ClickHouse/dbms/include/DB/IO/CompressedReadBufferBase.h

#pragma once

#ifdef USE_QUICKLZ
	struct qlz_state_decompress;
#endif

#include <DB/Common/PODArray.h>


namespace DB
{

class ReadBuffer;

/** Basic functionality for implementation of
  *  CompressedReadBuffer, CompressedReadBufferFromFile and CachedCompressedReadBuffer.
  */
class CompressedReadBufferBase
{
protected:
	ReadBuffer * compressed_in;

	/// If 'compressed_in' buffer has whole compressed block - than use it. Otherwise copy parts of data to 'own_compressed_buffer'.
	PODArray<char> own_compressed_buffer;
	/// Points to memory, holding compressed block.
	char * compressed_buffer = nullptr;

#ifdef USE_QUICKLZ
	std::unique_ptr<qlz_state_decompress> qlz_state;
#else
	void * fixed_size_padding = nullptr;	/// ABI compatibility for USE_QUICKLZ
#endif

	/// Don't checksum on decompressing.
	bool disable_checksum = false;


	/// Read compressed data into compressed_buffer. Get size of decompressed data from block header. Checksum if need.
	/// Returns number of compressed bytes read.
	size_t readCompressedData(size_t & size_decompressed, size_t & size_compressed_without_checksum);

	void decompress(char * to, size_t size_decompressed, size_t size_compressed_without_checksum);

public:
	/// 'compressed_in' could be initialized lazily, but before first call of 'readCompressedData'.
	CompressedReadBufferBase(ReadBuffer * in = nullptr);
	~CompressedReadBufferBase();

	/** Disable checksums.
	  * For example, may be used when
	  *  compressed data is generated by client, that cannot calculate checksums, and fill checksums with zeros instead.
	  */
	void disableChecksumming()
	{
		disable_checksum = true;
	}
};

}