| /* |
| * 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.dump; |
| |
| import java.io.IOException; |
| import java.util.Arrays; |
| |
| import org.apache.commons.compress.archivers.zip.ZipEncoding; |
| import org.apache.commons.compress.utils.ByteUtils; |
| |
| /** |
| * Various utilities for dump archives. |
| */ |
| final class DumpArchiveUtil { |
| |
| /** |
| * Calculate checksum for buffer. |
| * |
| * @param buffer buffer containing tape segment header |
| * @return checksum |
| */ |
| public static int calculateChecksum(final byte[] buffer) { |
| int calc = 0; |
| for (int i = 0; i < 256; i++) { |
| calc += convert32(buffer, 4 * i); |
| } |
| return DumpArchiveConstants.CHECKSUM - (calc - convert32(buffer, 28)); |
| } |
| |
| /** |
| * Reads 2-byte integer from buffer. |
| * |
| * @param buffer The source buffer. |
| * @param offset Where to start reading. |
| * @return the 2-byte entry as an int. |
| */ |
| public static int convert16(final byte[] buffer, final int offset) { |
| return (int) ByteUtils.fromLittleEndian(buffer, offset, 2); |
| } |
| |
| /** |
| * Reads 4-byte integer from buffer. |
| * |
| * @param buffer The source buffer. |
| * @param offset Where to start reading. |
| * @return the 4-byte entry as an int. |
| */ |
| public static int convert32(final byte[] buffer, final int offset) { |
| return (int) ByteUtils.fromLittleEndian(buffer, offset, 4); |
| } |
| |
| /** |
| * Reads 8-byte integer from buffer. |
| * |
| * @param buffer The source buffer. |
| * @param offset Where to start reading. |
| * @return the 8-byte entry as a long. |
| */ |
| public static long convert64(final byte[] buffer, final int offset) { |
| return ByteUtils.fromLittleEndian(buffer, offset, 8); |
| } |
| |
| /** |
| * Decodes a byte array to a string. |
| */ |
| static String decode(final ZipEncoding encoding, final byte[] b, final int offset, final int len) throws IOException { |
| if (offset > offset + len) { |
| throw new IOException("Invalid offset/length combination"); |
| } |
| return encoding.decode(Arrays.copyOfRange(b, offset, offset + len)); |
| } |
| |
| /** |
| * Gets the ino associated with this buffer. |
| * |
| * @param buffer The source buffer. |
| * @return the ino associated with this buffer. |
| */ |
| public static int getIno(final byte[] buffer) { |
| return convert32(buffer, 20); |
| } |
| |
| /** |
| * Verifies that the buffer contains a tape segment header. |
| * |
| * @param buffer The source buffer. |
| * @return Whether the buffer contains a tape segment header. |
| */ |
| public static boolean verify(final byte[] buffer) { |
| if (buffer == null) { |
| return false; |
| } |
| // verify magic. for now only accept NFS_MAGIC. |
| final int magic = convert32(buffer, 24); |
| if (magic != DumpArchiveConstants.NFS_MAGIC) { |
| return false; |
| } |
| // verify checksum... |
| final int checksum = convert32(buffer, 28); |
| return checksum == calculateChecksum(buffer); |
| } |
| |
| /** |
| * Private constructor to prevent instantiation. |
| */ |
| private DumpArchiveUtil() { |
| } |
| } |