Added the initial traits for bufferstreams.

Bug: 290409936
Pair: jshargo
Test: Pending tests
Change-Id: I4d1344650bf7ce2a677e21e4c69e5884230b53a3

2 files changed, 137 insertions, 2 deletions

diff --git a/libs/bufferstreams/rust/Android.bp b/libs/bufferstreams/rust/Android.bp
index 95a85b550f..ff951487bc 100644
--- a/libs/bufferstreams/rust/Android.bp
+++ b/libs/bufferstreams/rust/Android.bp
@@ -17,7 +17,8 @@ rust_library {
     crate_name: "bufferstreams",
     srcs: ["src/lib.rs"],
     edition: "2021",
-    vendor_available: true,
-    host_supported: true,
+    rlibs: [
+        "libnativewindow_rs",
+    ],
     min_sdk_version: "30",
 }
diff --git a/libs/bufferstreams/rust/src/lib.rs b/libs/bufferstreams/rust/src/lib.rs
index 51f1c73c49..1d321c833d 100644
--- a/libs/bufferstreams/rust/src/lib.rs
+++ b/libs/bufferstreams/rust/src/lib.rs
@@ -14,9 +14,143 @@
 
 //! libbufferstreams: Reactive Streams for Graphics Buffers
 
+use nativewindow::*;
+use std::sync::{Arc, Weak};
+use std::time::Instant;
+
 /// This function will print Hello World.
 #[no_mangle]
 pub extern "C" fn hello() -> bool {
     println!("Hello world.");
     true
 }
+
+/// BufferPublishers provide buffers to BufferSusbscribers. Depending on the
+/// particular object in question, these could be allocated locally or provided
+/// over IPC.
+///
+/// BufferPublishers are required to adhere to the following, based on the
+/// reactive streams specification:
+/// *   The total number of on_next´s signalled by a Publisher to a Subscriber
+/// MUST be less than or equal to the total number of elements requested by that
+/// Subscriber´s Subscription at all times.
+/// *   A Publisher MAY signal fewer on_next than requested and terminate the
+/// Subscription by calling on_complete or on_error.
+/// *   on_subscribe, on_next, on_error and on_complete signaled to a Subscriber
+/// MUST be signaled serially.
+/// *   If a Publisher fails it MUST signal an on_error.
+/// *   If a Publisher terminates successfully (finite stream) it MUST signal an
+/// on_complete.
+/// *   If a Publisher signals either on_error or on_complete on a Subscriber,
+/// that Subscriber’s Subscription MUST be considered cancelled.
+/// *   Once a terminal state has been signaled (on_error, on_complete) it is
+/// REQUIRED that no further signals occur.
+/// *   If a Subscription is cancelled its Subscriber MUST eventually stop being
+///  signaled.
+/// *  A Publisher MAY support multiple Subscribers and decides whether each
+/// Subscription is unicast or multicast.
+pub trait BufferPublisher {
+    /// This function will create the subscription between the publisher and
+    /// the subscriber.
+    fn subscribe(&self, subscriber: Weak<dyn BufferSubscriber>);
+}
+
+/// BufferSubscribers can subscribe to BufferPublishers. They can request Frames
+/// via the BufferSubscription they get from the publisher, then receive Frames
+/// via on_next.
+///
+/// BufferSubcribers are required to adhere to the following, based on the
+/// reactive streams specification:
+/// *   The total number of on_next´s signalled by a Publisher to a Subscriber
+/// MUST be less than or equal to the total number of elements requested by that
+/// Subscriber´s Subscription at all times.
+/// *   A Publisher MAY signal fewer on_next than requested and terminate the
+/// Subscription by calling on_complete or on_error.
+/// *   on_subscribe, on_next, on_error and on_complete signaled to a Subscriber
+/// MUST be signaled serially.
+/// *   If a Publisher fails it MUST signal an on_error.
+/// *   If a Publisher terminates successfully (finite stream) it MUST signal an
+/// on_complete.
+/// *   If a Publisher signals either on_error or on_complete on a Subscriber,
+/// that Subscriber’s Subscription MUST be considered cancelled.
+/// *   Once a terminal state has been signaled (on_error, on_complete) it is
+/// REQUIRED that no further signals occur.
+/// *   If a Subscription is cancelled its Subscriber MUST eventually stop being
+/// signaled.
+/// *   Publisher.subscribe MAY be called as many times as wanted but MUST be
+/// with a different Subscriber each time.
+/// *   A Publisher MAY support multiple Subscribers and decides whether each
+/// Subscription is unicast or multicast.
+pub trait BufferSubscriber {
+    /// This function will be called at the beginning of the subscription.
+    fn on_subscribe(&self, subscription: Arc<dyn BufferSubscription>);
+    /// This function will be called for buffer that comes in.
+    fn on_next(&self, frame: Frame);
+    /// This function will be called in case of an error.
+    fn on_error(&self, error: BufferError);
+    /// This function will be called on finite streams when done.
+    fn on_complete(&self);
+}
+
+/// BufferSubscriptions serve as the bridge between BufferPublishers and
+/// BufferSubscribers. BufferSubscribers receive a BufferSubscription when they
+/// subscribe to a BufferPublisher via on_subscribe.
+/// This object is to be used by the BufferSubscriber to cancel its subscription
+/// or request more buffers.
+///
+/// BufferSubcriptions are required to adhere to the following, based on the
+/// reactive streams specification:
+/// *   Subscription.request and Subscription.cancel MUST only be called inside
+/// of its Subscriber context.
+/// *   The Subscription MUST allow the Subscriber to call Subscription.request
+/// synchronously from within on_next or on_subscribe.
+/// *   Subscription.request MUST place an upper bound on possible synchronous
+/// recursion between Publisher and Subscriber.
+/// *   Subscription.request SHOULD respect the responsivity of its caller by
+/// returning in a timely manner.
+/// *   Subscription.cancel MUST respect the responsivity of its caller by
+/// returning in a timely manner, MUST be idempotent and MUST be thread-safe.
+/// *   After the Subscription is cancelled, additional
+/// Subscription.request(n: u64) MUST be NOPs.
+/// *   After the Subscription is cancelled, additional Subscription.cancel()
+/// MUST be NOPs.
+/// *   While the Subscription is not cancelled, Subscription.request(n: u64)
+/// MUST register the given number of additional elements to be produced to the
+/// respective subscriber.
+/// *   While the Subscription is not cancelled, Subscription.request(n: u64)
+/// MUST signal on_error if the argument is <= 0. The cause message SHOULD
+/// explain that non-positive request signals are illegal.
+/// *  While the Subscription is not cancelled, Subscription.request(n: u64)
+/// MAY synchronously call on_next on this (or other) subscriber(s).
+/// *  While the Subscription is not cancelled, Subscription.request(n: u64)
+/// MAY synchronously call on_complete or on_error on this (or other)
+/// subscriber(s).
+/// *  While the Subscription is not cancelled, Subscription.cancel() MUST
+/// request the Publisher to eventually stop signaling its Subscriber. The
+/// operation is NOT REQUIRED to affect the Subscription immediately.
+/// *  While the Subscription is not cancelled, Subscription.cancel() MUST
+/// request the Publisher to eventually drop any references to the corresponding
+/// subscriber.
+/// *  While the Subscription is not cancelled, calling Subscription.cancel MAY
+/// cause the Publisher, if stateful, to transition into the shut-down state if
+/// no other Subscription exists at this point.
+/// *  Calling Subscription.cancel MUST return normally.
+/// *  Calling Subscription.request MUST return normally.
+pub trait BufferSubscription {
+    /// request
+    fn request(&self, n: u64);
+    /// cancel
+    fn cancel(&self);
+}
+/// Type used to describe errors produced by subscriptions.
+type BufferError = Box<dyn std::error::Error + Send + Sync + 'static>;
+
+/// Struct used to contain the buffer.
+pub struct Frame {
+    /// A handle to the C buffer interface.
+    pub buffer: AHardwareBuffer,
+    /// The time at which the buffer was dispatched.
+    pub present_time: Instant,
+    /// A fence used for reading/writing safely.
+    pub fence: i32,
+}