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Elasticsearch subproject :server
/*
* Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
* or more contributor license agreements. Licensed under the Elastic License
* 2.0 and the Server Side Public License, v 1; you may not use this file except
* in compliance with, at your election, the Elastic License 2.0 or the Server
* Side Public License, v 1.
*/
package org.elasticsearch.common;
import java.util.Base64;
import java.util.concurrent.atomic.AtomicInteger;
/**
* These are essentially flake ids, but we use 6 (not 8) bytes for timestamp, and use 3 (not 2) bytes for sequence number.
* For more information about flake ids, check out
* https://archive.fo/2015.07.08-082503/http://www.boundary.com/blog/2012/01/flake-a-decentralized-k-ordered-unique-id-generator-in-erlang/
*/
class LegacyTimeBasedUUIDGenerator implements UUIDGenerator {
// We only use bottom 3 bytes for the sequence number. Paranoia: init with random int so that if JVM/OS/machine goes down, clock slips
// backwards, and JVM comes back up, we are less likely to be on the same sequenceNumber at the same time:
private final AtomicInteger sequenceNumber = new AtomicInteger(SecureRandomHolder.INSTANCE.nextInt());
// Used to ensure clock moves forward:
private long lastTimestamp;
private static final byte[] SECURE_MUNGED_ADDRESS = MacAddressProvider.getSecureMungedAddress();
static {
assert SECURE_MUNGED_ADDRESS.length == 6;
}
/** Puts the lower numberOfLongBytes from l into the array, starting index pos. */
private static void putLong(byte[] array, long l, int pos, int numberOfLongBytes) {
for (int i = 0; i < numberOfLongBytes; ++i) {
array[pos + numberOfLongBytes - i - 1] = (byte) (l >>> (i * 8));
}
}
@Override
public String getBase64UUID() {
final int sequenceId = sequenceNumber.incrementAndGet() & 0xffffff;
long timestamp = System.currentTimeMillis();
synchronized (this) {
// Don't let timestamp go backwards, at least "on our watch" (while this JVM is running). We are still vulnerable if we are
// shut down, clock goes backwards, and we restart... for this we randomize the sequenceNumber on init to decrease chance of
// collision:
timestamp = Math.max(lastTimestamp, timestamp);
if (sequenceId == 0) {
// Always force the clock to increment whenever sequence number is 0, in case we have a long time-slip backwards:
timestamp++;
}
lastTimestamp = timestamp;
}
final byte[] uuidBytes = new byte[15];
// Only use lower 6 bytes of the timestamp (this will suffice beyond the year 10000):
putLong(uuidBytes, timestamp, 0, 6);
// MAC address adds 6 bytes:
System.arraycopy(SECURE_MUNGED_ADDRESS, 0, uuidBytes, 6, SECURE_MUNGED_ADDRESS.length);
// Sequence number adds 3 bytes:
putLong(uuidBytes, sequenceId, 12, 3);
assert 9 + SECURE_MUNGED_ADDRESS.length == uuidBytes.length;
return Base64.getUrlEncoder().withoutPadding().encodeToString(uuidBytes);
}
}