refactor(client): enhance HttpClientSseClientTransport with flexible customization API (#117)

- Add builder customizeClient() and customizeRequest() methods
- Enable HTTP client and request configuration through consumer-based customization
- Deprecate direct constructors in favor of the more flexible builder approach
- Add test coverage for customization capabilities

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

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

@@ -15,7 +15,7 @@ import org.testcontainers.containers.wait.strategy.Wait;
  *
  * @author Christian Tzolov
  */
-@Timeout(15) // Giving extra time beyond the client timeout
+@Timeout(15)
 class HttpSseMcpAsyncClientTests extends AbstractMcpAsyncClientTests {
 
 	String host = "http://localhost:3004";
@@ -29,7 +29,7 @@ class HttpSseMcpAsyncClientTests extends AbstractMcpAsyncClientTests {
 
 	@Override
 	protected McpClientTransport createMcpTransport() {
-		return new HttpClientSseClientTransport(host);
+		return HttpClientSseClientTransport.builder(host).build();
 	}
 
 	@Override

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

@@ -29,7 +29,7 @@ class HttpSseMcpSyncClientTests extends AbstractMcpSyncClientTests {
 
 	@Override
 	protected McpClientTransport createMcpTransport() {
-		return new HttpClientSseClientTransport(host);
+		return HttpClientSseClientTransport.builder(host).build();
 	}
 
 	@Override

mcp/src/test/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransportTests.java

@@ -4,9 +4,15 @@
 
 package io.modelcontextprotocol.client.transport;
 
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
 import java.time.Duration;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Consumer;
 import java.util.function.Function;
 
 import io.modelcontextprotocol.spec.McpSchema;
@@ -26,6 +32,8 @@ import org.springframework.http.codec.ServerSentEvent;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatCode;
 
+import com.fasterxml.jackson.databind.ObjectMapper;
+
 /**
  * Tests for the {@link HttpClientSseClientTransport} class.
  *
@@ -51,8 +59,8 @@ class HttpClientSseClientTransportTests {
 
 		private Sinks.Many<ServerSentEvent<String>> events = Sinks.many().unicast().onBackpressureBuffer();
 
-		public TestHttpClientSseClientTransport(String baseUri) {
-			super(baseUri);
+		public TestHttpClientSseClientTransport(final String baseUri) {
+			super(HttpClient.newHttpClient(), HttpRequest.newBuilder(), baseUri, "/sse", new ObjectMapper());
 		}
 
 		public int getInboundMessageCount() {
@@ -191,13 +199,14 @@ class HttpClientSseClientTransportTests {
 		StepVerifier.create(transport.sendMessage(testMessage)).verifyComplete();
 
 		// Message count should remain 0 after shutdown
-		assertThat(transport.getInboundMessageCount()).isEqualTo(0);
+		assertThat(transport.getInboundMessageCount()).isZero();
 	}
 
 	@Test
 	void testRetryBehavior() {
 		// Create a client that simulates connection failures
-		HttpClientSseClientTransport failingTransport = new HttpClientSseClientTransport("http://non-existent-host");
+		HttpClientSseClientTransport failingTransport = HttpClientSseClientTransport.builder("http://non-existent-host")
+			.build();
 
 		// Verify that the transport attempts to reconnect
 		StepVerifier.create(Mono.delay(Duration.ofSeconds(2))).expectNextCount(1).verifyComplete();
@@ -275,4 +284,84 @@ class HttpClientSseClientTransportTests {
 		assertThat(transport.getInboundMessageCount()).isEqualTo(3);
 	}
 
+	@Test
+	void testCustomizeClient() {
+		// Create an atomic boolean to verify the customizer was called
+		AtomicBoolean customizerCalled = new AtomicBoolean(false);
+
+		// Create a transport with the customizer
+		HttpClientSseClientTransport customizedTransport = HttpClientSseClientTransport.builder(host)
+			.customizeClient(builder -> {
+				builder.version(HttpClient.Version.HTTP_2);
+				customizerCalled.set(true);
+			})
+			.build();
+
+		// Verify the customizer was called
+		assertThat(customizerCalled.get()).isTrue();
+
+		// Clean up
+		customizedTransport.closeGracefully().block();
+	}
+
+	@Test
+	void testCustomizeRequest() {
+		// Create an atomic boolean to verify the customizer was called
+		AtomicBoolean customizerCalled = new AtomicBoolean(false);
+
+		// Create a reference to store the custom header value
+		AtomicReference<String> headerName = new AtomicReference<>();
+		AtomicReference<String> headerValue = new AtomicReference<>();
+
+		// Create a transport with the customizer
+		HttpClientSseClientTransport customizedTransport = HttpClientSseClientTransport.builder(host)
+			// Create a request customizer that adds a custom header
+			.customizeRequest(builder -> {
+				builder.header("X-Custom-Header", "test-value");
+				customizerCalled.set(true);
+
+				// Create a new request to verify the header was set
+				HttpRequest request = builder.uri(URI.create("http://example.com")).build();
+				headerName.set("X-Custom-Header");
+				headerValue.set(request.headers().firstValue("X-Custom-Header").orElse(null));
+			})
+			.build();
+
+		// Verify the customizer was called
+		assertThat(customizerCalled.get()).isTrue();
+
+		// Verify the header was set correctly
+		assertThat(headerName.get()).isEqualTo("X-Custom-Header");
+		assertThat(headerValue.get()).isEqualTo("test-value");
+
+		// Clean up
+		customizedTransport.closeGracefully().block();
+	}
+
+	@Test
+	void testChainedCustomizations() {
+		// Create atomic booleans to verify both customizers were called
+		AtomicBoolean clientCustomizerCalled = new AtomicBoolean(false);
+		AtomicBoolean requestCustomizerCalled = new AtomicBoolean(false);
+
+		// Create a transport with both customizers chained
+		HttpClientSseClientTransport customizedTransport = HttpClientSseClientTransport.builder(host)
+			.customizeClient(builder -> {
+				builder.connectTimeout(Duration.ofSeconds(30));
+				clientCustomizerCalled.set(true);
+			})
+			.customizeRequest(builder -> {
+				builder.header("X-Api-Key", "test-api-key");
+				requestCustomizerCalled.set(true);
+			})
+			.build();
+
+		// Verify both customizers were called
+		assertThat(clientCustomizerCalled.get()).isTrue();
+		assertThat(requestCustomizerCalled.get()).isTrue();
+
+		// Clean up
+		customizedTransport.closeGracefully().block();
+	}
+
 }