fix: ServerCapabilities should not enable logging by default (#463)

- Change LoggingCapabilities from default-initialized to nullable in ServerCapabilities
- Add check if server logging is enabled in McpAsyncClient before setting logging level
- Ensure McpAsyncServer always enables logging capabilities when built
- Ensure McpStatelessAsyncServer has disabled logging capability by default
- Update tests to verify logging capabilities can be null

Signed-off-by: Christian Tzolov <[email protected]>
Co-authored-by: Christian Tzolov <[email protected]>

Author: Randgalt

mcp-test/src/main/java/io/modelcontextprotocol/AbstractMcpClientServerIntegrationTests.java

@@ -950,7 +950,7 @@ void testLoggingNotification(String clientType) throws InterruptedException {
 		List<McpSchema.LoggingMessageNotification> receivedNotifications = new CopyOnWriteArrayList<>();
 
 		var clientBuilder = clientBuilders.get(clientType);
-		;
+
 		// Create server with a tool that sends logging notifications
 		McpServerFeatures.AsyncToolSpecification tool = McpServerFeatures.AsyncToolSpecification.builder()
 			.tool(Tool.builder()
@@ -999,7 +999,7 @@ void testLoggingNotification(String clientType) throws InterruptedException {
 			.build();
 
 		var mcpServer = prepareAsyncServerBuilder().serverInfo("test-server", "1.0.0")
-			.capabilities(ServerCapabilities.builder().logging().tools(true).build())
+			.capabilities(ServerCapabilities.builder().tools(true).build())
 			.tools(tool)
 			.build();
 

mcp/src/main/java/io/modelcontextprotocol/client/McpAsyncClient.java

@@ -869,6 +869,9 @@ public Mono<Void> setLoggingLevel(LoggingLevel loggingLevel) {
 		}
 
 		return this.initializer.withIntitialization("setting logging level", init -> {
+			if (init.initializeResult().capabilities().logging() == null) {
+				return Mono.error(new IllegalStateException("Server's Logging capabilities are not enabled!"));
+			}
 			var params = new McpSchema.SetLevelRequest(loggingLevel);
 			return init.mcpSession().sendRequest(McpSchema.METHOD_LOGGING_SET_LEVEL, params, OBJECT_TYPE_REF).then();
 		});

mcp/src/main/java/io/modelcontextprotocol/server/McpAsyncServer.java

@@ -132,7 +132,7 @@ public class McpAsyncServer {
 		this.mcpTransportProvider = mcpTransportProvider;
 		this.objectMapper = objectMapper;
 		this.serverInfo = features.serverInfo();
-		this.serverCapabilities = features.serverCapabilities();
+		this.serverCapabilities = features.serverCapabilities().mutate().logging().build();
 		this.instructions = features.instructions();
 		this.tools.addAll(withStructuredOutputHandling(jsonSchemaValidator, features.tools()));
 		this.resources.putAll(features.resources());
@@ -157,7 +157,7 @@ public class McpAsyncServer {
 		this.mcpTransportProvider = mcpTransportProvider;
 		this.objectMapper = objectMapper;
 		this.serverInfo = features.serverInfo();
-		this.serverCapabilities = features.serverCapabilities();
+		this.serverCapabilities = features.serverCapabilities().mutate().logging().build();
 		this.instructions = features.instructions();
 		this.tools.addAll(withStructuredOutputHandling(jsonSchemaValidator, features.tools()));
 		this.resources.putAll(features.resources());

mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java

@@ -548,7 +548,7 @@ public static class Builder {
 
 			private Map<String, Object> experimental;
 
-			private LoggingCapabilities logging = new LoggingCapabilities();
+			private LoggingCapabilities logging;
 
 			private PromptCapabilities prompts;
 

mcp/src/test/java/io/modelcontextprotocol/client/McpAsyncClientResponseHandlerTests.java

@@ -80,6 +80,7 @@ void testSuccessfulInitialization() {
 		assertThat(result).isNotNull();
 		assertThat(result.protocolVersion()).isEqualTo(transport.protocolVersions().get(0));
 		assertThat(result.capabilities()).isEqualTo(serverCapabilities);
+		assertThat(result.capabilities().logging()).isNull();
 		assertThat(result.serverInfo()).isEqualTo(serverInfo);
 		assertThat(result.instructions()).isEqualTo("Test instructions");