Unwrap request factory when creating RestClient from RestTemplate

This commit makes sure that, when building a RestClient based on the
configuration of a RestTemplate, the request factory is unwrapped if it
is a InterceptingClientHttpRequestFactory.

Closes spring-projectsgh-32038

spring-web/src/main/java/org/springframework/http/client/AbstractClientHttpRequestFactoryWrapper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,7 +24,7 @@
 
 /**
  * Abstract base class for {@link ClientHttpRequestFactory} implementations
- * that decorate another request factory.
+ * that decorate another delegate request factory.
  *
  * @author Arjen Poutsma
  * @since 3.1
@@ -54,6 +54,13 @@ public final ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) thr
 		return createRequest(uri, httpMethod, this.requestFactory);
 	}
 
+	/**
+	 * Return the delegate request factory.
+	 */
+	public ClientHttpRequestFactory getDelegate() {
+		return this.requestFactory;
+	}
+
 	/**
 	 * Create a new {@link ClientHttpRequest} for the specified URI and HTTP method
 	 * by using the passed-on request factory.

spring-web/src/main/java/org/springframework/web/client/DefaultRestClientBuilder.java

@@ -32,6 +32,7 @@
 import org.springframework.http.client.ClientHttpRequestInitializer;
 import org.springframework.http.client.ClientHttpRequestInterceptor;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
+import org.springframework.http.client.InterceptingClientHttpRequestFactory;
 import org.springframework.http.client.JdkClientHttpRequestFactory;
 import org.springframework.http.client.JettyClientHttpRequestFactory;
 import org.springframework.http.client.SimpleClientHttpRequestFactory;
@@ -177,7 +178,7 @@ public DefaultRestClientBuilder(RestTemplate restTemplate) {
 		this.statusHandlers = new ArrayList<>();
 		this.statusHandlers.add(StatusHandler.fromErrorHandler(restTemplate.getErrorHandler()));
 
-		this.requestFactory = restTemplate.getRequestFactory();
+		this.requestFactory = getRequestFactory(restTemplate);
 		this.messageConverters = new ArrayList<>(restTemplate.getMessageConverters());
 
 		if (!CollectionUtils.isEmpty(restTemplate.getInterceptors())) {
@@ -190,6 +191,16 @@ public DefaultRestClientBuilder(RestTemplate restTemplate) {
 		this.observationConvention = restTemplate.getObservationConvention();
 	}
 
+	private static ClientHttpRequestFactory getRequestFactory(RestTemplate restTemplate) {
+		ClientHttpRequestFactory requestFactory = restTemplate.getRequestFactory();
+		if (requestFactory instanceof InterceptingClientHttpRequestFactory interceptingClientHttpRequestFactory) {
+			return interceptingClientHttpRequestFactory.getDelegate();
+		}
+		else {
+			return requestFactory;
+		}
+	}
+
 
 	@Override
 	public RestClient.Builder baseUrl(String baseUrl) {

spring-web/src/test/java/org/springframework/web/client/RestClientBuilderTests.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2002-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.client;
+
+import java.lang.reflect.Field;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.http.client.ClientHttpRequestInitializer;
+import org.springframework.http.client.ClientHttpRequestInterceptor;
+import org.springframework.http.client.JettyClientHttpRequestFactory;
+import org.springframework.http.client.support.BasicAuthenticationInterceptor;
+import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.StringHttpMessageConverter;
+import org.springframework.web.util.DefaultUriBuilderFactory;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+
+/**
+ * @author Arjen Poutsma
+ */
+public class RestClientBuilderTests {
+
+	@SuppressWarnings("unchecked")
+	@Test
+	void createFromRestTemplate() throws NoSuchFieldException, IllegalAccessException {
+		JettyClientHttpRequestFactory requestFactory = new JettyClientHttpRequestFactory();
+		DefaultUriBuilderFactory uriBuilderFactory = new DefaultUriBuilderFactory();
+		ResponseErrorHandler errorHandler = new DefaultResponseErrorHandler();
+		List<HttpMessageConverter<?>> restTemplateMessageConverters = List.of(new StringHttpMessageConverter());
+		ClientHttpRequestInterceptor interceptor = new BasicAuthenticationInterceptor("foo", "bar");
+		ClientHttpRequestInitializer initializer = request -> {};
+
+		RestTemplate restTemplate = new RestTemplate(requestFactory);
+		restTemplate.setUriTemplateHandler(uriBuilderFactory);
+		restTemplate.setErrorHandler(errorHandler);
+		restTemplate.setMessageConverters(restTemplateMessageConverters);
+		restTemplate.setInterceptors(List.of(interceptor));
+		restTemplate.setClientHttpRequestInitializers(List.of(initializer));
+
+		RestClient.Builder builder = RestClient.builder(restTemplate);
+		assertThat(builder).isInstanceOf(DefaultRestClientBuilder.class);
+		DefaultRestClientBuilder defaultBuilder = (DefaultRestClientBuilder) builder;
+
+		assertThat(fieldValue("requestFactory", defaultBuilder)).isSameAs(requestFactory);
+		assertThat(fieldValue("uriBuilderFactory", defaultBuilder)).isSameAs(uriBuilderFactory);
+
+		List<StatusHandler> statusHandlers = (List<StatusHandler>) fieldValue("statusHandlers", defaultBuilder);
+		assertThat(statusHandlers).hasSize(1);
+
+		List<HttpMessageConverter<?>> restClientMessageConverters =
+				(List<HttpMessageConverter<?>>) fieldValue("messageConverters", defaultBuilder);
+		assertThat(restClientMessageConverters).containsExactlyElementsOf(restClientMessageConverters);
+
+		List<ClientHttpRequestInterceptor> interceptors =
+				(List<ClientHttpRequestInterceptor>) fieldValue("interceptors", defaultBuilder);
+		assertThat(interceptors).containsExactly(interceptor);
+
+		List<ClientHttpRequestInitializer> initializers =
+				(List<ClientHttpRequestInitializer>) fieldValue("initializers", defaultBuilder);
+		assertThat(initializers).containsExactly(initializer);
+	}
+
+	private static Object fieldValue(String name, DefaultRestClientBuilder instance)
+			throws NoSuchFieldException, IllegalAccessException {
+
+		Field field = DefaultRestClientBuilder.class.getDeclaredField(name);
+		field.setAccessible(true);
+
+		return field.get(instance);
+	}
+}