Refactor the mcp-core module

- The core module has been refactored to remove unnecessary abstraction
  between the SSE transport and the STDIO transport.
- Tests have been improved and no longer complain about multiple
  subscriptions to single-subscriber Sink.
- SSE transport layer is now assuming non-blocking execution and no longer
  makes thread hops when not needed.
- Decouple ObjectMapper and error handling from AbstractMcpTransport
  and remove later.

Additional improvements:

- Rename transport classes to better reflect client-side role (*ServerTransport -> *ClientTransport)
- Introduce fluent builder pattern for client configuration
- Simplify DefaultMcpSession by removing ObjectMapper dependency
- Move unmarshal responsibility to transport layer
- Update documentation and diagrams to reflect new architecture
- Clean up test implementations

Author: chemicL

README.md

@@ -1,33 +1,31 @@
 # Spring AI MCP
 
-Java SDK for the Model Context Protocol (MCP), providing seamless integration between Java and Spring applications and MCP-compliant AI models and tools.
+Java SDK for the Model Context Protocol (MCP), providing seamless integration between Java and Spring applications and MCP-compliant AI resources and tools.
 
 ## Overview
 
-Spring AI MCP is an experimental project that provides Java and Spring Framework integration for the [Model Context Protocol](https://modelcontextprotocol.org/docs/concepts/architecture). It enables Spring applications to interact with AI models and tools through a standardized interface, supporting both synchronous and asynchronous communication patterns.
+Spring AI MCP is an experimental project that provides Java and Spring Framework integration for the [Model Context Protocol](https://modelcontextprotocol.org/docs/concepts/architecture). It enables Java applications to interact with AI models and tools through a standardized interface, supporting both synchronous and asynchronous communication patterns.
 
 <img src="spring-ai-mcp-architecture.jpg" width="600">
 
 ## Modules
 
 The project consists of two main modules:
 
-### [spring-ai-mcp-core](./spring-ai-mcp-core/README.md)
+### [mcp-core](./spring-ai-mcp-core/README.md)
 
 The core module provides a Java implementation of the Model Context Protocol specification. It includes:
 - Synchronous and asynchronous client implementations
-- Standard MCP operations support (tool discovery, resource management, prompt handling)
-- Stdio-based server transport
-- Reactive programming support using Project Reactor
+- Standard MCP operations support (tool discovery, resource management, prompt handling). Support for request and notificaiotn handling.
+- [Stdio](https://spec.modelcontextprotocol.io/specification/basic/transports/#stdio) and [SSE](https://spec.modelcontextprotocol.io/specification/basic/transports/#http-with-sse) transport implementations. 
+- [Find more](./spring-ai-mcp-core/README.md).
 
-[find more](./spring-ai-mcp-core/README.md)
-
-### [spring-ai-mcp-spring](./spring-ai-mcp-spring/README.md)
+### [mcp-spring](./spring-ai-mcp-spring/README.md)
 
 The Spring integration module provides Spring-specific functionality:
 - Integration with Spring AI's function calling system
 - Spring-friendly abstractions for MCP clients
-- Automatic conversion between JSON and Java objects for tool arguments
+- Auto-configurations (WIP)
 
 ## Requirements
 

spring-ai-mcp-core/README.md

@@ -20,7 +20,6 @@ This SDK implements the Model Context Protocol, enabling seamless integration wi
 - Multiple transport implementations:
   - Stdio-based transport for process-based communication
   - SSE-based transport for HTTP streaming
-- Reactive programming support using Project Reactor
 - Configurable request timeouts
 - Customizable JSON serialization/deserialization
 
@@ -32,43 +31,37 @@ Add the following dependency to your Maven project:
 <dependency>
     <groupId>org.springframework.experimental</groupId>
     <artifactId>spring-ai-mcp-core</artifactId>
-    <version>0.1.0</version>
+    <version>0.2.0-SNAPSHOT</version>
 </dependency>
 ```
 
-## Documentation
-
-Detailed UML class diagrams showing the relationships between components can be found in [docs/class-diagrams.puml](docs/class-diagrams.puml). The diagrams include:
-- Core Components: Shows the main interfaces, classes, and their relationships
-- Message Flow: Illustrates the message and resource type hierarchies
-
 ## Usage
 
 ### Transport Layer Options
 
 The SDK provides two transport implementations:
 
-#### StdioServerTransport
+#### StdioClientTransport
 Standard I/O based transport for process-based communication with MCP servers:
 
 ```java
 ServerParameters params = ServerParameters.builder("npx")
     .args("-y", "@modelcontextprotocol/server-everything", "dir")
     .build();
-McpTransport transport = new StdioServerTransport(params);
+McpTransport transport = new StdioClientTransport(params);
 ```
 
-#### SseServerTransport
+#### SseClientTransport
 Server-Sent Events (SSE) based transport following the MCP HTTP with SSE transport specification:
 
 ```java
 WebClient.Builder webClientBuilder = WebClient.builder()
     .baseUrl("http://your-mcp-server");
-McpTransport transport = new SseServerTransport(webClientBuilder);
+McpTransport transport = new SseClientTransport(webClientBuilder);
 
 // Or with custom ObjectMapper
 ObjectMapper mapper = new ObjectMapper();
-McpTransport transport = new SseServerTransport(webClientBuilder, mapper);
+McpTransport transport = new SseClientTransport(webClientBuilder, mapper);
 ```
 
 The SSE transport provides:
@@ -87,7 +80,7 @@ ServerParameters params = ServerParameters.builder("npx")
     .args("-y", "@modelcontextprotocol/server-everything", "dir")
     .build();
 
-try (McpSyncClient client = McpClient.sync(new StdioServerTransport(params))) {
+try (McpSyncClient client = McpClient.sync(new StdioClientTransport(params))) {
     // Initialize connection with protocol version and capabilities
     McpSchema.InitializeResult initResult = client.initialize();
 
@@ -123,7 +116,7 @@ ServerParameters params = ServerParameters.builder("npx")
 
 // Initialize async client with custom timeout and object mapper
 McpAsyncClient client = McpClient.async(
-    new StdioServerTransport(params),
+    new StdioClientTransport(params),
     Duration.ofSeconds(30),
     new ObjectMapper()
 );
@@ -172,11 +165,11 @@ The SDK follows a layered architecture with clear separation of concerns:
 - **McpAsyncClient**: Primary async implementation using Project Reactor for non-blocking operations
 - **McpSyncClient**: Synchronous wrapper around the async client for blocking operations
 - **McpSession**: Core session interface defining communication patterns
-- **McpTransport**: Transport layer interface for server communication
+- **McpTransport**: Transport layer interface for client/server communication
 - **McpSchema**: Comprehensive protocol schema definitions
-- **DefaultMcpSession**: Base implementation of the session management
-- **StdioServerTransport**: Standard I/O based server communication
-- **SseServerTransport**: HTTP-based transport using Server-Sent Events for bidirectional communication
+- **DefaultMcpSession**: Default implementation of the session management
+- **StdioClientTransport**: Standard I/O based client to server communication
+- **SseClientTransport**: HTTP-based transport using Server-Sent Events for bidirectional client-sever communication
 
 <img src="docs/spring-ai-mcp-uml-classdiagram.svg" width="600"/>
 

spring-ai-mcp-core/docs/CLIENT.SSE.TRANSPORT.md

@@ -2,7 +2,7 @@
 
 ## Overview
 
-The `SseServerTransport` class implements the Model Context Protocol (MCP) HTTP with SSE transport specification, providing a bidirectional communication channel between clients and servers. This implementation is part of the Spring AI MCP Core library and follows the [MCP HTTP with SSE Transport Specification](https://spec.modelcontextprotocol.io/specification/basic/transports/#http-with-sse).
+The `SseClientTransport` class implements the Model Context Protocol (MCP) HTTP with SSE transport specification, providing a bidirectional communication channel between clients and servers. This implementation is part of the Spring AI MCP Core library and follows the [MCP HTTP with SSE Transport Specification](https://spec.modelcontextprotocol.io/specification/basic/transports/#http-with-sse).
 
 ## Key Features
 
@@ -53,7 +53,7 @@ WebClient.Builder webClientBuilder = WebClient.builder()
     .baseUrl("http://localhost:3001");
 
 // Initialize transport
-SseServerTransport transport = new SseServerTransport(webClientBuilder);
+SseClientTransport transport = new SseClientTransport(webClientBuilder);
 
 // Create a JSON-RPC request
 JSONRPCRequest request = new JSONRPCRequest(
@@ -141,4 +141,4 @@ The implementation includes comprehensive tests covering:
 - Shutdown procedures
 - Edge cases and failure scenarios
 
-For detailed test examples, see `SseServerTransportTests.java`.
+For detailed test examples, see `SseClientTransportTests.java`.

spring-ai-mcp-core/docs/CLIENT.STDIO.TRANSPORT.md

@@ -1,6 +1,6 @@
-# StdioServerTransport
+# StdioClientTransport
 
-The `StdioServerTransport` class implements the [MCP Stdio Transport](https://spec.modelcontextprotocol.io/specification/basic/transports/#stdio) specification, providing communication with MCP servers over standard input/output streams.
+The `StdioClientTransport` class implements the [MCP Stdio Transport](https://spec.modelcontextprotocol.io/specification/basic/transports/#stdio) specification, providing communication with MCP servers over standard input/output streams.
 
 ## Overview
 
@@ -84,7 +84,7 @@ ServerParameters params = ServerParameters.builder()
     .build();
 
 // Create transport
-StdioServerTransport transport = new StdioServerTransport(params);
+StdioClientTransport transport = new StdioClientTransport(params);
 
 // Start transport
 transport.start();

spring-ai-mcp-core/docs/class-diagrams.puml

@@ -1,25 +1,18 @@
 @startuml Core Components
 
 interface McpTransport {
-  +void start()
+  +Mono<Void> connect(Function<Mono<JSONRPCMessage>, 
+                       Mono<JSONRPCMessage>> handler)
+  +Mono<Void> sendMessage()
   +void close()
   +Mono<Void> closeGracefully()
-  +void setInboudMessageHandler()
-  +void setInboundErrorHandler()
-  +Mono<Void> sendMessage()
-}
-
-abstract class AbstractMcpTransport {
-  #ObjectMapper objectMapper
-  #getInboundSink()
-  #getOutboundSink()
-  #getErrorSink()
 }
 
 interface McpSession {
-  +<T> Mono<T> sendRequest()
-  +Mono<Void> sendNotification()
+  +<T> Mono<T> sendRequest(String method, Object requestParams, TypeReference<T> typeRef)
+  +Mono<Void> sendNotification(String method, Map<String, Object> params)
   +Mono<Void> closeGracefully()
+  +close()
 }
 
 class DefaultMcpSession {
@@ -52,12 +45,12 @@ class McpSyncClient {
   +GetPromptResult getPrompt()
 }
 
-class StdioServerTransport {
+class StdioClientTransport {
   -Process serverProcess
   -ServerParameters parameters
 }
 
-class SseServerTransport {
+class SseClientTransport {
   -WebClient webClient
 }
 
@@ -74,11 +67,10 @@ class McpError {
   -String message
 }
 
-McpTransport <|.. AbstractMcpTransport
-AbstractMcpTransport <|-- StdioServerTransport
-AbstractMcpTransport <|-- SseServerTransport
+McpTransport <|-- StdioClientTransport
+McpTransport <|-- SseClientTransport
 McpSession <|-- DefaultMcpSession
-DefaultMcpSession <|-- McpAsyncClient
+DefaultMcpSession --o McpAsyncClient
 McpClient ..> McpAsyncClient : creates
 McpClient ..> McpSyncClient : creates
 McpSyncClient o-- McpAsyncClient