binder: Don't report onReady() for a closed Inbound

Inbound.onTransportReady() unconditionally forwarded onReady() to the
listener, so flow control unblocking concurrently with a close could
invoke onReady() after closed(), which must be the listener's final
callback.

Only skip the listener, not the Outbound: a server stream's close may
still be sitting in its Outbound waiting for the transmit window to
open.

Author: jdcormie

binder/src/main/java/io/grpc/binder/internal/Inbound.java

@@ -313,8 +313,13 @@ final void onTransportReady() {
     Outbound outbound = null;
     StreamListener listener = null;
     synchronized (this) {
+      // closed() is always the listener's final callback.
+      if (!isClosed()) {
+        listener = this.listener;
+      }
+      // But poke the Outbound even if we're closed since a server stream's close could be sitting
+      // in it, blocked on flow control.
       outbound = this.outbound;
-      listener = this.listener;
     }
     if (listener != null) {
       listener.onReady();

binder/src/test/java/io/grpc/binder/internal/ClientInboundTest.java

@@ -410,6 +410,20 @@ public void transactionsIgnoredAfterClosed() throws Exception {
     assertThat(listener.getReadMessages()).isEmpty();
   }
 
+  @Test
+  public void transportReadyAfterClosed_doesNotReportOnReady() throws Exception {
+    newStreamTxnToClientBuilder(nextTxIndex++).withPrefix(new Metadata()).dispatchTo(inbound);
+    newOutOfBandCloseTxnBuilder(Status.CANCELLED).dispatchTo(inbound);
+    drainExecutors();
+    assertThat(listener.isClosed()).isTrue();
+
+    // Simulates BinderTransport.handleAcknowledgedBytes() picking this Inbound out of ongoingCalls
+    // just before a concurrent close (e.g. cancel()) unregistered it. FakeClientStreamListener
+    // throws if onReady() is invoked after closed().
+    inbound.onTransportReady();
+    drainExecutors();
+  }
+
   @Test
   public void allInOneUnaryTransaction() throws Exception {
     newStreamTxnToClientBuilder(0)