/*

* Copyright 2002-2015 the original author or authors.

*

* Licensed 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

*

* https://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.

*/

/*

* This class was taken from Spring https://github.com/spring-projects/spring-framework/blob/main/spring-core/src/main/java/org/springframework/util/AlternativeJdkIdGenerator.java

* as a way to get a more performant UUID generator for use as request ids. SecureRandom can be expensive

* to run on each request as per https://github.com/graphql-java/graphql-java/issues/3435, so this uses SecureRandom

* at application start and then the cheaper Random class each call after that.

*/

package graphql.util;

import graphql.Internal;

import java.math.BigInteger;

import java.security.SecureRandom;

import java.util.Random;

import java.util.UUID;

/**

* An id generator that uses {@link SecureRandom} for the initial seed and

* {@link Random} thereafter. This provides a better balance between securely random ids and performance.

*

* @author Rossen Stoyanchev

* @author Rob Winch

*/

@Internal

public class IdGenerator {

private static final IdGenerator idGenerator = new IdGenerator();

public static UUID uuid() {

return idGenerator.generateId();

}

private final Random random;

public IdGenerator() {

SecureRandom secureRandom = new SecureRandom();

byte[] seed = new byte[8];

secureRandom.nextBytes(seed);

this.random = new Random(new BigInteger(seed).longValue());

}

public UUID generateId() {

byte[] randomBytes = new byte[16];

this.random.nextBytes(randomBytes);

long mostSigBits = 0;

for (int i = 0; i < 8; i++) {

mostSigBits = (mostSigBits << 8) | (randomBytes[i] & 0xff);

}

long leastSigBits = 0;

for (int i = 8; i < 16; i++) {

leastSigBits = (leastSigBits << 8) | (randomBytes[i] & 0xff);

}

return new UUID(mostSigBits, leastSigBits);

}

}