Merge branch '6.2.x'

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

@@ -477,7 +477,14 @@ final class DefaultRestClient implements RestClient {
 
 		@Override
 		public RequestBodySpec body(StreamingHttpOutputMessage.Body body) {
-			this.body = request -> body.writeTo(request.getBody());
+			this.body = request -> {
+				if (request instanceof StreamingHttpOutputMessage streamingMessage) {
+					streamingMessage.setBody(body);
+				}
+				else {
+					body.writeTo(request.getBody());
+				}
+			};
 			return this;
 		}
 

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

@@ -16,6 +16,7 @@
 
 package org.springframework.web.client;
 
+import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
@@ -44,6 +45,7 @@ import org.springframework.http.HttpStatus;
 import org.springframework.http.HttpStatusCode;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
+import org.springframework.http.StreamingHttpOutputMessage;
 import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.http.client.ClientHttpRequestInterceptor;
 import org.springframework.http.client.ClientHttpResponse;
@@ -53,6 +55,7 @@ import org.springframework.http.client.JettyClientHttpRequestFactory;
 import org.springframework.http.client.ReactorClientHttpRequestFactory;
 import org.springframework.http.client.SimpleClientHttpRequestFactory;
 import org.springframework.util.CollectionUtils;
+import org.springframework.util.FastByteArrayOutputStream;
 import org.springframework.util.FileCopyUtils;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -602,6 +605,30 @@ class RestClientIntegrationTests {
 		});
 	}
 
+	@ParameterizedRestClientTest // gh-35102
+	void postStreamingBody(ClientHttpRequestFactory requestFactory) {
+		startServer(requestFactory);
+		prepareResponse(response -> response.setResponseCode(200));
+
+		StreamingHttpOutputMessage.Body testBody = out -> {
+			assertThat(out).as("Not a streaming response").isNotInstanceOf(FastByteArrayOutputStream.class);
+			new ByteArrayInputStream("test-data".getBytes(UTF_8)).transferTo(out);
+		};
+
+		ResponseEntity<Void> result = this.restClient.post()
+				.uri("/streaming/body")
+				.body(testBody)
+				.retrieve()
+				.toBodilessEntity();
+
+		assertThat(result.getStatusCode()).isEqualTo(HttpStatus.OK);
+
+		expectRequestCount(1);
+		expectRequest(request -> {
+			assertThat(request.getPath()).isEqualTo("/streaming/body");
+			assertThat(request.getBody().readUtf8()).isEqualTo("test-data");
+		});
+	}
 
 	@ParameterizedRestClientTest
 	void statusHandler(ClientHttpRequestFactory requestFactory) {