RtlCompressBuffer function (ntifs.h)

Article
09/28/2023

The RtlCompressBuffer function compresses a buffer and can be used by a file system driver to facilitate the implementation of file compression.

Syntax

NT_RTL_COMPRESS_API NTSTATUS RtlCompressBuffer(
  [in]  USHORT CompressionFormatAndEngine,
  [in]  PUCHAR UncompressedBuffer,
  [in]  ULONG  UncompressedBufferSize,
  [out] PUCHAR CompressedBuffer,
  [in]  ULONG  CompressedBufferSize,
  [in]  ULONG  UncompressedChunkSize,
  [out] PULONG FinalCompressedSize,
  [in]  PVOID  WorkSpace
);

Parameters

[in] CompressionFormatAndEngine

A bitmask that specifies the compression format and engine type. This parameter must be set to a valid bitwise OR combination of one format type and one engine type. For example, COMPRESSION_FORMAT_LZNT1 | COMPRESSION_ENGINE_STANDARD.

The meanings of these, and other related values, are as follows.

Value	Meaning
COMPRESSION_FORMAT_NONE	Not supported by this function.
COMPRESSION_FORMAT_DEFAULT	Not supported by this function.
COMPRESSION_FORMAT_LZNT1	The function will perform LZ compression.
COMPRESSION_FORMAT_XPRESS	The function will perform Xpress compression.
COMPRESSION_FORMAT_XPRESS_HUFF	The function will perform Xpress Huffman compression.
COMPRESSION_ENGINE_STANDARD	The UncompressedBuffer buffer is compressed using an algorithm that provides a balance between data compression and performance. This value cannot be used with COMPRESSION_ENGINE_MAXIMUM.
COMPRESSION_ENGINE_MAXIMUM	The UncompressedBuffer buffer is compressed using an algorithm that provides maximum data compression but with relatively slower performance. This value cannot be used with COMPRESSION_ENGINE_STANDARD.
COMPRESSION_ENGINE_HIBER	Not supported by this function.

[in] UncompressedBuffer

A pointer to a caller-allocated buffer (allocated from paged or non-paged pool) that contains the data to be compressed. This parameter is required and cannot be NULL.

[in] UncompressedBufferSize

The size, in bytes, of the UncompressedBuffer buffer.

[out] CompressedBuffer

A pointer to a caller-allocated buffer (allocated from paged or non-paged pool) that receives the compressed data. This parameter is required and cannot be NULL.

[in] CompressedBufferSize

The size, in bytes, of the CompressedBuffer buffer.

[in] UncompressedChunkSize

The chunk size to use when compressing the UncompressedBuffer buffer. This parameter must be one of the following values: 512, 1024, 2048, or 4096. The operating system uses 4096, and the recommended value for this parameter is also 4096.

[out] FinalCompressedSize

A pointer to a caller-allocated variable that receives the size, in bytes, of the compressed data stored in CompressedBuffer. This parameter is required and cannot be NULL.

[in] WorkSpace

A pointer to a caller-allocated work space buffer used by the RtlCompressBuffer function during compression. Use the RtlGetCompressionWorkSpaceSize function to determine the correct work space buffer size.

Return value

RtlCompressBuffer returns an appropriate error status value, such as one of the following.

Return code	Description
STATUS_SUCCESS	The UncompressedBuffer buffer was successfully compressed.
STATUS_BUFFER_ALL_ZEROS	The UncompressedBuffer buffer was successfully compressed, but this buffer contains only zeros.
STATUS_INVALID_PARAMETER	An invalid compression format was specified through the CompressionFormat parameter. If CompressionFormat is either COMPRESSION_FORMAT_NONE or COMPRESSION_FORMAT_DEFAULT (but not both), this value is returned.
STATUS_UNSUPPORTED_COMPRESSION	An invalid compression format was specified through the CompressionFormat parameter. If CompressionFormat is not one of the following, STATUS_UNSUPPORTED_COMPRESSION is returned: COMPRESSION_FORMAT_LZNT1, COMPRESSION_FORMAT_XPRESS, COMPRESSION_FORMAT_XPRESS_HUFF
STATUS_NOT_SUPPORTED	An invalid compression engine was specified through the CompressionFormatAndEngine parameter. If CompressionFormatAndEngine is not COMPRESSION_ENGINE_STANDARD or COMPRESSION_ENGINE_MAXIMUM (but not both), this value is returned.
STATUS_BUFFER_TOO_SMALL	The compressed buffer is too small to hold the compressed data. That is, FinalCompressedSize is greater than CompressedBufferSize.

Remarks

The RtlCompressBuffer function takes as input an uncompressed buffer and produces its compressed equivalent provided that the compressed data fits within the specified destination buffer.

To determine the correct buffer size for the WorkSpace parameter, use the RtlGetCompressionWorkSpaceSize function.

To decompress a compressed buffer, use the RtlDecompressBuffer function.

To extract an uncompressed fragment from a compressed buffer, use the RtlDecompressFragment function.

Requirements

Requirement	Value
Minimum supported client	Windows XP
Target Platform	Universal
Header	ntifs.h (include Fltkernel.h, Ntifs.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	<= APC_LEVEL