1 files changed, 139 insertions, 0 deletions
diff --git a/src/main/java/de/measite/minidns/LRUCache.java b/src/main/java/de/measite/minidns/LRUCache.java
new file mode 100644
index 00000000..132bf794
--- /dev/null
+++ b/src/main/java/de/measite/minidns/LRUCache.java
@@ -0,0 +1,139 @@
+package de.measite.minidns;
+
+import java.util.LinkedHashMap;
+import java.util.Map.Entry;
+
+/**
+ * LRU based DNSCache backed by a LinkedHashMap.
+ */
+public class LRUCache implements DNSCache {
+
+    /**
+     * Internal miss count.
+     */
+    protected long missCount = 0l;
+
+    /**
+     * Internal expire count (subset of misses that was caused by expire).
+     */
+    protected long expireCount = 0l;
+
+    /**
+     * Internal hit count.
+     */
+    protected long hitCount = 0l;
+
+    /**
+     * The internal capacity of the backend cache.
+     */
+    protected int capacity;
+
+    /**
+     * The upper bound of the ttl. All longer TTLs will be capped by this ttl.
+     */
+    protected long maxTTL;
+
+    /**
+     * The backend cache.
+     */
+    protected LinkedHashMap<Question, DNSMessage> backend;
+
+    /**
+     * Create a new LRUCache with given capacity and upper bound ttl.
+     * @param capacity The internal capacity.
+     * @param maxTTL The upper bound for any ttl.
+     */
+    @SuppressWarnings("serial")
+    public LRUCache(final int capacity, final long maxTTL) {
+        this.capacity = capacity;
+        this.maxTTL = maxTTL;
+        backend = new LinkedHashMap<Question,DNSMessage>(
+                Math.min(capacity, 11), 0.75f, true)
+            {
+                @Override
+                protected boolean removeEldestEntry(
+                        Entry<Question, DNSMessage> eldest) {
+                    return size() > capacity;
+                }
+            };
+    }
+
+    /**
+     * Create a new LRUCache with given capacity.
+     * @param capacity
+     */
+    public LRUCache(final int capacity) {
+        this(capacity, Long.MAX_VALUE);
+    }
+
+    @Override
+    public synchronized void put(Question q, DNSMessage message) {
+        if (message.getReceiveTimestamp() <= 0l) {
+            return;
+        }
+        backend.put(q, message);
+    }
+
+    @Override
+    public synchronized DNSMessage get(Question q) {
+        DNSMessage message = backend.get(q);
+        if (message == null) {
+            missCount++;
+            return null;
+        }
+
+        long ttl = maxTTL;
+        for (Record r : message.getAnswers()) {
+            ttl = Math.min(ttl, r.ttl);
+        }
+        for (Record r : message.getAdditionalResourceRecords()) {
+            ttl = Math.min(ttl, r.ttl);
+        }
+        if (message.getReceiveTimestamp() + ttl > System.currentTimeMillis()) {
+            missCount++;
+            expireCount++;
+            backend.remove(q);
+            return null;
+        } else {
+            hitCount++;
+            return message;
+        }
+    }
+
+    /**
+     * Clear all entries in this cache.
+     */
+    public synchronized void clear() {
+        backend.clear();
+        missCount = 0l;
+        hitCount = 0l;
+        expireCount = 0l;
+    }
+
+    /**
+     * Get the miss count of this cache which is the number of fruitless
+     * get calls since this cache was last resetted.
+     * @return The number of cache misses.
+     */
+    public long getMissCount() {
+        return missCount;
+    }
+
+    /**
+     * The number of expires (cache hits that have had a ttl to low to be
+     * retrieved).
+     * @return The expire count.
+     */
+    public long getExpireCount() {
+        return expireCount;
+    }
+
+    /**
+     * The cache hit count (all sucessful calls to get).
+     * @return The hit count.
+     */
+    public long getHitCount() {
+        return hitCount;
+    }
+
+}