Allow repeatable writes in StreamingHttpOutputMessage

This commit adds a repeatable property to
StreamingHttpOutputMessage.Body, indicating that the body can be written
 multiple times. In HttpComponentsClientHttpRequest, this property is
 exposed via org.apache.hc.core5.http.HttpEntity.isRepeatable, to allow
 for redirects.

Closes gh-31449

spring-web/src/main/java/org/springframework/http/StreamingHttpOutputMessage.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -50,6 +50,18 @@ public interface StreamingHttpOutputMessage extends HttpOutputMessage {
 		 * @throws IOException in case of I/O errors
 		 */
 		void writeTo(OutputStream outputStream) throws IOException;
+
+		/**
+		 * Indicates whether this body is capable of
+		 * {@linkplain #writeTo(OutputStream) writing its data} more than
+		 * once. Default implementation returns {@code false}.
+		 * @return {@code true} if this body can be written repeatedly,
+		 * {@code false} otherwise
+		 * @since 6.1
+		 */
+		default boolean repeatable() {
+			return false;
+		}
 	}
 
 }

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

@@ -17,6 +17,7 @@
 package org.springframework.http.client;
 
 import java.io.IOException;
+import java.io.OutputStream;
 import java.net.URI;
 
 import org.springframework.http.HttpHeaders;
@@ -55,7 +56,17 @@ final class BufferingClientHttpRequestWrapper extends AbstractBufferingClientHtt
 		this.request.getHeaders().putAll(headers);
 
 		if (this.request instanceof StreamingHttpOutputMessage streamingHttpOutputMessage) {
-			streamingHttpOutputMessage.setBody(outputStream -> StreamUtils.copy(bufferedOutput, outputStream));
+			streamingHttpOutputMessage.setBody(new StreamingHttpOutputMessage.Body() {
+				@Override
+				public void writeTo(OutputStream outputStream) throws IOException {
+					StreamUtils.copy(bufferedOutput, outputStream);
+				}
+
+				@Override
+				public boolean repeatable() {
+					return true;
+				}
+			});
 		}
 		else {
 			StreamUtils.copy(bufferedOutput, this.request.getBody());

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

@@ -153,12 +153,12 @@ final class HttpComponentsClientHttpRequest extends AbstractStreamingClientHttpR
 
 		@Override
 		public boolean isRepeatable() {
-			return false;
+			return this.body.repeatable();
 		}
 
 		@Override
 		public boolean isStreaming() {
-			return true;
+			return false;
 		}
 
 		@Override