fix: Ensure messageId is required for a Message. Allow the messageId to be randomly generated if not set when using the Message.Builder (#261)

# Description

Thank you for opening a Pull Request!
Before submitting your PR, there are a few things you can do to make
sure it goes smoothly:

- [x] Follow the [`CONTRIBUTING` Guide](../CONTRIBUTING.md).
- [x] Make your Pull Request title in the
<https://www.conventionalcommits.org/> specification.
- Important Prefixes for
[release-please](https://github.com/googleapis/release-please):
- `fix:` which represents bug fixes, and correlates to a
[SemVer](https://semver.org/) patch.
- `feat:` represents a new feature, and correlates to a SemVer minor.
- `feat!:`, or `fix!:`, `refactor!:`, etc., which represent a breaking
change (indicated by the `!`) and will result in a SemVer major.
- [x] Ensure the tests pass
- [x] Appropriate READMEs were updated (if necessary)

Fixes #<issue_number_goes_here> 🦕

Author: fjuma

server-common/src/test/java/io/a2a/server/agentexecution/RequestContextTest.java

@@ -1,6 +1,8 @@
 package io.a2a.server.agentexecution;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -23,8 +25,6 @@
 
 public class RequestContextTest {
 
-    private static final String MESSAGE_ID = "123";
-    
     @Test
     public void testInitWithoutParams() {
         RequestContext context = new RequestContext(null, null, null, null, null, null);
@@ -37,7 +37,7 @@ public void testInitWithoutParams() {
 
     @Test
     public void testInitWithParamsNoIds() {
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
 
         UUID taskId = UUID.fromString("00000000-0000-0000-0000-000000000001");
@@ -61,7 +61,7 @@ public void testInitWithParamsNoIds() {
     @Test
     public void testInitWithTaskId() {
         String taskId = "task-123";
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId(taskId).build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId(taskId).build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
 
         RequestContext context = new RequestContext(mockParams, taskId, null, null, null, null);
@@ -73,7 +73,7 @@ public void testInitWithTaskId() {
     @Test
     public void testInitWithContextId() {
         String contextId = "context-456";
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).contextId(contextId).build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).contextId(contextId).build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
         RequestContext context = new RequestContext(mockParams, null, contextId, null, null, null);
 
@@ -85,7 +85,7 @@ public void testInitWithContextId() {
     public void testInitWithBothIds() {
         String taskId = "task-123";
         String contextId = "context-456";
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId(taskId).contextId(contextId).build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId(taskId).contextId(contextId).build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
         RequestContext context = new RequestContext(mockParams, taskId, contextId, null, null, null);
 
@@ -97,7 +97,7 @@ public void testInitWithBothIds() {
 
     @Test
     public void testInitWithTask() {
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).build();
         var mockTask = new Task.Builder().id("task-123").contextId("context-456").status(new TaskStatus(TaskState.COMPLETED)).build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
 
@@ -132,7 +132,7 @@ public void testAttachRelatedTask() {
     @Test
     public void testCheckOrGenerateTaskIdWithExistingTaskId() {
         String existingId = "existing-task-id";
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId(existingId).build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId(existingId).build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
 
         RequestContext context = new RequestContext(mockParams, null, null, null, null, null);
@@ -145,7 +145,7 @@ public void testCheckOrGenerateTaskIdWithExistingTaskId() {
     public void testCheckOrGenerateContextIdWithExistingContextId() {
         String existingId = "existing-context-id";
 
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).contextId(existingId).build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).contextId(existingId).build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
 
         RequestContext context = new RequestContext(mockParams, null, null, null, null, null);
@@ -156,7 +156,7 @@ public void testCheckOrGenerateContextIdWithExistingContextId() {
 
     @Test
     public void testInitRaisesErrorOnTaskIdMismatch() {
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId("task-123").build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId("task-123").build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
         var mockTask = new Task.Builder().id("task-123").contextId("context-456").status(new TaskStatus(TaskState.COMPLETED)).build();
 
@@ -168,7 +168,7 @@ public void testInitRaisesErrorOnTaskIdMismatch() {
 
     @Test
     public void testInitRaisesErrorOnContextIdMismatch() {
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId("task-123").contextId("context-456").build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId("task-123").contextId("context-456").build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
         var mockTask = new Task.Builder().id("task-123").contextId("context-456").status(new TaskStatus(TaskState.COMPLETED)).build();
 
@@ -200,7 +200,7 @@ public void testMessagePropertyWithoutParams() {
 
     @Test
     public void testMessagePropertyWithParams() {
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
 
         RequestContext context = new RequestContext(mockParams, null, null, null, null, null);
@@ -212,7 +212,7 @@ public void testInitWithExistingIdsInMessage() {
         String existingTaskId = "existing-task-id";
         String existingContextId = "existing-context-id";
 
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart("")))
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart("")))
                 .taskId(existingTaskId).contextId(existingContextId).build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
 
@@ -224,7 +224,7 @@ public void testInitWithExistingIdsInMessage() {
 
     @Test
     public void testInitWithTaskIdAndExistingTaskIdMatch() {
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId("task-123").contextId("context-456").build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId("task-123").contextId("context-456").build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
         var mockTask = new Task.Builder().id("task-123").contextId("context-456").status(new TaskStatus(TaskState.COMPLETED)).build();
 
@@ -237,7 +237,7 @@ public void testInitWithTaskIdAndExistingTaskIdMatch() {
 
     @Test
     public void testInitWithContextIdAndExistingContextIdMatch() {
-        var mockMessage = new Message.Builder().messageId(MESSAGE_ID).role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId("task-123").contextId("context-456").build();
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).taskId("task-123").contextId("context-456").build();
         var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
         var mockTask = new Task.Builder().id("task-123").contextId("context-456").status(new TaskStatus(TaskState.COMPLETED)).build();
 
@@ -247,4 +247,23 @@ public void testInitWithContextIdAndExistingContextIdMatch() {
         assertEquals(mockTask.getContextId(), context.getContextId());
         assertEquals(mockTask, context.getTask());
     }
+
+    @Test
+    void testMessageBuilderGeneratesId() {
+        var mockMessage = new Message.Builder().role(Message.Role.USER).parts(List.of(new TextPart(""))).build();
+        var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
+
+        RequestContext context = new RequestContext(mockParams, null, null, null, null, null);
+        assertNotNull(mockMessage.getMessageId());
+        assertFalse(mockMessage.getMessageId().isEmpty());
+    }
+
+    @Test
+    void testMessageBuilderUsesProvidedId() {
+        var mockMessage = new Message.Builder().messageId("123").role(Message.Role.USER).parts(List.of(new TextPart(""))).build();
+        var mockParams = new MessageSendParams.Builder().message(mockMessage).build();
+
+        RequestContext context = new RequestContext(mockParams, null, null, null, null, null);
+        assertEquals("123", mockMessage.getMessageId());
+    }
 }

server-common/src/test/java/io/a2a/server/tasks/TaskUpdaterTest.java

@@ -25,10 +25,8 @@
 public class TaskUpdaterTest {
     public static final String TEST_TASK_ID = "test-task-id";
     public static final String TEST_TASK_CONTEXT_ID = "test-task-context-id";
-    private static final String TEST_MESSAGE_ID = "123";
 
     private static final Message SAMPLE_MESSAGE = new Message.Builder()
-            .messageId(TEST_MESSAGE_ID)
             .taskId(TEST_TASK_ID)
             .contextId(TEST_TASK_CONTEXT_ID)
             .parts(new TextPart("Test message"))

spec/src/main/java/io/a2a/spec/Message.java

@@ -187,7 +187,8 @@ public Builder metadata(Map<String, Object> metadata) {
         }
 
         public Message build() {
-            return new Message(role, parts, messageId, contextId, taskId, referenceTaskIds, metadata);
+            return new Message(role, parts, messageId == null ? UUID.randomUUID().toString() : messageId,
+                    contextId, taskId, referenceTaskIds, metadata);
         }
     }
 }

transport/jsonrpc/src/test/java/io/a2a/transport/jsonrpc/handler/JSONRPCHandlerTest.java

@@ -718,7 +718,6 @@ public void testOnResubscribeExistingTaskSuccess() {
 
         // We need to send some events in order for those to end up in the queue
         Message message = new Message.Builder()
-                .messageId("123")
                 .taskId(MINIMAL_TASK.getId())
                 .contextId(MINIMAL_TASK.getContextId())
                 .role(Message.Role.AGENT)