# CRLCache.java

    /*
     *  Licensed to the Apache Software Foundation (ASF) under one
     *  or more contributor license agreements.  See the NOTICE file
     *  distributed with this work for additional information
     *  regarding copyright ownership.  The ASF 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.certificatevalidation.crl;

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

    import org.apache.synapse.commons.jmx.MBeanRegistrar;
    import org.apache.synapse.transport.certificatevalidation.cache.CacheController;
    import org.apache.synapse.transport.certificatevalidation.cache.CacheManager;
    import org.apache.synapse.transport.certificatevalidation.cache.ManageableCache;
    import org.apache.synapse.transport.certificatevalidation.cache.ManageableCacheValue;

    import java.security.cert.X509CRL;
    import java.util.Date;
    import java.util.Iterator;
    import java.util.Map;
    import java.util.concurrent.ConcurrentHashMap;

    /**
     * Since a CRL maps to a CRL URL, the CRLCache should have x509CRL entries against CRL URLs.
     * This cache is a Singleton since it is shared by any transport which needs SSL certificate validation
     * and more than one CRLCache should not be allowed per system.
     */
    public class CRLCache implements ManageableCache {

        private static volatile CRLCache cache;
        private static volatile Map<String, CRLCacheValue> hashMap = new ConcurrentHashMap<String, CRLCacheValue>();
        private static volatile Iterator<Map.Entry<String, CRLCacheValue>> iterator = hashMap.entrySet().iterator();
        private static volatile CacheManager cacheManager;
        private static CRLVerifier crlVerifier = new CRLVerifier(null);
        private static final Log log = LogFactory.getLog(CRLCache.class);

        private CRLCache() {
        }

        public static CRLCache getCache() {
            //Double checked locking
            if (cache == null) {
                synchronized (CRLCache.class) {
                    if (cache == null) {
                        cache = new CRLCache();
                    }
                }
            }
            return cache;
        }

        /**
         * This initialize the Cache with a CacheManager. If this method is called, a cache manager will not be used.
         *
         * @param size max size of the cache
         * @param delay defines how frequently the CacheManager will be started
         */
        public void init(int size, int delay) {
            if (cacheManager == null) {
                synchronized (CRLCache.class) {
                    if (cacheManager == null) {
                        cacheManager = new CacheManager(cache, size, delay);
                        CacheController mbean = new CacheController(cache,cacheManager);
                        MBeanRegistrar.getInstance().registerMBean(mbean, "CacheController", "CRLCacheController");
                    }
                }
            }
        }

        /**
         * This method is needed by the cache Manager to go through the cache entries to remove invalid values or
         * to remove LRU cache values if the cache has reached its max size.
         * Todo: Can move to an abstract class.
         *
         * @return next cache value of the cache.
         */
        public synchronized ManageableCacheValue getNextCacheValue() {
            //changes to the map are reflected on the keySet. And its iterator is weakly consistent. so will never
            //throw concurrent modification exception.
            if (iterator.hasNext()) {
                return hashMap.get(iterator.next().getKey());
            } else {
                resetIterator();
                return null;
            }
        }

        /**
         * To get the current cache size (size of the hash map).
         */
        public synchronized int getCacheSize() {
            return hashMap.size();
        }

        public void resetIterator() {
            iterator = hashMap.entrySet().iterator();
        }

        private synchronized void replaceNewCacheValue(CRLCacheValue cacheValue) {
            //If someone has updated with the new value before current Thread.
            if (cacheValue.isValid())
                return;

            try {
                String crlUrl = cacheValue.crlUrl;
                X509CRL x509CRL = crlVerifier.downloadCRLFromWeb(crlUrl);
                this.setCacheValue(crlUrl, x509CRL);
            } catch (Exception e) {
                log.info("Cant replace old CacheValue with new CacheValue. So remove", e);
                //If cant be replaced remove.
                cacheValue.removeThisCacheValue();
            }
        }

        public synchronized X509CRL getCacheValue(String crlUrl) {
            CRLCacheValue cacheValue = hashMap.get(crlUrl);
            if (cacheValue != null) {
                //If who ever gets this cache value before Cache manager task found its invalid, update it and get the
                // new value.
                if (!cacheValue.isValid()) {
                    cacheValue.updateCacheWithNewValue();
                    CRLCacheValue crlCacheValue = hashMap.get(crlUrl);
                    return (crlCacheValue != null ? crlCacheValue.getValue() : null);
                }

                return cacheValue.getValue();
            } else
                return null;
        }

        public synchronized void setCacheValue(String crlUrl, X509CRL crl) {
            CRLCacheValue cacheValue = new CRLCacheValue(crlUrl, crl);
            log.info("Before set- HashMap size " + hashMap.size());
            hashMap.put(crlUrl, cacheValue);
            log.info("After set - HashMap size " + hashMap.size());
        }

        public synchronized void removeCacheValue(String crlUrl) {
            log.info("Before remove - HashMap size " + hashMap.size());
            hashMap.remove(crlUrl);
            log.info("After remove - HashMap size " + hashMap.size());

        }

        /**
         * This is the wrapper class of the actual cache value which is a X509CRL.
         */
        private class CRLCacheValue implements ManageableCacheValue {

            private String crlUrl;
            private X509CRL crl;
            private long timeStamp = System.currentTimeMillis();

            public CRLCacheValue(String crlUrl, X509CRL crl) {
                this.crlUrl = crlUrl;
                this.crl = crl;
            }

            public String getKey() {
                return crlUrl;
            }

            public X509CRL getValue() {
                timeStamp = System.currentTimeMillis();
                return crl;
            }

            /**
             * CRL has a validity period. We can reuse a downloaded CRL within that period.
             */
            public boolean isValid() {
                Date today = new Date();
                Date nextUpdate = crl.getNextUpdate();
                return nextUpdate != null && nextUpdate.after(today);
            }

            public long getTimeStamp() {
                return timeStamp;
            }

            /**
             * Used by cacheManager to remove invalid entries.
             */
            public void removeThisCacheValue() {
                removeCacheValue(crlUrl);
            }

            public void updateCacheWithNewValue() {
                replaceNewCacheValue(this);
            }
        }
    }