Refactoring external contribution

Created abstract CharSequence decoder, which is extended by
StringDecoder and CharBufferDecoder.

See gh-29741

Author: poutsma

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

@@ -0,0 +1,205 @@
+/*
+ * Copyright 2002-2023 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.codec;
+
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import org.springframework.core.ResolvableType;
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DataBufferUtils;
+import org.springframework.core.io.buffer.LimitedDataBufferList;
+import org.springframework.core.log.LogFormatUtils;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+import org.springframework.util.MimeType;
+
+/**
+ * Abstract base class that decodes from a data buffer stream to a
+ * {@code CharSequence} stream.
+ *
+ * @author Arjen Poutsma
+ * @since 6.1
+ * @param <T> the character sequence type
+ */
+public abstract class AbstractCharSequenceDecoder<T extends CharSequence> extends AbstractDataBufferDecoder<T> {
+
+	/** The default charset to use, i.e. "UTF-8". */
+	public static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8;
+
+	/** The default delimiter strings to use, i.e. {@code \r\n} and {@code \n}. */
+	public static final List<String> DEFAULT_DELIMITERS = List.of("\r\n", "\n");
+
+
+	private final List<String> delimiters;
+
+	private final boolean stripDelimiter;
+
+	private Charset defaultCharset = DEFAULT_CHARSET;
+
+	private final ConcurrentMap<Charset, byte[][]> delimitersCache = new ConcurrentHashMap<>();
+
+
+	/**
+	 * Create a new {@code AbstractCharSequenceDecoder} with the given parameters.
+	 */
+	protected AbstractCharSequenceDecoder(List<String> delimiters, boolean stripDelimiter, MimeType... mimeTypes) {
+		super(mimeTypes);
+		Assert.notEmpty(delimiters, "'delimiters' must not be empty");
+		this.delimiters = new ArrayList<>(delimiters);
+		this.stripDelimiter = stripDelimiter;
+	}
+
+
+	/**
+	 * Set the default character set to fall back on if the MimeType does not specify any.
+	 * <p>By default this is {@code UTF-8}.
+	 * @param defaultCharset the charset to fall back on
+	 */
+	public void setDefaultCharset(Charset defaultCharset) {
+		this.defaultCharset = defaultCharset;
+	}
+
+	/**
+	 * Return the configured {@link #setDefaultCharset(Charset) defaultCharset}.
+	 */
+	public Charset getDefaultCharset() {
+		return this.defaultCharset;
+	}
+
+
+	@Override
+	public final Flux<T> decode(Publisher<DataBuffer> input, ResolvableType elementType,
+			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
+
+		byte[][] delimiterBytes = getDelimiterBytes(mimeType);
+
+		LimitedDataBufferList chunks = new LimitedDataBufferList(getMaxInMemorySize());
+		DataBufferUtils.Matcher matcher = DataBufferUtils.matcher(delimiterBytes);
+
+		return Flux.from(input)
+				.concatMapIterable(buffer -> processDataBuffer(buffer, matcher, chunks))
+				.concatWith(Mono.defer(() -> {
+					if (chunks.isEmpty()) {
+						return Mono.empty();
+					}
+					DataBuffer lastBuffer = chunks.get(0).factory().join(chunks);
+					chunks.clear();
+					return Mono.just(lastBuffer);
+				}))
+				.doFinally(signalType -> chunks.releaseAndClear())
+				.doOnDiscard(DataBuffer.class, DataBufferUtils::release)
+				.map(buffer -> decode(buffer, elementType, mimeType, hints));
+	}
+
+	private byte[][] getDelimiterBytes(@Nullable MimeType mimeType) {
+		return this.delimitersCache.computeIfAbsent(getCharset(mimeType), charset -> {
+			byte[][] result = new byte[this.delimiters.size()][];
+			for (int i = 0; i < this.delimiters.size(); i++) {
+				result[i] = this.delimiters.get(i).getBytes(charset);
+			}
+			return result;
+		});
+	}
+
+	private Collection<DataBuffer> processDataBuffer(DataBuffer buffer, DataBufferUtils.Matcher matcher,
+			LimitedDataBufferList chunks) {
+
+		boolean release = true;
+		try {
+			List<DataBuffer> result = null;
+			do {
+				int endIndex = matcher.match(buffer);
+				if (endIndex == -1) {
+					chunks.add(buffer);
+					release = false;
+					break;
+				}
+				DataBuffer split = buffer.split(endIndex + 1);
+				if (result == null) {
+					result = new ArrayList<>();
+				}
+				int delimiterLength = matcher.delimiter().length;
+				if (chunks.isEmpty()) {
+					if (this.stripDelimiter) {
+						split.writePosition(split.writePosition() - delimiterLength);
+					}
+					result.add(split);
+				}
+				else {
+					chunks.add(split);
+					DataBuffer joined = buffer.factory().join(chunks);
+					if (this.stripDelimiter) {
+						joined.writePosition(joined.writePosition() - delimiterLength);
+					}
+					result.add(joined);
+					chunks.clear();
+				}
+			}
+			while (buffer.readableByteCount() > 0);
+			return (result != null ? result : Collections.emptyList());
+		}
+		finally {
+			if (release) {
+				DataBufferUtils.release(buffer);
+			}
+		}
+	}
+
+	@Override
+	public final T decode(DataBuffer dataBuffer, ResolvableType elementType,
+			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
+
+		Charset charset = getCharset(mimeType);
+		T value = decodeInternal(dataBuffer, charset);
+		DataBufferUtils.release(dataBuffer);
+		LogFormatUtils.traceDebug(logger, traceOn -> {
+			String formatted = LogFormatUtils.formatValue(value, !traceOn);
+			return Hints.getLogPrefix(hints) + "Decoded " + formatted;
+		});
+		return value;
+	}
+
+	private Charset getCharset(@Nullable MimeType mimeType) {
+		if (mimeType != null) {
+			Charset charset = mimeType.getCharset();
+			if (charset != null) {
+				return charset;
+			}
+		}
+		return getDefaultCharset();
+	}
+
+
+	/**
+	 * Template method that decodes the given data buffer into {@code T}, given
+	 * the charset.
+	 */
+	protected abstract T decodeInternal(DataBuffer dataBuffer, Charset charset);
+
+}