[GitHub] [tomcat] rmannibucau commented on a diff in pull request #607: Added RateLimitFilter

["rmannibucau (via GitHub)" <gi...@apache.org>]

rmannibucau commented on code in PR #607:
URL: https://github.com/apache/tomcat/pull/607#discussion_r1184594119


##########
java/org/apache/catalina/util/TimeBucketCounter.java:
##########
@@ -0,0 +1,217 @@
+/*
+ * 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.catalina.util;
+
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * this class maintains a thread safe hash map that has timestamp-based buckets
+ * followed by a string for a key, and a counter for a value. each time the
+ * increment() method is called it adds the key if it does not exist, increments
+ * its value and returns it.
+ *
+ * a maintenance thread cleans up keys that are prefixed by previous timestamp
+ * buckets.
+ */
+public class TimeBucketCounter {
+
+    /**
+     * Map to hold the buckets
+     */
+    private final ConcurrentHashMap<String, AtomicInteger> map = new ConcurrentHashMap<>();
+
+    /**
+     * Milliseconds bucket size as a Power of 2 for bit shift math, e.g.
+     * 16 for 65_536ms which is about 1:05 minute
+     */
+    private final int numBits;
+
+    /**
+     * ratio of actual duration to config duration
+     */
+    private final double ratio;
+
+    /**
+     * flag for the maintenance thread
+     */
+    volatile boolean isRunning = false;
+
+    /**
+     *
+     * @param bucketDuration duration in seconds, e.g. for 1 minute pass 60
+     */
+    public TimeBucketCounter(int bucketDuration) {
+
+        int durationMillis = bucketDuration * 1000;
+
+        int bits = 0;
+        int pof2 = nextPowerOf2(durationMillis);
+        int bitCheck = pof2;
+        while (bitCheck > 1) {
+            bitCheck = pof2 >> ++bits;
+        }
+
+        this.numBits = bits;
+
+        this.ratio = ratioToPowerOf2(durationMillis);
+
+        int cleanupsPerBucketDuration = (durationMillis >= 60_000) ? 6 : 3;
+        Thread mt = new MaintenanceThread(durationMillis / cleanupsPerBucketDuration);
+        mt.start();
+    }
+
+    /**
+     * increments the counter for the passed identifier in the current time
+     * bucket and returns the new value
+     *
+     * @param identifier an identifier for which we want to maintain count, e.g. IP Address
+     * @return the count within the current time bucket
+     */
+    public final int increment(String identifier) {
+        String key = getCurrentBucketPrefix() + "-" + identifier;
+        AtomicInteger ai = map.computeIfAbsent(key, v -> new AtomicInteger());
+        return ai.incrementAndGet();

Review Comment:
   Ok-ish but so should maybe be written as a limitation in the filter class javadoc cause rate limiting is way more generic than current impl (which is ok but reading the doc it is not obvious IMHO).



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