src/main/java/org/apache/commons/compress/utils/ArchiveUtils.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.compress.utils;

import java.io.UnsupportedEncodingException;

import org.apache.commons.compress.archivers.ArchiveEntry;

/**
 * Generic Archive utilities
 */
public class ArchiveUtils {

    /** Private constructor to prevent instantiation of this utility class. */
    private ArchiveUtils(){
    }

    /**
     * Generates a string containing the name, isDirectory setting and size of an entry.
     * <p>
     * For example:
     * <pre>
     * -    2000 main.c
     * d     100 testfiles
     * </pre>
     * 
     * @param entry the entry
     * @return the representation of the entry
     */
    public static String toString(ArchiveEntry entry){
        StringBuilder sb = new StringBuilder();
        sb.append(entry.isDirectory()? 'd' : '-');// c.f. "ls -l" output
        String size = Long.toString(entry.getSize());
        sb.append(' ');
        // Pad output to 7 places, leading spaces
        for(int i=7; i > size.length(); i--){
            sb.append(' ');
        }
        sb.append(size);
        sb.append(' ').append(entry.getName());
        return sb.toString();
    }

    /**
     * Check if buffer contents matches Ascii String.
     * 
     * @param expected expected string
     * @param buffer the buffer
     * @param offset offset to read from
     * @param length length of the buffer
     * @return {@code true} if buffer is the same as the expected string
     */
    public static boolean matchAsciiBuffer(
            String expected, byte[] buffer, int offset, int length){
        byte[] buffer1;
        try {
            buffer1 = expected.getBytes(CharsetNames.US_ASCII);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e); // Should not happen
        }
        return isEqual(buffer1, 0, buffer1.length, buffer, offset, length, false);
    }

    /**
     * Check if buffer contents matches Ascii String.
     * 
     * @param expected the expected strin
     * @param buffer the buffer
     * @return {@code true} if buffer is the same as the expected string
     */
    public static boolean matchAsciiBuffer(String expected, byte[] buffer){
        return matchAsciiBuffer(expected, buffer, 0, buffer.length);
    }

    /**
     * Convert a string to Ascii bytes.
     * Used for comparing "magic" strings which need to be independent of the default Locale.
     * 
     * @param inputString string to convert
     * @return the bytes
     */
    public static byte[] toAsciiBytes(String inputString){
        try {
            return inputString.getBytes(CharsetNames.US_ASCII);
        } catch (UnsupportedEncodingException e) {
           throw new RuntimeException(e); // Should never happen
        }
    }

    /**
     * Convert an input byte array to a String using the ASCII character set.
     * 
     * @param inputBytes bytes to convert
     * @return the bytes, interpreted as an Ascii string
     */
    public static String toAsciiString(final byte[] inputBytes){
        try {
            return new String(inputBytes, CharsetNames.US_ASCII);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e); // Should never happen
        }
    }

    /**
     * Convert an input byte array to a String using the ASCII character set.
     * 
     * @param inputBytes input byte array
     * @param offset offset within array
     * @param length length of array
     * @return the bytes, interpreted as an Ascii string
     */
    public static String toAsciiString(final byte[] inputBytes, int offset, int length){
        try {
            return new String(inputBytes, offset, length, CharsetNames.US_ASCII);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e); // Should never happen
        }
    }

    /**
     * Compare byte buffers, optionally ignoring trailing nulls
     * 
     * @param buffer1 first buffer
     * @param offset1 first offset
     * @param length1 first length
     * @param buffer2 second buffer
     * @param offset2 second offset
     * @param length2 second length
     * @param ignoreTrailingNulls whether to ignore trailing nulls
     * @return {@code true} if buffer1 and buffer2 have same contents, having regard to trailing nulls
     */
    public static boolean isEqual(
            final byte[] buffer1, final int offset1, final int length1,
            final byte[] buffer2, final int offset2, final int length2,
            boolean ignoreTrailingNulls){
        int minLen=length1 < length2 ? length1 : length2;
        for (int i=0; i < minLen; i++){
            if (buffer1[offset1+i] != buffer2[offset2+i]){
                return false;
            }
        }
        if (length1 == length2){
            return true;
        }
        if (ignoreTrailingNulls){
            if (length1 > length2){
                for(int i = length2; i < length1; i++){
                    if (buffer1[offset1+i] != 0){
                        return false;
                    }
                }
            } else {
                for(int i = length1; i < length2; i++){
                    if (buffer2[offset2+i] != 0){
                        return false;
                    }
                }
            }
            return true;
        }
        return false;
    }

    /**
     * Compare byte buffers
     * 
     * @param buffer1 the first buffer
     * @param offset1 the first offset
     * @param length1 the first length
     * @param buffer2 the second buffer
     * @param offset2 the second offset
     * @param length2 the second length
     * @return {@code true} if buffer1 and buffer2 have same contents
     */
    public static boolean isEqual(
            final byte[] buffer1, final int offset1, final int length1,
            final byte[] buffer2, final int offset2, final int length2){
        return isEqual(buffer1, offset1, length1, buffer2, offset2, length2, false);
    }

    /**
     * Compare byte buffers
     * 
     * @param buffer1 the first buffer
     * @param buffer2 the second buffer
     * @return {@code true} if buffer1 and buffer2 have same contents
     */
    public static boolean isEqual(final byte[] buffer1, final byte[] buffer2 ){
        return isEqual(buffer1, 0, buffer1.length, buffer2, 0, buffer2.length, false);
    }

    /**
     * Compare byte buffers, optionally ignoring trailing nulls
     * 
     * @param buffer1 the first buffer
     * @param buffer2 the second buffer 
     * @param ignoreTrailingNulls whether to ignore tariling nulls
     * @return {@code true} if buffer1 and buffer2 have same contents
     */
    public static boolean isEqual(final byte[] buffer1, final byte[] buffer2, boolean ignoreTrailingNulls){
        return isEqual(buffer1, 0, buffer1.length, buffer2, 0, buffer2.length, ignoreTrailingNulls);
    }

    /**
     * Compare byte buffers, ignoring trailing nulls
     * 
     * @param buffer1 the first buffer
     * @param offset1 the first offset
     * @param length1 the first length
     * @param buffer2 the second buffer
     * @param offset2 the second offset
     * @param length2 the second length
     * @return {@code true} if buffer1 and buffer2 have same contents, having regard to trailing nulls
     */
    public static boolean isEqualWithNull(
            final byte[] buffer1, final int offset1, final int length1,
            final byte[] buffer2, final int offset2, final int length2){
        return isEqual(buffer1, offset1, length1, buffer2, offset2, length2, true);
    }
    
    /**
     * Returns true if the first N bytes of an array are all zero
     * 
     * @param a
     *            The array to check
     * @param size
     *            The number of characters to check (not the size of the array)
     * @return true if the first N bytes are zero
     */
    public static boolean isArrayZero(byte[] a, int size) {
        for (int i = 0; i < size; i++) {
            if (a[i] != 0) {
                return false;
            }
        }
        return true;
    }
}