content-length support in EncoderHttpMessageWriter

EncoderHttpMessageWriter checks explicitly for Mono publishers and sets
the content length, if it is known for the given data item.

Issue: SPR-16542

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -55,4 +55,8 @@ 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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -56,4 +56,8 @@ 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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -62,13 +62,8 @@ public class CharSequenceEncoder extends AbstractEncoder<CharSequence> {
 			DataBufferFactory bufferFactory, ResolvableType elementType,
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
 
-		Charset charset;
-		if (mimeType != null && mimeType.getCharset() != null) {
-			charset = mimeType.getCharset();
-		}
-		else {
-			 charset = DEFAULT_CHARSET;
-		}
+		Charset charset = getCharset(mimeType);
+
 		return Flux.from(inputStream).map(charSequence -> {
 			CharBuffer charBuffer = CharBuffer.wrap(charSequence);
 			ByteBuffer byteBuffer = charset.encode(charBuffer);
@@ -76,6 +71,21 @@ public class CharSequenceEncoder extends AbstractEncoder<CharSequence> {
 		});
 	}
 
+	private Charset getCharset(@Nullable MimeType mimeType) {
+		Charset charset;
+		if (mimeType != null && mimeType.getCharset() != null) {
+			charset = mimeType.getCharset();
+		}
+		else {
+			 charset = DEFAULT_CHARSET;
+		}
+		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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -55,4 +55,8 @@ public class DataBufferEncoder extends AbstractEncoder<DataBuffer> {
 		return Flux.from(inputStream);
 	}
 
+	@Override
+	public Long getContentLength(DataBuffer dataBuffer, MimeType mimeType) {
+		return (long) dataBuffer.readableByteCount();
+	}
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -67,6 +67,17 @@ 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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -16,11 +16,14 @@
 
 package org.springframework.core.codec;
 
+import java.io.IOException;
 import java.util.Map;
+import java.util.OptionalLong;
 
 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;
@@ -68,4 +71,17 @@ 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;
+	}
+
 }