Shortcut handling of bodyToFlux(DataBuffer.class)

Given that the body is a Flux<DataBuffer> there probably could be a
Flux<DataBuffer> body();

At least bodyToFlux(DataBuffer.class) which is used when mutating and
is a common case should not incur overhead.

See gh-24680

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultClientResponse.java

@@ -30,6 +30,7 @@
 
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.codec.Hints;
+import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DataBufferUtils;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpRequest;
@@ -66,6 +67,8 @@ class DefaultClientResponse implements ClientResponse {
 
 	private final Supplier<HttpRequest> requestSupplier;
 
+	private final BodyExtractor.Context bodyExtractorContext;
+
 
 	public DefaultClientResponse(ClientHttpResponse response, ExchangeStrategies strategies,
 			String logPrefix, String requestDescription, Supplier<HttpRequest> requestSupplier) {
@@ -76,6 +79,22 @@ public DefaultClientResponse(ClientHttpResponse response, ExchangeStrategies str
 		this.logPrefix = logPrefix;
 		this.requestDescription = requestDescription;
 		this.requestSupplier = requestSupplier;
+		this.bodyExtractorContext = new BodyExtractor.Context() {
+			@Override
+			public List<HttpMessageReader<?>> messageReaders() {
+				return strategies.messageReaders();
+			}
+
+			@Override
+			public Optional<ServerHttpResponse> serverResponse() {
+				return Optional.empty();
+			}
+
+			@Override
+			public Map<String, Object> hints() {
+				return Hints.from(Hints.LOG_PREFIX_HINT, logPrefix);
+			}
+		};
 	}
 
 
@@ -107,22 +126,7 @@ public MultiValueMap<String, ResponseCookie> cookies() {
 	@SuppressWarnings("unchecked")
 	@Override
 	public <T> T body(BodyExtractor<T, ? super ClientHttpResponse> extractor) {
-		T result = extractor.extract(this.response, new BodyExtractor.Context() {
-			@Override
-			public List<HttpMessageReader<?>> messageReaders() {
-				return strategies.messageReaders();
-			}
-
-			@Override
-			public Optional<ServerHttpResponse> serverResponse() {
-				return Optional.empty();
-			}
-
-			@Override
-			public Map<String, Object> hints() {
-				return Hints.from(Hints.LOG_PREFIX_HINT, logPrefix);
-			}
-		});
+		T result = extractor.extract(this.response, this.bodyExtractorContext);
 		String description = "Body from " + this.requestDescription + " [DefaultClientResponse]";
 		if (result instanceof Mono) {
 			return (T) ((Mono<?>) result).checkpoint(description);
@@ -146,8 +150,10 @@ public <T> Mono<T> bodyToMono(ParameterizedTypeReference<T> elementTypeRef) {
 	}
 
 	@Override
+	@SuppressWarnings("unchecked")
 	public <T> Flux<T> bodyToFlux(Class<? extends T> elementClass) {
-		return body(BodyExtractors.toFlux(elementClass));
+		return elementClass.equals(DataBuffer.class) ?
+				(Flux<T>) body(BodyExtractors.toDataBuffers()) : body(BodyExtractors.toFlux(elementClass));
 	}
 
 	@Override

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultServerRequest.java

@@ -36,6 +36,7 @@
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.codec.DecodingException;
 import org.springframework.core.codec.Hints;
+import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.http.HttpCookie;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpRange;
@@ -195,8 +196,10 @@ public <T> Mono<T> bodyToMono(ParameterizedTypeReference<T> typeReference) {
 	}
 
 	@Override
+	@SuppressWarnings("unchecked")
 	public <T> Flux<T> bodyToFlux(Class<? extends T> elementClass) {
-		Flux<T> flux = body(BodyExtractors.toFlux(elementClass));
+		Flux<T> flux = (elementClass.equals(DataBuffer.class) ?
+				(Flux<T>) request().getBody() : body(BodyExtractors.toFlux(elementClass)));
 		return flux.onErrorMap(UnsupportedMediaTypeException.class, ERROR_MAPPER)
 				.onErrorMap(DecodingException.class, DECODING_MAPPER);
 	}