Use ByteArrayDecoder in DefaultClientResponse::createException

This commit changes DefaultClientResponse::createException to use
the ByteArrayDecoder, instead of converting to DataBuffers and
turning these into a byte array.

Closes gh-27666

Author: poutsma

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

@@ -195,13 +195,7 @@ public <T> Mono<ResponseEntity<List<T>>> toEntityList(ParameterizedTypeReference
 
 	@Override
 	public Mono<WebClientResponseException> createException() {
-		return DataBufferUtils.join(body(BodyExtractors.toDataBuffers()))
-				.map(dataBuffer -> {
-					byte[] bytes = new byte[dataBuffer.readableByteCount()];
-					dataBuffer.read(bytes);
-					DataBufferUtils.release(dataBuffer);
-					return bytes;
-				})
+		return bodyToMono(byte[].class)
 				.defaultIfEmpty(EMPTY)
 				.onErrorReturn(ex -> !(ex instanceof Error), EMPTY)
 				.map(bodyBytes -> {

spring-webflux/src/test/java/org/springframework/web/reactive/function/client/DefaultClientResponseTests.java

@@ -30,6 +30,7 @@
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.ParameterizedTypeReference;
+import org.springframework.core.codec.ByteArrayDecoder;
 import org.springframework.core.codec.StringDecoder;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DefaultDataBuffer;
@@ -48,6 +49,7 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.Assertions.entry;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
 import static org.springframework.web.reactive.function.BodyExtractors.toMono;
@@ -328,6 +330,29 @@ public void toEntityListTypeReference() {
 		assertThat(result.getHeaders().getContentType()).isEqualTo(MediaType.TEXT_PLAIN);
 	}
 
+	@Test
+	public void createException() {
+		byte[] bytes = "foo".getBytes(StandardCharsets.UTF_8);
+		DefaultDataBuffer dataBuffer = DefaultDataBufferFactory.sharedInstance.wrap(ByteBuffer.wrap(bytes));
+		Flux<DataBuffer> body = Flux.just(dataBuffer);
+		httpHeaders.setContentType(MediaType.TEXT_PLAIN);
+		given(mockResponse.getStatusCode()).willReturn(HttpStatus.NOT_FOUND);
+		given(mockResponse.getRawStatusCode()).willReturn(HttpStatus.NOT_FOUND.value());
+		given(mockResponse.getBody()).willReturn(body);
+
+		List<HttpMessageReader<?>> messageReaders = Collections.singletonList(
+				new DecoderHttpMessageReader<>(new ByteArrayDecoder()));
+		given(mockExchangeStrategies.messageReaders()).willReturn(messageReaders);
+
+		Mono<WebClientResponseException> resultMono = defaultClientResponse.createException();
+		WebClientResponseException exception = resultMono.block();
+		assertThat(exception.getStatusCode()).isEqualTo(HttpStatus.NOT_FOUND);
+		assertThat(exception.getMessage()).isEqualTo("404 Not Found");
+		assertThat(exception.getHeaders()).containsExactly(entry("Content-Type",
+				Collections.singletonList("text/plain")));
+		assertThat(exception.getResponseBodyAsByteArray()).isEqualTo(bytes);
+	}
+
 
 	private void mockTextPlainResponse(Flux<DataBuffer> body) {
 		httpHeaders.setContentType(MediaType.TEXT_PLAIN);