com/android/net/module/util/HexDump.java

/*
 * Copyright (C) 2021 The Android Open Source Project
 *
 * 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
 *
 *      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 com.android.net.module.util;

import android.annotation.Nullable;

/**
 * Hex utility functions.
 */
public class HexDump {
    private static final char[] HEX_DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            'A', 'B', 'C', 'D', 'E', 'F' };
    private static final char[] HEX_LOWER_CASE_DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7',
            '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

    /**
     * Dump the hex string corresponding to the specified byte array.
     *
     * @param array byte array to be dumped.
     */
    public static String dumpHexString(@Nullable byte[] array) {
        if (array == null) return "(null)";
        return dumpHexString(array, 0, array.length);
    }

    /**
     * Dump the hex string corresponding to the specified byte array.
     *
     * @param array byte array to be dumped.
     * @param offset the offset in array where dump should start.
     * @param length the length of bytes to be dumped.
     */
    public static String dumpHexString(@Nullable byte[] array, int offset, int length) {
        if (array == null) return "(null)";
        StringBuilder result = new StringBuilder();

        byte[] line = new byte[16];
        int lineIndex = 0;

        result.append("\n0x");
        result.append(toHexString(offset));

        for (int i = offset; i < offset + length; i++) {
            if (lineIndex == 16) {
                result.append(" ");

                for (int j = 0; j < 16; j++) {
                    if (line[j] > ' ' && line[j] < '~') {
                        result.append(new String(line, j, 1));
                    } else {
                        result.append(".");
                    }
                }

                result.append("\n0x");
                result.append(toHexString(i));
                lineIndex = 0;
            }

            byte b = array[i];
            result.append(" ");
            result.append(HEX_DIGITS[(b >>> 4) & 0x0F]);
            result.append(HEX_DIGITS[b & 0x0F]);

            line[lineIndex++] = b;
        }

        if (lineIndex != 16) {
            int count = (16 - lineIndex) * 3;
            count++;
            for (int i = 0; i < count; i++) {
                result.append(" ");
            }

            for (int i = 0; i < lineIndex; i++) {
                if (line[i] > ' ' && line[i] < '~') {
                    result.append(new String(line, i, 1));
                } else {
                    result.append(".");
                }
            }
        }

        return result.toString();
    }

    /**
     * Convert a byte to an uppercase hex string.
     *
     * @param b the byte to be converted.
     */
    public static String toHexString(byte b) {
        return toHexString(toByteArray(b));
    }

    /**
     * Convert a byte array to an uppercase hex string.
     *
     * @param array the byte array to be converted.
     */
    public static String toHexString(byte[] array) {
        return toHexString(array, 0, array.length, true);
    }

    /**
     * Convert a byte array to a hex string.
     *
     * @param array the byte array to be converted.
     * @param upperCase whether the converted hex string should be uppercase or not.
     */
    public static String toHexString(byte[] array, boolean upperCase) {
        return toHexString(array, 0, array.length, upperCase);
    }

    /**
     * Convert a byte array to hex string.
     *
     * @param array the byte array to be converted.
     * @param offset the offset in array where conversion should start.
     * @param length the length of bytes to be converted.
     */
    public static String toHexString(byte[] array, int offset, int length) {
        return toHexString(array, offset, length, true);
    }

    /**
     * Convert a byte array to hex string.
     *
     * @param array the byte array to be converted.
     * @param offset the offset in array where conversion should start.
     * @param length the length of bytes to be converted.
     * @param upperCase whether the converted hex string should be uppercase or not.
     */
    public static String toHexString(byte[] array, int offset, int length, boolean upperCase) {
        char[] digits = upperCase ? HEX_DIGITS : HEX_LOWER_CASE_DIGITS;
        char[] buf = new char[length * 2];

        int bufIndex = 0;
        for (int i = offset; i < offset + length; i++) {
            byte b = array[i];
            buf[bufIndex++] = digits[(b >>> 4) & 0x0F];
            buf[bufIndex++] = digits[b & 0x0F];
        }

        return new String(buf);
    }

    /**
     * Convert an integer to hex string.
     *
     * @param i the integer to be converted.
     */
    public static String toHexString(int i) {
        return toHexString(toByteArray(i));
    }

    /**
     * Convert a byte to byte array.
     *
     * @param b the byte to be converted.
     */
    public static byte[] toByteArray(byte b) {
        byte[] array = new byte[1];
        array[0] = b;
        return array;
    }

    /**
     * Convert an integer to byte array.
     *
     * @param i the integer to be converted.
     */
    public static byte[] toByteArray(int i) {
        byte[] array = new byte[4];

        array[3] = (byte) (i & 0xFF);
        array[2] = (byte) ((i >> 8) & 0xFF);
        array[1] = (byte) ((i >> 16) & 0xFF);
        array[0] = (byte) ((i >> 24) & 0xFF);

        return array;
    }

    private static int toByte(char c) {
        if (c >= '0' && c <= '9') return (c - '0');
        if (c >= 'A' && c <= 'F') return (c - 'A' + 10);
        if (c >= 'a' && c <= 'f') return (c - 'a' + 10);

        throw new RuntimeException("Invalid hex char '" + c + "'");
    }

    /**
     * Convert a hex string to a byte array.
     *
     * @param hexString the string to be converted.
     */
    public static byte[] hexStringToByteArray(String hexString) {
        int length = hexString.length();
        byte[] buffer = new byte[length / 2];

        for (int i = 0; i < length; i += 2) {
            buffer[i / 2] =
                    (byte) ((toByte(hexString.charAt(i)) << 4) | toByte(hexString.charAt(i + 1)));
        }

        return buffer;
    }

    /**
     * Convert a byte to hex string and append it to StringBuilder.
     *
     * @param sb StringBuilder instance.
     * @param b the byte to be converted.
     * @param upperCase whether the converted hex string should be uppercase or not.
     */
    public static StringBuilder appendByteAsHex(StringBuilder sb, byte b, boolean upperCase) {
        char[] digits = upperCase ? HEX_DIGITS : HEX_LOWER_CASE_DIGITS;
        sb.append(digits[(b >> 4) & 0xf]);
        sb.append(digits[b & 0xf]);
        return sb;
    }
}