feat: Add progress notification support for MCP operations (#407)

Implement progress tracking for long-running operations with:
- New ProgressNotification schema and client/server support
- Progress consumer handlers in sync/async client builders
- Server exchange methods for sending progress updates
- Comprehensive integration tests
- Backwards compatibility maintained
- Add additional tests

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

mcp-test/src/main/java/io/modelcontextprotocol/client/AbstractMcpAsyncClientTests.java

@@ -12,8 +12,10 @@ import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 
 import java.time.Duration;
 import java.util.ArrayList;
+import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
@@ -49,6 +51,7 @@ import io.modelcontextprotocol.spec.McpSchema.UnsubscribeRequest;
 import io.modelcontextprotocol.spec.McpTransport;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
+import reactor.core.publisher.Sinks;
 import reactor.test.StepVerifier;
 
 /**
@@ -420,7 +423,7 @@ public abstract class AbstractMcpAsyncClientTests {
 				.consumeNextWith(result -> {
 					assertThat(result.prompts()).isNotNull();
 					// Verify that the returned list is immutable
-					assertThatThrownBy(() -> result.prompts().add(new Prompt("test", "Test", "test", null)))
+					assertThatThrownBy(() -> result.prompts().add(new Prompt("test", "test", "test", null)))
 						.isInstanceOf(UnsupportedOperationException.class);
 				})
 				.verifyComplete();
@@ -792,4 +795,39 @@ public abstract class AbstractMcpAsyncClientTests {
 			});
 	}
 
+	// ---------------------------------------
+	// Progress Notification Tests
+	// ---------------------------------------
+
+	@Test
+	void testProgressConsumer() {
+		Sinks.Many<McpSchema.ProgressNotification> sink = Sinks.many().unicast().onBackpressureBuffer();
+		List<McpSchema.ProgressNotification> receivedNotifications = new CopyOnWriteArrayList<>();
+
+		withClient(createMcpTransport(), builder -> builder.progressConsumer(notification -> {
+			receivedNotifications.add(notification);
+			sink.tryEmitNext(notification);
+			return Mono.empty();
+		}), client -> {
+			StepVerifier.create(client.initialize()).expectNextMatches(Objects::nonNull).verifyComplete();
+
+			// Call a tool that sends progress notifications
+			CallToolRequest request = CallToolRequest.builder()
+				.name("longRunningOperation")
+				.arguments(Map.of("duration", 1, "steps", 2))
+				.progressToken("test-token")
+				.build();
+
+			StepVerifier.create(client.callTool(request)).consumeNextWith(result -> {
+				assertThat(result).isNotNull();
+			}).verifyComplete();
+
+			// Use StepVerifier to verify the progress notifications via the sink
+			StepVerifier.create(sink.asFlux()).expectNextCount(2).thenCancel().verify(Duration.ofSeconds(3));
+
+			assertThat(receivedNotifications).hasSize(2);
+			assertThat(receivedNotifications.get(0).progressToken()).isEqualTo("test-token");
+		});
+	}
+
 }

mcp-test/src/main/java/io/modelcontextprotocol/client/AbstractMcpSyncClientTests.java

@@ -13,6 +13,9 @@ import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import java.time.Duration;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
@@ -648,4 +651,48 @@ public abstract class AbstractMcpSyncClientTests {
 			});
 	}
 
+	// ---------------------------------------
+	// Progress Notification Tests
+	// ---------------------------------------
+
+	@Test
+	void testProgressConsumer() {
+		AtomicInteger progressNotificationCount = new AtomicInteger(0);
+		List<McpSchema.ProgressNotification> receivedNotifications = new CopyOnWriteArrayList<>();
+		CountDownLatch latch = new CountDownLatch(2);
+
+		withClient(createMcpTransport(), builder -> builder.progressConsumer(notification -> {
+			System.out.println("Received progress notification: " + notification);
+			receivedNotifications.add(notification);
+			progressNotificationCount.incrementAndGet();
+			latch.countDown();
+		}), client -> {
+			client.initialize();
+
+			// Call a tool that sends progress notifications
+			CallToolRequest request = CallToolRequest.builder()
+				.name("longRunningOperation")
+				.arguments(Map.of("duration", 1, "steps", 2))
+				.progressToken("test-token")
+				.build();
+
+			CallToolResult result = client.callTool(request);
+
+			assertThat(result).isNotNull();
+
+			try {
+				// Wait for progress notifications to be processed
+				latch.await(3, TimeUnit.SECONDS);
+			}
+			catch (InterruptedException e) {
+				e.printStackTrace();
+			}
+
+			assertThat(progressNotificationCount.get()).isEqualTo(2);
+
+			assertThat(receivedNotifications).isNotEmpty();
+			assertThat(receivedNotifications.get(0).progressToken()).isEqualTo("test-token");
+		});
+	}
+
 }