Base32.java

/**
 *
 * Copyright 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
 *
 *     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.jivesoftware.smack.util.stringencoder;

import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;

/**
 * Base32 string encoding is useful for when filenames case-insensitive filesystems are encoded.
 * Base32 representation takes roughly 20% more space then Base64.
 *
 * @author Florian Schmaus
 * Based on code by Brian Wellington (bwelling@xbill.org)
 * @see <a href="http://en.wikipedia.org/wiki/Base32">Base32 Wikipedia entry</a>
 *
 */
public class Base32 {

    private static final StringEncoder<String> base32Stringencoder = new StringEncoder<String>() {

        @Override
        public String encode(String string) {
            return Base32.encode(string);
        }

        @Override
        public String decode(String string) {
            return Base32.decode(string);
        }

    };
    private static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";

    public static StringEncoder<String> getStringEncoder() {
        return base32Stringencoder;
    }

    public static String decode(String str) {
        ByteArrayOutputStream bs = new ByteArrayOutputStream();
        byte[] raw = str.getBytes(StandardCharsets.UTF_8);

        for (int i = 0; i < raw.length; i++) {
            char c = (char) raw[i];
            if (!Character.isWhitespace(c)) {
                c = Character.toUpperCase(c);
                bs.write((byte) c);
            }
        }

        while (bs.size() % 8 != 0)
            bs.write('8');

        byte[] in = bs.toByteArray();

        bs.reset();
        DataOutputStream ds = new DataOutputStream(bs);

        for (int i = 0; i < in.length / 8; i++) {
            short[] s = new short[8];
            int[] t = new int[5];

            int padlen = 8;
            for (int j = 0; j < 8; j++) {
                char c = (char) in[i * 8 + j];
                if (c == '8')
                    break;
                s[j] = (short) ALPHABET.indexOf(in[i * 8 + j]);
                if (s[j] < 0)
                    return null;
                padlen--;
            }
            int blocklen = paddingToLen(padlen);
            if (blocklen < 0)
                return null;

            // all 5 bits of 1st, high 3 (of 5) of 2nd
            t[0] = (s[0] << 3) | s[1] >> 2;
            // lower 2 of 2nd, all 5 of 3rd, high 1 of 4th
            t[1] = ((s[1] & 0x03) << 6) | (s[2] << 1) | (s[3] >> 4);
            // lower 4 of 4th, high 4 of 5th
            t[2] = ((s[3] & 0x0F) << 4) | ((s[4] >> 1) & 0x0F);
            // lower 1 of 5th, all 5 of 6th, high 2 of 7th
            t[3] = (s[4] << 7) | (s[5] << 2) | (s[6] >> 3);
            // lower 3 of 7th, all of 8th
            t[4] = ((s[6] & 0x07) << 5) | s[7];

            try {
                for (int j = 0; j < blocklen; j++)
                    ds.writeByte((byte) (t[j] & 0xFF));
            } catch (IOException e) {
                // This should not happen.
                throw new AssertionError(e);
            }
        }

        String res = new String(bs.toByteArray(), StandardCharsets.UTF_8);
        return res;
    }

    public static String encode(String str) {
        byte[] b = str.getBytes(StandardCharsets.UTF_8);
        ByteArrayOutputStream os = new ByteArrayOutputStream();

        for (int i = 0; i < (b.length + 4) / 5; i++) {
            short[] s = new short[5];
            int[] t = new int[8];

            int blocklen = 5;
            for (int j = 0; j < 5; j++) {
                if ((i * 5 + j) < b.length)
                    s[j] = (short) (b[i * 5 + j] & 0xFF);
                else {
                    s[j] = 0;
                    blocklen--;
                }
            }
            int padlen = lenToPadding(blocklen);

            // convert the 5 byte block into 8 characters (values 0-31).

            // upper 5 bits from first byte
            t[0] = (byte) ((s[0] >> 3) & 0x1F);
            // lower 3 bits from 1st byte, upper 2 bits from 2nd.
            t[1] = (byte) (((s[0] & 0x07) << 2) | ((s[1] >> 6) & 0x03));
            // bits 5-1 from 2nd.
            t[2] = (byte) ((s[1] >> 1) & 0x1F);
            // lower 1 bit from 2nd, upper 4 from 3rd
            t[3] = (byte) (((s[1] & 0x01) << 4) | ((s[2] >> 4) & 0x0F));
            // lower 4 from 3rd, upper 1 from 4th.
            t[4] = (byte) (((s[2] & 0x0F) << 1) | ((s[3] >> 7) & 0x01));
            // bits 6-2 from 4th
            t[5] = (byte) ((s[3] >> 2) & 0x1F);
            // lower 2 from 4th, upper 3 from 5th;
            t[6] = (byte) (((s[3] & 0x03) << 3) | ((s[4] >> 5) & 0x07));
            // lower 5 from 5th;
            t[7] = (byte) (s[4] & 0x1F);

            // write out the actual characters.
            for (int j = 0; j < t.length - padlen; j++) {
                char c = ALPHABET.charAt(t[j]);
                os.write(c);
            }
        }
        String res = new String(os.toByteArray(), StandardCharsets.UTF_8);
        return res;
    }

    private static int lenToPadding(int blocklen) {
        switch (blocklen) {
        case 1:
            return 6;
        case 2:
            return 4;
        case 3:
            return 3;
        case 4:
            return 1;
        case 5:
            return 0;
        default:
            return -1;
        }
    }

    private static int paddingToLen(int padlen) {
        switch (padlen) {
        case 6:
            return 1;
        case 4:
            return 2;
        case 3:
            return 3;
        case 1:
            return 4;
        case 0:
            return 5;
        default:
            return -1;
        }
    }

}