/*
* This file is part of the Heritrix web crawler (crawler.archive.org).
*
* Licensed to the Internet Archive (IA) by one or more individual
* contributors.
*
* The IA 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.archive.util.zip;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.CRC32;
import java.util.zip.Deflater;
import java.util.zip.GZIPInputStream;
/**
* Read in the GZIP header.
*
* See RFC1952 for specification on what the header looks like.
* Assumption is that stream is cued-up with the gzip header as the
* next thing to be read.
*
* <p>Of <a href="http://jguru.com/faq/view.jsp?EID=13647">Java
* and unsigned bytes</a>. That is, its always a signed int in
* java no matter what the qualifier whether byte, char, etc.
*
* <p>Add accessors for optional filename, comment and MTIME.
*
* @author stack
*/
public class GzipHeader {
/**
* Length of minimal GZIP header.
*
* See RFC1952 for explaination of value of 10.
*/
public static final int MINIMAL_GZIP_HEADER_LENGTH = 10;
/**
* Total length of the gzip header.
*/
protected int length = 0;
/**
* The GZIP header FLG byte.
*/
protected int flg;
/**
* GZIP header XFL byte.
*/
private int xfl;
/**
* GZIP header OS byte.
*/
private int os;
/**
* Extra header field content.
*/
private byte [] fextra = null;
/**
* GZIP header MTIME field.
*/
private int mtime;
/**
* Shutdown constructor.
*
* Must pass an input stream.
*/
public GzipHeader() {
super();
}
/**
* Constructor.
*
* This constructor advances the stream past any gzip header found.
*
* @param in InputStream to read from.
* @throws IOException
*/
public GzipHeader(InputStream in) throws IOException {
super();
readHeader(in);
}
/**
* Read in gzip header.
*
* Advances the stream past the gzip header.
* @param in InputStream.
*
* @throws IOException Throws if does not start with GZIP Header.
*/
public void readHeader(InputStream in) throws IOException {
CRC32 crc = new CRC32();
crc.reset();
if (!testGzipMagic(in, crc)) {
throw new NoGzipMagicException();
}
this.length += 2;
if (readByte(in, crc) != Deflater.DEFLATED) {
throw new IOException("Unknown compression");
}
this.length++;
// Get gzip header flag.
this.flg = readByte(in, crc);
this.length++;
// Get MTIME.
this.mtime = readInt(in, crc);
this.length += 4;
// Read XFL and OS.
this.xfl = readByte(in, crc);
this.length++;
this.os = readByte(in, crc);
this.length++;
// Skip optional extra field -- stuff w/ alexa stuff in it.
final int FLG_FEXTRA = 4;
if ((this.flg & FLG_FEXTRA) == FLG_FEXTRA) {
int count = readShort(in, crc);
this.length +=2;
this.fextra = new byte[count];
readByte(in, crc, this.fextra, 0, count);
this.length += count;
}
// Skip file name. It ends in null.
final int FLG_FNAME = 8;
if ((this.flg & FLG_FNAME) == FLG_FNAME) {
while (readByte(in, crc) != 0) {
this.length++;
}
}
// Skip file comment. It ends in null.
final int FLG_FCOMMENT = 16; // File comment
if ((this.flg & FLG_FCOMMENT) == FLG_FCOMMENT) {
while (readByte(in, crc) != 0) {
this.length++;
}
}
// Check optional CRC.
final int FLG_FHCRC = 2;
if ((this.flg & FLG_FHCRC) == FLG_FHCRC) {
int calcCrc = (int)(crc.getValue() & 0xffff);
if (readShort(in, crc) != calcCrc) {
throw new IOException("Bad header CRC");
}
this.length += 2;
}
}
/**
* Test gzip magic is next in the stream.
* Reads two bytes. Caller needs to manage resetting stream.
* @param in InputStream to read.
* @return true if found gzip magic. False otherwise
* or an IOException (including EOFException).
* @throws IOException
*/
public boolean testGzipMagic(InputStream in) throws IOException {
return testGzipMagic(in, null);
}
/**
* Test gzip magic is next in the stream.
* Reads two bytes. Caller needs to manage resetting stream.
* @param in InputStream to read.
* @param crc CRC to update.
* @return true if found gzip magic. False otherwise
* or an IOException (including EOFException).
* @throws IOException
*/
public boolean testGzipMagic(InputStream in, CRC32 crc)
throws IOException {
return readShort(in, crc) == GZIPInputStream.GZIP_MAGIC;
}
/**
* Read an int.
*
* We do not expect to get a -1 reading. If we do, we throw exception.
* Update the crc as we go.
*
* @param in InputStream to read.
* @param crc CRC to update.
* @return int read.
*
* @throws IOException
*/
private int readInt(InputStream in, CRC32 crc) throws IOException {
int s = readShort(in, crc);
return ((readShort(in, crc) << 16) & 0xffff0000) | s;
}
/**
* Read a short.
*
* We do not expect to get a -1 reading. If we do, we throw exception.
* Update the crc as we go.
*
* @param in InputStream to read.
* @param crc CRC to update.
* @return Short read.
*
* @throws IOException
*/
private int readShort(InputStream in, CRC32 crc) throws IOException {
int b = readByte(in, crc);
return ((readByte(in, crc) << 8) & 0x00ff00) | b;
}
/**
* Read a byte.
*
* We do not expect to get a -1 reading. If we do, we throw exception.
* Update the crc as we go.
*
* @param in InputStream to read.
* @return Byte read.
*
* @throws IOException
*/
protected int readByte(InputStream in) throws IOException {
return readByte(in, null);
}
/**
* Read a byte.
*
* We do not expect to get a -1 reading. If we do, we throw exception.
* Update the crc as we go.
*
* @param in InputStream to read.
* @param crc CRC to update.
* @return Byte read.
*
* @throws IOException
*/
protected int readByte(InputStream in, CRC32 crc) throws IOException {
int b = in.read();
if (b == -1) {
throw new EOFException();
}
if (crc != null) {
crc.update(b);
}
return b & 0xff;
}
/**
* Read a byte.
*
* We do not expect to get a -1 reading. If we do, we throw exception.
* Update the crc as we go.
*
* @param in InputStream to read.
* @param crc CRC to update.
* @param buffer Buffer to read into.
* @param offset Offset to start filling buffer at.
* @param length How much to read.
* @return Bytes read.
*
* @throws IOException
*/
protected int readByte(InputStream in, CRC32 crc, byte [] buffer,
int offset, int length)
throws IOException {
for (int i = offset; i < length; i++) {
buffer[offset + i] = (byte)readByte(in, crc);
}
return length;
}
/**
* @return Returns the fextra.
*/
public byte[] getFextra() {
return this.fextra;
}
/**
* @return Returns the flg.
*/
public int getFlg() {
return this.flg;
}
/**
* @return Returns the os.
*/
public int getOs() {
return this.os;
}
/**
* @return Returns the xfl.
*/
public int getXfl() {
return this.xfl;
}
/**
* @return Returns the mtime.
*/
public int getMtime() {
return this.mtime;
}
/**
* @return Returns the length.
*/
public int getLength() {
return length;
}
}