test: add integration tests for JSON serialization in gRPC messages

Verify that JsonFormat (from protobuf-java-util, backed by Gson) is
accessible from a WildFly deployment, as enabled by the optional
com.google.code.gson dependency added to the com.google.protobuf module.

- JsonGreeterServiceImpl: service impl that uses JsonFormat to round-trip
  the request through JSON serialization before building the response
- JsonSerializationTest: Arquillian integration test that deploys the
  service and verifies the call succeeds over a plaintext connection
- Add protobuf-java-util as provided dependency to the testsuite pom
  (it is available in WildFly at runtime; needed only for compilation)

Closes #510

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: jmesnil

testsuite/integration/subsystem/pom.xml

@@ -76,6 +76,11 @@
             <groupId>org.wildfly.grpc</groupId>
             <artifactId>wildfly-grpc-subsystem</artifactId>
         </dependency>
+        <dependency>
+            <groupId>com.google.protobuf</groupId>
+            <artifactId>protobuf-java-util</artifactId>
+            <scope>provided</scope>
+        </dependency>
     </dependencies>
 
     <build>

testsuite/integration/subsystem/src/test/java/org/wildfly/feature/pack/grpc/test/json/JsonGreeterServiceImpl.java

@@ -0,0 +1,38 @@
+/*
+ *  Copyright The WildFly Authors
+ *  SPDX-License-Identifier: Apache-2.0
+ */
+package org.wildfly.feature.pack.grpc.test.json;
+
+import com.google.protobuf.util.JsonFormat;
+
+import io.grpc.stub.StreamObserver;
+import messages.HelloReply;
+import messages.HelloRequest;
+
+import org.wildfly.feature.pack.grpc.test.helloworld.GreeterGrpc;
+
+/**
+ * A gRPC service implementation that uses {@link JsonFormat} to serialize and deserialize
+ * the request message. This verifies that JSON serialization (backed by Gson) is accessible
+ * from a WildFly deployment.
+ */
+public class JsonGreeterServiceImpl extends GreeterGrpc.GreeterImplBase {
+
+    @Override
+    public void sayHello(HelloRequest request, StreamObserver<HelloReply> responseObserver) {
+        try {
+            // Serialize request to JSON and parse it back to verify JsonFormat works
+            String json = JsonFormat.printer().print(request);
+            HelloRequest.Builder builder = HelloRequest.newBuilder();
+            JsonFormat.parser().merge(json, builder);
+            HelloRequest parsedRequest = builder.build();
+
+            String name = parsedRequest.getName();
+            responseObserver.onNext(HelloReply.newBuilder().setMessage("Hello " + name).build());
+            responseObserver.onCompleted();
+        } catch (Exception e) {
+            responseObserver.onError(e);
+        }
+    }
+}

testsuite/integration/subsystem/src/test/java/org/wildfly/feature/pack/grpc/test/json/JsonSerializationTest.java

@@ -0,0 +1,66 @@
+/*
+ *  Copyright The WildFly Authors
+ *  SPDX-License-Identifier: Apache-2.0
+ */
+package org.wildfly.feature.pack.grpc.test.json;
+
+import java.util.concurrent.TimeUnit;
+
+import org.jboss.arquillian.container.test.api.Deployment;
+import org.jboss.arquillian.container.test.api.RunAsClient;
+import org.jboss.arquillian.junit.Arquillian;
+import org.jboss.shrinkwrap.api.Archive;
+import org.jboss.shrinkwrap.api.ShrinkWrap;
+import org.jboss.shrinkwrap.api.spec.WebArchive;
+import org.junit.AfterClass;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.wildfly.feature.pack.grpc.test.helloworld.GreeterGrpc;
+
+import io.grpc.ManagedChannel;
+import io.grpc.ManagedChannelBuilder;
+import messages.HelloReply;
+import messages.HelloRequest;
+
+/**
+ * Verifies that JSON serialization (via {@code com.google.protobuf.util.JsonFormat}) works
+ * inside a WildFly deployment, as enabled by the Gson dependency added to the
+ * {@code com.google.protobuf} WildFly module.
+ */
+@RunWith(Arquillian.class)
+@RunAsClient
+public class JsonSerializationTest {
+
+    private static final String TARGET = "localhost:9555";
+
+    private static ManagedChannel channel;
+    private static GreeterGrpc.GreeterBlockingStub blockingStub;
+
+    @Deployment
+    public static Archive<?> createTestArchive() {
+        WebArchive war = ShrinkWrap.create(WebArchive.class, "JsonSerializationTest.war");
+        war.addClasses(JsonGreeterServiceImpl.class, GreeterGrpc.class);
+        war.addPackage(HelloRequest.class.getPackage());
+        return war;
+    }
+
+    @BeforeClass
+    public static void beforeClass() {
+        channel = ManagedChannelBuilder.forTarget(TARGET).usePlaintext().build();
+        blockingStub = GreeterGrpc.newBlockingStub(channel);
+    }
+
+    @AfterClass
+    public static void afterClass() throws Exception {
+        channel.shutdownNow().awaitTermination(5, TimeUnit.SECONDS);
+    }
+
+    @Test
+    public void helloWithJsonSerialization() {
+        HelloRequest request = HelloRequest.newBuilder().setName("Bob").build();
+        HelloReply reply = blockingStub.sayHello(request);
+        Assert.assertEquals("Hello Bob", reply.getMessage());
+    }
+}