feat: implement Streamable HTTP transport and refactor SSE transport to reactive streams

This change imporves the transport layer with reactive patterns and adds support for
the latest MCP specification while maintaining backward compatibility with existing SSE transport.

- Add HttpClientStreamableHttpTransport implementing 2025-03-26 MCP Streamable HTTP spec
- Add ResponseSubscribers utility for handling SSE and JSON HTTP responses
- Refactor HttpClientSseClientTransport to use reactive streams instead of CompletableFuture
  - Replace FlowSseClient with direct reactive stream handling
  - Use Disposable-based connection management instead of CountDownLatch
  - Replace message endpoint discovery with Sinks.One approach
- Add resiliency tests using Toxiproxy for network failure scenarios
- Minor type safety improvements in StdioClientTransport and DefaultMcpTransportStream

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

Author: tzolov

mcp-spring/mcp-spring-webflux/src/test/java/io/modelcontextprotocol/client/WebClientStreamableHttpAsyncClientTests.java

@@ -1,12 +1,12 @@
 package io.modelcontextprotocol.client;
 
-import io.modelcontextprotocol.client.transport.WebClientStreamableHttpTransport;
-import io.modelcontextprotocol.spec.McpClientTransport;
 import org.junit.jupiter.api.Timeout;
+import org.springframework.web.reactive.function.client.WebClient;
 import org.testcontainers.containers.GenericContainer;
 import org.testcontainers.containers.wait.strategy.Wait;
 
-import org.springframework.web.reactive.function.client.WebClient;
+import io.modelcontextprotocol.client.transport.WebClientStreamableHttpTransport;
+import io.modelcontextprotocol.spec.McpClientTransport;
 
 @Timeout(15)
 public class WebClientStreamableHttpAsyncClientTests extends AbstractMcpAsyncClientTests {

mcp-spring/mcp-spring-webflux/src/test/java/io/modelcontextprotocol/client/WebClientStreamableHttpSyncClientTests.java

@@ -1,12 +1,12 @@
 package io.modelcontextprotocol.client;
 
-import io.modelcontextprotocol.client.transport.WebClientStreamableHttpTransport;
-import io.modelcontextprotocol.spec.McpClientTransport;
 import org.junit.jupiter.api.Timeout;
+import org.springframework.web.reactive.function.client.WebClient;
 import org.testcontainers.containers.GenericContainer;
 import org.testcontainers.containers.wait.strategy.Wait;
 
-import org.springframework.web.reactive.function.client.WebClient;
+import io.modelcontextprotocol.client.transport.WebClientStreamableHttpTransport;
+import io.modelcontextprotocol.spec.McpClientTransport;
 
 @Timeout(15)
 public class WebClientStreamableHttpSyncClientTests extends AbstractMcpSyncClientTests {

mcp/pom.xml

@@ -141,11 +141,11 @@
 
 		<!-- Mockito cannot mock this class: class java.net.http.HttpClient. the bytebuddy helps. -->
 		<dependency>
-            <groupId>net.bytebuddy</groupId>
-            <artifactId>byte-buddy</artifactId>
-            <version>${byte-buddy.version}</version>
-            <scope>test</scope>
-        </dependency>
+			<groupId>net.bytebuddy</groupId>
+			<artifactId>byte-buddy</artifactId>
+			<version>${byte-buddy.version}</version>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>io.projectreactor</groupId>
 			<artifactId>reactor-test</artifactId>
@@ -202,6 +202,14 @@
 			<scope>test</scope>
 		</dependency>
 
+		<dependency>
+			<groupId>org.testcontainers</groupId>
+			<artifactId>toxiproxy</artifactId>
+			<version>${toxiproxy.version}</version>
+			<scope>test</scope>
+		</dependency>
+
+
 	</dependencies>