Eliminate the need for Encoder#getContentLength

Issue: SPR-16892

spring-core/src/main/java/org/springframework/core/codec/ByteArrayEncoder.java

@@ -55,8 +55,4 @@ public class ByteArrayEncoder extends AbstractEncoder<byte[]> {
 		return Flux.from(inputStream).map(bufferFactory::wrap);
 	}
 
-	@Override
-	public Long getContentLength(byte[] bytes, @Nullable MimeType mimeType) {
-		return (long) bytes.length;
-	}
 }

spring-core/src/main/java/org/springframework/core/codec/ByteBufferEncoder.java

@@ -56,8 +56,4 @@ public class ByteBufferEncoder extends AbstractEncoder<ByteBuffer> {
 		return Flux.from(inputStream).map(bufferFactory::wrap);
 	}
 
-	@Override
-	public Long getContentLength(ByteBuffer byteBuffer, @Nullable MimeType mimeType) {
-		return (long) byteBuffer.array().length;
-	}
 }

spring-core/src/main/java/org/springframework/core/codec/CharSequenceEncoder.java

@@ -82,11 +82,6 @@ public class CharSequenceEncoder extends AbstractEncoder<CharSequence> {
 		return charset;
 	}
 
-	@Override
-	public Long getContentLength(CharSequence data, @Nullable MimeType mimeType) {
-		return (long) data.toString().getBytes(getCharset(mimeType)).length;
-	}
-
 	/**
 	 * Create a {@code CharSequenceEncoder} that supports only "text/plain".
 	 */

spring-core/src/main/java/org/springframework/core/codec/DataBufferEncoder.java

@@ -55,9 +55,4 @@ public class DataBufferEncoder extends AbstractEncoder<DataBuffer> {
 		return Flux.from(inputStream);
 	}
 
-	@Override
-	public Long getContentLength(DataBuffer dataBuffer, @Nullable MimeType mimeType) {
-		return (long) dataBuffer.readableByteCount();
-	}
-
 }

spring-core/src/main/java/org/springframework/core/codec/Encoder.java

@@ -67,17 +67,6 @@ public interface Encoder<T> {
 	Flux<DataBuffer> encode(Publisher<? extends T> inputStream, DataBufferFactory bufferFactory,
 			ResolvableType elementType, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints);
 
-	/**
-	 * Return the length for the given item, if known.
-	 * @param t the item to check
-	 * @return the length in bytes, or {@code null} if not known.
-	 * @since 5.0.5
-	 */
-	@Nullable
-	default Long getContentLength(T t, @Nullable MimeType mimeType) {
-		return null;
-	}
-
 	/**
 	 * Return the list of mime types this encoder supports.
 	 */

spring-core/src/main/java/org/springframework/core/codec/ResourceEncoder.java

@@ -16,13 +16,11 @@
 
 package org.springframework.core.codec;
 
-import java.io.IOException;
 import java.util.Map;
 
 import reactor.core.publisher.Flux;
 
 import org.springframework.core.ResolvableType;
-import org.springframework.core.io.InputStreamResource;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DataBufferFactory;
@@ -70,17 +68,4 @@ public class ResourceEncoder extends AbstractSingleValueEncoder<Resource> {
 		return DataBufferUtils.read(resource, dataBufferFactory, this.bufferSize);
 	}
 
-	@Override
-	public Long getContentLength(Resource resource, @Nullable MimeType mimeType) {
-		// Don't consume InputStream...
-		if (InputStreamResource.class != resource.getClass()) {
-			try {
-				return resource.contentLength();
-			}
-			catch (IOException ignored) {
-			}
-		}
-		return null;
-	}
-
 }

spring-web/src/main/java/org/springframework/http/codec/EncoderHttpMessageWriter.java

@@ -28,6 +28,7 @@ import reactor.core.publisher.Mono;
 import org.springframework.core.ResolvableType;
 import org.springframework.core.codec.Encoder;
 import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DataBufferFactory;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.MediaType;
 import org.springframework.http.ReactiveHttpOutputMessage;
@@ -98,23 +99,18 @@ public class EncoderHttpMessageWriter<T> implements HttpMessageWriter<T> {
 			@Nullable MediaType mediaType, ReactiveHttpOutputMessage message, Map<String, Object> hints) {
 
 		MediaType contentType = updateContentType(message, mediaType);
-		HttpHeaders headers = message.getHeaders();
-
-		if (headers.getContentLength() < 0 && !headers.containsKey(HttpHeaders.TRANSFER_ENCODING)) {
-			if (inputStream instanceof Mono) {
-				// This works because we don't actually commit until after the first signal...
-				inputStream = ((Mono<T>) inputStream).doOnNext(data -> {
-					Long contentLength = this.encoder.getContentLength(data, contentType);
-					if (contentLength != null) {
-						headers.setContentLength(contentLength);
-					}
-				});
-			}
-		}
 
 		Flux<DataBuffer> body = this.encoder.encode(
 				inputStream, message.bufferFactory(), elementType, contentType, hints);
 
+		// Response is not committed until the first signal...
+		if (inputStream instanceof Mono) {
+			HttpHeaders headers = message.getHeaders();
+			if (headers.getContentLength() < 0 && !headers.containsKey(HttpHeaders.TRANSFER_ENCODING)) {
+				body = body.doOnNext(data -> headers.setContentLength(data.readableByteCount()));
+			}
+		}
+
 		return (isStreamingMediaType(contentType) ?
 				message.writeAndFlushWith(body.map(Flux::just)) : message.writeWith(body));
 	}

spring-web/src/main/java/org/springframework/http/codec/ResourceHttpMessageWriter.java

@@ -31,6 +31,7 @@ import org.springframework.core.ResolvableType;
 import org.springframework.core.codec.ResourceDecoder;
 import org.springframework.core.codec.ResourceEncoder;
 import org.springframework.core.codec.ResourceRegionEncoder;
+import org.springframework.core.io.InputStreamResource;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DataBufferFactory;
@@ -119,9 +120,9 @@ public class ResourceHttpMessageWriter implements HttpMessageWriter<Resource> {
 		headers.setContentType(resourceMediaType);
 
 		if (headers.getContentLength() < 0) {
-			Long contentLength = this.encoder.getContentLength(resource, mediaType);
-			if (contentLength != null) {
-				headers.setContentLength(contentLength);
+			long length = lengthOf(resource);
+			if (length != -1) {
+				headers.setContentLength(length);
 			}
 		}
 
@@ -141,6 +142,18 @@ public class ResourceHttpMessageWriter implements HttpMessageWriter<Resource> {
 		return MediaTypeFactory.getMediaType(resource).orElse(MediaType.APPLICATION_OCTET_STREAM);
 	}
 
+	private static long lengthOf(Resource resource) {
+		// Don't consume InputStream...
+		if (InputStreamResource.class != resource.getClass()) {
+			try {
+				return resource.contentLength();
+			}
+			catch (IOException ignored) {
+			}
+		}
+		return -1;
+	}
+
 	private static Optional<Mono<Void>> zeroCopy(Resource resource, @Nullable ResourceRegion region,
 			ReactiveHttpOutputMessage message) {
 
@@ -192,8 +205,8 @@ public class ResourceHttpMessageWriter implements HttpMessageWriter<Resource> {
 			if (regions.size() == 1){
 				ResourceRegion region = regions.get(0);
 				headers.setContentType(resourceMediaType);
-				Long contentLength = this.encoder.getContentLength(resource, mediaType);
-				if (contentLength != null) {
+				long contentLength = lengthOf(resource);
+				if (contentLength != -1) {
 					long start = region.getPosition();
 					long end = start + region.getCount() - 1;
 					end = Math.min(end, contentLength - 1);

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/RequestMappingMessageConversionIntegrationTests.java

@@ -128,45 +128,59 @@ public class RequestMappingMessageConversionIntegrationTests extends AbstractReq
 	@Test
 	public void personResponseBody() throws Exception {
 		Person expected = new Person("Robert");
-		assertEquals(expected, performGet("/person-response/person", JSON, Person.class).getBody());
+		ResponseEntity<Person> responseEntity = performGet("/person-response/person", JSON, Person.class);
+		assertEquals(17, responseEntity.getHeaders().getContentLength());
+		assertEquals(expected, responseEntity.getBody());
 	}
 
 	@Test
 	public void personResponseBodyWithCompletableFuture() throws Exception {
 		Person expected = new Person("Robert");
-		assertEquals(expected, performGet("/person-response/completable-future", JSON, Person.class).getBody());
+		ResponseEntity<Person> responseEntity = performGet("/person-response/completable-future", JSON, Person.class);
+		assertEquals(17, responseEntity.getHeaders().getContentLength());
+		assertEquals(expected, responseEntity.getBody());
 	}
 
 	@Test
 	public void personResponseBodyWithMono() throws Exception {
 		Person expected = new Person("Robert");
-		assertEquals(expected, performGet("/person-response/mono", JSON, Person.class).getBody());
+		ResponseEntity<Person> responseEntity = performGet("/person-response/mono", JSON, Person.class);
+		assertEquals(17, responseEntity.getHeaders().getContentLength());
+		assertEquals(expected, responseEntity.getBody());
 	}
 
 	@Test
 	public void personResponseBodyWithMonoDeclaredAsObject() throws Exception {
 		Person expected = new Person("Robert");
-		assertEquals(expected, performGet("/person-response/mono-declared-as-object", JSON, Person.class).getBody());
+		ResponseEntity<Person> entity = performGet("/person-response/mono-declared-as-object", JSON, Person.class);
+		assertEquals(17, entity.getHeaders().getContentLength());
+		assertEquals(expected, entity.getBody());
 	}
 
 	@Test
 	public void personResponseBodyWithSingle() throws Exception {
 		Person expected = new Person("Robert");
-		assertEquals(expected, performGet("/person-response/single", JSON, Person.class).getBody());
+		ResponseEntity<Person> entity = performGet("/person-response/single", JSON, Person.class);
+		assertEquals(17, entity.getHeaders().getContentLength());
+		assertEquals(expected, entity.getBody());
 	}
 
 	@Test
 	public void personResponseBodyWithMonoResponseEntity() throws Exception {
 		Person expected = new Person("Robert");
-		assertEquals(expected, performGet("/person-response/mono-response-entity", JSON, Person.class).getBody());
+		ResponseEntity<Person> entity = performGet("/person-response/mono-response-entity", JSON, Person.class);
+		assertEquals(17, entity.getHeaders().getContentLength());
+		assertEquals(expected, entity.getBody());
 	}
 
 	@Test // SPR-16172
 	public void personResponseBodyWithMonoResponseEntityXml() throws Exception {
 
-		String actual = performGet("/person-response/mono-response-entity-xml",
-				new HttpHeaders(), String.class).getBody();
+		String url = "/person-response/mono-response-entity-xml";
+		ResponseEntity<String> entity = performGet(url, new HttpHeaders(), String.class);
+		String actual = entity.getBody();
 
+		assertEquals(91, entity.getHeaders().getContentLength());
 		assertEquals("<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?>" +
 				"<person><name>Robert</name></person>", actual);
 	}
@@ -174,13 +188,17 @@ public class RequestMappingMessageConversionIntegrationTests extends AbstractReq
 	@Test
 	public void personResponseBodyWithList() throws Exception {
 		List<?> expected = asList(new Person("Robert"), new Person("Marie"));
-		assertEquals(expected, performGet("/person-response/list", JSON, PERSON_LIST).getBody());
+		ResponseEntity<List<Person>> entity = performGet("/person-response/list", JSON, PERSON_LIST);
+		assertEquals(36, entity.getHeaders().getContentLength());
+		assertEquals(expected, entity.getBody());
 	}
 
 	@Test
 	public void personResponseBodyWithPublisher() throws Exception {
 		List<?> expected = asList(new Person("Robert"), new Person("Marie"));
-		assertEquals(expected, performGet("/person-response/publisher", JSON, PERSON_LIST).getBody());
+		ResponseEntity<List<Person>> entity = performGet("/person-response/publisher", JSON, PERSON_LIST);
+		assertEquals(-1, entity.getHeaders().getContentLength());
+		assertEquals(expected, entity.getBody());
 	}
 
 	@Test