WIP

client/base/src/main/java/io/a2a/client/MessageEvent.java

@@ -21,6 +21,19 @@ public MessageEvent(Message message) {
     public Message getMessage() {
         return message;
     }
-}
-
 
+    @Override
+    public String toString() {
+        String messageAsString = "{"
+                + "role=" + message.getRole()
+                + ", parts=" + message.getParts()
+                + ", messageId=" + message.getMessageId()
+                + ", contextId=" + message.getContextId()
+                + ", taskId=" + message.getTaskId()
+                + ", metadata=" + message.getMetadata()
+                + ", kind=" + message.getKind()
+                + ", referenceTaskIds=" + message.getReferenceTaskIds()
+                + ", extensions=" + message.getExtensions() + '}';
+        return "MessageEvent{" + "message=" + messageAsString + '}';
+    }
+}

examples/helloworld/client/pom.xml

@@ -12,7 +12,7 @@
 
     <artifactId>a2a-java-sdk-examples-client</artifactId>
 
-    <name>Java SDK A2A Examples</name>
+        <name>Java SDK A2A HelloWorld Example - Client</name>
     <description>Examples for the Java SDK for the Agent2Agent Protocol (A2A)</description>
 
     <dependencies>

examples/helloworld/client/src/main/java/io/a2a/examples/helloworld/HelloWorldClient.java

@@ -12,16 +12,18 @@
 import io.a2a.A2A;
 
 import io.a2a.client.Client;
-import io.a2a.client.ClientBuilder;
 import io.a2a.client.ClientEvent;
 import io.a2a.client.MessageEvent;
 import io.a2a.client.http.A2ACardResolver;
 import io.a2a.client.transport.jsonrpc.JSONRPCTransport;
 import io.a2a.client.transport.jsonrpc.JSONRPCTransportConfig;
+import io.a2a.client.transport.spi.interceptors.ClientCallContext;
+import io.a2a.common.A2AHeaders;
 import io.a2a.spec.AgentCard;
 import io.a2a.spec.Message;
 import io.a2a.spec.Part;
 import io.a2a.spec.TextPart;
+import java.util.Collections;
 
 /**
  * A simple example of using the A2A Java SDK to communicate with an A2A server.
@@ -61,6 +63,7 @@ public static void main(String[] args) {
             List<BiConsumer<ClientEvent, AgentCard>> consumers = new ArrayList<>();
             consumers.add((event, agentCard) -> {
                 if (event instanceof MessageEvent messageEvent) {
+                    System.out.println("Received client MessageEvent: " + messageEvent);
                     Message responseMessage = messageEvent.getMessage();
                     StringBuilder textBuilder = new StringBuilder();
                     if (responseMessage.getParts() != null) {
@@ -89,11 +92,11 @@ public static void main(String[] args) {
                     .streamingErrorHandler(streamingErrorHandler)
                     .withTransport(JSONRPCTransport.class, new JSONRPCTransportConfig())
                     .build();
+            ClientCallContext clientContext = new ClientCallContext(Collections.emptyMap(), Map.of(A2AHeaders.X_A2A_EXTENSIONS, "https://github.com/a2aproject/a2a-samples/extensions/timestamp/v1"));
 
             Message message = A2A.toUserMessage(MESSAGE_TEXT); // the message ID will be automatically generated for you
-
             System.out.println("Sending message: " + MESSAGE_TEXT);
-            client.sendMessage(message);
+            client.sendMessage(message, clientContext);
             System.out.println("Message sent successfully. Responses will be handled by the configured consumers.");
 
             try {

examples/helloworld/server/pom.xml

@@ -12,14 +12,19 @@
 
     <artifactId>a2a-java-sdk-examples-server</artifactId>
 
-    <name>Java SDK A2A Examples</name>
+    <name>Java SDK A2A HelloWorld Example - Server</name>
     <description>Examples for the Java SDK for the Agent2Agent Protocol (A2A)</description>
 
     <dependencies>
         <dependency>
             <groupId>io.github.a2asdk</groupId>
             <artifactId>a2a-java-sdk-client</artifactId>
         </dependency>
+        <dependency>
+            <groupId>io.github.a2asdk</groupId>
+            <artifactId>a2a-java-timestamp-extension</artifactId>
+            <version>${project.version}</version>
+        </dependency>
         <dependency>
             <groupId>io.github.a2asdk</groupId>
             <artifactId>a2a-java-sdk-reference-jsonrpc</artifactId>

examples/helloworld/server/src/main/java/io/a2a/examples/helloworld/AgentExecutorProducer.java

@@ -7,6 +7,7 @@
 import io.a2a.server.agentexecution.RequestContext;
 import io.a2a.server.events.EventQueue;
 import io.a2a.A2A;
+import io.a2a.extension.timestamp.TimeStampAgentExecutorWrapper;
 import io.a2a.spec.JSONRPCError;
 import io.a2a.spec.UnsupportedOperationError;
 
@@ -15,7 +16,7 @@ public class AgentExecutorProducer {
 
     @Produces
     public AgentExecutor agentExecutor() {
-        return new AgentExecutor() {
+        return new TimeStampAgentExecutorWrapper(new AgentExecutor() {
             @Override
             public void execute(RequestContext context, EventQueue eventQueue) throws JSONRPCError {
                 eventQueue.enqueueEvent(A2A.toAgentMessage("Hello World"));
@@ -25,6 +26,6 @@ public void execute(RequestContext context, EventQueue eventQueue) throws JSONRP
             public void cancel(RequestContext context, EventQueue eventQueue) throws JSONRPCError {
                 throw new UnsupportedOperationError();
             }
-        };
+        });
     }
 }

extensions/timestamp/pom.xml

@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>io.github.a2asdk</groupId>
+        <artifactId>a2a-java-sdk-parent</artifactId>
+        <version>0.4.0.Alpha1-SNAPSHOT</version>
+        <relativePath>../../pom.xml</relativePath>
+    </parent>
+
+    <artifactId>a2a-java-timestamp-extension</artifactId>
+    <name>A2A Java SDK :: Extension :: Timestamp</name>
+    <description>Simple Timestamp Extension</description>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.github.a2asdk</groupId>
+            <artifactId>a2a-java-sdk-server-common</artifactId>
+        </dependency>
+        <!-- Test dependencies -->
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-junit-jupiter</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+</project>

extensions/timestamp/src/main/java/io/a2a/extension/timestamp/TimeStampAgentExecutorWrapper.java

@@ -0,0 +1,51 @@
+package io.a2a.extension.timestamp;
+
+import io.a2a.server.agentexecution.AgentExecutor;
+import io.a2a.server.agentexecution.RequestContext;
+import io.a2a.server.events.EventQueue;
+import io.a2a.spec.JSONRPCError;
+import java.util.logging.Logger;
+
+public class TimeStampAgentExecutorWrapper implements AgentExecutor {
+
+    public static final String CORE_PATH = "github.com/a2aproject/a2a-samples/extensions/timestamp/v1";
+    public static final String URI = "https://" + CORE_PATH;
+    public static final String TIMESTAMP_FIELD = CORE_PATH + "/timestamp";
+
+    private static final Logger logger = Logger.getLogger(TimeStampAgentExecutorWrapper.class.getName());
+    private final AgentExecutor delegate;
+
+    public TimeStampAgentExecutorWrapper(AgentExecutor delegate) {
+        this.delegate = delegate;
+    }
+
+    @Override
+    public void execute(RequestContext context, EventQueue eventQueue) throws JSONRPCError {
+        if(isActivated(context)) {
+            delegate.execute(context, new TimeStampEventQueue(eventQueue));
+        } else {
+            delegate.execute(context, eventQueue);
+        }
+    }
+
+    @Override
+    public void cancel(RequestContext context, EventQueue eventQueue) throws JSONRPCError {
+        if(isActivated(context)) {
+            delegate.cancel(context, new TimeStampEventQueue(eventQueue));
+        } else {
+            delegate.cancel(context, eventQueue);
+        }
+    }
+
+    private boolean isActivated(final RequestContext context) {
+        if (context.getCallContext().isExtensionActivated(URI)) {
+            return true;
+        }
+        if (context.getCallContext().isExtensionRequested(URI)) {
+            logger.info("Activated extension: " + URI);
+            context.getCallContext().activateExtension(URI);
+            return true;
+        }
+        return false;
+    }
+}

extensions/timestamp/src/main/java/io/a2a/extension/timestamp/TimeStampEventQueue.java

@@ -0,0 +1,133 @@
+package io.a2a.extension.timestamp;
+
+import static io.a2a.extension.timestamp.TimeStampAgentExecutorWrapper.TIMESTAMP_FIELD;
+import static io.a2a.extension.timestamp.TimeStampAgentExecutorWrapper.URI;
+
+import io.a2a.server.events.EventQueue;
+import io.a2a.spec.Artifact;
+import io.a2a.spec.Event;
+import io.a2a.spec.Message;
+import io.a2a.spec.Task;
+import io.a2a.spec.TaskArtifactUpdateEvent;
+import io.a2a.spec.TaskStatusUpdateEvent;
+import java.time.OffsetDateTime;
+import java.time.ZoneOffset;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class TimeStampEventQueue extends EventQueue {
+
+    private final EventQueue delegate;
+
+    public TimeStampEventQueue(EventQueue delegate) {
+        this.delegate = delegate;
+    }
+
+    @Override
+    public void enqueueEvent(Event event) {
+        this.delegate.enqueueEvent(timestampEvent(event));
+    }
+
+    private Event timestampEvent(Event event) {
+        if (event instanceof Message message) {
+            return processMessage(message);
+        }
+        if (event instanceof TaskArtifactUpdateEvent taskArtifactUpdateEvent) {
+            return processTaskArtifactUpdateEvent(taskArtifactUpdateEvent);
+        }
+        if (event instanceof TaskStatusUpdateEvent taskStatusUpdateEvent) {
+            return processTaskStatusUpdateEvent(taskStatusUpdateEvent);
+        }
+        if (event instanceof Task task) {
+            return processTask(task);
+        }
+        return event;
+    }
+
+    private Message processMessage(Message message) {
+        Map<String, Object> metadata = message.getMetadata() == null ? new HashMap<>() : new HashMap<>(message.getMetadata());
+        if (!metadata.containsKey(TIMESTAMP_FIELD)) {
+            metadata.put(TIMESTAMP_FIELD, OffsetDateTime.now(ZoneOffset.UTC));
+        }
+        List<String> extensions = message.getExtensions() == null ? new ArrayList<>() : new ArrayList<>(message.getExtensions());
+        if (!extensions.contains(URI)) {
+            extensions.add(URI);
+        }
+        return new Message.Builder(message).metadata(metadata).extensions(extensions).build();
+    }
+
+    private Task processTask(Task task) {
+        Map<String, Object> metadata = task.getMetadata() == null ? new HashMap<>() : new HashMap<>(task.getMetadata());
+        if (!metadata.containsKey(TIMESTAMP_FIELD)) {
+            metadata.put(TIMESTAMP_FIELD, OffsetDateTime.now(ZoneOffset.UTC));
+        }  
+        List<Artifact> artifacts = new ArrayList<>();
+        for (Artifact artifact : task.getArtifacts()) {
+            artifacts.add(processArtifact(artifact));
+        }
+        return new Task.Builder(task).artifacts(artifacts).metadata(metadata).build();
+    }
+
+    private TaskStatusUpdateEvent processTaskStatusUpdateEvent(TaskStatusUpdateEvent taskStatusUpdateEvent) {
+        Map<String, Object> metadata = taskStatusUpdateEvent.getMetadata() == null ? new HashMap<>() : new HashMap<>(taskStatusUpdateEvent.getMetadata());
+        if (!metadata.containsKey(TIMESTAMP_FIELD)) {
+            metadata.put(TIMESTAMP_FIELD, OffsetDateTime.now(ZoneOffset.UTC));
+        }
+        return new TaskStatusUpdateEvent.Builder(taskStatusUpdateEvent).metadata(metadata).build();
+    }
+
+    private TaskArtifactUpdateEvent processTaskArtifactUpdateEvent(TaskArtifactUpdateEvent taskArtifactUpdateEvent) {
+        Map<String, Object> metadata = taskArtifactUpdateEvent.getMetadata() == null ? new HashMap<>() : new HashMap<>(taskArtifactUpdateEvent.getMetadata());
+        if (!metadata.containsKey(TIMESTAMP_FIELD)) {
+            metadata.put(TIMESTAMP_FIELD, OffsetDateTime.now(ZoneOffset.UTC));
+        }
+        if (taskArtifactUpdateEvent.getArtifact() != null) {
+            return new TaskArtifactUpdateEvent.Builder(taskArtifactUpdateEvent).artifact(processArtifact(taskArtifactUpdateEvent.getArtifact())).metadata(metadata).build();
+        }
+        return new TaskArtifactUpdateEvent.Builder(taskArtifactUpdateEvent).metadata(metadata).build();
+    }
+
+    private Artifact processArtifact(Artifact artifact) {
+        Map<String, Object> metadata = artifact.metadata() == null ? new HashMap<>() : new HashMap<>(artifact.metadata());
+        if (!metadata.containsKey(TIMESTAMP_FIELD)) {
+            metadata.put(TIMESTAMP_FIELD, OffsetDateTime.now(ZoneOffset.UTC));
+        }
+        List<String> extensions = artifact.extensions() == null ? new ArrayList<>() : new ArrayList<>(artifact.extensions());
+        if (!extensions.contains(URI)) {
+            extensions.add(URI);
+        }
+        return new Artifact.Builder(artifact).metadata(metadata).extensions(extensions).build();
+    }
+
+    @Override
+    public void awaitQueuePollerStart() throws InterruptedException {
+        this.delegate.awaitQueuePollerStart();
+    }
+
+    @Override
+    public void close() {
+        this.delegate.close();
+    }
+
+    @Override
+    public void close(boolean immediate) {
+        this.delegate.close(immediate);
+    }
+
+    @Override
+    public void close(boolean immediate, boolean notifyParent) {
+        this.delegate.close(immediate, notifyParent);
+    }
+
+    @Override
+    public void signalQueuePollerStarted() {
+        this.delegate.signalQueuePollerStarted();
+    }
+
+    @Override
+    public EventQueue tap() {
+        return this;
+    }
+}