binder: Give tests the ability to decorate a server's client binder

Author: jdcormie

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

@@ -70,6 +70,7 @@ public final class BinderServer implements InternalServer, LeakSafeOneWayBinder.
   private final LeakSafeOneWayBinder hostServiceBinder;
   private final BinderTransportSecurity.ServerPolicyChecker serverPolicyChecker;
   private final InboundParcelablePolicy inboundParcelablePolicy;
+  private final OneWayBinderProxy.Decorator clientBinderDecorator;
 
   @GuardedBy("this")
   private ServerListener listener;
@@ -92,6 +93,7 @@ private BinderServer(Builder builder) {
         ImmutableList.copyOf(checkNotNull(builder.streamTracerFactories, "streamTracerFactories"));
     this.serverPolicyChecker = BinderInternal.createPolicyChecker(builder.serverSecurityPolicy);
     this.inboundParcelablePolicy = builder.inboundParcelablePolicy;
+    this.clientBinderDecorator = builder.clientBinderDecorator;
     hostServiceBinder = new LeakSafeOneWayBinder(this);
   }
 
@@ -183,7 +185,7 @@ public synchronized boolean handleTransaction(int code, Parcel parcel) {
                   executorServicePool,
                   attrsBuilder.build(),
                   streamTracerFactories,
-                  OneWayBinderProxy.IDENTITY_DECORATOR,
+                  clientBinderDecorator,
                   callbackBinder);
           transport.start(listener.transportCreated(transport));
           return true;
@@ -225,6 +227,7 @@ public static class Builder {
         SharedResourcePool.forResource(GrpcUtil.TIMER_SERVICE);
     ServerSecurityPolicy serverSecurityPolicy = SecurityPolicies.serverInternalOnly();
     InboundParcelablePolicy inboundParcelablePolicy = InboundParcelablePolicy.DEFAULT;
+    OneWayBinderProxy.Decorator clientBinderDecorator = OneWayBinderProxy.IDENTITY_DECORATOR;
 
     public BinderServer build() {
       return new BinderServer(this);
@@ -295,5 +298,19 @@ public Builder setInboundParcelablePolicy(InboundParcelablePolicy inboundParcela
           checkNotNull(inboundParcelablePolicy, "inboundParcelablePolicy");
       return this;
     }
+
+    /**
+     * Sets the {@link OneWayBinderProxy.Decorator} to be applied to this server's "client Binders".
+     *
+     * <p>Tests can use this to capture post-setup transactions from server to client. The specified
+     * decorator will be applied every time a client connects. The decorated result will be used for
+     * all subsequent transactions to this client from the new ServerTransport.
+     *
+     * <p>Optional, {@link OneWayBinderProxy#IDENTITY_DECORATOR} is the default.
+     */
+    public Builder setClientBinderDecorator(OneWayBinderProxy.Decorator clientBinderDecorator) {
+      this.clientBinderDecorator = checkNotNull(clientBinderDecorator);
+      return this;
+    }
   }
 }