Using {@code GZIPInputStream} is easier than {@link ZipInputStream} * because GZIP is only for compression, and is not a container for multiple files. * This code decompresses the data from a GZIP stream, similar to the {@code gunzip(1)} utility. *
* InputStream is = ...
* GZIPInputStream zis = new GZIPInputStream(new BufferedInputStream(is));
* try {
* // Reading from 'zis' gets you the uncompressed bytes...
* processStream(zis);
* } finally {
* zis.close();
* }
*
*/
public class GZIPInputStream extends InflaterInputStream {
private static final int FCOMMENT = 16;
private static final int FEXTRA = 4;
private static final int FHCRC = 2;
private static final int FNAME = 8;
/**
* The magic header for the GZIP format.
*/
public static final int GZIP_MAGIC = 0x8b1f;
/**
* The checksum algorithm used when handling uncompressed data.
*/
protected CRC32 crc = new CRC32();
/**
* Indicates the end of the input stream.
*/
protected boolean eos = false;
/**
* Construct a {@code GZIPInputStream} to read from GZIP data from the
* underlying stream.
*
* @param is
* the {@code InputStream} to read data from.
* @throws IOException
* if an {@code IOException} occurs.
*/
public GZIPInputStream(InputStream is) throws IOException {
this(is, BUF_SIZE);
}
/**
* Construct a {@code GZIPInputStream} to read from GZIP data from the
* underlying stream. Set the internal buffer size to {@code size}.
*
* @param is
* the {@code InputStream} to read data from.
* @param size
* the internal read buffer size.
* @throws IOException
* if an {@code IOException} occurs.
*/
public GZIPInputStream(InputStream is, int size) throws IOException {
super(is, new Inflater(true), size);
byte[] header = new byte[10];
readFully(header, 0, header.length);
short magic = Memory.peekShort(header, 0, ByteOrder.LITTLE_ENDIAN);
if (magic != (short) GZIP_MAGIC) {
throw new IOException(String.format("unknown format (magic number %x)", magic));
}
int flags = header[3];
boolean hcrc = (flags & FHCRC) != 0;
if (hcrc) {
crc.update(header, 0, header.length);
}
if ((flags & FEXTRA) != 0) {
readFully(header, 0, 2);
if (hcrc) {
crc.update(header, 0, 2);
}
int length = Memory.peekShort(header, 0, ByteOrder.LITTLE_ENDIAN) & 0xffff;
while (length > 0) {
int max = length > buf.length ? buf.length : length;
int result = in.read(buf, 0, max);
if (result == -1) {
throw new EOFException();
}
if (hcrc) {
crc.update(buf, 0, result);
}
length -= result;
}
}
if ((flags & FNAME) != 0) {
readZeroTerminated(hcrc);
}
if ((flags & FCOMMENT) != 0) {
readZeroTerminated(hcrc);
}
if (hcrc) {
readFully(header, 0, 2);
short crc16 = Memory.peekShort(header, 0, ByteOrder.LITTLE_ENDIAN);
if ((short) crc.getValue() != crc16) {
throw new IOException("CRC mismatch");
}
crc.reset();
}
}
/**
* Closes this stream and any underlying streams.
*/
@Override
public void close() throws IOException {
eos = true;
super.close();
}
/**
* Reads and decompresses GZIP data from the underlying stream into the
* given buffer.
*/
@Override
public int read(byte[] buffer, int offset, int byteCount) throws IOException {
if (closed) {
throw new IOException("Stream is closed");
}
if (eos) {
return -1;
}
Arrays.checkOffsetAndCount(buffer.length, offset, byteCount);
int bytesRead;
try {
bytesRead = super.read(buffer, offset, byteCount);
} finally {
eos = eof; // update eos after every read(), even when it throws
}
if (bytesRead != -1) {
crc.update(buffer, offset, bytesRead);
}
if (eos) {
verifyCrc();
}
return bytesRead;
}
private void verifyCrc() throws IOException {
// Get non-compressed bytes read by fill
int size = inf.getRemaining();
final int trailerSize = 8; // crc (4 bytes) + total out (4 bytes)
byte[] b = new byte[trailerSize];
int copySize = (size > trailerSize) ? trailerSize : size;
System.arraycopy(buf, len - size, b, 0, copySize);
readFully(b, copySize, trailerSize - copySize);
if (Memory.peekInt(b, 0, ByteOrder.LITTLE_ENDIAN) != (int) crc.getValue()) {
throw new IOException("CRC mismatch");
}
if (Memory.peekInt(b, 4, ByteOrder.LITTLE_ENDIAN) != inf.getTotalOut()) {
throw new IOException("Size mismatch");
}
}
private void readFully(byte[] buffer, int offset, int length) throws IOException {
int result;
while (length > 0) {
result = in.read(buffer, offset, length);
if (result == -1) {
throw new EOFException();
}
offset += result;
length -= result;
}
}
private void readZeroTerminated(boolean hcrc) throws IOException {
int result;
while ((result = in.read()) > 0) {
if (hcrc) {
crc.update(result);
}
}
if (result == -1) {
throw new EOFException();
}
// Add the zero
if (hcrc) {
crc.update(result);
}
}
}