unwrap(),
+            get_expected_selinux_context()
+        );
+    }
+
+    #[tokio::test]
+    async fn get_selinux_context_async_to_sync() {
+        let service_name = "get_selinux_context";
+        let _process = ScopedServiceProcess::new(service_name);
+        let test_client: Strong<dyn IATest<Tokio>> =
+            binder_tokio::get_interface(service_name).await.expect("Did not get manager binder service");
+        let test_client = test_client.into_sync();
+        assert_eq!(
+            test_client.get_selinux_context().unwrap(),
+            get_expected_selinux_context()
+        );
+    }
+
     struct Bools {
         binder_died: Arc<AtomicBool>,
         binder_dealloc: Arc<AtomicBool>,
-- 
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