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Spring WebSocket
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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
 *
 *      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.web.socket.sockjs.client;

import java.net.URI;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.lang.Nullable;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.util.concurrent.SettableListenableFuture;
import org.springframework.web.client.HttpServerErrorException;
import org.springframework.web.socket.TextMessage;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.WebSocketSession;
import org.springframework.web.socket.sockjs.frame.SockJsFrame;
import org.springframework.web.socket.sockjs.transport.TransportType;

/**
 * Abstract base class for XHR transport implementations to extend.
 *
 * @author Rossen Stoyanchev
 * @since 4.1
 */
public abstract class AbstractXhrTransport implements XhrTransport {

	protected static final String PRELUDE;

	static {
		byte[] bytes = new byte[2048];
		Arrays.fill(bytes, (byte) 'h');
		PRELUDE = new String(bytes, SockJsFrame.CHARSET);
	}


	protected final Log logger = LogFactory.getLog(getClass());

	private boolean xhrStreamingDisabled;


	@Override
	public List getTransportTypes() {
		return (isXhrStreamingDisabled() ? Collections.singletonList(TransportType.XHR) :
				Arrays.asList(TransportType.XHR_STREAMING, TransportType.XHR));
	}

	/**
	 * An {@code XhrTransport} can support both the "xhr_streaming" and "xhr"
	 * SockJS server transports. From a client perspective there is no
	 * implementation difference.
	 * Typically an {@code XhrTransport} is used as "XHR streaming" first and
	 * then, if that fails, as "XHR". In some cases however it may be helpful to
	 * suppress XHR streaming so that only XHR is attempted.
	 * By default this property is set to {@code false} which means both
	 * "XHR streaming" and "XHR" apply.
	 */
	public void setXhrStreamingDisabled(boolean disabled) {
		this.xhrStreamingDisabled = disabled;
	}

	/**
	 * Whether XHR streaming is disabled or not.
	 */
	@Override
	public boolean isXhrStreamingDisabled() {
		return this.xhrStreamingDisabled;
	}


	// Transport methods

	@Override
	public ListenableFuture connect(TransportRequest request, WebSocketHandler handler) {
		SettableListenableFuture connectFuture = new SettableListenableFuture<>();
		XhrClientSockJsSession session = new XhrClientSockJsSession(request, handler, this, connectFuture);
		request.addTimeoutTask(session.getTimeoutTask());

		URI receiveUrl = request.getTransportUrl();
		if (logger.isDebugEnabled()) {
			logger.debug("Starting XHR " +
					(isXhrStreamingDisabled() ? "Polling" : "Streaming") + "session url=" + receiveUrl);
		}

		HttpHeaders handshakeHeaders = new HttpHeaders();
		handshakeHeaders.putAll(request.getHandshakeHeaders());

		connectInternal(request, handler, receiveUrl, handshakeHeaders, session, connectFuture);
		return connectFuture;
	}

	protected abstract void connectInternal(TransportRequest request, WebSocketHandler handler,
			URI receiveUrl, HttpHeaders handshakeHeaders, XhrClientSockJsSession session,
			SettableListenableFuture connectFuture);


	// InfoReceiver methods

	@Override
	public String executeInfoRequest(URI infoUrl, @Nullable HttpHeaders headers) {
		if (logger.isDebugEnabled()) {
			logger.debug("Executing SockJS Info request, url=" + infoUrl);
		}
		HttpHeaders infoRequestHeaders = new HttpHeaders();
		if (headers != null) {
			infoRequestHeaders.putAll(headers);
		}
		ResponseEntity response = executeInfoRequestInternal(infoUrl, infoRequestHeaders);
		if (response.getStatusCode() != HttpStatus.OK) {
			if (logger.isErrorEnabled()) {
				logger.error("SockJS Info request (url=" + infoUrl + ") failed: " + response);
			}
			throw new HttpServerErrorException(response.getStatusCode());
		}
		if (logger.isTraceEnabled()) {
			logger.trace("SockJS Info request (url=" + infoUrl + ") response: " + response);
		}
		String result = response.getBody();
		return (result != null ? result : "");
	}

	protected abstract ResponseEntity executeInfoRequestInternal(URI infoUrl, HttpHeaders headers);


	// XhrTransport methods

	@Override
	public void executeSendRequest(URI url, HttpHeaders headers, TextMessage message) {
		if (logger.isTraceEnabled()) {
			logger.trace("Starting XHR send, url=" + url);
		}
		ResponseEntity response = executeSendRequestInternal(url, headers, message);
		if (response.getStatusCode() != HttpStatus.NO_CONTENT) {
			if (logger.isErrorEnabled()) {
				logger.error("XHR send request (url=" + url + ") failed: " + response);
			}
			throw new HttpServerErrorException(response.getStatusCode());
		}
		if (logger.isTraceEnabled()) {
			logger.trace("XHR send request (url=" + url + ") response: " + response);
		}
	}

	protected abstract ResponseEntity executeSendRequestInternal(
			URI url, HttpHeaders headers, TextMessage message);

}