mirror of
https://github.com/internetarchive/heritrix3.git
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345 lines
8.9 KiB
Java
345 lines
8.9 KiB
Java
/* GzipHeader
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*
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* $Id$
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*
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* Created on July 5, 2004
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*
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* Copyright (C) 2004 Internet Archive.
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*
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* This file is part of the Heritrix web crawler (crawler.archive.org).
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*
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* Heritrix is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser Public License as published by
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* the Free Software Foundation; either version 2.1 of the License, or
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* any later version.
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*
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* Heritrix is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser Public License for more details.
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*
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* You should have received a copy of the GNU Lesser Public License
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* along with Heritrix; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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package org.archive.io;
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import java.io.EOFException;
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import java.io.IOException;
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import java.io.InputStream;
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import java.util.zip.CRC32;
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import java.util.zip.Deflater;
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import java.util.zip.GZIPInputStream;
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/**
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* Read in the GZIP header.
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*
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* See RFC1952 for specification on what the header looks like.
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* Assumption is that stream is cued-up with the gzip header as the
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* next thing to be read.
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*
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* <p>Of <a href="http://jguru.com/faq/view.jsp?EID=13647">Java
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* and unsigned bytes</a>. That is, its always a signed int in
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* java no matter what the qualifier whether byte, char, etc.
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*
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* <p>Add accessors for optional filename, comment and MTIME.
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*
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* @author stack
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*/
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public class GzipHeader {
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/**
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* Length of minimal GZIP header.
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*
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* See RFC1952 for explaination of value of 10.
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*/
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public static final int MINIMAL_GZIP_HEADER_LENGTH = 10;
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/**
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* Total length of the gzip header.
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*/
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protected int length = 0;
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/**
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* The GZIP header FLG byte.
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*/
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protected int flg;
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/**
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* GZIP header XFL byte.
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*/
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private int xfl;
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/**
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* GZIP header OS byte.
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*/
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private int os;
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/**
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* Extra header field content.
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*/
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private byte [] fextra = null;
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/**
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* GZIP header MTIME field.
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*/
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private int mtime;
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/**
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* Shutdown constructor.
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*
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* Must pass an input stream.
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*/
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public GzipHeader() {
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super();
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}
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/**
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* Constructor.
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*
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* This constructor advances the stream past any gzip header found.
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*
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* @param in InputStream to read from.
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* @throws IOException
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*/
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public GzipHeader(InputStream in) throws IOException {
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super();
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readHeader(in);
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}
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/**
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* Read in gzip header.
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*
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* Advances the stream past the gzip header.
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* @param in InputStream.
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*
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* @throws IOException Throws if does not start with GZIP Header.
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*/
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public void readHeader(InputStream in) throws IOException {
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CRC32 crc = new CRC32();
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crc.reset();
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if (!testGzipMagic(in, crc)) {
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throw new NoGzipMagicException();
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}
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this.length += 2;
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if (readByte(in, crc) != Deflater.DEFLATED) {
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throw new IOException("Unknown compression");
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}
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this.length++;
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// Get gzip header flag.
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this.flg = readByte(in, crc);
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this.length++;
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// Get MTIME.
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this.mtime = readInt(in, crc);
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this.length += 4;
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// Read XFL and OS.
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this.xfl = readByte(in, crc);
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this.length++;
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this.os = readByte(in, crc);
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this.length++;
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// Skip optional extra field -- stuff w/ alexa stuff in it.
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final int FLG_FEXTRA = 4;
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if ((this.flg & FLG_FEXTRA) == FLG_FEXTRA) {
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int count = readShort(in, crc);
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this.length +=2;
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this.fextra = new byte[count];
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readByte(in, crc, this.fextra, 0, count);
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this.length += count;
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}
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// Skip file name. It ends in null.
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final int FLG_FNAME = 8;
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if ((this.flg & FLG_FNAME) == FLG_FNAME) {
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while (readByte(in, crc) != 0) {
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this.length++;
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}
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}
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// Skip file comment. It ends in null.
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final int FLG_FCOMMENT = 16; // File comment
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if ((this.flg & FLG_FCOMMENT) == FLG_FCOMMENT) {
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while (readByte(in, crc) != 0) {
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this.length++;
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}
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}
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// Check optional CRC.
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final int FLG_FHCRC = 2;
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if ((this.flg & FLG_FHCRC) == FLG_FHCRC) {
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int calcCrc = (int)(crc.getValue() & 0xffff);
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if (readShort(in, crc) != calcCrc) {
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throw new IOException("Bad header CRC");
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}
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this.length += 2;
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}
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}
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/**
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* Test gzip magic is next in the stream.
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* Reads two bytes. Caller needs to manage resetting stream.
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* @param in InputStream to read.
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* @return true if found gzip magic. False otherwise
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* or an IOException (including EOFException).
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* @throws IOException
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*/
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public boolean testGzipMagic(InputStream in) throws IOException {
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return testGzipMagic(in, null);
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}
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/**
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* Test gzip magic is next in the stream.
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* Reads two bytes. Caller needs to manage resetting stream.
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* @param in InputStream to read.
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* @param crc CRC to update.
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* @return true if found gzip magic. False otherwise
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* or an IOException (including EOFException).
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* @throws IOException
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*/
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public boolean testGzipMagic(InputStream in, CRC32 crc)
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throws IOException {
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return readShort(in, crc) == GZIPInputStream.GZIP_MAGIC;
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}
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/**
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* Read an int.
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*
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* We do not expect to get a -1 reading. If we do, we throw exception.
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* Update the crc as we go.
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*
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* @param in InputStream to read.
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* @param crc CRC to update.
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* @return int read.
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*
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* @throws IOException
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*/
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private int readInt(InputStream in, CRC32 crc) throws IOException {
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int s = readShort(in, crc);
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return ((readShort(in, crc) << 16) & 0xffff0000) | s;
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}
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/**
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* Read a short.
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*
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* We do not expect to get a -1 reading. If we do, we throw exception.
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* Update the crc as we go.
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*
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* @param in InputStream to read.
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* @param crc CRC to update.
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* @return Short read.
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*
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* @throws IOException
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*/
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private int readShort(InputStream in, CRC32 crc) throws IOException {
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int b = readByte(in, crc);
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return ((readByte(in, crc) << 8) & 0x00ff00) | b;
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}
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/**
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* Read a byte.
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*
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* We do not expect to get a -1 reading. If we do, we throw exception.
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* Update the crc as we go.
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*
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* @param in InputStream to read.
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* @return Byte read.
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*
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* @throws IOException
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*/
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protected int readByte(InputStream in) throws IOException {
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return readByte(in, null);
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}
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/**
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* Read a byte.
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*
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* We do not expect to get a -1 reading. If we do, we throw exception.
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* Update the crc as we go.
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*
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* @param in InputStream to read.
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* @param crc CRC to update.
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* @return Byte read.
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*
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* @throws IOException
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*/
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protected int readByte(InputStream in, CRC32 crc) throws IOException {
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int b = in.read();
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if (b == -1) {
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throw new EOFException();
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}
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if (crc != null) {
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crc.update(b);
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}
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return b & 0xff;
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}
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/**
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* Read a byte.
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*
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* We do not expect to get a -1 reading. If we do, we throw exception.
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* Update the crc as we go.
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*
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* @param in InputStream to read.
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* @param crc CRC to update.
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* @param buffer Buffer to read into.
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* @param offset Offset to start filling buffer at.
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* @param length How much to read.
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* @return Bytes read.
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*
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* @throws IOException
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*/
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protected int readByte(InputStream in, CRC32 crc, byte [] buffer,
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int offset, int length)
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throws IOException {
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for (int i = offset; i < length; i++) {
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buffer[offset + i] = (byte)readByte(in, crc);
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}
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return length;
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}
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/**
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* @return Returns the fextra.
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*/
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public byte[] getFextra() {
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return this.fextra;
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}
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/**
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* @return Returns the flg.
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*/
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public int getFlg() {
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return this.flg;
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}
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/**
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* @return Returns the os.
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*/
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public int getOs() {
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return this.os;
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}
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/**
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* @return Returns the xfl.
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*/
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public int getXfl() {
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return this.xfl;
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}
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/**
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* @return Returns the mtime.
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*/
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public int getMtime() {
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return this.mtime;
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}
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/**
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* @return Returns the length.
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*/
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public int getLength() {
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return length;
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}
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}
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