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Apache Commons Compress defines an API for working with compression and archive formats. These include bzip2, gzip, pack200, LZMA, XZ, Snappy, traditional Unix Compress, DEFLATE, DEFLATE64, LZ4, Brotli, Zstandard and ar, cpio, jar, tar, zip, dump, 7z, arj.
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/*
 * 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.compress.archivers.zip;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * This ZipEncoding implementation implements a simple 8bit character
 * set, which mets the following restrictions:
 * 
 * 
 * Characters 0x0000 to 0x007f are encoded as the corresponding
 *        byte values 0x00 to 0x7f.
 * All byte codes from 0x80 to 0xff are mapped to a unique unicode
 *       character in the range 0x0080 to 0x7fff. (No support for
 *       UTF-16 surrogates)
 * 
 * 
 * These restrictions most notably apply to the most prominent
 * omissions of java-1.4's {@link java.nio.charset.Charset Charset}
 * implementation, Cp437 and Cp850.
 * 
 * The methods of this class are reentrant.
 * @Immutable
 */
class Simple8BitZipEncoding implements ZipEncoding {

    /**
     * A character entity, which is put to the reverse mapping table
     * of a simple encoding.
     */
    private static final class Simple8BitChar implements Comparable {
        public final char unicode;
        public final byte code;

        Simple8BitChar(byte code, char unicode) {
            this.code = code;
            this.unicode = unicode;
        }

        public int compareTo(Simple8BitChar a) {
            return this.unicode - a.unicode;
        }

        @Override
        public String toString() {
            return "0x" + Integer.toHexString(0xffff & unicode)
                + "->0x" + Integer.toHexString(0xff & code);
        }

        @Override
        public boolean equals(Object o) {
            if (o instanceof Simple8BitChar) {
                Simple8BitChar other = (Simple8BitChar) o;
                return unicode == other.unicode && code == other.code;
            }
            return false;
        }

        @Override
        public int hashCode() {
            return unicode;
        }
    }

    /**
     * The characters for byte values of 128 to 255 stored as an array of
     * 128 chars.
     */
    private final char[] highChars;

    /**
     * A list of {@link Simple8BitChar} objects sorted by the unicode
     * field.  This list is used to binary search reverse mapping of
     * unicode characters with a character code greater than 127.
     */
    private final List reverseMapping;

    /**
     * @param highChars The characters for byte values of 128 to 255
     * stored as an array of 128 chars.
     */
    public Simple8BitZipEncoding(char[] highChars) {
        this.highChars = highChars.clone();
        List temp =
            new ArrayList(this.highChars.length);

        byte code = 127;

        for (char highChar : this.highChars) {
            temp.add(new Simple8BitChar(++code, highChar));
        }

        Collections.sort(temp);
        this.reverseMapping = Collections.unmodifiableList(temp);
    }

    /**
     * Return the character code for a given encoded byte.
     * 
     * @param b The byte to decode.
     * @return The associated character value.
     */
    public char decodeByte(byte b) {
        // code 0-127
        if (b >= 0) {
            return (char) b;
        }

        // byte is signed, so 128 == -128 and 255 == -1
        return this.highChars[128 + b];
    }

    /**
     * @param c The character to encode.
     * @return Whether the given unicode character is covered by this encoding.
     */
    public boolean canEncodeChar(char c) {

        if (c >= 0 && c < 128) {
            return true;
        }

        Simple8BitChar r = this.encodeHighChar(c);
        return r != null;
    }

    /**
     * Pushes the encoded form of the given character to the given byte buffer.
     * 
     * @param bb The byte buffer to write to.
     * @param c The character to encode.
     * @return Whether the given unicode character is covered by this encoding.
     *         If {@code false} is returned, nothing is pushed to the
     *         byte buffer. 
     */
    public boolean pushEncodedChar(ByteBuffer bb, char c) {

        if (c >= 0 && c < 128) {
            bb.put((byte) c);
            return true;
        }

        Simple8BitChar r = this.encodeHighChar(c);
        if (r == null) {
            return false;
        }
        bb.put(r.code);
        return true;
    }

    /**
     * @param c A unicode character in the range from 0x0080 to 0x7f00
     * @return A Simple8BitChar, if this character is covered by this encoding.
     *         A {@code null} value is returned, if this character is not
     *         covered by this encoding.
     */
    private Simple8BitChar encodeHighChar(char c) {
        // for performance an simplicity, yet another reincarnation of
        // binary search...
        int i0 = 0;
        int i1 = this.reverseMapping.size();

        while (i1 > i0) {

            int i = i0 + (i1 - i0) / 2;

            Simple8BitChar m = this.reverseMapping.get(i);

            if (m.unicode == c) {
                return m;
            }

            if (m.unicode < c) {
                i0 = i + 1;
            } else {
                i1 = i;
            }
        }

        if (i0 >= this.reverseMapping.size()) {
            return null;
        }

        Simple8BitChar r = this.reverseMapping.get(i0);

        if (r.unicode != c) {
            return null;
        }

        return r;
    }

    /**
     * @see
     * org.apache.commons.compress.archivers.zip.ZipEncoding#canEncode(java.lang.String)
     */
    public boolean canEncode(String name) {

        for (int i=0;i