src/main/java/org/apache/commons/fileupload/util/mime/Base64Decoder.java

/*
 * 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.commons.fileupload.util.mime;

import java.io.IOException;
import java.io.OutputStream;

/**
 * @since 1.3
 */
final class Base64Decoder {

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

    protected byte    padding = (byte)'=';

    /*
     * set up the decoding table.
     */
    protected final byte[] decodingTable = new byte[256];

    protected void initialiseDecodingTable() {
        for (int i = 0; i < encodingTable.length; i++) {
            decodingTable[encodingTable[i]] = (byte)i;
        }
    }

    public Base64Decoder() {
        initialiseDecodingTable();
    }

    private boolean ignore(
        char    c) {
        return (c == '\n' || c =='\r' || c == '\t' || c == ' ');
    }

    /**
     * decode the base 64 encoded byte data writing it to the given output stream,
     * whitespace characters will be ignored.
     *
     * @return the number of bytes produced.
     */
    public int decode(
        byte[]                data,
        int                    off,
        int                    length,
        OutputStream    out)
        throws IOException {
        byte    b1, b2, b3, b4;
        int        outLen = 0;

        int        end = off + length;

        while (end > 0) {
            if (!ignore((char)data[end - 1])) {
                break;
            }

            end--;
        }

        int  i = off;
        int  finish = end - 4;

        while (i < finish) {
            while ((i < finish) && ignore((char)data[i])) {
                i++;
            }

            b1 = decodingTable[data[i++]];

            while ((i < finish) && ignore((char)data[i])) {
                i++;
            }

            b2 = decodingTable[data[i++]];

            while ((i < finish) && ignore((char)data[i])) {
                i++;
            }

            b3 = decodingTable[data[i++]];

            while ((i < finish) && ignore((char)data[i])) {
                i++;
            }

            b4 = decodingTable[data[i++]];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            out.write((b3 << 6) | b4);

            outLen += 3;
        }

        if (data[end - 2] == padding) {
            b1 = decodingTable[data[end - 4]];
            b2 = decodingTable[data[end - 3]];

            out.write((b1 << 2) | (b2 >> 4));

            outLen += 1;
        } else if (data[end - 1] == padding) {
            b1 = decodingTable[data[end - 4]];
            b2 = decodingTable[data[end - 3]];
            b3 = decodingTable[data[end - 2]];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));

            outLen += 2;
        } else {
            b1 = decodingTable[data[end - 4]];
            b2 = decodingTable[data[end - 3]];
            b3 = decodingTable[data[end - 2]];
            b4 = decodingTable[data[end - 1]];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            out.write((b3 << 6) | b4);

            outLen += 3;
        }

        return outLen;
    }

}