Fix for #793 - public (or protected) constructors to allow subclassing for extensions

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

@@ -42,6 +42,7 @@
 import org.slf4j.LoggerFactory;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
+import reactor.util.context.ContextView;
 
 /**
  * The Model Context Protocol (MCP) client implementation that provides asynchronous
@@ -181,7 +182,7 @@ public class McpAsyncClient {
 	 * @param features the MCP Client supported features. responses against output
 	 * schemas.
 	 */
-	McpAsyncClient(McpClientTransport transport, Duration requestTimeout, Duration initializationTimeout,
+	public McpAsyncClient(McpClientTransport transport, Duration requestTimeout, Duration initializationTimeout,
 			JsonSchemaValidator jsonSchemaValidator, McpClientFeatures.Async features) {
 
 		Assert.notNull(transport, "Transport must not be null");
@@ -317,13 +318,20 @@ public class McpAsyncClient {
 		};
 
 		this.initializer = new LifecycleInitializer(clientCapabilities, clientInfo, transport.protocolVersions(),
-				initializationTimeout, ctx -> new McpClientSession(requestTimeout, transport, requestHandlers,
-						notificationHandlers, con -> con.contextWrite(ctx)),
+				initializationTimeout,
+				ctx -> buildClientSession(requestTimeout, transport, requestHandlers, notificationHandlers, ctx),
 				postInitializationHook);
 
 		this.transport.setExceptionHandler(this.initializer::handleException);
 	}
 
+	protected McpClientSession buildClientSession(Duration requestTimeout, McpClientTransport transport,
+			Map<String, RequestHandler<?>> requestHandlers, Map<String, NotificationHandler> notificationHandlers,
+			ContextView ctx) {
+		return new McpClientSession(requestTimeout, transport, requestHandlers, notificationHandlers,
+				con -> con.contextWrite(ctx));
+	}
+
 	/**
 	 * Get the current initialization result.
 	 * @return the initialization result.

mcp-core/src/main/java/io/modelcontextprotocol/client/McpClientFeatures.java

@@ -46,7 +46,7 @@
  * @see McpSchema.Implementation
  * @see McpSchema.ClientCapabilities
  */
-class McpClientFeatures {
+public class McpClientFeatures {
 
 	/**
 	 * Asynchronous client features specification providing the capabilities and request
@@ -64,7 +64,7 @@ class McpClientFeatures {
 	 * @param elicitationHandler the elicitation handler.
 	 * @param enableCallToolSchemaCaching whether to enable call tool schema caching.
 	 */
-	record Async(McpSchema.Implementation clientInfo, McpSchema.ClientCapabilities clientCapabilities,
+	public record Async(McpSchema.Implementation clientInfo, McpSchema.ClientCapabilities clientCapabilities,
 			Map<String, McpSchema.Root> roots, List<Function<List<McpSchema.Tool>, Mono<Void>>> toolsChangeConsumers,
 			List<Function<List<McpSchema.Resource>, Mono<Void>>> resourcesChangeConsumers,
 			List<Function<List<McpSchema.ResourceContents>, Mono<Void>>> resourcesUpdateConsumers,

mcp-core/src/main/java/io/modelcontextprotocol/client/McpSyncClient.java

@@ -64,7 +64,7 @@ public class McpSyncClient implements AutoCloseable {
 	// is not a requirement?
 	private static final long DEFAULT_CLOSE_TIMEOUT_MS = 10_000L;
 
-	private final McpAsyncClient delegate;
+	protected final McpAsyncClient delegate;
 
 	private final Supplier<McpTransportContext> contextProvider;
 
@@ -75,7 +75,7 @@ public class McpSyncClient implements AutoCloseable {
 	 * @param contextProvider the supplier of context before calling any non-blocking
 	 * operation on underlying delegate
 	 */
-	McpSyncClient(McpAsyncClient delegate, Supplier<McpTransportContext> contextProvider) {
+	public McpSyncClient(McpAsyncClient delegate, Supplier<McpTransportContext> contextProvider) {
 		Assert.notNull(delegate, "The delegate can not be null");
 		Assert.notNull(contextProvider, "The contextProvider can not be null");
 		this.delegate = delegate;

mcp-core/src/main/java/io/modelcontextprotocol/json/TypeRef.java

@@ -32,6 +32,10 @@ protected TypeRef() {
 		this.type = ((ParameterizedType) superClass).getActualTypeArguments()[0];
 	}
 
+	protected TypeRef(Type type) {
+		this.type = type;
+	}
+
 	/**
 	 * Returns the captured type information.
 	 * @return the Type representing the actual type argument captured by this TypeRef

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

@@ -91,35 +91,35 @@ public class McpAsyncServer {
 
 	private static final Logger logger = LoggerFactory.getLogger(McpAsyncServer.class);
 
-	private final McpServerTransportProviderBase mcpTransportProvider;
+	protected final McpServerTransportProviderBase mcpTransportProvider;
 
-	private final McpJsonMapper jsonMapper;
+	protected final McpJsonMapper jsonMapper;
 
-	private final JsonSchemaValidator jsonSchemaValidator;
+	protected final JsonSchemaValidator jsonSchemaValidator;
 
-	private final McpSchema.ServerCapabilities serverCapabilities;
+	protected final McpSchema.ServerCapabilities serverCapabilities;
 
-	private final McpSchema.Implementation serverInfo;
+	protected final McpSchema.Implementation serverInfo;
 
-	private final String instructions;
+	protected final String instructions;
 
-	private final CopyOnWriteArrayList<McpServerFeatures.AsyncToolSpecification> tools = new CopyOnWriteArrayList<>();
+	protected final CopyOnWriteArrayList<McpServerFeatures.AsyncToolSpecification> tools = new CopyOnWriteArrayList<>();
 
-	private final ConcurrentHashMap<String, McpServerFeatures.AsyncResourceSpecification> resources = new ConcurrentHashMap<>();
+	protected final ConcurrentHashMap<String, McpServerFeatures.AsyncResourceSpecification> resources = new ConcurrentHashMap<>();
 
-	private final ConcurrentHashMap<String, McpServerFeatures.AsyncResourceTemplateSpecification> resourceTemplates = new ConcurrentHashMap<>();
+	protected final ConcurrentHashMap<String, McpServerFeatures.AsyncResourceTemplateSpecification> resourceTemplates = new ConcurrentHashMap<>();
 
-	private final ConcurrentHashMap<String, McpServerFeatures.AsyncPromptSpecification> prompts = new ConcurrentHashMap<>();
+	protected final ConcurrentHashMap<String, McpServerFeatures.AsyncPromptSpecification> prompts = new ConcurrentHashMap<>();
 
 	// FIXME: this field is deprecated and should be remvoed together with the
 	// broadcasting loggingNotification.
 	private LoggingLevel minLoggingLevel = LoggingLevel.DEBUG;
 
-	private final ConcurrentHashMap<McpSchema.CompleteReference, McpServerFeatures.AsyncCompletionSpecification> completions = new ConcurrentHashMap<>();
+	protected final ConcurrentHashMap<McpSchema.CompleteReference, McpServerFeatures.AsyncCompletionSpecification> completions = new ConcurrentHashMap<>();
 
-	private List<String> protocolVersions;
+	protected List<String> protocolVersions;
 
-	private McpUriTemplateManagerFactory uriTemplateManagerFactory = new DefaultMcpUriTemplateManagerFactory();
+	protected McpUriTemplateManagerFactory uriTemplateManagerFactory = new DefaultMcpUriTemplateManagerFactory();
 
 	/**
 	 * Create a new McpAsyncServer with the given transport provider and capabilities.
@@ -128,7 +128,7 @@ public class McpAsyncServer {
 	 * @param features The MCP server supported features.
 	 * @param jsonMapper The JsonMapper to use for JSON serialization/deserialization
 	 */
-	McpAsyncServer(McpServerTransportProvider mcpTransportProvider, McpJsonMapper jsonMapper,
+	public McpAsyncServer(McpServerTransportProvider mcpTransportProvider, McpJsonMapper jsonMapper,
 			McpServerFeatures.Async features, Duration requestTimeout,
 			McpUriTemplateManagerFactory uriTemplateManagerFactory, JsonSchemaValidator jsonSchemaValidator) {
 		this.mcpTransportProvider = mcpTransportProvider;
@@ -153,7 +153,7 @@ public class McpAsyncServer {
 				requestTimeout, transport, this::asyncInitializeRequestHandler, requestHandlers, notificationHandlers));
 	}
 
-	McpAsyncServer(McpStreamableServerTransportProvider mcpTransportProvider, McpJsonMapper jsonMapper,
+	public McpAsyncServer(McpStreamableServerTransportProvider mcpTransportProvider, McpJsonMapper jsonMapper,
 			McpServerFeatures.Async features, Duration requestTimeout,
 			McpUriTemplateManagerFactory uriTemplateManagerFactory, JsonSchemaValidator jsonSchemaValidator) {
 		this.mcpTransportProvider = mcpTransportProvider;
@@ -178,7 +178,7 @@ public class McpAsyncServer {
 				this::asyncInitializeRequestHandler, requestHandlers, notificationHandlers));
 	}
 
-	private Map<String, McpNotificationHandler> prepareNotificationHandlers(McpServerFeatures.Async features) {
+	protected Map<String, McpNotificationHandler> prepareNotificationHandlers(McpServerFeatures.Async features) {
 		Map<String, McpNotificationHandler> notificationHandlers = new HashMap<>();
 
 		notificationHandlers.put(McpSchema.METHOD_NOTIFICATION_INITIALIZED, (exchange, params) -> Mono.empty());
@@ -196,7 +196,7 @@ private Map<String, McpNotificationHandler> prepareNotificationHandlers(McpServe
 		return notificationHandlers;
 	}
 
-	private Map<String, McpRequestHandler<?>> prepareRequestHandlers() {
+	protected Map<String, McpRequestHandler<?>> prepareRequestHandlers() {
 		Map<String, McpRequestHandler<?>> requestHandlers = new HashMap<>();
 
 		// Initialize request handlers for standard MCP methods

mcp-core/src/main/java/io/modelcontextprotocol/server/McpServerFeatures.java

@@ -39,7 +39,7 @@ public class McpServerFeatures {
 	 * roots list changes
 	 * @param instructions The server instructions text
 	 */
-	record Async(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
+	public record Async(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
 			List<McpServerFeatures.AsyncToolSpecification> tools, Map<String, AsyncResourceSpecification> resources,
 			Map<String, McpServerFeatures.AsyncResourceTemplateSpecification> resourceTemplates,
 			Map<String, McpServerFeatures.AsyncPromptSpecification> prompts,
@@ -59,7 +59,7 @@ record Async(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities s
 		 * the roots list changes
 		 * @param instructions The server instructions text
 		 */
-		Async(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
+		public Async(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
 				List<McpServerFeatures.AsyncToolSpecification> tools, Map<String, AsyncResourceSpecification> resources,
 				Map<String, McpServerFeatures.AsyncResourceTemplateSpecification> resourceTemplates,
 				Map<String, McpServerFeatures.AsyncPromptSpecification> prompts,
@@ -101,7 +101,7 @@ record Async(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities s
 		 * @return a specification which is protected from blocking calls specified by the
 		 * user.
 		 */
-		static Async fromSync(Sync syncSpec, boolean immediateExecution) {
+		public static Async fromSync(Sync syncSpec, boolean immediateExecution) {
 			List<McpServerFeatures.AsyncToolSpecification> tools = new ArrayList<>();
 			for (var tool : syncSpec.tools()) {
 				tools.add(AsyncToolSpecification.fromSync(tool, immediateExecution));
@@ -153,7 +153,7 @@ static Async fromSync(Sync syncSpec, boolean immediateExecution) {
 	 * roots list changes
 	 * @param instructions The server instructions text
 	 */
-	record Sync(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
+	public record Sync(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
 			List<McpServerFeatures.SyncToolSpecification> tools,
 			Map<String, McpServerFeatures.SyncResourceSpecification> resources,
 			Map<String, McpServerFeatures.SyncResourceTemplateSpecification> resourceTemplates,
@@ -173,7 +173,7 @@ record Sync(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities se
 		 * the roots list changes
 		 * @param instructions The server instructions text
 		 */
-		Sync(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
+		public Sync(McpSchema.Implementation serverInfo, McpSchema.ServerCapabilities serverCapabilities,
 				List<McpServerFeatures.SyncToolSpecification> tools,
 				Map<String, McpServerFeatures.SyncResourceSpecification> resources,
 				Map<String, McpServerFeatures.SyncResourceTemplateSpecification> resourceTemplates,
@@ -354,7 +354,8 @@ public static Builder builder() {
 	public record AsyncResourceSpecification(McpSchema.Resource resource,
 			BiFunction<McpAsyncServerExchange, McpSchema.ReadResourceRequest, Mono<McpSchema.ReadResourceResult>> readHandler) {
 
-		static AsyncResourceSpecification fromSync(SyncResourceSpecification resource, boolean immediateExecution) {
+		public static AsyncResourceSpecification fromSync(SyncResourceSpecification resource,
+				boolean immediateExecution) {
 			// FIXME: This is temporary, proper validation should be implemented
 			if (resource == null) {
 				return null;
@@ -394,7 +395,7 @@ static AsyncResourceSpecification fromSync(SyncResourceSpecification resource, b
 	public record AsyncResourceTemplateSpecification(McpSchema.ResourceTemplate resourceTemplate,
 			BiFunction<McpAsyncServerExchange, McpSchema.ReadResourceRequest, Mono<McpSchema.ReadResourceResult>> readHandler) {
 
-		static AsyncResourceTemplateSpecification fromSync(SyncResourceTemplateSpecification resource,
+		public static AsyncResourceTemplateSpecification fromSync(SyncResourceTemplateSpecification resource,
 				boolean immediateExecution) {
 			// FIXME: This is temporary, proper validation should be implemented
 			if (resource == null) {
@@ -442,7 +443,7 @@ static AsyncResourceTemplateSpecification fromSync(SyncResourceTemplateSpecifica
 	public record AsyncPromptSpecification(McpSchema.Prompt prompt,
 			BiFunction<McpAsyncServerExchange, McpSchema.GetPromptRequest, Mono<McpSchema.GetPromptResult>> promptHandler) {
 
-		static AsyncPromptSpecification fromSync(SyncPromptSpecification prompt, boolean immediateExecution) {
+		public static AsyncPromptSpecification fromSync(SyncPromptSpecification prompt, boolean immediateExecution) {
 			// FIXME: This is temporary, proper validation should be implemented
 			if (prompt == null) {
 				return null;
@@ -482,7 +483,7 @@ public record AsyncCompletionSpecification(McpSchema.CompleteReference reference
 		 * @return an asynchronous wrapper of the provided sync specification, or
 		 * {@code null} if input is null
 		 */
-		static AsyncCompletionSpecification fromSync(SyncCompletionSpecification completion,
+		public static AsyncCompletionSpecification fromSync(SyncCompletionSpecification completion,
 				boolean immediateExecution) {
 			if (completion == null) {
 				return null;

mcp-core/src/main/java/io/modelcontextprotocol/server/McpStatelessAsyncServer.java

@@ -51,9 +51,9 @@ public class McpStatelessAsyncServer {
 
 	private static final Logger logger = LoggerFactory.getLogger(McpStatelessAsyncServer.class);
 
-	private final McpStatelessServerTransport mcpTransportProvider;
+	protected final McpStatelessServerTransport mcpTransportProvider;
 
-	private final McpJsonMapper jsonMapper;
+	protected final McpJsonMapper jsonMapper;
 
 	private final McpSchema.ServerCapabilities serverCapabilities;
 
@@ -77,7 +77,7 @@ public class McpStatelessAsyncServer {
 
 	private final JsonSchemaValidator jsonSchemaValidator;
 
-	McpStatelessAsyncServer(McpStatelessServerTransport mcpTransport, McpJsonMapper jsonMapper,
+	public McpStatelessAsyncServer(McpStatelessServerTransport mcpTransport, McpJsonMapper jsonMapper,
 			McpStatelessServerFeatures.Async features, Duration requestTimeout,
 			McpUriTemplateManagerFactory uriTemplateManagerFactory, JsonSchemaValidator jsonSchemaValidator) {
 		this.mcpTransportProvider = mcpTransport;