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/*
 * 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.
 * You may obtain a copy of the License at
 *
 *      http://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.http.codec;

import java.nio.CharBuffer;
import java.nio.charset.StandardCharsets;
import java.time.Duration;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.function.IntPredicate;

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.ResolvableType;
import org.springframework.core.codec.CodecException;
import org.springframework.core.codec.Decoder;
import org.springframework.core.codec.StringDecoder;
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.io.buffer.DefaultDataBufferFactory;
import org.springframework.http.MediaType;
import org.springframework.http.ReactiveHttpInputMessage;
import org.springframework.lang.Nullable;

import static java.util.stream.Collectors.joining;

/**
 * Reader that supports a stream of {@link ServerSentEvent}s and also plain
 * {@link Object}s which is the same as an {@link ServerSentEvent} with data only.
 *
 * @author Sebastien Deleuze
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public class ServerSentEventHttpMessageReader implements HttpMessageReader {

	private static final IntPredicate NEWLINE_DELIMITER = b -> b == '\n' || b == '\r';

	private static final DataBufferFactory bufferFactory = new DefaultDataBufferFactory();

	private static final StringDecoder stringDecoder = StringDecoder.textPlainOnly();


	@Nullable
	private final Decoder decoder;


	/**
	 * Constructor without a {@code Decoder}. In this mode only {@code String}
	 * is supported as the data of an event.
	 */
	public ServerSentEventHttpMessageReader() {
		this(null);
	}

	/**
	 * Constructor with JSON {@code Decoder} for decoding to Objects.
	 * Support for decoding to {@code String} event data is built-in.
	 */
	public ServerSentEventHttpMessageReader(@Nullable Decoder decoder) {
		this.decoder = decoder;
	}


	/**
	 * Return the configured {@code Decoder}.
	 */
	@Nullable
	public Decoder getDecoder() {
		return this.decoder;
	}

	@Override
	public List getReadableMediaTypes() {
		return Collections.singletonList(MediaType.TEXT_EVENT_STREAM);
	}

	@Override
	public boolean canRead(ResolvableType elementType, @Nullable MediaType mediaType) {
		return (MediaType.TEXT_EVENT_STREAM.includes(mediaType) || isServerSentEvent(elementType));
	}

	private boolean isServerSentEvent(ResolvableType elementType) {
		Class rawClass = elementType.getRawClass();
		return (rawClass != null && ServerSentEvent.class.isAssignableFrom(rawClass));
	}


	@Override
	public Flux read(ResolvableType elementType, ReactiveHttpInputMessage message,
			Map hints) {

		boolean shouldWrap = isServerSentEvent(elementType);
		ResolvableType valueType = (shouldWrap ? elementType.getGeneric(0) : elementType);

		return Flux.from(message.getBody())
				.concatMap(ServerSentEventHttpMessageReader::splitOnNewline)
				.map(buffer -> {
					CharBuffer charBuffer = StandardCharsets.UTF_8.decode(buffer.asByteBuffer());
					DataBufferUtils.release(buffer);
					return charBuffer.toString();
				})
				.bufferUntil(line -> line.equals("\n"))
				.concatMap(rawLines -> {
					String[] lines = rawLines.stream().collect(joining()).split("\\r?\\n");
					ServerSentEvent event = buildEvent(lines, valueType, hints);
					return (shouldWrap ? Mono.just(event) : Mono.justOrEmpty(event.data()));
				})
				.cast(Object.class);
	}

	private static Flux splitOnNewline(DataBuffer dataBuffer) {
		List results = new ArrayList<>();
		int startIdx = 0;
		int endIdx;
		final int limit = dataBuffer.readableByteCount();
		do {
			endIdx = dataBuffer.indexOf(NEWLINE_DELIMITER, startIdx);
			int length = endIdx != -1 ? endIdx - startIdx + 1 : limit - startIdx;
			DataBuffer token = dataBuffer.slice(startIdx, length);
			results.add(DataBufferUtils.retain(token));
			startIdx = endIdx + 1;
		}
		while (startIdx < limit && endIdx != -1);
		DataBufferUtils.release(dataBuffer);
		return Flux.fromIterable(results);
	}

	private ServerSentEvent buildEvent(String[] lines, ResolvableType valueType,
			Map hints) {

		ServerSentEvent.Builder sseBuilder = ServerSentEvent.builder();
		StringBuilder mutableData = new StringBuilder();
		StringBuilder mutableComment = new StringBuilder();

		for (String line : lines) {
			if (line.startsWith("id:")) {
				sseBuilder.id(line.substring(3));
			}
			else if (line.startsWith("event:")) {
				sseBuilder.event(line.substring(6));
			}
			else if (line.startsWith("data:")) {
				mutableData.append(line.substring(5)).append("\n");
			}
			else if (line.startsWith("retry:")) {
				sseBuilder.retry(Duration.ofMillis(Long.valueOf(line.substring(6))));
			}
			else if (line.startsWith(":")) {
				mutableComment.append(line.substring(1)).append("\n");
			}
		}
		if (mutableData.length() > 0) {
			String data = mutableData.toString();
			sseBuilder.data(decodeData(data, valueType, hints));
		}
		if (mutableComment.length() > 0) {
			String comment = mutableComment.toString();
			sseBuilder.comment(comment.substring(0, comment.length() - 1));
		}
		return sseBuilder.build();
	}

	@Nullable
	private Object decodeData(String data, ResolvableType dataType, Map hints) {
		if (String.class == dataType.resolve()) {
			return data.substring(0, data.length() - 1);
		}

		if (this.decoder == null) {
			return Flux.error(new CodecException("No SSE decoder configured and the data is not String."));
		}

		byte[] bytes = data.getBytes(StandardCharsets.UTF_8);
		Mono input = Mono.just(bufferFactory.wrap(bytes));

		return this.decoder
				.decodeToMono(input, dataType, MediaType.TEXT_EVENT_STREAM, hints)
				.block(Duration.ZERO);
	}

	@Override
	public Mono readMono(ResolvableType elementType, ReactiveHttpInputMessage message,
			Map hints) {

		// We're ahead of String + "*/*"
		// Let's see if we can aggregate the output (lest we time out)...

		if (String.class.equals(elementType.getRawClass())) {
			Flux body = message.getBody();
			return stringDecoder.decodeToMono(body, elementType, null, null).cast(Object.class);
		}

		return Mono.error(new UnsupportedOperationException(
				"ServerSentEventHttpMessageReader only supports reading stream of events as a Flux"));
	}

}
 















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