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/*
 * Copyright (c) 2008-2019 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.cometd.server;

import java.io.IOException;
import java.util.Collections;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.cometd.bayeux.server.BayeuxServer;
import org.cometd.bayeux.server.ServerSession;
import org.cometd.server.transport.AbstractHttpTransport;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * The CometD Servlet maps HTTP requests to the {@link org.cometd.server.transport.AbstractHttpTransport}
 * of a {@link BayeuxServer} instance.
 * The {@link BayeuxServer} instance is searched in the servlet context under the {@link BayeuxServer#ATTRIBUTE}
 * attribute; if it is found then it is used without further configuration, otherwise a new {@link BayeuxServer}
 * instance is created and configured using the init parameters of this servlet.
 */
public class CometDServlet extends HttpServlet {
    private static final long serialVersionUID = 3637310585741732936L;

    protected final Logger _logger = LoggerFactory.getLogger(getClass());
    private BayeuxServerImpl _bayeux;

    @Override
    public void init() throws ServletException {
        try {
            boolean export = false;
            _bayeux = (BayeuxServerImpl)getServletContext().getAttribute(BayeuxServer.ATTRIBUTE);
            if (_bayeux == null) {
                export = true;
                _bayeux = newBayeuxServer();

                // Transfer all servlet init parameters to the BayeuxServer implementation
                for (String initParamName : Collections.list(getInitParameterNames())) {
                    _bayeux.setOption(initParamName, getInitParameter(initParamName));
                }

                // Add the ServletContext to the options
                _bayeux.setOption(ServletContext.class.getName(), getServletContext());
            }

            _bayeux.start();

            if (export) {
                getServletContext().setAttribute(BayeuxServer.ATTRIBUTE, _bayeux);
            }
        } catch (Exception x) {
            throw new ServletException(x);
        }
    }

    public BayeuxServerImpl getBayeux() {
        return _bayeux;
    }

    protected BayeuxServerImpl newBayeuxServer() {
        return new BayeuxServerImpl();
    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        if ("OPTIONS".equals(request.getMethod())) {
            serviceOptions(request, response);
            return;
        }

        AbstractHttpTransport transport = _bayeux.findHttpTransport(request);
        if (transport == null) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "Unknown Bayeux Transport");
        } else {
            transport.handle(request, response);
        }
    }

    protected void serviceOptions(HttpServletRequest request, HttpServletResponse response) {
        // OPTIONS requests are made by browsers that are CORS compliant
        // (see http://www.w3.org/TR/cors/) during a "preflight request".
        // Preflight requests happen for each different new URL, then results are cached
        // by the browser.
        // For the Bayeux protocol, preflight requests happen for URLs such as
        // "/cometd/handshake", "/cometd/connect", etc, since the Bayeux clients append
        // the Bayeux message type to the base Bayeux server URL.
        // Just return 200 OK, there is nothing more to add to such requests.
    }

    /**
     * @see javax.servlet.GenericServlet#destroy()
     */
    @Override
    public void destroy() {
        for (ServerSession session : _bayeux.getSessions()) {
            ((ServerSessionImpl)session).cancelSchedule();
        }

        try {
            _bayeux.stop();
        } catch (Exception x) {
            if (_logger.isDebugEnabled()) {
                _logger.debug("", x);
            }
        } finally {
            _bayeux = null;
            getServletContext().removeAttribute(BayeuxServer.ATTRIBUTE);
        }
    }
}