Add a libbinder_rs wrapper around the new ARpc APIs

This allows rust clients to set up client connections to binder RPC
services underneath the libbinder_rs service manager APIs.

Test: atest binderRpcTest vm_accessor_test
Bug: 358427181
Change-Id: I05f1c5ff4e3447262eaf9df8250c9d99e3414559

5 files changed, 250 insertions, 2 deletions

diff --git a/libs/binder/rust/Android.bp b/libs/binder/rust/Android.bp
index 2deb25457e..4545d7bb2e 100644
--- a/libs/binder/rust/Android.bp
+++ b/libs/binder/rust/Android.bp
@@ -15,6 +15,8 @@ rust_library {
         "libbinder_ndk_sys",
         "libdowncast_rs",
         "liblibc",
+        "liblog_rust",
+        "libnix",
     ],
     host_supported: true,
     vendor_available: true,
@@ -79,6 +81,9 @@ rust_library {
     shared_libs: [
         "libbinder_ndk",
     ],
+    rustlibs: [
+        "liblibc",
+    ],
     host_supported: true,
     vendor_available: true,
     product_available: true,
@@ -129,9 +134,18 @@ rust_bindgen {
         // rustified
         "libbinder_ndk_bindgen_flags.txt",
     ],
+    bindgen_flags: [
+        "--blocklist-type",
+        "sockaddr",
+        "--raw-line",
+        "use libc::sockaddr;",
+    ],
     shared_libs: [
         "libbinder_ndk",
     ],
+    rustlibs: [
+        "liblibc",
+    ],
     host_supported: true,
     vendor_available: true,
     product_available: true,
@@ -185,6 +199,8 @@ rust_test {
         "libbinder_ndk_sys",
         "libdowncast_rs",
         "liblibc",
+        "liblog_rust",
+        "libnix",
     ],
 }
 
@@ -196,4 +212,7 @@ rust_test {
     auto_gen_config: true,
     clippy_lints: "none",
     lints: "none",
+    rustlibs: [
+        "liblibc",
+    ],
 }
diff --git a/libs/binder/rust/src/lib.rs b/libs/binder/rust/src/lib.rs
index e70f4f0232..9d4ed3331b 100644
--- a/libs/binder/rust/src/lib.rs
+++ b/libs/binder/rust/src/lib.rs
@@ -104,6 +104,8 @@ mod proxy;
 mod service;
 #[cfg(not(trusty))]
 mod state;
+#[cfg(not(any(android_vendor, android_vndk)))]
+mod system_only;
 
 use binder_ndk_sys as sys;
 
@@ -120,6 +122,8 @@ pub use service::{
 };
 #[cfg(not(trusty))]
 pub use state::{ProcessState, ThreadState};
+#[cfg(not(any(android_vendor, android_vndk)))]
+pub use system_only::{Accessor, ConnectionInfo};
 
 /// Binder result containing a [`Status`] on error.
 pub type Result<T> = std::result::Result<T, Status>;
diff --git a/libs/binder/rust/src/system_only.rs b/libs/binder/rust/src/system_only.rs
new file mode 100644
index 0000000000..a91d84d865
--- /dev/null
+++ b/libs/binder/rust/src/system_only.rs
@@ -0,0 +1,187 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+use crate::proxy::SpIBinder;
+use crate::sys;
+
+use std::ffi::{c_void, CStr, CString};
+use std::os::raw::c_char;
+
+use libc::sockaddr;
+use nix::sys::socket::{SockaddrLike, UnixAddr, VsockAddr};
+use std::sync::Arc;
+use std::{fmt, ptr};
+
+/// Rust wrapper around ABinderRpc_Accessor objects for RPC binder service management.
+///
+/// Dropping the `Accessor` will drop the underlying object and the binder it owns.
+pub struct Accessor {
+    accessor: *mut sys::ABinderRpc_Accessor,
+}
+
+impl fmt::Debug for Accessor {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "ABinderRpc_Accessor({:p})", self.accessor)
+    }
+}
+
+/// Socket connection info required for libbinder to connect to a service.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ConnectionInfo {
+    /// For vsock connection
+    Vsock(VsockAddr),
+    /// For unix domain socket connection
+    Unix(UnixAddr),
+}
+
+/// Safety: A `Accessor` is a wrapper around `ABinderRpc_Accessor` which is
+/// `Sync` and `Send`. As
+/// `ABinderRpc_Accessor` is threadsafe, this structure is too.
+/// The Fn owned the Accessor has `Sync` and `Send` properties
+unsafe impl Send for Accessor {}
+
+/// Safety: A `Accessor` is a wrapper around `ABinderRpc_Accessor` which is
+/// `Sync` and `Send`. As `ABinderRpc_Accessor` is threadsafe, this structure is too.
+/// The Fn owned the Accessor has `Sync` and `Send` properties
+unsafe impl Sync for Accessor {}
+
+impl Accessor {
+    /// Create a new accessor that will call the given callback when its
+    /// connection info is required.
+    /// The callback object and all objects it captures are owned by the Accessor
+    /// and will be deleted some time after the Accessor is Dropped. If the callback
+    /// is being called when the Accessor is Dropped, the callback will not be deleted
+    /// immediately.
+    pub fn new<F>(instance: &str, callback: F) -> Accessor
+    where
+        F: Fn(&str) -> Option<ConnectionInfo> + Send + Sync + 'static,
+    {
+        let callback: *mut c_void = Arc::into_raw(Arc::new(callback)) as *mut c_void;
+        let inst = CString::new(instance).unwrap();
+
+        // Safety: The function pointer is a valid connection_info callback.
+        // This call returns an owned `ABinderRpc_Accessor` pointer which
+        // must be destroyed via `ABinderRpc_Accessor_delete` when no longer
+        // needed.
+        // When the underlying ABinderRpc_Accessor is deleted, it will call
+        // the cookie_decr_refcount callback to release its strong ref.
+        let accessor = unsafe {
+            sys::ABinderRpc_Accessor_new(
+                inst.as_ptr(),
+                Some(Self::connection_info::<F>),
+                callback,
+                Some(Self::cookie_decr_refcount::<F>),
+            )
+        };
+
+        Accessor { accessor }
+    }
+
+    /// Get the underlying binder for this Accessor for when it needs to be either
+    /// registered with service manager or sent to another process.
+    pub fn as_binder(&self) -> Option<SpIBinder> {
+        // Safety: `ABinderRpc_Accessor_asBinder` returns either a null pointer or a
+        // valid pointer to an owned `AIBinder`. Either of these values is safe to
+        // pass to `SpIBinder::from_raw`.
+        unsafe { SpIBinder::from_raw(sys::ABinderRpc_Accessor_asBinder(self.accessor)) }
+    }
+
+    /// Callback invoked from C++ when the connection info is needed.
+    ///
+    /// # Safety
+    ///
+    /// The `instance` parameter must be a non-null pointer to a valid C string for
+    /// CStr::from_ptr. The memory must contain a valid null terminator at the end of
+    /// the string within isize::MAX from the pointer. The memory must not be mutated for
+    /// the duration of this function  call and must be valid for reads from the pointer
+    /// to the null terminator.
+    /// The `cookie` parameter must be the cookie for an `Arc<F>` and
+    /// the caller must hold a ref-count to it.
+    unsafe extern "C" fn connection_info<F>(
+        instance: *const c_char,
+        cookie: *mut c_void,
+    ) -> *mut binder_ndk_sys::ABinderRpc_ConnectionInfo
+    where
+        F: Fn(&str) -> Option<ConnectionInfo> + Send + Sync + 'static,
+    {
+        if cookie.is_null() || instance.is_null() {
+            log::error!("Cookie({cookie:p}) or instance({instance:p}) is null!");
+            return ptr::null_mut();
+        }
+        // Safety: The caller promises that `cookie` is for an Arc<F>.
+        let callback = unsafe { (cookie as *const F).as_ref().unwrap() };
+
+        // Safety: The caller in libbinder_ndk will have already verified this is a valid
+        // C string
+        let inst = unsafe {
+            match CStr::from_ptr(instance).to_str() {
+                Ok(s) => s,
+                Err(err) => {
+                    log::error!("Failed to get a valid C string! {err:?}");
+                    return ptr::null_mut();
+                }
+            }
+        };
+
+        let connection = match callback(inst) {
+            Some(con) => con,
+            None => {
+                return ptr::null_mut();
+            }
+        };
+
+        match connection {
+            ConnectionInfo::Vsock(addr) => {
+                // Safety: The sockaddr is being copied in the NDK API
+                unsafe { sys::ABinderRpc_ConnectionInfo_new(addr.as_ptr(), addr.len()) }
+            }
+            ConnectionInfo::Unix(addr) => {
+                // Safety: The sockaddr is being copied in the NDK API
+                // The cast is from sockaddr_un* to sockaddr*.
+                unsafe {
+                    sys::ABinderRpc_ConnectionInfo_new(addr.as_ptr() as *const sockaddr, addr.len())
+                }
+            }
+        }
+    }
+
+    /// Callback that decrements the ref-count.
+    /// This is invoked from C++ when a binder is unlinked.
+    ///
+    /// # Safety
+    ///
+    /// The `cookie` parameter must be the cookie for an `Arc<F>` and
+    /// the owner must give up a ref-count to it.
+    unsafe extern "C" fn cookie_decr_refcount<F>(cookie: *mut c_void)
+    where
+        F: Fn(&str) -> Option<ConnectionInfo> + Send + Sync + 'static,
+    {
+        // Safety: The caller promises that `cookie` is for an Arc<F>.
+        unsafe { Arc::decrement_strong_count(cookie as *const F) };
+    }
+}
+
+impl Drop for Accessor {
+    fn drop(&mut self) {
+        // Safety: `self.accessor` is always a valid, owned
+        // `ABinderRpc_Accessor` pointer returned by
+        // `ABinderRpc_Accessor_new` when `self` was created. This delete
+        // method can only be called once when `self` is dropped.
+        unsafe {
+            sys::ABinderRpc_Accessor_delete(self.accessor);
+        }
+    }
+}
diff --git a/libs/binder/rust/sys/BinderBindings.hpp b/libs/binder/rust/sys/BinderBindings.hpp
index 65fa2ca905..bd666fe0d7 100644
--- a/libs/binder/rust/sys/BinderBindings.hpp
+++ b/libs/binder/rust/sys/BinderBindings.hpp
@@ -20,6 +20,7 @@
 #include <android/binder_parcel.h>
 #include <android/binder_parcel_platform.h>
 #include <android/binder_process.h>
+#include <android/binder_rpc.h>
 #include <android/binder_shell.h>
 #include <android/binder_stability.h>
 #include <android/binder_status.h>
diff --git a/libs/binder/rust/tests/integration.rs b/libs/binder/rust/tests/integration.rs
index 5359832da1..bdb7e4a8d8 100644
--- a/libs/binder/rust/tests/integration.rs
+++ b/libs/binder/rust/tests/integration.rs
@@ -384,8 +384,8 @@ mod tests {
     use std::time::Duration;
 
     use binder::{
-        BinderFeatures, DeathRecipient, FromIBinder, IBinder, Interface, SpIBinder, StatusCode,
-        Strong,
+        Accessor, BinderFeatures, DeathRecipient, FromIBinder, IBinder, Interface, SpIBinder,
+        StatusCode, Strong,
     };
     // Import from impl API for testing only, should not be necessary as long as
     // you are using AIDL.
@@ -908,6 +908,43 @@ mod tests {
         assert_eq!(service.test().unwrap(), service_name);
     }
 
+    struct ToBeDeleted {
+        deleted: Arc<AtomicBool>,
+    }
+
+    impl Drop for ToBeDeleted {
+        fn drop(&mut self) {
+            assert!(!self.deleted.load(Ordering::Relaxed));
+            self.deleted.store(true, Ordering::Relaxed);
+        }
+    }
+
+    #[test]
+    fn test_accessor_callback_destruction() {
+        let deleted: Arc<AtomicBool> = Arc::new(AtomicBool::new(false));
+        {
+            let accessor: Accessor;
+            {
+                let helper = ToBeDeleted { deleted: deleted.clone() };
+                let get_connection_info = move |_instance: &str| {
+                    // Capture this object so we can see it get destructed
+                    // after the parent scope
+                    let _ = &helper;
+                    None
+                };
+                accessor = Accessor::new("foo.service", get_connection_info);
+            }
+
+            match accessor.as_binder() {
+                Some(_) => {
+                    assert!(!deleted.load(Ordering::Relaxed));
+                }
+                None => panic!("failed to get that accessor binder"),
+            }
+        }
+        assert!(deleted.load(Ordering::Relaxed));
+    }
+
     #[tokio::test]
     async fn reassociate_rust_binder_async() {
         let service_name = "testing_service";