patrickfav/bytes-java

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src/main/java/at/favre/lib/bytes/Base64.java

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/*
 * Copyright 2017 Patrick Favre-Bulle
 *
 * 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 at.favre.lib.bytes;

import java.util.Arrays;

/**
 * From https://github.com/square/okio/blob/okio-parent-1.15.0/okio/src/main/java/okio/Base64.java
 * under Apache 2 license.
 *
 * @author Alexander Y. Kleymenov
 */
final class Base64 {
    private Base64() {
    }

    private static final byte[] MAP = new byte[]{
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',
            'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
            'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4',
            '5', '6', '7', '8', '9', '+', '/'
    };

    private static final byte[] URL_MAP = new byte[]{
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',
            'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
            'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4',
            '5', '6', '7', '8', '9', '-', '_'
    };

    static byte[] decode(CharSequence in) {
        // Ignore trailing '=' padding and whitespace from the input.
        int limit = in.length();
        for (; limit > 0; limit--) {
            char c = in.charAt(limit - 1);
            if (c != '=' && c != '\n' && c != '\r' && c != ' ' && c != '\t') {
                break;
            }
        }

        // If the input includes whitespace, this output array will be longer than necessary.
        byte[] out = new byte[(int) (limit * 6L / 8L)];
        int outCount = 0;
        int inCount = 0;

        int word = 0;
        for (int pos = 0; pos < limit; pos++) {
            char c = in.charAt(pos);

            int bits;
            if (c >= 'A' && c <= 'Z') {
                // char ASCII value
                //  A    65    0
                //  Z    90    25 (ASCII - 65)
                bits = c - 65;
            } else if (c >= 'a' && c <= 'z') {
                // char ASCII value
                //  a    97    26
                //  z    122   51 (ASCII - 71)
                bits = c - 71;
            } else if (c >= '0' && c <= '9') {
                // char ASCII value
                //  0    48    52
                //  9    57    61 (ASCII + 4)
                bits = c + 4;
            } else if (c == '+' || c == '-') {
                bits = 62;
            } else if (c == '/' || c == '_') {
                bits = 63;
            } else if (c == '\n' || c == '\r' || c == ' ' || c == '\t') {
                continue;
            } else {
                throw new IllegalArgumentException("invalid character to decode: " + c);
            }

            // Append this char's 6 bits to the word.
            word = (word << 6) | (byte) bits;

            // For every 4 chars of input, we accumulate 24 bits of output. Emit 3 bytes.
            inCount++;
            if (inCount % 4 == 0) {
                out[outCount++] = (byte) (word >> 16);
                out[outCount++] = (byte) (word >> 8);
                out[outCount++] = (byte) word;
            }
        }

        int lastWordChars = inCount % 4;
        if (lastWordChars == 1) {
            // We read 1 char followed by "===". But 6 bits is a truncated byte! Fail.
            return null;
        } else if (lastWordChars == 2) {
            // We read 2 chars followed by "==". Emit 1 byte with 8 of those 12 bits.
            word = word << 12;
            out[outCount++] = (byte) (word >> 16);
        } else if (lastWordChars == 3) {
            // We read 3 chars, followed by "=". Emit 2 bytes for 16 of those 18 bits.
            word = word << 6;
            out[outCount++] = (byte) (word >> 16);
            out[outCount++] = (byte) (word >> 8);
        }

        // If we sized our out array perfectly, we're done.
        if (outCount == out.length) return out;

        // Copy the decoded bytes to a new, right-sized array.
        return Arrays.copyOfRange(out, 0, outCount);
    }

    static byte[] encode(byte[] in) {
        return encode(in, false, true);
    }

    static byte[] encode(byte[] in, boolean urlSafe, boolean usePadding) {
        return encode(in, urlSafe ? URL_MAP : MAP, usePadding);
    }

    private static byte[] encode(byte[] in, byte[] map, boolean usePadding) {
        int length = outLength(in.length, usePadding);
        byte[] out = new byte[length];
        int index = 0, end = in.length - in.length % 3;
        for (int i = 0; i < end; i += 3) {
            out[index++] = map[(in[i] & 0xff) >> 2];
            out[index++] = map[((in[i] & 0x03) << 4) | ((in[i + 1] & 0xff) >> 4)];
            out[index++] = map[((in[i + 1] & 0x0f) << 2) | ((in[i + 2] & 0xff) >> 6)];
            out[index++] = map[(in[i + 2] & 0x3f)];
        }
        switch (in.length % 3) {
            case 1:
                out[index++] = map[(in[end] & 0xff) >> 2];
                out[index++] = map[(in[end] & 0x03) << 4];
                if (usePadding) {
                    out[index++] = '=';
                    out[index] = '=';
                }
                break;
            case 2:
                out[index++] = map[(in[end] & 0xff) >> 2];
                out[index++] = map[((in[end] & 0x03) << 4) | ((in[end + 1] & 0xff) >> 4)];
                out[index++] = map[((in[end + 1] & 0x0f) << 2)];

                if (usePadding) {
                    out[index] = '=';
                }
                break;
        }
        return out;
    }

    private static int outLength(int srclen, boolean doPadding) {
        int len;
        if (doPadding) {
            len = 4 * ((srclen + 2) / 3);
        } else {
            int n = srclen % 3;
            len = 4 * (srclen / 3) + (n == 0 ? 0 : n + 1);
        }
        return len;
    }
}