refactor: move and rename HTTP request customizers to dedicated package (#453)

- Move Mcp(Async)HttpRequestCustomizer from client.transport to client.transport.customizer
- Rename (Async)HttpRequestCustomizer to Mcp(Async)HttpRequestCustomizer
- Add DelegatingMcpAsyncHttpRequestCustomizer and DelegatingMcpSyncHttpRequestCustomizer for composing multiple customizers
- Update all references across transport classes and tests
- Improve package organization and naming consistency with MCP prefix

mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransport.java

@@ -22,6 +22,8 @@ import org.slf4j.LoggerFactory;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
 
+import io.modelcontextprotocol.client.transport.customizer.McpAsyncHttpRequestCustomizer;
+import io.modelcontextprotocol.client.transport.customizer.McpSyncHttpRequestCustomizer;
 import io.modelcontextprotocol.client.transport.ResponseSubscribers.ResponseEvent;
 import io.modelcontextprotocol.spec.McpClientTransport;
 import io.modelcontextprotocol.spec.McpSchema;
@@ -112,7 +114,7 @@ public class HttpClientSseClientTransport implements McpClientTransport {
 	/**
 	 * Customizer to modify requests before they are executed.
 	 */
-	private final AsyncHttpRequestCustomizer httpRequestCustomizer;
+	private final McpAsyncHttpRequestCustomizer httpRequestCustomizer;
 
 	/**
 	 * Creates a new transport instance with default HTTP client and object mapper.
@@ -186,7 +188,7 @@ public class HttpClientSseClientTransport implements McpClientTransport {
 	@Deprecated(forRemoval = true)
 	HttpClientSseClientTransport(HttpClient httpClient, HttpRequest.Builder requestBuilder, String baseUri,
 			String sseEndpoint, ObjectMapper objectMapper) {
-		this(httpClient, requestBuilder, baseUri, sseEndpoint, objectMapper, AsyncHttpRequestCustomizer.NOOP);
+		this(httpClient, requestBuilder, baseUri, sseEndpoint, objectMapper, McpAsyncHttpRequestCustomizer.NOOP);
 	}
 
 	/**
@@ -202,7 +204,7 @@ public class HttpClientSseClientTransport implements McpClientTransport {
 	 * @throws IllegalArgumentException if objectMapper, clientBuilder, or headers is null
 	 */
 	HttpClientSseClientTransport(HttpClient httpClient, HttpRequest.Builder requestBuilder, String baseUri,
-			String sseEndpoint, ObjectMapper objectMapper, AsyncHttpRequestCustomizer httpRequestCustomizer) {
+			String sseEndpoint, ObjectMapper objectMapper, McpAsyncHttpRequestCustomizer httpRequestCustomizer) {
 		Assert.notNull(objectMapper, "ObjectMapper must not be null");
 		Assert.hasText(baseUri, "baseUri must not be empty");
 		Assert.hasText(sseEndpoint, "sseEndpoint must not be empty");
@@ -246,7 +248,7 @@ public class HttpClientSseClientTransport implements McpClientTransport {
 
 		private HttpRequest.Builder requestBuilder = HttpRequest.newBuilder();
 
-		private AsyncHttpRequestCustomizer httpRequestCustomizer = AsyncHttpRequestCustomizer.NOOP;
+		private McpAsyncHttpRequestCustomizer httpRequestCustomizer = McpAsyncHttpRequestCustomizer.NOOP;
 
 		private Duration connectTimeout = Duration.ofSeconds(10);
 
@@ -352,16 +354,16 @@ public class HttpClientSseClientTransport implements McpClientTransport {
 		 * executing them.
 		 * <p>
 		 * This overrides the customizer from
-		 * {@link #asyncHttpRequestCustomizer(AsyncHttpRequestCustomizer)}.
+		 * {@link #asyncHttpRequestCustomizer(McpAsyncHttpRequestCustomizer)}.
 		 * <p>
-		 * Do NOT use a blocking {@link SyncHttpRequestCustomizer} in a non-blocking
+		 * Do NOT use a blocking {@link McpSyncHttpRequestCustomizer} in a non-blocking
-		 * context. Use {@link #asyncHttpRequestCustomizer(AsyncHttpRequestCustomizer)}
+		 * context. Use {@link #asyncHttpRequestCustomizer(McpAsyncHttpRequestCustomizer)}
 		 * instead.
 		 * @param syncHttpRequestCustomizer the request customizer
 		 * @return this builder
 		 */
-		public Builder httpRequestCustomizer(SyncHttpRequestCustomizer syncHttpRequestCustomizer) {
+		public Builder httpRequestCustomizer(McpSyncHttpRequestCustomizer syncHttpRequestCustomizer) {
-			this.httpRequestCustomizer = AsyncHttpRequestCustomizer.fromSync(syncHttpRequestCustomizer);
+			this.httpRequestCustomizer = McpAsyncHttpRequestCustomizer.fromSync(syncHttpRequestCustomizer);
 			return this;
 		}
 
@@ -370,13 +372,13 @@ public class HttpClientSseClientTransport implements McpClientTransport {
 		 * executing them.
 		 * <p>
 		 * This overrides the customizer from
-		 * {@link #httpRequestCustomizer(SyncHttpRequestCustomizer)}.
+		 * {@link #httpRequestCustomizer(McpSyncHttpRequestCustomizer)}.
 		 * <p>
 		 * Do NOT use a blocking implementation in a non-blocking context.
 		 * @param asyncHttpRequestCustomizer the request customizer
 		 * @return this builder
 		 */
-		public Builder asyncHttpRequestCustomizer(AsyncHttpRequestCustomizer asyncHttpRequestCustomizer) {
+		public Builder asyncHttpRequestCustomizer(McpAsyncHttpRequestCustomizer asyncHttpRequestCustomizer) {
 			this.httpRequestCustomizer = asyncHttpRequestCustomizer;
 			return this;
 		}

mcp/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java

@@ -25,6 +25,8 @@ import org.slf4j.LoggerFactory;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
 
+import io.modelcontextprotocol.client.transport.customizer.McpAsyncHttpRequestCustomizer;
+import io.modelcontextprotocol.client.transport.customizer.McpSyncHttpRequestCustomizer;
 import io.modelcontextprotocol.client.transport.ResponseSubscribers.ResponseEvent;
 import io.modelcontextprotocol.spec.DefaultMcpTransportSession;
 import io.modelcontextprotocol.spec.DefaultMcpTransportStream;
@@ -113,7 +115,7 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 
 	private final boolean resumableStreams;
 
-	private final AsyncHttpRequestCustomizer httpRequestCustomizer;
+	private final McpAsyncHttpRequestCustomizer httpRequestCustomizer;
 
 	private final AtomicReference<DefaultMcpTransportSession> activeSession = new AtomicReference<>();
 
@@ -123,7 +125,7 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 
 	private HttpClientStreamableHttpTransport(ObjectMapper objectMapper, HttpClient httpClient,
 			HttpRequest.Builder requestBuilder, String baseUri, String endpoint, boolean resumableStreams,
-			boolean openConnectionOnStartup, AsyncHttpRequestCustomizer httpRequestCustomizer) {
+			boolean openConnectionOnStartup, McpAsyncHttpRequestCustomizer httpRequestCustomizer) {
 		this.objectMapper = objectMapper;
 		this.httpClient = httpClient;
 		this.requestBuilder = requestBuilder;
@@ -598,7 +600,7 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 
 		private HttpRequest.Builder requestBuilder = HttpRequest.newBuilder();
 
-		private AsyncHttpRequestCustomizer httpRequestCustomizer = AsyncHttpRequestCustomizer.NOOP;
+		private McpAsyncHttpRequestCustomizer httpRequestCustomizer = McpAsyncHttpRequestCustomizer.NOOP;
 
 		private Duration connectTimeout = Duration.ofSeconds(10);
 
@@ -709,16 +711,16 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 		 * executing them.
 		 * <p>
 		 * This overrides the customizer from
-		 * {@link #asyncHttpRequestCustomizer(AsyncHttpRequestCustomizer)}.
+		 * {@link #asyncHttpRequestCustomizer(McpAsyncHttpRequestCustomizer)}.
 		 * <p>
-		 * Do NOT use a blocking {@link SyncHttpRequestCustomizer} in a non-blocking
+		 * Do NOT use a blocking {@link McpSyncHttpRequestCustomizer} in a non-blocking
-		 * context. Use {@link #asyncHttpRequestCustomizer(AsyncHttpRequestCustomizer)}
+		 * context. Use {@link #asyncHttpRequestCustomizer(McpAsyncHttpRequestCustomizer)}
 		 * instead.
 		 * @param syncHttpRequestCustomizer the request customizer
 		 * @return this builder
 		 */
-		public Builder httpRequestCustomizer(SyncHttpRequestCustomizer syncHttpRequestCustomizer) {
+		public Builder httpRequestCustomizer(McpSyncHttpRequestCustomizer syncHttpRequestCustomizer) {
-			this.httpRequestCustomizer = AsyncHttpRequestCustomizer.fromSync(syncHttpRequestCustomizer);
+			this.httpRequestCustomizer = McpAsyncHttpRequestCustomizer.fromSync(syncHttpRequestCustomizer);
 			return this;
 		}
 
@@ -727,13 +729,13 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
 		 * executing them.
 		 * <p>
 		 * This overrides the customizer from
-		 * {@link #httpRequestCustomizer(SyncHttpRequestCustomizer)}.
+		 * {@link #httpRequestCustomizer(McpSyncHttpRequestCustomizer)}.
 		 * <p>
 		 * Do NOT use a blocking implementation in a non-blocking context.
 		 * @param asyncHttpRequestCustomizer the request customizer
 		 * @return this builder
 		 */
-		public Builder asyncHttpRequestCustomizer(AsyncHttpRequestCustomizer asyncHttpRequestCustomizer) {
+		public Builder asyncHttpRequestCustomizer(McpAsyncHttpRequestCustomizer asyncHttpRequestCustomizer) {
 			this.httpRequestCustomizer = asyncHttpRequestCustomizer;
 			return this;
 		}

mcp/src/main/java/io/modelcontextprotocol/client/transport/customizer/DelegatingMcpAsyncHttpRequestCustomizer.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2024-2025 the original author or authors.
+ */
+package io.modelcontextprotocol.client.transport.customizer;
+
+import io.modelcontextprotocol.util.Assert;
+import java.net.URI;
+import java.net.http.HttpRequest;
+import java.util.List;
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Mono;
+
+/**
+ * Composable {@link McpAsyncHttpRequestCustomizer} that applies multiple customizers, in
+ * order.
+ *
+ * @author Daniel Garnier-Moiroux
+ */
+public class DelegatingMcpAsyncHttpRequestCustomizer implements McpAsyncHttpRequestCustomizer {
+
+	private final List<McpAsyncHttpRequestCustomizer> customizers;
+
+	public DelegatingMcpAsyncHttpRequestCustomizer(List<McpAsyncHttpRequestCustomizer> customizers) {
+		Assert.notNull(customizers, "Customizers must not be null");
+		this.customizers = customizers;
+	}
+
+	@Override
+	public Publisher<HttpRequest.Builder> customize(HttpRequest.Builder builder, String method, URI endpoint,
+			String body) {
+		var result = Mono.just(builder);
+		for (var customizer : this.customizers) {
+			result = result.flatMap(b -> Mono.from(customizer.customize(b, method, endpoint, body)));
+		}
+		return result;
+	}
+
+}

mcp/src/main/java/io/modelcontextprotocol/client/transport/customizer/DelegatingMcpSyncHttpRequestCustomizer.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2024-2025 the original author or authors.
+ */
+
+package io.modelcontextprotocol.client.transport.customizer;
+
+import io.modelcontextprotocol.util.Assert;
+import java.net.URI;
+import java.net.http.HttpRequest;
+import java.util.List;
+
+/**
+ * Composable {@link McpSyncHttpRequestCustomizer} that applies multiple customizers, in
+ * order.
+ *
+ * @author Daniel Garnier-Moiroux
+ */
+public class DelegatingMcpSyncHttpRequestCustomizer implements McpSyncHttpRequestCustomizer {
+
+	private final List<McpSyncHttpRequestCustomizer> delegates;
+
+	public DelegatingMcpSyncHttpRequestCustomizer(List<McpSyncHttpRequestCustomizer> customizers) {
+		Assert.notNull(customizers, "Customizers must not be null");
+		this.delegates = customizers;
+	}
+
+	@Override
+	public void customize(HttpRequest.Builder builder, String method, URI endpoint, String body) {
+		this.delegates.forEach(delegate -> delegate.customize(builder, method, endpoint, body));
+	}
+
+}

mcp/src/main/java/io/modelcontextprotocol/client/transport/customizer/McpAsyncHttpRequestCustomizer.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2024-2025 the original author or authors.
+ */
+
+package io.modelcontextprotocol.client.transport.customizer;
+
+import java.net.URI;
+import java.net.http.HttpRequest;
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Mono;
+import reactor.core.scheduler.Schedulers;
+import reactor.util.annotation.Nullable;
+
+/**
+ * Customize {@link HttpRequest.Builder} before executing the request, in either SSE or
+ * Streamable HTTP transport.
+ * <p>
+ * When used in a non-blocking context, implementations MUST be non-blocking.
+ *
+ * @author Daniel Garnier-Moiroux
+ */
+public interface McpAsyncHttpRequestCustomizer {
+
+	Publisher<HttpRequest.Builder> customize(HttpRequest.Builder builder, String method, URI endpoint,
+			@Nullable String body);
+
+	McpAsyncHttpRequestCustomizer NOOP = new Noop();
+
+	/**
+	 * Wrap a sync implementation in an async wrapper.
+	 * <p>
+	 * Do NOT wrap a blocking implementation for use in a non-blocking context. For a
+	 * blocking implementation, consider using {@link Schedulers#boundedElastic()}.
+	 */
+	static McpAsyncHttpRequestCustomizer fromSync(McpSyncHttpRequestCustomizer customizer) {
+		return (builder, method, uri, body) -> Mono.fromSupplier(() -> {
+			customizer.customize(builder, method, uri, body);
+			return builder;
+		});
+	}
+
+	class Noop implements McpAsyncHttpRequestCustomizer {
+
+		@Override
+		public Publisher<HttpRequest.Builder> customize(HttpRequest.Builder builder, String method, URI endpoint,
+				String body) {
+			return Mono.just(builder);
+		}
+
+	}
+
+}

mcp/src/main/java/io/modelcontextprotocol/client/transport/customizer/McpSyncHttpRequestCustomizer.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2024-2025 the original author or authors.
+ */
+
+package io.modelcontextprotocol.client.transport.customizer;
+
+import java.net.URI;
+import java.net.http.HttpRequest;
+import reactor.util.annotation.Nullable;
+
+/**
+ * Customize {@link HttpRequest.Builder} before executing the request, either in SSE or
+ * Streamable HTTP transport.
+ *
+ * @author Daniel Garnier-Moiroux
+ */
+public interface McpSyncHttpRequestCustomizer {
+
+	void customize(HttpRequest.Builder builder, String method, URI endpoint, @Nullable String body);
+
+}

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

@@ -15,6 +15,8 @@ import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
+import io.modelcontextprotocol.client.transport.customizer.McpAsyncHttpRequestCustomizer;
+import io.modelcontextprotocol.client.transport.customizer.McpSyncHttpRequestCustomizer;
 import io.modelcontextprotocol.spec.McpSchema;
 import io.modelcontextprotocol.spec.McpSchema.JSONRPCRequest;
 import org.junit.jupiter.api.AfterAll;
@@ -72,7 +74,7 @@ class HttpClientSseClientTransportTests {
 		public TestHttpClientSseClientTransport(final String baseUri) {
 			super(HttpClient.newBuilder().version(HttpClient.Version.HTTP_1_1).build(),
 					HttpRequest.newBuilder().header("Content-Type", "application/json"), baseUri, "/sse",
-					new ObjectMapper(), AsyncHttpRequestCustomizer.NOOP);
+					new ObjectMapper(), McpAsyncHttpRequestCustomizer.NOOP);
 		}
 
 		public int getInboundMessageCount() {
@@ -389,7 +391,7 @@ class HttpClientSseClientTransportTests {
 
 	@Test
 	void testRequestCustomizer() {
-		var mockCustomizer = mock(SyncHttpRequestCustomizer.class);
+		var mockCustomizer = mock(McpSyncHttpRequestCustomizer.class);
 
 		// Create a transport with the customizer
 		var customizedTransport = HttpClientSseClientTransport.builder(host)
@@ -423,7 +425,7 @@ class HttpClientSseClientTransportTests {
 
 	@Test
 	void testAsyncRequestCustomizer() {
-		var mockCustomizer = mock(AsyncHttpRequestCustomizer.class);
+		var mockCustomizer = mock(McpAsyncHttpRequestCustomizer.class);
 		when(mockCustomizer.customize(any(), any(), any(), any()))
 			.thenAnswer(invocation -> Mono.just(invocation.getArguments()[0]));
 

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

@@ -22,6 +22,7 @@ import org.junit.jupiter.api.Timeout;
 
 import com.sun.net.httpserver.HttpServer;
 
+import io.modelcontextprotocol.client.transport.customizer.McpSyncHttpRequestCustomizer;
 import io.modelcontextprotocol.server.transport.TomcatTestUtil;
 import io.modelcontextprotocol.spec.McpSchema;
 import io.modelcontextprotocol.spec.ProtocolVersions;
@@ -70,7 +71,7 @@ public class HttpClientStreamableHttpTransportEmptyJsonResponseTest {
 	void testNotificationInitialized() throws URISyntaxException {
 
 		var uri = new URI(host + "/mcp");
-		var mockRequestCustomizer = mock(SyncHttpRequestCustomizer.class);
+		var mockRequestCustomizer = mock(McpSyncHttpRequestCustomizer.class);
 		var transport = HttpClientStreamableHttpTransport.builder(host)
 			.httpRequestCustomizer(mockRequestCustomizer)
 			.build();

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

@@ -4,6 +4,8 @@
 
 package io.modelcontextprotocol.client.transport;
 
+import io.modelcontextprotocol.client.transport.customizer.McpAsyncHttpRequestCustomizer;
+import io.modelcontextprotocol.client.transport.customizer.McpSyncHttpRequestCustomizer;
 import io.modelcontextprotocol.spec.McpSchema;
 import java.net.URI;
 import java.net.URISyntaxException;
@@ -63,7 +65,7 @@ class HttpClientStreamableHttpTransportTest {
 	@Test
 	void testRequestCustomizer() throws URISyntaxException {
 		var uri = new URI(host + "/mcp");
-		var mockRequestCustomizer = mock(SyncHttpRequestCustomizer.class);
+		var mockRequestCustomizer = mock(McpSyncHttpRequestCustomizer.class);
 
 		var transport = HttpClientStreamableHttpTransport.builder(host)
 			.httpRequestCustomizer(mockRequestCustomizer)
@@ -88,7 +90,7 @@ class HttpClientStreamableHttpTransportTest {
 	@Test
 	void testAsyncRequestCustomizer() throws URISyntaxException {
 		var uri = new URI(host + "/mcp");
-		var mockRequestCustomizer = mock(AsyncHttpRequestCustomizer.class);
+		var mockRequestCustomizer = mock(McpAsyncHttpRequestCustomizer.class);
 		when(mockRequestCustomizer.customize(any(), any(), any(), any()))
 			.thenAnswer(invocation -> Mono.just(invocation.getArguments()[0]));
 

mcp/src/test/java/io/modelcontextprotocol/client/transport/customizer/DelegatingMcpAsyncHttpRequestCustomizerTest.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2024-2025 the original author or authors.
+ */
+
+package io.modelcontextprotocol.client.transport.customizer;
+
+import java.net.URI;
+import java.net.http.HttpRequest;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+/**
+ * Tests for {@link DelegatingMcpAsyncHttpRequestCustomizer}.
+ *
+ * @author Daniel Garnier-Moiroux
+ */
+class DelegatingMcpAsyncHttpRequestCustomizerTest {
+
+	private static final URI TEST_URI = URI.create("https://example.com");
+
+	private final HttpRequest.Builder TEST_BUILDER = HttpRequest.newBuilder(TEST_URI);
+
+	@Test
+	void delegates() {
+		var mockCustomizer = mock(McpAsyncHttpRequestCustomizer.class);
+		when(mockCustomizer.customize(any(), any(), any(), any()))
+			.thenAnswer(invocation -> Mono.just(invocation.getArguments()[0]));
+		var customizer = new DelegatingMcpAsyncHttpRequestCustomizer(List.of(mockCustomizer));
+
+		StepVerifier.create(customizer.customize(TEST_BUILDER, "GET", TEST_URI, "{\"everybody\": \"needs somebody\"}"))
+			.expectNext(TEST_BUILDER)
+			.verifyComplete();
+
+		verify(mockCustomizer).customize(TEST_BUILDER, "GET", TEST_URI, "{\"everybody\": \"needs somebody\"}");
+	}
+
+	@Test
+	void delegatesInOrder() {
+		var customizer = new DelegatingMcpAsyncHttpRequestCustomizer(
+				List.of((builder, method, uri, body) -> Mono.just(builder.copy().header("x-test", "one")),
+						(builder, method, uri, body) -> Mono.just(builder.copy().header("x-test", "two"))));
+
+		var headers = Mono
+			.from(customizer.customize(TEST_BUILDER, "GET", TEST_URI, "{\"everybody\": \"needs somebody\"}"))
+			.map(HttpRequest.Builder::build)
+			.map(HttpRequest::headers)
+			.flatMapIterable(h -> h.allValues("x-test"));
+
+		StepVerifier.create(headers).expectNext("one").expectNext("two").verifyComplete();
+	}
+
+	@Test
+	void constructorRequiresNonNull() {
+		assertThatThrownBy(() -> new DelegatingMcpAsyncHttpRequestCustomizer(null))
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("Customizers must not be null");
+	}
+
+}

mcp/src/test/java/io/modelcontextprotocol/client/transport/customizer/DelegatingMcpSyncHttpRequestCustomizerTest.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2024-2025 the original author or authors.
+ */
+
+package io.modelcontextprotocol.client.transport.customizer;
+
+import java.net.URI;
+import java.net.http.HttpRequest;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.mockito.Mockito.verify;
+
+/**
+ * Tests for {@link DelegatingMcpSyncHttpRequestCustomizer}.
+ *
+ * @author Daniel Garnier-Moiroux
+ */
+class DelegatingMcpSyncHttpRequestCustomizerTest {
+
+	private static final URI TEST_URI = URI.create("https://example.com");
+
+	private final HttpRequest.Builder TEST_BUILDER = HttpRequest.newBuilder(TEST_URI);
+
+	@Test
+	void delegates() {
+		var mockCustomizer = Mockito.mock(McpSyncHttpRequestCustomizer.class);
+		var customizer = new DelegatingMcpSyncHttpRequestCustomizer(List.of(mockCustomizer));
+
+		customizer.customize(TEST_BUILDER, "GET", TEST_URI, "{\"everybody\": \"needs somebody\"}");
+
+		verify(mockCustomizer).customize(TEST_BUILDER, "GET", TEST_URI, "{\"everybody\": \"needs somebody\"}");
+	}
+
+	@Test
+	void delegatesInOrder() {
+		var testHeaderName = "x-test";
+		var customizer = new DelegatingMcpSyncHttpRequestCustomizer(
+				List.of((builder, method, uri, body) -> builder.header(testHeaderName, "one"),
+						(builder, method, uri, body) -> builder.header(testHeaderName, "two")));
+
+		customizer.customize(TEST_BUILDER, "GET", TEST_URI, "");
+		var request = TEST_BUILDER.build();
+
+		assertThat(request.headers().allValues(testHeaderName)).containsExactly("one", "two");
+	}
+
+	@Test
+	void constructorRequiresNonNull() {
+		assertThatThrownBy(() -> new DelegatingMcpAsyncHttpRequestCustomizer(null))
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("Customizers must not be null");
+	}
+
+}