{

virtual ~ICompressionCodec() = default;

/// Byte which indicates codec in compressed file

virtual uint8_t getMethodByte() const = 0;

/// Codec description, for example "ZSTD(2)" or "LZ4,LZ4HC(5)"

virtual ASTPtr getCodecDesc() const;

/// Codec description with "CODEC" prefix, for example "CODEC(ZSTD(2))" or

/// "CODEC(LZ4,LZ4HC(5))"

ASTPtr getFullCodecDesc() const;

/// Hash, that depends on codec ast and optional parameters like data type

virtual void updateHash(SipHash & hash) const = 0;

UInt64 getHash() const;

/// Compressed bytes from uncompressed source to dest. Dest should preallocate memory

virtual UInt32 compress(const char * source, UInt32 source_size, char * dest) const;

/// Decompress bytes from compressed source to dest. Dest should preallocate memory;

UInt32 decompress(const char * source, UInt32 source_size, char * dest) const;

/// Exact compressed payload size (no header) for the given input. std::nullopt if this codec cannot determine its output size cheaply.

/// Same value as doCompressData would return, computed without actually compressing.

virtual std::optional<UInt32> tryGetCompressedSize(const char * /*source*/, UInt32 /*source_size*/) const { return std::nullopt; }

/// Report decompression errors as CANNOT_DECOMPRESS, not CORRUPTED_DATA

void setExternalDataFlag() { decompression_error_code = ErrorCodes::CANNOT_DECOMPRESS; }

/// Number of bytes, that will be used to compress uncompressed_size bytes with current codec

virtual UInt32 getCompressedReserveSize(UInt32 uncompressed_size) const

{

return getHeaderSize() + getMaxCompressedDataSize(uncompressed_size);

}

/// Some codecs (LZ4, for example) require additional bytes at end of buffer

virtual UInt32 getAdditionalSizeAtTheEndOfBuffer() const { return 0; }

/// Size of header in compressed data on disk

static constexpr UInt8 getHeaderSize() { return COMPRESSED_BLOCK_HEADER_SIZE; }

/// Read size of compressed block from compressed source

UInt32 readCompressedBlockSize(const char * source) const;

/// Read size of decompressed block from compressed source

UInt32 readDecompressedBlockSize(const char * source) const;

/// Does the codec need to know the vector (Array) dimension before compression?

virtual bool needsVectorDimensionUpfront() const { return false; }

/// Setting dimension is useful for vector codecs (only SZ3 codec at the moment).

virtual void setAndCheckVectorDimension(size_t /*dimension*/);

/// Read method byte from compressed source

static uint8_t readMethod(const char * source);

/// Return true if this codec actually compressing something. Otherwise it can be just transformation that helps compression (e.g. Delta).

virtual bool isCompression() const = 0;

/// Is it a generic compression algorithm like lz4, zstd. Usually it does not make sense to apply generic compression more than single time.

virtual bool isGenericCompression() const = 0;

/// If it is a post-processing codec such as encryption. Usually it does not make sense to apply non-post-processing codecs after this.

virtual bool isEncryption() const { return false; }

/// If it is a specialized codec for floating-point time series. Applying it to non-floating point data is suspicious.

virtual bool isFloatingPointTimeSeriesCodec() const { return false; }

/// If the codec's purpose is to calculate deltas between consecutive values.

virtual bool isDeltaCompression() const { return false; }

virtual bool isLossyCompression() const { return false; }

/// It is a codec available only for evaluation purposes and not meant to be used in production.

/// It will not be allowed to use unless the user will turn off the safety switch.

virtual bool isExperimental() const { return false; }

/// If it does nothing.

virtual bool isNone() const { return false; }

// Returns a string with a high level codec description.

virtual String getDescription() const = 0;

/// This is used for fuzz testing

friend int LLVMFuzzerTestOneInput(const uint8_t * data, size_t size);

/// Upper bound on the compressed data size without the header. While compressing, a codec may temporarily write more bytes

/// into `dest` than its final result, so the bound covers those writes too and may exceed the actual compressed size.

virtual UInt32 getMaxCompressedDataSize(UInt32 uncompressed_size) const { return uncompressed_size; }

/// Actually compress data without header

virtual UInt32 doCompressData(const char * source, UInt32 source_size, char * dest) const = 0;

/// Actually decompress data without header

virtual UInt32 doDecompressData(const char * source, UInt32 source_size, char * dest, UInt32 uncompressed_size) const = 0;

/// Construct and set codec description from codec name and arguments. Must be called in codec constructor.

void setCodecDescription(const String & name, const ASTs & arguments);

void setCodecDescription(const String & name) { setCodecDescription(name, ASTs{}); }

int decompression_error_code = ErrorCodes::CORRUPTED_DATA;

ASTPtr full_codec_desc;