org.apache.accumulo.test.merkle.MerkleTree.java Source code

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Here is the source code for org.apache.accumulo.test.merkle.MerkleTree.java

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/*
 * 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.accumulo.test.merkle;

import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.apache.accumulo.core.util.Pair;

import com.google.common.collect.Iterables;

/**
 * 
 */
public class MerkleTree {
    protected List<MerkleTreeNode> leaves;
    protected String digestAlgorithm;

    public MerkleTree(List<MerkleTreeNode> leaves, String digestAlgorithm) {
        this.leaves = leaves;
        this.digestAlgorithm = digestAlgorithm;
    }

    public MerkleTreeNode getRootNode() throws NoSuchAlgorithmException {
        ArrayList<MerkleTreeNode> buffer = new ArrayList<>(leaves.size());
        buffer.addAll(leaves);

        while (buffer.size() > 1) {
            // Find two nodes that we want to roll up
            Pair<Integer, Integer> pairToJoin = findNextPair(buffer);

            // Make a parent node from them
            MerkleTreeNode parent = new MerkleTreeNode(
                    Arrays.asList(buffer.get(pairToJoin.getFirst()), buffer.get(pairToJoin.getSecond())),
                    digestAlgorithm);

            // Insert it back into the "tree" at the position of the first child
            buffer.set(pairToJoin.getFirst(), parent);

            // Remove the second child completely
            buffer.remove(pairToJoin.getSecond().intValue());

            // "recurse"
        }

        return Iterables.getOnlyElement(buffer);
    }

    protected Pair<Integer, Integer> findNextPair(List<MerkleTreeNode> nodes) {
        int i = 0, j = 1;
        while (i < nodes.size() && j < nodes.size()) {
            MerkleTreeNode left = nodes.get(i), right = nodes.get(j);

            // At the same level
            if (left.getLevel() == right.getLevel()) {
                return new Pair<Integer, Integer>(i, j);
            }

            // Peek to see if we have another element
            if (j + 1 < nodes.size()) {
                // If we do, try to match those
                i++;
                j++;
            } else {
                // Otherwise, the last two elements must be paired
                return new Pair<Integer, Integer>(i, j);
            }
        }

        if (2 < nodes.size()) {
            throw new IllegalStateException(
                    "Should not have exited loop without pairing two elements when we have at least 3 nodes");
        } else if (2 == nodes.size()) {
            return new Pair<Integer, Integer>(0, 1);
        } else {
            throw new IllegalStateException("Must have at least two nodes to pair");
        }
    }
}