# DeliveryAgent.java

    /*
     *  Copyright (c) 2005-2008, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
     *
     *  WSO2 Inc. licenses this file to you 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.apache.synapse.transport.passthru;

    import org.apache.axis2.AxisFault;
    import org.apache.axis2.addressing.EndpointReference;
    import org.apache.axis2.context.MessageContext;
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.apache.http.HttpHost;
    import org.apache.http.conn.routing.HttpRoute;
    import org.apache.http.nio.NHttpClientConnection;
    import org.apache.http.nio.reactor.IOSession;
    import org.apache.http.protocol.HttpContext;
    import org.apache.synapse.commons.CorrelationConstants;
    import org.apache.synapse.transport.http.conn.LoggingNHttpServerConnection;
    import org.apache.synapse.transport.http.conn.ProxyConfig;
    import org.apache.synapse.transport.http.conn.SynapseDebugInfoHolder;
    import org.apache.synapse.transport.passthru.config.PassThroughConfigPNames;
    import org.apache.synapse.transport.passthru.config.PassThroughConfiguration;
    import org.apache.synapse.transport.passthru.config.TargetConfiguration;
    import org.apache.synapse.transport.passthru.connections.TargetConnections;
    import org.apache.synapse.transport.passthru.util.TargetRequestFactory;

    import java.io.OutputStream;
    import java.net.MalformedURLException;
    import java.net.URL;
    import java.util.Map;
    import java.util.Queue;
    import java.util.concurrent.ConcurrentHashMap;
    import java.util.concurrent.ConcurrentLinkedQueue;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;

    /**
     * This class acts as a gateway for differed delivery of the messages. When a message is to be
     * delivered it is submitted to this class. If a connection is available to the target this
     * class will try to deliver the message immediately over that connection. If a connection is
     * not available it will queue the message and request a connection from the pool. When a new
     * connection is available a queued message will be sent through it.
     */
    public class DeliveryAgent {

        private static final Log log = LogFactory.getLog(DeliveryAgent.class);
        private static final String SYNAPSE_ARTIFACT_TYPE = "SYNAPSE_ARTIFACT_TYPE";
        private static final String SSE = "SSE";
        private static final String SSE_TARGET_CONNECTION = "SSE_TARGET_CONNECTION";
        private static final String SSE_TARGET_CONNECTIONS = "SSE_TARGET_CONNECTIONS";

        /**
         * This Map holds the messages that need to be delivered. But at the moment maximum
         * number of connections to the host:pair is being used. So these messages has to wait
         * until a new connection is available.
         */
        private Map<HttpRoute, Queue<MessageContext>> waitingMessages =
                new ConcurrentHashMap<HttpRoute, Queue<MessageContext>>();

        /** The connection management */
        private TargetConnections targetConnections;

        /** Configuration of the sender */
        private TargetConfiguration targetConfiguration;

        /** Proxy config */
        private ProxyConfig proxyConfig;

        /** The maximum number of messages that can wait for a connection */
        private int maxWaitingMessages;

        private TargetErrorHandler targetErrorHandler;

        /** Lock for synchronizing access */
        private Lock lock = new ReentrantLock();

        /**
         * Create a delivery agent with the target configuration and connection management.
         *
         * @param targetConfiguration configuration of the sender
         * @param targetConnections connection management
         */
        public DeliveryAgent(TargetConfiguration targetConfiguration,
                             TargetConnections targetConnections,
                             ProxyConfig proxyConfig) {
            this.targetConfiguration = targetConfiguration;
            this.targetConnections = targetConnections;
            this.proxyConfig = proxyConfig;
            this.targetErrorHandler = new TargetErrorHandler(targetConfiguration);
            PassThroughConfiguration conf = PassThroughConfiguration.getInstance();
            this.maxWaitingMessages = conf.getIntProperty(PassThroughConfigPNames.MAX_MESSAGES_PER_HOST_PORT,
                    Integer.MAX_VALUE);
        }

        /**
         * This method queues the message for delivery. If a connection is already existing for
         * the destination epr, the message will be delivered immediately. Otherwise message has
         * to wait until a connection is established. In this case this method will inform the
         * system about the need for a connection.
         *
         * @param msgContext the message context to be sent
         * @param epr the endpoint to which the message should be sent
         * @throws AxisFault if an error occurs
         *
         * @return false if connection can not be acquired due to connection limit exceeds or queue limit exceeds
         *         else return true
         */
        public boolean submit(MessageContext msgContext, EndpointReference epr)
                throws AxisFault {
            try {
                if (log.isDebugEnabled()) {
                    log.debug("Submitting request for MessageID: " + msgContext.getMessageID());
                }
                URL url = new URL(epr.getAddress());
                String scheme = url.getProtocol() != null ? url.getProtocol() : "http";
                String hostname = url.getHost();
                int port = url.getPort();
                if (port == -1) {
                    // use default
                    if ("http".equals(scheme)) {
                        port = 80;
                    } else if ("https".equals(scheme)) {
                        port = 443;
                    }
                }
                HttpHost target = new HttpHost(hostname, port, scheme);
                boolean secure = "https".equalsIgnoreCase(target.getSchemeName());

                HttpHost proxy = proxyConfig.selectProxy(target);
                msgContext.setProperty(PassThroughConstants.PROXY_PROFILE_TARGET_HOST, target.getHostName());

                HttpRoute route;
                if (proxy != null) {
                    route = new HttpRoute(target, null, proxy, secure);
                } else {
                    route = new HttpRoute(target, null, secure);
                }

                // first we queue the message
                Queue<MessageContext> queue = null;
                NHttpClientConnection conn = null;
                lock.lock();
                try {
                    queue = waitingMessages.get(route);
                    if (queue == null) {
                        queue = new ConcurrentLinkedQueue<MessageContext>();
                        waitingMessages.put(route, queue);
                    }
                    if (queue.size() >= maxWaitingMessages) {
                        msgContext.setProperty(PassThroughConstants.INTERNAL_EXCEPTION_ORIGIN,
                                PassThroughConstants.INTERNAL_ORIGIN_ERROR_HANDLER);
                        log.warn("Delivery agent queue length exceeds the maximum number of waiting messages");
                        if (msgContext != null) {
                            targetErrorHandler.handleError(msgContext, ErrorCodes.CONNECTION_TIMEOUT,
                                    "Number of queued messages exceeds the limit",
                                    null, ProtocolState.REQUEST_READY);
                        }
                        return false;
                    }

                    queue.add(msgContext);
                    conn = targetConnections.getConnection(route, msgContext, targetErrorHandler, queue);
                    if (conn == null && msgContext != null && "true".equalsIgnoreCase(
                            (String) msgContext.getProperty(PassThroughConstants.CONNECTION_LIMIT_EXCEEDS))) {
                        msgContext.removeProperty(PassThroughConstants.CONNECTION_LIMIT_EXCEEDS);
                        return false;
                    }

                } finally {
                    lock.unlock();
                }

                if (conn != null) {
                    if (log.isDebugEnabled()) {
                        log.debug("Connection found from pool for MessageID: " + msgContext.getMessageID() +
                                ", conn: " + conn.toString());
                    }
                	conn.resetInput();
                	conn.resetOutput();
                    MessageContext messageContext = queue.poll();

                    if (messageContext != null) {
                        tryNextMessage(messageContext, route, conn);
                    }
                }

            } catch (MalformedURLException e) {
                handleException("Malformed URL in the target EPR", e);
            }
            return true;
        }

        public void errorConnecting(HttpRoute route, int errorCode, String message, Exception exceptionToRaise) {
            Queue<MessageContext> queue = waitingMessages.get(route);
            if (queue != null) {
                MessageContext msgCtx = queue.poll();

                if (msgCtx != null) {
                    msgCtx.setProperty(PassThroughConstants.INTERNAL_EXCEPTION_ORIGIN,
                            PassThroughConstants.INTERNAL_ORIGIN_ERROR_HANDLER);
                    targetErrorHandler.handleError(msgCtx, errorCode,
                            "Error connecting to the back end", exceptionToRaise,
                            ProtocolState.REQUEST_READY);
                    synchronized (msgCtx) {
                        msgCtx.setProperty(PassThroughConstants.WAIT_BUILDER_IN_STREAM_COMPLETE,
                                Boolean.TRUE);
                        msgCtx.notifyAll();
                    }
                }
            } else {
                throw new IllegalStateException("Queue cannot be null for: " + route);
            }
        }

    	public void errorConnecting(HttpRoute route, int errorCode, String message) {
    		errorConnecting(route, errorCode, message, null);
    	}

        /**
         * Notification for a connection availability. When this occurs a message in the
         * queue for delivery will be tried.
         *
         * @param host name of the remote host
         * @param port remote port number
         */
        public void connected(HttpRoute route, NHttpClientConnection conn) {
            if (log.isDebugEnabled()) {
                log.debug("Connection established conn: " + conn.toString());
            }
            Queue<MessageContext> queue = null;
            lock.lock();
            try {
                queue = waitingMessages.get(route);
            } finally {
                lock.unlock();
            }

            while (queue.size() > 0) {
                if(conn == null) {
                    conn = targetConnections.getExistingConnection(route);
                }
                if (conn != null) {
                    MessageContext messageContext = queue.poll();

                    if (messageContext != null) {
                        tryNextMessage(messageContext, route, conn);
                        conn = null;
                    }
                } else {
                    break;
                }
            }
            //releasing the connection to pool when connection is not null and message queue is empty,
            //otherwise connection remains in busyConnections pool till it gets timeout and It is not used.
            if(conn != null && TargetContext.getState(conn) == ProtocolState.REQUEST_READY) {
                targetConfiguration.getConnections().releaseConnection(conn);
            }
        }

        private void tryNextMessage(MessageContext messageContext, HttpRoute route, NHttpClientConnection conn) {
            if (conn != null) {
                try {
                    HttpContext ctx = conn.getContext();
                    /*
                    * If the flow is SSE we need to set references to target connection and targetConnections
                    * in the source connection to access them and shut down target connection when source connection is
                    * broken.
                    * */
                    if (SSE.equals(messageContext.getProperty(SYNAPSE_ARTIFACT_TYPE))) {
                        LoggingNHttpServerConnection sourceConnection = (LoggingNHttpServerConnection)
                                ((ServerWorker) messageContext.getProperty(
                                "OutTransportInfo")).getRequestContext().getProperty
                                        (PassThroughConstants.PASS_THROUGH_SOURCE_CONNECTION);
                        if (sourceConnection != null) {
                            sourceConnection.getIOSession().setAttribute(SSE_TARGET_CONNECTIONS, targetConnections);
                            sourceConnection.getIOSession().setAttribute(SSE_TARGET_CONNECTION, conn);
                        }
                    }
                    ctx.setAttribute(CorrelationConstants.CORRELATION_ID,
                                     messageContext.getProperty(CorrelationConstants.CORRELATION_ID));

                    ctx.setAttribute(PassThroughConstants.REQUEST_MESSAGE_CONTEXT, messageContext);
                    TargetContext.updateState(conn, ProtocolState.REQUEST_READY);
                    TargetContext.get(conn).setRequestMsgCtx(messageContext);
                    if (log.isDebugEnabled()) {
                        log.debug("Trying to send the message, MessageID:" + messageContext.getMessageID() +
                                ", conn:" + conn.toString());
                    }
                    submitRequest(conn, route, messageContext);
                } catch (AxisFault e) {
                    log.error("IO error while sending the request out", e);
                }
            }
        }

        private void submitRequest(NHttpClientConnection conn, HttpRoute route, MessageContext msgContext) throws AxisFault {
            if (log.isDebugEnabled()) {
                log.debug("Submitting new request MessageID:"
                        + msgContext.getMessageID() +" to the connection: " + conn);
            }

            if (SynapseDebugInfoHolder.getInstance().isDebuggerEnabled()) {
                conn.getContext().setAttribute(SynapseDebugInfoHolder.SYNAPSE_WIRE_LOG_HOLDER_PROPERTY,
                                               msgContext.getProperty(SynapseDebugInfoHolder.SYNAPSE_WIRE_LOG_HOLDER_PROPERTY));
                conn.getContext().setAttribute(SynapseDebugInfoHolder.SYNAPSE_WIRE_LOG_MEDIATOR_ID_PROPERTY,
                                               msgContext.getProperty(SynapseDebugInfoHolder.SYNAPSE_WIRE_LOG_MEDIATOR_ID_PROPERTY));
            }
            TargetRequest request = TargetRequestFactory.create(msgContext, route, targetConfiguration);
            TargetContext.setRequest(conn, request);

            Pipe pipe = (Pipe) msgContext.getProperty(PassThroughConstants.PASS_THROUGH_PIPE);
            if (pipe != null) {
                pipe.attachConsumer(conn);
                request.connect(pipe);
                if (Boolean.TRUE.equals(msgContext.getProperty(PassThroughConstants.MESSAGE_BUILDER_INVOKED))) {
                    synchronized (msgContext) {
                        OutputStream out = pipe.getOutputStream();
                        msgContext.setProperty(PassThroughConstants.BUILDER_OUTPUT_STREAM, out);
                        msgContext.setProperty(PassThroughConstants.WAIT_BUILDER_IN_STREAM_COMPLETE, Boolean.TRUE);
                        msgContext.notifyAll();
                    }
                    return;
                }
            }

            conn.requestOutput();
        }

        /**
         * Throws an AxisFault if an error occurs at this level
         * @param s a message describing the error
         * @param e original exception leads to the error condition
         * @throws AxisFault wrapping the original exception
         */
        private void handleException(String s, Exception e) throws AxisFault {
            log.error(s, e);
            throw new AxisFault(s, e);
        }
    }