#61: Support null values for callbacks to support Future<Void> completion.

Author: astonbitecode

java/src/main/java/org/astonbitecode/j4rs/api/invocation/JsonInvocationImpl.java

@@ -91,14 +91,10 @@ public void invokeAsyncToChannel(final long channelAddress, final String methodN
         try {
             NativeCallbackToRustFutureSupport callback = newCallbackForAsyncToChannel(channelAddress);
             invokeAsyncMethod(methodName, gen.generateArgObjects(args)).handle((o, t) -> {
-                if (o != null) {
-                    callback.doCallbackSuccess(o);
-                } else if (t != null) {
+                if (t != null) {
                     callback.doCallbackFailure(t);
                 } else {
-                    String message = String.format("Error while handling the future returned by the invocation of method %s of class %s",
-                            methodName, getObjectClassName());
-                    throw new InvocationException(message);
+                    callback.doCallbackSuccess(o);
                 }
                 return Void.TYPE;
             });

java/src/main/java/org/astonbitecode/j4rs/api/invocation/NativeCallbackToRustFutureSupport.java

@@ -15,6 +15,7 @@
 package org.astonbitecode.j4rs.api.invocation;
 
 import org.astonbitecode.j4rs.api.Instance;
+import org.astonbitecode.j4rs.api.value.NullObject;
 import org.astonbitecode.j4rs.errors.InvocationException;
 import org.astonbitecode.j4rs.rust.RustPointer;
 
@@ -46,10 +47,14 @@ static void initialize(String libname) {
      * @param obj The {@link Object} to pass in the callback.
      */
     public void doCallbackSuccess(Object obj) {
-        if (channelPointerOpt.isPresent() && obj != null) {
-            docallbacktochannel(channelPointerOpt.get().getAddress(), InstanceGenerator.create(obj, obj.getClass()));
+        if (channelPointerOpt.isPresent()) {
+            if (obj != null) {
+                docallbacktochannel(channelPointerOpt.get().getAddress(), InstanceGenerator.create(obj, obj.getClass()));
+            } else {
+                docallbacktochannel(channelPointerOpt.get().getAddress(), InstanceGenerator.create(null, NullObject.class));
+            }
         } else {
-            throw new InvocationException("Cannot do callback. Please make sure that you don't try to access this method while being in the constructor of your class (that extends NativeCallbackSupport)");
+            throw new InvocationException("Cannot do callback. Please make sure that you don't try to access this method while being in the constructor of your class (that extends NativeCallbackToRustFutureSupport)");
         }
     }
 

java/src/main/java/org/astonbitecode/j4rs/tests/MyTest.java

@@ -153,6 +153,12 @@ public Future<String> getErrorWithFuture(String message) {
         });
     }
 
+    public Future<Void> executeVoidFuture(String message) {
+        return executor.submit(() -> {
+            return null;
+        });
+    }
+
     public static Future<String> getErrorWithFutureStatic(String string) {
         return executor.submit(() -> string);
     }

rust/src/async_api/mod.rs

@@ -183,6 +183,16 @@ mod api_unit_tests {
         Ok(())
     }
 
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn invoke_void_future() -> errors::Result<()> {
+        let s_test = "j4rs_rust";
+        let jvm = JvmBuilder::new().build()?;
+        let my_test = jvm.create_instance("org.astonbitecode.j4rs.tests.MyTest", &[])?;
+        let instance_res = jvm.invoke_async(&my_test, "executeVoidFuture", &[InvocationArg::try_from(s_test)?]).await;
+        assert!(instance_res.is_ok());
+        Ok(())
+    }
+
     // #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn _memory_leaks_invoke_async_instances() -> errors::Result<()> {
         let jvm = JvmBuilder::new().build()?;