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/*
 * Copyright 2002-2022 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.http.codec;

import java.nio.charset.StandardCharsets;
import java.time.Duration;
import java.util.Collections;
import java.util.List;
import java.util.Map;

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.DataBufferLimitException;
import org.springframework.core.io.buffer.DefaultDataBufferFactory;
import org.springframework.http.MediaType;
import org.springframework.http.ReactiveHttpInputMessage;
import org.springframework.lang.Nullable;

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

	private static final ResolvableType STRING_TYPE = ResolvableType.forClass(String.class);


	@Nullable
	private final Decoder decoder;

	private final StringDecoder lineDecoder = StringDecoder.textPlainOnly();


	/**
	 * 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;
	}

	/**
	 * Configure a limit on the maximum number of bytes per SSE event which are
	 * buffered before the event is parsed.
	 * 

Note that the {@link #getDecoder() data decoder}, if provided, must * also be customized accordingly to raise the limit if necessary in order * to be able to parse the data portion of the event. *

By default this is set to 256K. * @param byteCount the max number of bytes to buffer, or -1 for unlimited * @since 5.1.13 */ public void setMaxInMemorySize(int byteCount) { this.lineDecoder.setMaxInMemorySize(byteCount); } /** * Return the {@link #setMaxInMemorySize configured} byte count limit. * @since 5.1.13 */ public int getMaxInMemorySize() { return this.lineDecoder.getMaxInMemorySize(); } @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) { return ServerSentEvent.class.isAssignableFrom(elementType.toClass()); } @Override public Flux read( ResolvableType elementType, ReactiveHttpInputMessage message, Map hints) { LimitTracker limitTracker = new LimitTracker(); boolean shouldWrap = isServerSentEvent(elementType); ResolvableType valueType = (shouldWrap ? elementType.getGeneric() : elementType); return this.lineDecoder.decode(message.getBody(), STRING_TYPE, null, hints) .doOnNext(limitTracker::afterLineParsed) .bufferUntil(String::isEmpty) .concatMap(lines -> { Object event = buildEvent(lines, valueType, shouldWrap, hints); return (event != null ? Mono.just(event) : Mono.empty()); }); } @Nullable private Object buildEvent(List lines, ResolvableType valueType, boolean shouldWrap, Map hints) { ServerSentEvent.Builder sseBuilder = (shouldWrap ? ServerSentEvent.builder() : null); StringBuilder data = null; StringBuilder comment = null; for (String line : lines) { if (line.startsWith("data:")) { int length = line.length(); if (length > 5) { int index = (line.charAt(5) != ' ' ? 5 : 6); if (length > index) { data = (data != null ? data : new StringBuilder()); data.append(line, index, line.length()); data.append('\n'); } } } else if (shouldWrap) { if (line.startsWith("id:")) { sseBuilder.id(line.substring(3).trim()); } else if (line.startsWith("event:")) { sseBuilder.event(line.substring(6).trim()); } else if (line.startsWith("retry:")) { sseBuilder.retry(Duration.ofMillis(Long.parseLong(line.substring(6).trim()))); } else if (line.startsWith(":")) { comment = (comment != null ? comment : new StringBuilder()); comment.append(line.substring(1).trim()).append('\n'); } } } Object decodedData = (data != null ? decodeData(data, valueType, hints) : null); if (shouldWrap) { if (comment != null) { sseBuilder.comment(comment.substring(0, comment.length() - 1)); } if (decodedData != null) { sseBuilder.data(decodedData); } return sseBuilder.build(); } else { return decodedData; } } @Nullable private Object decodeData(StringBuilder data, ResolvableType dataType, Map hints) { if (String.class == dataType.resolve()) { return data.substring(0, data.length() - 1); } if (this.decoder == null) { throw new CodecException("No SSE decoder configured and the data is not String."); } byte[] bytes = data.toString().getBytes(StandardCharsets.UTF_8); DataBuffer buffer = DefaultDataBufferFactory.sharedInstance.wrap(bytes); // wrapping only, no allocation return this.decoder.decode(buffer, dataType, MediaType.TEXT_EVENT_STREAM, hints); } @Override public Mono readMono( ResolvableType elementType, ReactiveHttpInputMessage message, Map hints) { // In order of readers, we're ahead of String + "*/*" // If this is called, simply delegate to StringDecoder if (elementType.resolve() == String.class) { Flux body = message.getBody(); return this.lineDecoder.decodeToMono(body, elementType, null, null).cast(Object.class); } return Mono.error(new UnsupportedOperationException( "ServerSentEventHttpMessageReader only supports reading stream of events as a Flux")); } private class LimitTracker { private int accumulated = 0; public void afterLineParsed(String line) { if (getMaxInMemorySize() < 0) { return; } if (line.isEmpty()) { this.accumulated = 0; } if (line.length() > Integer.MAX_VALUE - this.accumulated) { raiseLimitException(); } else { this.accumulated += line.length(); if (this.accumulated > getMaxInMemorySize()) { raiseLimitException(); } } } private void raiseLimitException() { // Do not release here, it's likely down via doOnDiscard.. throw new DataBufferLimitException("Exceeded limit on max bytes to buffer : " + getMaxInMemorySize()); } } }