/**
* Creates CompressionInputStream to be used to read off uncompressed data in one of the two
* reading modes. i.e. Continuous or Blocked reading modes
*
* @param seekableIn The InputStream
* @param start The start offset into the compressed stream
* @param end The end offset into the compressed stream
* @param readMode Controls whether progress is reported continuously or only at block boundaries.
* @return CompressionInputStream for BZip2 aligned at block boundaries
*/
public SplitCompressionInputStream createInputStream(
InputStream seekableIn, Decompressor decompressor, long start, long end, READ_MODE readMode)
throws IOException {
if (!(seekableIn instanceof Seekable)) {
throw new IOException("seekableIn must be an instance of " + Seekable.class.getName());
}
// find the position of first BZip2 start up marker
((Seekable) seekableIn).seek(0);
// BZip2 start of block markers are of 6 bytes. But the very first block
// also has "BZh9", making it 10 bytes. This is the common case. But at
// time stream might start without a leading BZ.
final long FIRST_BZIP2_BLOCK_MARKER_POSITION =
CBZip2InputStream.numberOfBytesTillNextMarker(seekableIn);
long adjStart = Math.max(0L, start - FIRST_BZIP2_BLOCK_MARKER_POSITION);
((Seekable) seekableIn).seek(adjStart);
SplitCompressionInputStream in =
new BZip2CompressionInputStream(seekableIn, adjStart, end, readMode);
// The following if clause handles the following case:
// Assume the following scenario in BZip2 compressed stream where
// . represent compressed data.
// .....[48 bit Block].....[48 bit Block].....[48 bit Block]...
// ........................[47 bits][1 bit].....[48 bit Block]...
// ................................^[Assume a Byte alignment here]
// ........................................^^[current position of stream]
// .....................^^[We go back 10 Bytes in stream and find a Block marker]
// ........................................^^[We align at wrong position!]
// ...........................................................^^[While this pos is correct]
if (in.getPos() <= start) {
((Seekable) seekableIn).seek(start);
in = new BZip2CompressionInputStream(seekableIn, start, end, readMode);
}
return in;
}
