# StreamInterceptorsLoader.java

    /*
     * Copyright (c) 2021, 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.util;

    import org.apache.axiom.om.OMElement;
    import org.apache.axiom.om.OMNode;
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.apache.synapse.commons.util.MiscellaneousUtil;
    import org.apache.synapse.commons.util.PropertyHelper;
    import org.apache.synapse.transport.passthru.StreamInterceptor;

    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.Iterator;
    import java.util.List;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    import javax.xml.namespace.QName;

    public class StreamInterceptorsLoader {

        StreamInterceptorsLoader() {
        }

        private static Log log = LogFactory.getLog(StreamInterceptorsLoader.class);

        private static final QName ROOT_Q = new QName("interceptors");
        private static final QName INTERCEPTOR_Q = new QName("interceptor");
        private static final QName CLASS_Q = new QName("class");
        private static final QName NAME_ATT = new QName("name");
        private static final QName PARAM_Q = new QName("parameter");
        private static final QName VALUE_ATT = new QName("value");

        private static List<StreamInterceptor> interceptors = new ArrayList<>();

        private static boolean isLoadedAlready = false;

        private static Lock lock = new ReentrantLock();

        /**
         * Load and get all synapse interceptors
         *
         * @return List of loaded synapse interceptors
         */
        public static List<StreamInterceptor> getInterceptors() {

            if (!isLoadedAlready) {
                try {
                    lock.lock();
                    if (!isLoadedAlready) {
                        loadInterceptors();
                        isLoadedAlready = true;
                    }
                } finally {
                    lock.unlock();
                }
            }
            return Collections.unmodifiableList(interceptors);
        }

        private static void loadInterceptors() {

            OMElement interceptorsConfig = MiscellaneousUtil.loadXMLConfig(RelayConstants.STREAM_INTERCEPTOR_FILE);
            if (interceptorsConfig != null) {

                if (!ROOT_Q.equals(interceptorsConfig.getQName())) {
                    handleException("Invalid interceptor configuration file");
                }

                Iterator iterator = interceptorsConfig.getChildrenWithName(INTERCEPTOR_Q);
                while (iterator.hasNext()) {
                    OMElement interceptorElem = (OMElement) iterator.next();
                    if (interceptorElem.getAttribute(CLASS_Q) != null) {
                        String className = interceptorElem.getAttributeValue(CLASS_Q);
                        if (!"".equals(className)) {
                            StreamInterceptor interceptor = createInterceptor(className);
                            interceptors.add(interceptor);
                            populateParameters(interceptorElem, interceptor);
                        } else {
                            handleException("Class name is one or more interceptor");
                        }
                    } else {
                        handleException("Class name is one or more interceptor");
                    }
                }
            }
        }

        private static StreamInterceptor createInterceptor(String classFQName) {

            Object obj = null;
            try {
                obj = Class.forName(classFQName).newInstance();
            } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {
                handleException("Error creating Interceptor for class name : " + classFQName, e);
            }
            if (obj instanceof StreamInterceptor) {
                return (StreamInterceptor) obj;
            } else {
                handleException(
                        "Error creating StreamInterceptor. The Interceptor should be of type org.apache.synapse.transport.passthru.StreamInterceptor");
            }
            return null;
        }

        private static void populateParameters(OMElement handlerElem, StreamInterceptor interceptor) {

            for (Iterator it = handlerElem.getChildrenWithName(PARAM_Q); it.hasNext(); ) {
                OMElement child = (OMElement) it.next();

                String propName = child.getAttribute(NAME_ATT).getAttributeValue();
                if (propName == null) {
                    handleException("StreamInterceptor parameter must contain the name attribute");
                } else {
                    if (child.getAttribute(VALUE_ATT) != null) {
                        String value = child.getAttribute(VALUE_ATT).getAttributeValue();
                        interceptor.addProperty(propName, value);
                        PropertyHelper.setInstanceProperty(propName, value, interceptor);
                    } else {
                        OMNode omElt = child.getFirstElement();
                        if (omElt != null) {
                            interceptor.addProperty(propName, omElt);
                            PropertyHelper.setInstanceProperty(propName, omElt, interceptor);
                        } else {
                            handleException(
                                    "StreamInterceptor parameter must contain name and value attributes, or a name and a child XML fragment");
                        }
                    }
                }
            }
        }

        private static void handleException(String msg) {
            log.error(msg);
            throw new RuntimeException(msg);
        }

        private static void handleException(String msg, Exception ex) {
            log.error(msg, ex);
            throw new RuntimeException(msg, ex);
        }
    }