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package biz.paluch.logging.gelf.intern;
import java.io.IOException;
import java.io.OutputStream;
import java.util.zip.CRC32;
import java.util.zip.Deflater;
import java.util.zip.DeflaterOutputStream;
/**
* This class implements a stream filter for writing compressed data in the GZIP file format. It's an adoption of
* {@link java.util.zip.GZIPOutputStream} but with a notable difference regarding re-usability:
*
*
Expose {@link #reset()} to reset CRC32 and the deflater
*
Don't write the GZIP header upon construction but expose {@link #writeHeader()}
*
*
* @author Mark Paluch
* @since 1.11
*/
class ReusableGzipOutputStream extends DeflaterOutputStream {
/**
* CRC-32 of uncompressed data.
*/
private final CRC32 crc = new CRC32();
/*
* GZIP header magic number.
*/
private static final int GZIP_MAGIC = 0x8b1f;
/*
* Trailer size in bytes.
*
*/
private static final int TRAILER_SIZE = 8;
/**
* Creates a new output stream with the specified buffer size and flush mode.
*
* @param out the output stream
* @exception IOException If an I/O error has occurred.
* @exception IllegalArgumentException if {@code size <= 0}
*
* @since 1.7
*/
public ReusableGzipOutputStream(OutputStream out) throws IOException {
super(out, new Deflater(Deflater.DEFAULT_COMPRESSION, true));
crc.reset();
}
/**
* Writes array of bytes to the compressed output stream. This method will block until all the bytes are written.
*
* @param buf the data to be written
* @param off the start offset of the data
* @param len the length of the data
* @exception IOException If an I/O error has occurred.
*/
@Override
public synchronized void write(byte[] buf, int off, int len) throws IOException {
super.write(buf, off, len);
crc.update(buf, off, len);
}
/**
* Finishes writing compressed data to the output stream without closing the underlying stream. Use this method when
* applying multiple filters in succession to the same output stream.
*
* @exception IOException if an I/O error has occurred
*/
@Override
public void finish() throws IOException {
if (!def.finished()) {
def.finish();
while (!def.finished()) {
int len = def.deflate(buf, 0, buf.length);
if (def.finished() && len <= buf.length - TRAILER_SIZE) {
// last deflater buffer. Fit trailer at the end
writeTrailer(buf, len);
len = len + TRAILER_SIZE;
out.write(buf, 0, len);
return;
}
if (len > 0)
out.write(buf, 0, len);
}
// if we can't fit the trailer at the end of the last
// deflater buffer, we write it separately
byte[] trailer = new byte[TRAILER_SIZE];
writeTrailer(trailer, 0);
out.write(trailer);
}
}
/*
* Writes GZIP member header.
*/
public void writeHeader() throws IOException {
out.write(new byte[] { (byte) GZIP_MAGIC, // Magic number (short)
(byte) (GZIP_MAGIC >> 8), // Magic number (short)
Deflater.DEFLATED, // Compression method (CM)
0, // Flags (FLG)
0, // Modification time MTIME (int)
0, // Modification time MTIME (int)
0, // Modification time MTIME (int)
0, // Modification time MTIME (int)
0, // Extra flags (XFLG)
0 // Operating system (OS)
});
}
/*
* Writes GZIP member trailer to a byte array, starting at a given offset.
*/
private void writeTrailer(byte[] buf, int offset) {
writeInt((int) crc.getValue(), buf, offset); // CRC-32 of uncompr. data
writeInt(def.getTotalIn(), buf, offset + 4); // Number of uncompr. bytes
}
/*
* Writes integer in Intel byte order to a byte array, starting at a given offset.
*/
private void writeInt(int i, byte[] buf, int offset) {
writeShort(i & 0xffff, buf, offset);
writeShort((i >> 16) & 0xffff, buf, offset + 2);
}
/*
* Writes short integer in Intel byte order to a byte array, starting at a given offset
*/
private void writeShort(int s, byte[] buf, int offset) {
buf[offset] = (byte) (s & 0xff);
buf[offset + 1] = (byte) ((s >> 8) & 0xff);
}
public void reset() {
crc.reset();
def.reset();
}
}
