/*
 * 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.tomcat.util.security;

/**
 * Encode an MD5 digest into a String.
 * <p>
 * The 128 bit MD5 hash is converted into a 32 character long String.
 * Each character of the String is the hexadecimal representation of 4 bits
 * of the digest.
 *
 * @author Remy Maucherat
 */
public final class MD5Encoder {


    private MD5Encoder() {
        // Hide default constructor for utility class
    }


    private static final char[] hexadecimal = {'0', '1', '2', '3', '4', '5',
        '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};


    /**
     * Encodes the 128 bit (16 bytes) MD5 into a 32 character String.
     *
     * @param binaryData Array containing the digest
     *
     * @return Encoded MD5, or null if encoding failed
     */
    public static String encode(byte[] binaryData) {

        if (binaryData.length != 16)
            return null;

        char[] buffer = new char[32];

        for (int i=0; i<16; i++) {
            int low = binaryData[i] & 0x0f;
            int high = (binaryData[i] & 0xf0) >> 4;
            buffer[i*2] = hexadecimal[high];
            buffer[i*2 + 1] = hexadecimal[low];
        }

        return new String(buffer);
    }
}