HttpHeaderResponseDecorator checks for "Transfer-Encoding"

This commit extends the fix from b86c11cc9b
by checking for both existing Content-Length and Transfer-Encoding.

Closes gh-25908

spring-web/src/main/java/org/springframework/http/server/reactive/HttpHeadResponseDecorator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -16,8 +16,6 @@
 
 package org.springframework.http.server.reactive;
 
-import java.util.function.BiFunction;
-
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -41,24 +39,30 @@ public class HttpHeadResponseDecorator extends ServerHttpResponseDecorator {
 
 
 	/**
-	 * Apply {@link Flux#reduce(Object, BiFunction) reduce} on the body, count
-	 * the number of bytes produced, release data buffers without writing, and
-	 * set the {@literal Content-Length} header.
+	 * Consume and release the body without writing.
+	 * <p>If the headers contain neither Content-Length nor Transfer-Encoding,
+	 * count the bytes and set Content-Length.
 	 */
 	@Override
 	public final Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
-		return Flux.from(body)
-				.reduce(0, (current, buffer) -> {
-					int next = current + buffer.readableByteCount();
-					DataBufferUtils.release(buffer);
-					return next;
-				})
-				.doOnNext(length -> {
-					if (length > 0 || getHeaders().getFirst(HttpHeaders.CONTENT_LENGTH) == null) {
-						getHeaders().setContentLength(length);
-					}
-				})
-				.then();
+		if (shouldSetContentLength()) {
+			return Flux.from(body)
+					.reduce(0, (current, buffer) -> {
+						int next = current + buffer.readableByteCount();
+						DataBufferUtils.release(buffer);
+						return next;
+					})
+					.doOnNext(length -> getHeaders().setContentLength(length))
+					.then();
+		}
+		else {
+			return Flux.from(body).then();
+		}
+	}
+
+	private boolean shouldSetContentLength() {
+		return (getHeaders().getFirst(HttpHeaders.CONTENT_LENGTH) == null &&
+				getHeaders().getFirst(HttpHeaders.TRANSFER_ENCODING) == null);
 	}
 
 	/**

spring-web/src/test/java/org/springframework/http/server/reactive/HttpHeadResponseDecoratorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -25,6 +25,7 @@ import reactor.core.publisher.Flux;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.NettyDataBufferFactory;
 import org.springframework.core.testfixture.io.buffer.LeakAwareDataBufferFactory;
+import org.springframework.http.HttpHeaders;
 import org.springframework.web.testfixture.http.server.reactive.MockServerHttpResponse;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -63,6 +64,12 @@ public class HttpHeadResponseDecoratorTests {
 		assertThat(this.response.getHeaders().getContentLength()).isEqualTo(length);
 	}
 
+	@Test // gh-25908
+	public void writeWithGivenTransferEncoding() {
+		this.response.getHeaders().add(HttpHeaders.TRANSFER_ENCODING, "chunked");
+		this.response.writeWith(Flux.empty()).block();
+		assertThat(this.response.getHeaders().getContentLength()).isEqualTo(-1);
+	}
 
 	private DataBuffer toDataBuffer(String s) {
 		DataBuffer buffer = this.bufferFactory.allocateBuffer();