Use Jackson SequenceWriter for streaming

Before this commit, the AbstractJackson2Encoder instantiated a
ObjectWriter per value. This is not an issue for single values or
non-streaming scenarios (which effectively are the same, because in the
latter values are collected into a list until offered to Jackson).
However, this does create a problem for SMILE, because it allows for
shared references that do not match up when writing each value with a
new ObjectWriter, resulting in errors parsing the result.

This commit uses Jackson's SequenceWriter for streaming scenarios,
allowing Jackson to reuse the same context for writing multiple values,
fixing the issue described above.

Closes gh-24198

Author: poutsma

spring-web/src/main/java/org/springframework/http/codec/json/AbstractJackson2Encoder.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.
@@ -17,7 +17,6 @@
 package org.springframework.http.codec.json;
 
 import java.io.IOException;
-import java.io.OutputStream;
 import java.lang.annotation.Annotation;
 import java.nio.charset.Charset;
 import java.util.ArrayList;
@@ -29,9 +28,11 @@
 import com.fasterxml.jackson.core.JsonEncoding;
 import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.core.util.ByteArrayBuilder;
 import com.fasterxml.jackson.databind.JavaType;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.ObjectWriter;
+import com.fasterxml.jackson.databind.SequenceWriter;
 import com.fasterxml.jackson.databind.exc.InvalidDefinitionException;
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
@@ -44,7 +45,6 @@
 import org.springframework.core.codec.Hints;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DataBufferFactory;
-import org.springframework.core.io.buffer.DataBufferUtils;
 import org.springframework.core.log.LogFormatUtils;
 import org.springframework.http.MediaType;
 import org.springframework.http.codec.HttpMessageEncoder;
@@ -115,65 +115,53 @@ public Flux<DataBuffer> encode(Publisher<?> inputStream, DataBufferFactory buffe
 		Assert.notNull(bufferFactory, "'bufferFactory' must not be null");
 		Assert.notNull(elementType, "'elementType' must not be null");
 
-		JsonEncoding encoding = getJsonEncoding(mimeType);
-
 		if (inputStream instanceof Mono) {
-			return Mono.from(inputStream).map(value ->
-					encodeValue(value, mimeType, bufferFactory, elementType, hints, encoding)).flux();
+			return Mono.from(inputStream)
+					.map(value -> encodeValue(value, bufferFactory, elementType, mimeType, hints))
+					.flux();
 		}
 		else {
-			return this.streamingMediaTypes.stream()
-					.filter(mediaType -> mediaType.isCompatibleWith(mimeType))
-					.findFirst()
-					.map(mediaType -> {
-						byte[] separator = STREAM_SEPARATORS.getOrDefault(mediaType, NEWLINE_SEPARATOR);
-						return Flux.from(inputStream).map(value -> {
-							DataBuffer buffer = encodeValue(
-									value, mimeType, bufferFactory, elementType, hints, encoding);
-							if (separator != null) {
-								buffer.write(separator);
-							}
-							return buffer;
-						});
-					})
-					.orElseGet(() -> {
-						ResolvableType listType = ResolvableType.forClassWithGenerics(List.class, elementType);
-						return Flux.from(inputStream).collectList().map(list ->
-								encodeValue(list, mimeType, bufferFactory, listType, hints, encoding)).flux();
-					});
-		}
-	}
-
-	private DataBuffer encodeValue(Object value, @Nullable MimeType mimeType, DataBufferFactory bufferFactory,
-			ResolvableType elementType, @Nullable Map<String, Object> hints, JsonEncoding encoding) {
+			byte[] separator = streamSeparator(mimeType);
+			if (separator != null) { // streaming
+				try {
+					ObjectWriter writer = createObjectWriter(elementType, mimeType, hints);
+					ByteArrayBuilder byteBuilder = new ByteArrayBuilder(writer.getFactory()._getBufferRecycler());
+					JsonEncoding encoding = getJsonEncoding(mimeType);
+					JsonGenerator generator = getObjectMapper().getFactory().createGenerator(byteBuilder, encoding);
+					SequenceWriter sequenceWriter = writer.writeValues(generator);
+
+					return Flux.from(inputStream)
+							.map(value -> encodeStreamingValue(value, bufferFactory, hints, sequenceWriter, byteBuilder,
+									separator));
+				}
+				catch (IOException ex) {
+					return Flux.error(ex);
+				}
+			}
+			else { // non-streaming
+				ResolvableType listType = ResolvableType.forClassWithGenerics(List.class, elementType);
+				return Flux.from(inputStream)
+						.collectList()
+						.map(list -> encodeValue(list, bufferFactory, listType, mimeType, hints))
+						.flux();
+			}
 
-		if (!Hints.isLoggingSuppressed(hints)) {
-			LogFormatUtils.traceDebug(logger, traceOn -> {
-				String formatted = LogFormatUtils.formatValue(value, !traceOn);
-				return Hints.getLogPrefix(hints) + "Encoding [" + formatted + "]";
-			});
 		}
+	}
 
-		JavaType javaType = getJavaType(elementType.getType(), null);
-		Class<?> jsonView = (hints != null ? (Class<?>) hints.get(Jackson2CodecSupport.JSON_VIEW_HINT) : null);
-		ObjectWriter writer = (jsonView != null ?
-				getObjectMapper().writerWithView(jsonView) : getObjectMapper().writer());
+	public DataBuffer encodeValue(Object value, DataBufferFactory bufferFactory,
+			ResolvableType valueType, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
 
-		if (javaType.isContainerType()) {
-			writer = writer.forType(javaType);
-		}
-
-		writer = customizeWriter(writer, mimeType, elementType, hints);
+		ObjectWriter writer = createObjectWriter(valueType, mimeType, hints);
+		ByteArrayBuilder byteBuilder = new ByteArrayBuilder(writer.getFactory()._getBufferRecycler());
+		JsonEncoding encoding = getJsonEncoding(mimeType);
 
-		DataBuffer buffer = bufferFactory.allocateBuffer();
-		boolean release = true;
-		OutputStream outputStream = buffer.asOutputStream();
+		logValue(hints, value);
 
 		try {
-			JsonGenerator generator = getObjectMapper().getFactory().createGenerator(outputStream, encoding);
+			JsonGenerator generator = getObjectMapper().getFactory().createGenerator(byteBuilder, encoding);
 			writer.writeValue(generator, value);
 			generator.flush();
-			release = false;
 		}
 		catch (InvalidDefinitionException ex) {
 			throw new CodecException("Type definition error: " + ex.getType(), ex);
@@ -182,24 +170,97 @@ private DataBuffer encodeValue(Object value, @Nullable MimeType mimeType, DataBu
 			throw new EncodingException("JSON encoding error: " + ex.getOriginalMessage(), ex);
 		}
 		catch (IOException ex) {
-			throw new IllegalStateException("Unexpected I/O error while writing to data buffer",
+			throw new IllegalStateException("Unexpected I/O error while writing to byte array builder",
 					ex);
 		}
-		finally {
-			if (release) {
-				DataBufferUtils.release(buffer);
-			}
+
+		byte[] bytes = byteBuilder.toByteArray();
+		DataBuffer buffer = bufferFactory.allocateBuffer(bytes.length);
+		buffer.write(bytes);
+
+		return buffer;
+	}
+
+	private DataBuffer encodeStreamingValue(Object value, DataBufferFactory bufferFactory, @Nullable Map<String, Object> hints,
+			SequenceWriter sequenceWriter, ByteArrayBuilder byteArrayBuilder, byte[] separator) {
+
+		logValue(hints, value);
+
+		try {
+			sequenceWriter.write(value);
+			sequenceWriter.flush();
 		}
+		catch (InvalidDefinitionException ex) {
+			throw new CodecException("Type definition error: " + ex.getType(), ex);
+		}
+		catch (JsonProcessingException ex) {
+			throw new EncodingException("JSON encoding error: " + ex.getOriginalMessage(), ex);
+		}
+		catch (IOException ex) {
+			throw new IllegalStateException("Unexpected I/O error while writing to byte array builder",
+					ex);
+		}
+
+		byte[] bytes = byteArrayBuilder.toByteArray();
+		byteArrayBuilder.reset();
+
+		int offset;
+		int length;
+		if (bytes.length > 0 && bytes[0] == ' ') {
+			// SequenceWriter writes an unnecessary space in between values
+			offset = 1;
+			length = bytes.length - 1;
+		}
+		else {
+			offset = 0;
+			length = bytes.length;
+		}
+		DataBuffer buffer = bufferFactory.allocateBuffer(length + separator.length);
+		buffer.write(bytes, offset, length);
+		buffer.write(separator);
 
 		return buffer;
 	}
 
+	private void logValue(@Nullable Map<String, Object> hints, Object value) {
+		if (!Hints.isLoggingSuppressed(hints)) {
+			LogFormatUtils.traceDebug(logger, traceOn -> {
+				String formatted = LogFormatUtils.formatValue(value, !traceOn);
+				return Hints.getLogPrefix(hints) + "Encoding [" + formatted + "]";
+			});
+		}
+	}
+
+	private ObjectWriter createObjectWriter(ResolvableType valueType, @Nullable MimeType mimeType,
+			@Nullable Map<String, Object> hints) {
+		JavaType javaType = getJavaType(valueType.getType(), null);
+		Class<?> jsonView = (hints != null ? (Class<?>) hints.get(Jackson2CodecSupport.JSON_VIEW_HINT) : null);
+		ObjectWriter writer = (jsonView != null ?
+				getObjectMapper().writerWithView(jsonView) : getObjectMapper().writer());
+
+		if (javaType.isContainerType()) {
+			writer = writer.forType(javaType);
+		}
+
+		return customizeWriter(writer, mimeType, valueType, hints);
+	}
+
 	protected ObjectWriter customizeWriter(ObjectWriter writer, @Nullable MimeType mimeType,
 			ResolvableType elementType, @Nullable Map<String, Object> hints) {
 
 		return writer;
 	}
 
+	@Nullable
+	private byte[] streamSeparator(@Nullable MimeType mimeType) {
+		for (MediaType streamingMediaType : this.streamingMediaTypes) {
+			if (streamingMediaType.isCompatibleWith(mimeType)) {
+				return STREAM_SEPARATORS.getOrDefault(streamingMediaType, NEWLINE_SEPARATOR);
+			}
+		}
+		return null;
+	}
+
 	/**
 	 * Determine the JSON encoding to use for the given mime type.
 	 * @param mimeType the mime type as requested by the caller

spring-web/src/test/java/org/springframework/http/codec/json/Jackson2SmileEncoderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -20,23 +20,26 @@
 import java.io.UncheckedIOException;
 import java.util.Arrays;
 import java.util.List;
-import java.util.function.Consumer;
 
+import com.fasterxml.jackson.databind.MappingIterator;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import org.junit.Test;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
 
 import org.springframework.core.ResolvableType;
 import org.springframework.core.codec.AbstractEncoderTestCase;
 import org.springframework.core.io.buffer.DataBuffer;
-import org.springframework.core.io.buffer.support.DataBufferTestUtils;
+import org.springframework.core.io.buffer.DataBufferUtils;
 import org.springframework.http.codec.Pojo;
 import org.springframework.http.codec.ServerSentEvent;
 import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
 import org.springframework.util.MimeType;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
 import static org.springframework.core.io.buffer.DataBufferUtils.release;
 import static org.springframework.http.MediaType.APPLICATION_XML;
 
@@ -59,21 +62,6 @@ public Jackson2SmileEncoderTests() {
 
 	}
 
-	public Consumer<DataBuffer> pojoConsumer(Pojo expected) {
-		return dataBuffer -> {
-			try {
-				Pojo actual = this.mapper.reader().forType(Pojo.class)
-						.readValue(DataBufferTestUtils.dumpBytes(dataBuffer));
-				assertEquals(expected, actual);
-				release(dataBuffer);
-			}
-			catch (IOException ex) {
-				throw new UncheckedIOException(ex);
-			}
-		};
-	}
-
-
 	@Override
 	@Test
 	public void canEncode() {
@@ -106,7 +94,19 @@ public void encode() {
 		Flux<Pojo> input = Flux.fromIterable(list);
 
 		testEncode(input, Pojo.class, step -> step
-				.consumeNextWith(expect(list, List.class)));
+				.consumeNextWith(dataBuffer -> {
+					try {
+						Object actual = this.mapper.reader().forType(List.class)
+								.readValue(dataBuffer.asInputStream());
+						assertEquals(list, actual);
+					}
+					catch (IOException e) {
+						throw new UncheckedIOException(e);
+					}
+					finally {
+						release(dataBuffer);
+					}
+				}));
 	}
 
 	@Test
@@ -127,32 +127,30 @@ public void encodeAsStream() throws Exception {
 		Flux<Pojo> input = Flux.just(pojo1, pojo2, pojo3);
 		ResolvableType type = ResolvableType.forClass(Pojo.class);
 
-		testEncodeAll(input, type, step -> step
-				.consumeNextWith(expect(pojo1, Pojo.class))
-				.consumeNextWith(expect(pojo2, Pojo.class))
-				.consumeNextWith(expect(pojo3, Pojo.class))
-				.verifyComplete(),
-		STREAM_SMILE_MIME_TYPE, null);
+		Flux<DataBuffer> result = this.encoder
+				.encode(input, bufferFactory, type, STREAM_SMILE_MIME_TYPE, null);
+
+		Mono<MappingIterator<Pojo>> joined = DataBufferUtils.join(result)
+				.map(buffer -> {
+					try {
+						return this.mapper.reader().forType(Pojo.class).readValues(buffer.asInputStream(true));
+					}
+					catch (IOException ex) {
+						throw new UncheckedIOException(ex);
+					}
+				});
+
+		StepVerifier.create(joined)
+				.assertNext(iter -> {
+					assertTrue(iter.hasNext());
+					assertEquals(pojo1, iter.next());
+					assertTrue(iter.hasNext());
+					assertEquals(pojo2, iter.next());
+					assertTrue(iter.hasNext());
+					assertEquals(pojo3, iter.next());
+					assertFalse(iter.hasNext());
+				})
+				.verifyComplete();
 	}
 
-
-	private <T> Consumer<DataBuffer> expect(T expected, Class<T> expectedType) {
-		return dataBuffer -> {
-			try {
-				Object actual = this.mapper.reader().forType(expectedType)
-						.readValue(dataBuffer.asInputStream());
-				assertEquals(expected, actual);
-			}
-			catch (IOException e) {
-				throw new UncheckedIOException(e);
-			}
-			finally {
-				release(dataBuffer);
-			}
-		};
-
-	}
-
-
-
 }