Compose request customizers on the HTTP client transport builders

MIGRATION-2.0.md

@@ -213,7 +213,7 @@ Schemas that explicitly declare a different dialect via `$schema` are accepted w
 
 The deprecated `Builder.customizeRequest(Consumer<HttpRequest.Builder>)` method on `HttpClientSseClientTransport` and `HttpClientStreamableHttpTransport` has been removed.
 
-**Action:** Use `requestBuilder(HttpRequest.Builder)` for static request setup, or `httpRequestCustomizer(McpSyncHttpClientRequestCustomizer)` for per-request customization.
+**Action:** Use `requestBuilder(HttpRequest.Builder)` for static request setup, or `addHttpRequestCustomizer(McpSyncHttpClientRequestCustomizer)` for per-request customization.
 
 ### `protocolVersions()` default now advertises all known versions
 

conformance-tests/client-spring-http-client/src/main/java/io/modelcontextprotocol/conformance/client/scenario/PreRegistrationScenario.java

@@ -55,7 +55,7 @@ public void execute(String serverUrl) {
 
 		var customizer = new OAuth2ClientCredentialsSyncHttpRequestCustomizer(authorizedClientManager, REGISTRATION_ID);
 		HttpClientStreamableHttpTransport transport = HttpClientStreamableHttpTransport.builder(serverUrl)
-			.httpRequestCustomizer(customizer)
+			.addHttpRequestCustomizer(customizer)
 			.build();
 
 		var client = McpClient.sync(transport)

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

@@ -8,14 +8,15 @@
 import java.net.URI;
 import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
-import java.net.http.HttpResponse;
 import java.time.Duration;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
+import io.modelcontextprotocol.client.transport.customizer.DelegatingMcpAsyncHttpClientRequestCustomizer;
 import io.modelcontextprotocol.client.transport.customizer.McpAsyncHttpClientRequestCustomizer;
 import io.modelcontextprotocol.client.transport.customizer.McpSyncHttpClientRequestCustomizer;
 import io.modelcontextprotocol.common.McpTransportContext;
@@ -203,7 +204,7 @@ public static class Builder {
 
 		private HttpRequest.Builder requestBuilder = HttpRequest.newBuilder();
 
-		private McpAsyncHttpClientRequestCustomizer httpRequestCustomizer = McpAsyncHttpClientRequestCustomizer.NOOP;
+		private final List<McpAsyncHttpClientRequestCustomizer> httpRequestCustomizers = new ArrayList<>();
 
 		private Duration connectTimeout = Duration.ofSeconds(10);
 
@@ -286,36 +287,92 @@ public Builder jsonMapper(McpJsonMapper jsonMapper) {
 
 		/**
 		 * Sets the customizer for {@link HttpRequest.Builder}, to modify requests before
-		 * executing them.
+		 * executing them. The customizer is internally converted to
+		 * {@link McpAsyncHttpClientRequestCustomizer}.
 		 * <p>
-		 * This overrides the customizer from
-		 * {@link #asyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer)}.
+		 * This replaces all customizers previously registered on this builder.
 		 * <p>
 		 * Do NOT use a blocking {@link McpSyncHttpClientRequestCustomizer} in a
 		 * non-blocking context. Use
 		 * {@link #asyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer)}
 		 * instead.
 		 * @param syncHttpRequestCustomizer the request customizer
 		 * @return this builder
+		 * @deprecated Use {@link #addHttpRequestCustomizer} instead.
 		 */
+		@Deprecated
 		public Builder httpRequestCustomizer(McpSyncHttpClientRequestCustomizer syncHttpRequestCustomizer) {
-			this.httpRequestCustomizer = McpAsyncHttpClientRequestCustomizer.fromSync(syncHttpRequestCustomizer);
-			return this;
+			Assert.notNull(syncHttpRequestCustomizer, "syncHttpRequestCustomizer must not be null");
+			this.httpRequestCustomizers.clear();
+			return addHttpRequestCustomizer(syncHttpRequestCustomizer);
 		}
 
 		/**
 		 * Sets the customizer for {@link HttpRequest.Builder}, to modify requests before
 		 * executing them.
 		 * <p>
-		 * This overrides the customizer from
-		 * {@link #httpRequestCustomizer(McpSyncHttpClientRequestCustomizer)}.
+		 * This replaces all customizers previously registered on this builder.
 		 * <p>
 		 * Do NOT use a blocking implementation in a non-blocking context.
 		 * @param asyncHttpRequestCustomizer the request customizer
 		 * @return this builder
+		 * @deprecated Use {@link #addAsyncHttpRequestCustomizer} instead.
 		 */
+		@Deprecated
 		public Builder asyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer asyncHttpRequestCustomizer) {
-			this.httpRequestCustomizer = asyncHttpRequestCustomizer;
+			Assert.notNull(asyncHttpRequestCustomizer, "asyncHttpRequestCustomizer must not be null");
+			this.httpRequestCustomizers.clear();
+			return addAsyncHttpRequestCustomizer(asyncHttpRequestCustomizer);
+		}
+
+		/**
+		 * Adds a customizer for {@link HttpRequest.Builder}, to modify requests before
+		 * executing them. Customizers are applied in the order they are added, after
+		 * those already registered on this builder. The customizer is internally
+		 * converted to {@link McpAsyncHttpClientRequestCustomizer}.
+		 * <p>
+		 * Do NOT use a blocking {@link McpSyncHttpClientRequestCustomizer} in a
+		 * non-blocking context. Use
+		 * {@link #addAsyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer)}
+		 * instead.
+		 * @param syncHttpRequestCustomizer the request customizer
+		 * @return this builder
+		 */
+		public Builder addHttpRequestCustomizer(McpSyncHttpClientRequestCustomizer syncHttpRequestCustomizer) {
+			Assert.notNull(syncHttpRequestCustomizer, "syncHttpRequestCustomizer must not be null");
+			this.httpRequestCustomizers.add(McpAsyncHttpClientRequestCustomizer.fromSync(syncHttpRequestCustomizer));
+			return this;
+		}
+
+		/**
+		 * Adds a customizer for {@link HttpRequest.Builder}, to modify requests before
+		 * executing them. Customizers are applied in the order they are added, after
+		 * those already registered on this builder.
+		 * <p>
+		 * Do NOT use a blocking implementation in a non-blocking context.
+		 * @param asyncHttpRequestCustomizer the request customizer
+		 * @return this builder
+		 */
+		public Builder addAsyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer asyncHttpRequestCustomizer) {
+			Assert.notNull(asyncHttpRequestCustomizer, "asyncHttpRequestCustomizer must not be null");
+			this.httpRequestCustomizers.add(asyncHttpRequestCustomizer);
+			return this;
+		}
+
+		/**
+		 * Provides access to the mutable list of request customizers registered on this
+		 * builder, so they can be inspected, reordered, added or removed. Customizers are
+		 * applied in list order. Synchronous customizers registered through
+		 * {@link #httpRequestCustomizer(McpSyncHttpClientRequestCustomizer)} or
+		 * {@link #addHttpRequestCustomizer(McpSyncHttpClientRequestCustomizer)} appear in
+		 * the list wrapped as {@link McpAsyncHttpClientRequestCustomizer}.
+		 * @param customizersConsumer a consumer of the list of customizers
+		 * @return this builder
+		 */
+		public Builder asyncHttpRequestCustomizers(
+				Consumer<List<McpAsyncHttpClientRequestCustomizer>> customizersConsumer) {
+			Assert.notNull(customizersConsumer, "customizersConsumer must not be null");
+			customizersConsumer.accept(this.httpRequestCustomizers);
 			return this;
 		}
 
@@ -369,10 +426,19 @@ public Builder maxResponseSize(int maxResponseSize) {
 		public HttpClientSseClientTransport build() {
 			HttpClient httpClient = this.clientBuilder.connectTimeout(this.connectTimeout).build();
 			return new HttpClientSseClientTransport(httpClient, requestBuilder, baseUri, sseEndpoint,
-					jsonMapper == null ? McpJsonDefaults.getMapper() : jsonMapper, httpRequestCustomizer,
+					jsonMapper == null ? McpJsonDefaults.getMapper() : jsonMapper, httpRequestCustomizer(),
 					messageEndpointValidator, maxResponseSize);
 		}
 
+		private McpAsyncHttpClientRequestCustomizer httpRequestCustomizer() {
+			Assert.noNullElements(this.httpRequestCustomizers, "httpRequestCustomizers must not contain null elements");
+			return switch (this.httpRequestCustomizers.size()) {
+				case 0 -> McpAsyncHttpClientRequestCustomizer.NOOP;
+				case 1 -> this.httpRequestCustomizers.get(0);
+				default -> new DelegatingMcpAsyncHttpClientRequestCustomizer(List.copyOf(this.httpRequestCustomizers));
+			};
+		}
+
 	}
 
 	@Override

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

@@ -11,6 +11,7 @@
 import java.net.http.HttpResponse;
 import java.nio.ByteBuffer;
 import java.time.Duration;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.List;
@@ -22,6 +23,7 @@
 import java.util.function.Function;
 
 import io.modelcontextprotocol.client.McpAsyncClient;
+import io.modelcontextprotocol.client.transport.customizer.DelegatingMcpAsyncHttpClientRequestCustomizer;
 import io.modelcontextprotocol.client.transport.customizer.McpAsyncHttpClientRequestCustomizer;
 import io.modelcontextprotocol.client.transport.customizer.McpHttpClientAuthorizationErrorHandler;
 import io.modelcontextprotocol.client.transport.customizer.McpHttpClientTransportAuthorizationErrorHandler;
@@ -672,7 +674,7 @@ public static class Builder {
 
 		private HttpRequest.Builder requestBuilder = HttpRequest.newBuilder();
 
-		private McpAsyncHttpClientRequestCustomizer httpRequestCustomizer = McpAsyncHttpClientRequestCustomizer.NOOP;
+		private final List<McpAsyncHttpClientRequestCustomizer> httpRequestCustomizers = new ArrayList<>();
 
 		private Duration connectTimeout = Duration.ofSeconds(10);
 
@@ -776,36 +778,92 @@ public Builder openConnectionOnStartup(boolean openConnectionOnStartup) {
 
 		/**
 		 * Sets the customizer for {@link HttpRequest.Builder}, to modify requests before
-		 * executing them.
+		 * executing them. The customizer is internally converted to
+		 * {@link McpAsyncHttpClientRequestCustomizer}.
 		 * <p>
-		 * This overrides the customizer from
-		 * {@link #asyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer)}.
+		 * This replaces all customizers previously registered on this builder.
 		 * <p>
 		 * Do NOT use a blocking {@link McpSyncHttpClientRequestCustomizer} in a
 		 * non-blocking context. Use
 		 * {@link #asyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer)}
 		 * instead.
 		 * @param syncHttpRequestCustomizer the request customizer
 		 * @return this builder
+		 * @deprecated Use {@link #addHttpRequestCustomizer} instead.
 		 */
+		@Deprecated
 		public Builder httpRequestCustomizer(McpSyncHttpClientRequestCustomizer syncHttpRequestCustomizer) {
-			this.httpRequestCustomizer = McpAsyncHttpClientRequestCustomizer.fromSync(syncHttpRequestCustomizer);
-			return this;
+			Assert.notNull(syncHttpRequestCustomizer, "syncHttpRequestCustomizer must not be null");
+			this.httpRequestCustomizers.clear();
+			return addHttpRequestCustomizer(syncHttpRequestCustomizer);
 		}
 
 		/**
 		 * Sets the customizer for {@link HttpRequest.Builder}, to modify requests before
 		 * executing them.
 		 * <p>
-		 * This overrides the customizer from
-		 * {@link #httpRequestCustomizer(McpSyncHttpClientRequestCustomizer)}.
+		 * This replaces all customizers previously registered on this builder.
 		 * <p>
 		 * Do NOT use a blocking implementation in a non-blocking context.
 		 * @param asyncHttpRequestCustomizer the request customizer
 		 * @return this builder
+		 * @deprecated Use {@link #addAsyncHttpRequestCustomizer} instead.
 		 */
+		@Deprecated
 		public Builder asyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer asyncHttpRequestCustomizer) {
-			this.httpRequestCustomizer = asyncHttpRequestCustomizer;
+			Assert.notNull(asyncHttpRequestCustomizer, "asyncHttpRequestCustomizer must not be null");
+			this.httpRequestCustomizers.clear();
+			return addAsyncHttpRequestCustomizer(asyncHttpRequestCustomizer);
+		}
+
+		/**
+		 * Adds a customizer for {@link HttpRequest.Builder}, to modify requests before
+		 * executing them. Customizers are applied in the order they are added, after
+		 * those already registered on this builder. The customizer is internally
+		 * converted to {@link McpAsyncHttpClientRequestCustomizer}.
+		 * <p>
+		 * Do NOT use a blocking {@link McpSyncHttpClientRequestCustomizer} in a
+		 * non-blocking context. Use
+		 * {@link #addAsyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer)}
+		 * instead.
+		 * @param syncHttpRequestCustomizer the request customizer
+		 * @return this builder
+		 */
+		public Builder addHttpRequestCustomizer(McpSyncHttpClientRequestCustomizer syncHttpRequestCustomizer) {
+			Assert.notNull(syncHttpRequestCustomizer, "syncHttpRequestCustomizer must not be null");
+			this.httpRequestCustomizers.add(McpAsyncHttpClientRequestCustomizer.fromSync(syncHttpRequestCustomizer));
+			return this;
+		}
+
+		/**
+		 * Adds a customizer for {@link HttpRequest.Builder}, to modify requests before
+		 * executing them. Customizers are applied in the order they are added, after
+		 * those already registered on this builder.
+		 * <p>
+		 * Do NOT use a blocking implementation in a non-blocking context.
+		 * @param asyncHttpRequestCustomizer the request customizer
+		 * @return this builder
+		 */
+		public Builder addAsyncHttpRequestCustomizer(McpAsyncHttpClientRequestCustomizer asyncHttpRequestCustomizer) {
+			Assert.notNull(asyncHttpRequestCustomizer, "asyncHttpRequestCustomizer must not be null");
+			this.httpRequestCustomizers.add(asyncHttpRequestCustomizer);
+			return this;
+		}
+
+		/**
+		 * Provides access to the mutable list of request customizers registered on this
+		 * builder, so they can be inspected, reordered, added or removed. Customizers are
+		 * applied in list order. Synchronous customizers registered through
+		 * {@link #httpRequestCustomizer(McpSyncHttpClientRequestCustomizer)} or
+		 * {@link #addHttpRequestCustomizer(McpSyncHttpClientRequestCustomizer)} appear in
+		 * the list wrapped as {@link McpAsyncHttpClientRequestCustomizer}.
+		 * @param customizersConsumer a consumer of the list of customizers
+		 * @return this builder
+		 */
+		public Builder asyncHttpRequestCustomizers(
+				Consumer<List<McpAsyncHttpClientRequestCustomizer>> customizersConsumer) {
+			Assert.notNull(customizersConsumer, "customizersConsumer must not be null");
+			customizersConsumer.accept(this.httpRequestCustomizers);
 			return this;
 		}
 
@@ -910,7 +968,16 @@ public HttpClientStreamableHttpTransport build() {
 			HttpClient httpClient = this.clientBuilder.connectTimeout(this.connectTimeout).build();
 			return new HttpClientStreamableHttpTransport(jsonMapper == null ? McpJsonDefaults.getMapper() : jsonMapper,
 					httpClient, requestBuilder, baseUri, endpoint, resumableStreams, openConnectionOnStartup,
-					httpRequestCustomizer, authorizationErrorHandler, supportedProtocolVersions, maxResponseSize);
+					httpRequestCustomizer(), authorizationErrorHandler, supportedProtocolVersions, maxResponseSize);
+		}
+
+		private McpAsyncHttpClientRequestCustomizer httpRequestCustomizer() {
+			Assert.noNullElements(this.httpRequestCustomizers, "httpRequestCustomizers must not contain null elements");
+			return switch (this.httpRequestCustomizers.size()) {
+				case 0 -> McpAsyncHttpClientRequestCustomizer.NOOP;
+				case 1 -> this.httpRequestCustomizers.get(0);
+				default -> new DelegatingMcpAsyncHttpClientRequestCustomizer(List.copyOf(this.httpRequestCustomizers));
+			};
 		}
 
 	}

mcp-test/src/main/java/io/modelcontextprotocol/client/AbstractMcpAsyncClientTests.java

@@ -10,6 +10,7 @@
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.assertj.core.api.Assertions.fail;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assumptions.assumeTrue;
 
 import java.time.Duration;
 import java.util.ArrayList;
@@ -23,6 +24,7 @@
 import java.util.function.Consumer;
 import java.util.function.Function;
 
+import io.modelcontextprotocol.client.transport.customizer.McpAsyncHttpClientRequestCustomizer;
 import io.modelcontextprotocol.spec.McpSchema.ElicitFormRequest;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -67,6 +69,15 @@ public abstract class AbstractMcpAsyncClientTests {
 
 	abstract protected McpClientTransport createMcpTransport();
 
+	// Creates a client transport that applies request customizers, in the order they
+	// appear in the list. Subclasses whose transport supports
+	// McpAsyncHttpClientRequestCustomizer should override this; tests relying on it are
+	// skipped otherwise.
+	protected McpClientTransport createMcpTransport(
+			Consumer<List<McpAsyncHttpClientRequestCustomizer>> requestCustomizers) {
+		return null;
+	}
+
 	protected Duration getRequestTimeout() {
 		return Duration.ofSeconds(14);
 	}
@@ -126,6 +137,30 @@ <T> void verifyCallSucceedsWithImplicitInitialization(Function<McpAsyncClient, M
 		});
 	}
 
+	@Test
+	void testRequestCustomizersAreAppliedInOrder() {
+		var invocations = new CopyOnWriteArrayList<String>();
+		Function<String, McpAsyncHttpClientRequestCustomizer> recording = name -> (builder, method, endpoint, body,
+				context) -> {
+			invocations.add(name);
+			return Mono.just(builder);
+		};
+
+		var transport = createMcpTransport(customizers -> {
+			customizers.add(recording.apply("second"));
+			customizers.add(recording.apply("third"));
+			customizers.add(0, recording.apply("first"));
+		});
+		assumeTrue(transport != null, "Transport does not support request customizers");
+
+		withClient(transport, mcpAsyncClient -> {
+			StepVerifier.create(mcpAsyncClient.initialize()).expectNextCount(1).verifyComplete();
+			// Later requests may run concurrently, e.g. the Streamable HTTP GET
+			// stream, so only check the first one.
+			assertThat(invocations).startsWith("first", "second", "third");
+		});
+	}
+
 	@Test
 	void testConstructorWithInvalidArguments() {
 		assertThatThrownBy(() -> McpClient.async(null).build()).isInstanceOf(IllegalArgumentException.class)

mcp-test/src/test/java/io/modelcontextprotocol/client/HttpClientStreamableHttpAsyncClientTests.java

@@ -4,7 +4,11 @@
 
 package io.modelcontextprotocol.client;
 
+import java.util.List;
+import java.util.function.Consumer;
+
 import io.modelcontextprotocol.client.transport.HttpClientStreamableHttpTransport;
+import io.modelcontextprotocol.client.transport.customizer.McpAsyncHttpClientRequestCustomizer;
 import io.modelcontextprotocol.spec.McpClientTransport;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
@@ -29,6 +33,12 @@ protected McpClientTransport createMcpTransport() {
 		return HttpClientStreamableHttpTransport.builder(host).build();
 	}
 
+	@Override
+	protected McpClientTransport createMcpTransport(
+			Consumer<List<McpAsyncHttpClientRequestCustomizer>> requestCustomizers) {
+		return HttpClientStreamableHttpTransport.builder(host).asyncHttpRequestCustomizers(requestCustomizers).build();
+	}
+
 	@BeforeAll
 	static void startContainer() {
 		container.start();