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/*
* Copyright (c) 2019, Red Hat Inc. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
import java.lang.reflect.Constructor;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* @test
* @bug 8203190
* @summary Manual test to verify number of collisions in
* sun.security.ssl.SessionId.hashCode()
* @run main/manual SessionIdCollisionTest 100 20480 10000000
*/
/**
*
* Notes:
* - This is a manual test, not run automatically.
* - New default value of javax.net.ssl.sessionCacheSize in JDK 12+ is 20480
* - According to JDK-8210985 24 hours expired cache may exceed several million
* entries = > 10_000_000
*
* Example usage: java SessionIdCollissionTest 100 20480 10000000
*
* Expected outcome of running the test is to see fewer collisions and, more
* importantly fewer elements in buckets when there are collisions. See:
* http://mail.openjdk.java.net/pipermail/jdk8u-dev/2019-May/009345.html
*
*/
public class SessionIdCollisionTest {
private List<Integer> prepareHashCodes(int total) throws Exception {
Class<?> sessionIdClass = Class.forName("sun.security.ssl.SessionId");
Constructor<?> c = sessionIdClass.getDeclaredConstructor(byte[].class);
c.setAccessible(true);
// case of rejoinable session ids generates 32 random bytes
byte[] sessionIdBytes = new byte[32];
List<Integer> hashCodes = new ArrayList<>();
for (int i = 0; i < total; i++) {
SecureRandom random = new SecureRandom();
random.nextBytes(sessionIdBytes);
Object sessionId = c.newInstance(sessionIdBytes);
int hashCode = sessionId.hashCode();
hashCodes.add(hashCode);
}
return hashCodes;
}
private void printSummary(boolean withDistribution,
List<Integer> hashCodes) throws Exception {
final int bound = hashCodes.size();
Collections.sort(hashCodes);
int collisions = 0;
Map<Integer, List<Integer>> collCountsReverse = new HashMap<>();
for (int i = 0; i < bound - 1; i++) {
int oldval = hashCodes.get(i);
int nextval = hashCodes.get(i+1);
if (oldval == nextval) {
collisions++;
if (i == bound - 2) { // last elements
updateCollCountsReverse(collisions, collCountsReverse, oldval);
}
} else {
updateCollCountsReverse(collisions, collCountsReverse, oldval);
collisions = 0;
if (i == bound - 2) { // last elements
updateCollCountsReverse(collisions, collCountsReverse, nextval);
}
}
}
if (withDistribution) {
System.out.println("---- distribution ----");
}
int collCount = 0;
int maxLength = 0;
List<Integer> sorted = new ArrayList<>(collCountsReverse.size());
sorted.addAll(collCountsReverse.keySet());
Collections.sort(sorted);
for (Integer coll: sorted) {
List<Integer> hc = collCountsReverse.get(coll);
if (withDistribution) {
System.out.printf("Hashcodes with %02d collisions | " +
"hashCodes: %s\n", coll, hc.toString());
}
collCount += coll * hc.size();
if (coll > maxLength) {
maxLength = coll;
}
}
if (withDistribution) {
System.out.println("---- distribution ----");
}
System.out.println("Total number of collisions: " + collCount);
if (collCount > 0) {
System.out.println("Max length of collision list over all buckets: " +
maxLength);
}
}
private void updateCollCountsReverse(int collisions,
Map<Integer, List<Integer>> reverse, int val) {
List<Integer> hc = reverse.get(collisions);
if (hc == null) {
hc = new ArrayList<>();
hc.add(val);
reverse.put(collisions, hc);
} else {
hc.add(val);
}
}
public void doCollissionTest(int total) throws Exception {
System.out.println("Collision test for " + total + " sessions:");
System.out.println("------------------------------------------------");
List<Integer> hashcodes = prepareHashCodes(total);
printSummary(false, hashcodes);
System.out.println();
}
public static void main(String[] args) throws Exception {
if (args.length < 1) {
System.err.println("java " + SessionIdCollisionTest.class.getSimpleName() +
"<num-sessions> [<num-sessions> ...]");
System.exit(1);
}
SessionIdCollisionTest collTest = new SessionIdCollisionTest();
for (int i = 0; i < args.length; i++) {
int total = Integer.parseInt(args[i]);
collTest.doCollissionTest(total);
}
}
}
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