2016-10-24 14:07:53 +00:00
< html >
< head >
< meta http-equiv = "Content-Type" content = "text/html; charset=ISO-8859-1" >
< title > zstd 1.1.1 Manual< / title >
< / head >
< body >
< h1 > zstd 1.1.1 Manual< / h1 >
< hr >
< a name = "Contents" > < / a > < h2 > Contents< / h2 >
< ol >
< li > < a href = "#Chapter1" > Introduction< / a > < / li >
< li > < a href = "#Chapter2" > Version< / a > < / li >
< li > < a href = "#Chapter3" > Simple API< / a > < / li >
< li > < a href = "#Chapter4" > Explicit memory management< / a > < / li >
< li > < a href = "#Chapter5" > Simple dictionary API< / a > < / li >
< li > < a href = "#Chapter6" > Fast dictionary API< / a > < / li >
< li > < a href = "#Chapter7" > Streaming< / a > < / li >
< li > < a href = "#Chapter8" > Streaming compression - HowTo< / a > < / li >
< li > < a href = "#Chapter9" > Streaming decompression - HowTo< / a > < / li >
< li > < a href = "#Chapter10" > START OF ADVANCED AND EXPERIMENTAL FUNCTIONS< / a > < / li >
< li > < a href = "#Chapter11" > Advanced types< / a > < / li >
< li > < a href = "#Chapter12" > Advanced compression functions< / a > < / li >
< li > < a href = "#Chapter13" > Advanced decompression functions< / a > < / li >
< li > < a href = "#Chapter14" > Advanced streaming functions< / a > < / li >
< li > < a href = "#Chapter15" > Buffer-less and synchronous inner streaming functions< / a > < / li >
< li > < a href = "#Chapter16" > Buffer-less streaming compression (synchronous mode)< / a > < / li >
< li > < a href = "#Chapter17" > Buffer-less streaming decompression (synchronous mode)< / a > < / li >
< li > < a href = "#Chapter18" > Block functions< / a > < / li >
< / ol >
< hr >
< a name = "Chapter1" > < / a > < h2 > Introduction< / h2 > < pre >
2016-10-31 09:44:44 +00:00
zstd, short for Zstandard, is a fast lossless compression algorithm, targeting real-time compression scenarios
2016-10-24 14:07:53 +00:00
at zlib-level and better compression ratios. The zstd compression library provides in-memory compression and
decompression functions. The library supports compression levels from 1 up to ZSTD_maxCLevel() which is 22.
2016-10-31 09:44:44 +00:00
Levels >= 20, labelled `--ultra`, should be used with caution, as they require more memory.
2016-10-24 14:07:53 +00:00
Compression can be done in:
- a single step (described as Simple API)
- a single step, reusing a context (described as Explicit memory management)
2016-10-31 09:44:44 +00:00
- unbounded multiple steps (described as Streaming compression)
2016-10-24 14:07:53 +00:00
The compression ratio achievable on small data can be highly improved using compression with a dictionary in:
- a single step (described as Simple dictionary API)
- a single step, reusing a dictionary (described as Fast dictionary API)
2016-10-31 09:44:44 +00:00
Advanced experimental functions can be accessed using #define ZSTD_STATIC_LINKING_ONLY before including zstd.h.
These APIs shall never be used with a dynamic library.
2016-10-24 14:07:53 +00:00
They are not "stable", their definition may change in the future. Only static linking is allowed.
< BR > < / pre >
< a name = "Chapter2" > < / a > < h2 > Version< / h2 > < pre > < / pre >
< pre > < b > unsigned ZSTD_versionNumber (void); < / b > /**< returns version number of ZSTD * / < b >
< / b > < / pre > < BR >
< a name = "Chapter3" > < / a > < h2 > Simple API< / h2 > < pre > < / pre >
< pre > < b > size_t ZSTD_compress( void* dst, size_t dstCapacity,
const void* src, size_t srcSize,
int compressionLevel);
< / b > < p > Compresses `src` content as a single zstd compressed frame into already allocated `dst`.
Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
@return : compressed size written into `dst` (< = `dstCapacity),
or an error code if it fails (which can be tested using ZSTD_isError())
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_decompress( void* dst, size_t dstCapacity,
const void* src, size_t compressedSize);
< / b > < p > `compressedSize` : must be the _exact_ size of a single compressed frame.
`dstCapacity` is an upper bound of originalSize.
If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data.
@return : the number of bytes decompressed into `dst` (< = `dstCapacity`),
or an errorCode if it fails (which can be tested using ZSTD_isError())
< / p > < / pre > < BR >
< pre > < b > unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
< / b > < p > 'src' is the start of a zstd compressed frame.
@return : content size to be decompressed, as a 64-bits value _if known_, 0 otherwise.
note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
When `return==0`, data to decompress could be any size.
In which case, it's necessary to use streaming mode to decompress data.
Optionally, application can still use ZSTD_decompress() while relying on implied limits.
(For example, data may be necessarily cut into blocks < = 16 KB).
note 2 : decompressed size is always present when compression is done with ZSTD_compress()
note 3 : decompressed size can be very large (64-bits value),
potentially larger than what local system can handle as a single memory segment.
In which case, it's necessary to use streaming mode to decompress data.
note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified.
Always ensure result fits within application's authorized limits.
Each application can set its own limits.
note 5 : when `return==0`, if precise failure cause is needed, use ZSTD_getFrameParams() to know more.
< / p > < / pre > < BR >
< h3 > Helper functions< / h3 > < pre > < b > int ZSTD_maxCLevel(void); < / b > /*!< maximum compression level available * / < b >
size_t ZSTD_compressBound(size_t srcSize); < / b > /*!< maximum compressed size in worst case scenario * / < b >
unsigned ZSTD_isError(size_t code); < / b > /*!< tells if a ` size_t ` function result is an error code * / < b >
const char* ZSTD_getErrorName(size_t code); < / b > /*!< provides readable string from an error code * / < b >
< / b > < / pre > < BR >
< a name = "Chapter4" > < / a > < h2 > Explicit memory management< / h2 > < pre > < / pre >
< pre > < b > size_t ZSTD_compressCCtx(ZSTD_CCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize, int compressionLevel);
< / b > < p > Same as ZSTD_compress(), requires an allocated ZSTD_CCtx (see ZSTD_createCCtx())
< / p > < / pre > < BR >
< h3 > Decompression context< / h3 > < pre > < b > typedef struct ZSTD_DCtx_s ZSTD_DCtx;
ZSTD_DCtx* ZSTD_createDCtx(void);
size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx);
< / b > < / pre > < BR >
< pre > < b > size_t ZSTD_decompressDCtx(ZSTD_DCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
< / b > < p > Same as ZSTD_decompress(), requires an allocated ZSTD_DCtx (see ZSTD_createDCtx())
< / p > < / pre > < BR >
< a name = "Chapter5" > < / a > < h2 > Simple dictionary API< / h2 > < pre > < / pre >
< pre > < b > size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx,
void* dst, size_t dstCapacity,
const void* src, size_t srcSize,
const void* dict,size_t dictSize,
int compressionLevel);
< / b > < p > Compression using a predefined Dictionary (see dictBuilder/zdict.h).
Note : This function load the dictionary, resulting in significant startup delay.
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx,
void* dst, size_t dstCapacity,
const void* src, size_t srcSize,
const void* dict,size_t dictSize);
< / b > < p > Decompression using a predefined Dictionary (see dictBuilder/zdict.h).
Dictionary must be identical to the one used during compression.
Note : This function load the dictionary, resulting in significant startup delay
< / p > < / pre > < BR >
< a name = "Chapter6" > < / a > < h2 > Fast dictionary API< / h2 > < pre > < / pre >
< pre > < b > ZSTD_CDict* ZSTD_createCDict(const void* dict, size_t dictSize, int compressionLevel);
2016-10-31 09:44:44 +00:00
< / b > < p > When compressing multiple messages / blocks with the same dictionary, it's recommended to load it just once.
ZSTD_createCDict() will create a digested dictionary, ready to start future compression operations without startup delay.
ZSTD_CDict can be created once and used by multiple threads concurrently, as its usage is read-only.
2016-10-24 14:07:53 +00:00
`dict` can be released after ZSTD_CDict creation
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_freeCDict(ZSTD_CDict* CDict);
2016-10-31 09:44:44 +00:00
< / b > < p > Function frees memory allocated by ZSTD_createCDict()
2016-10-24 14:07:53 +00:00
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx,
void* dst, size_t dstCapacity,
const void* src, size_t srcSize,
const ZSTD_CDict* cdict);
< / b > < p > Compression using a digested Dictionary.
Faster startup than ZSTD_compress_usingDict(), recommended when same dictionary is used multiple times.
Note that compression level is decided during dictionary creation
< / p > < / pre > < BR >
< pre > < b > ZSTD_DDict* ZSTD_createDDict(const void* dict, size_t dictSize);
< / b > < p > Create a digested dictionary, ready to start decompression operation without startup delay.
`dict` can be released after creation
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_freeDDict(ZSTD_DDict* ddict);
< / b > < p > Function frees memory allocated with ZSTD_createDDict()
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
void* dst, size_t dstCapacity,
const void* src, size_t srcSize,
const ZSTD_DDict* ddict);
< / b > < p > Decompression using a digested Dictionary
Faster startup than ZSTD_decompress_usingDict(), recommended when same dictionary is used multiple times.
< / p > < / pre > < BR >
< a name = "Chapter7" > < / a > < h2 > Streaming< / h2 > < pre > < / pre >
< pre > < b > typedef struct ZSTD_inBuffer_s {
const void* src; < / b > /**< start of input buffer * / < b >
size_t size; < / b > /**< size of input buffer * / < b >
size_t pos; < / b > /**< position where reading stopped . Will be updated . Necessarily 0 < = pos < = size * / < b >
} ZSTD_inBuffer;
< / b > < / pre > < BR >
< pre > < b > typedef struct ZSTD_outBuffer_s {
void* dst; < / b > /**< start of output buffer * / < b >
size_t size; < / b > /**< size of output buffer * / < b >
size_t pos; < / b > /**< position where writing stopped . Will be updated . Necessarily 0 < = pos < = size * / < b >
} ZSTD_outBuffer;
< / b > < / pre > < BR >
< a name = "Chapter8" > < / a > < h2 > Streaming compression - HowTo< / h2 > < pre >
A ZSTD_CStream object is required to track streaming operation.
Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources.
ZSTD_CStream objects can be reused multiple times on consecutive compression operations.
2016-10-31 09:44:44 +00:00
It is recommended to re-use ZSTD_CStream in situations where many streaming operations will be achieved consecutively,
since it will play nicer with system's memory, by re-using already allocated memory.
Use one separate ZSTD_CStream per thread for parallel execution.
2016-10-24 14:07:53 +00:00
2016-10-31 09:44:44 +00:00
Start a new compression by initializing ZSTD_CStream.
2016-10-24 14:07:53 +00:00
Use ZSTD_initCStream() to start a new compression operation.
Use ZSTD_initCStream_usingDict() for a compression which requires a dictionary.
Use ZSTD_compressStream() repetitively to consume input stream.
The function will automatically update both `pos` fields.
Note that it may not consume the entire input, in which case `pos < size ` ,
and it's up to the caller to present again remaining data.
@return : a size hint, preferred nb of bytes to use as input for next function call
(it's just a hint, to help latency a little, any other value will work fine)
(note : the size hint is guaranteed to be < = ZSTD_CStreamInSize() )
or an error code, which can be tested using ZSTD_isError().
At any moment, it's possible to flush whatever data remains within buffer, using ZSTD_flushStream().
`output->pos` will be updated.
Note some content might still be left within internal buffer if `output->size` is too small.
@return : nb of bytes still present within internal buffer (0 if it's empty)
or an error code, which can be tested using ZSTD_isError().
ZSTD_endStream() instructs to finish a frame.
It will perform a flush and write frame epilogue.
The epilogue is required for decoders to consider a frame completed.
Similar to ZSTD_flushStream(), it may not be able to flush the full content if `output->size` is too small.
In which case, call again ZSTD_endStream() to complete the flush.
@return : nb of bytes still present within internal buffer (0 if it's empty)
or an error code, which can be tested using ZSTD_isError().
< BR > < / pre >
< h3 > Streaming compression functions< / h3 > < pre > < b > typedef struct ZSTD_CStream_s ZSTD_CStream;
ZSTD_CStream* ZSTD_createCStream(void);
size_t ZSTD_freeCStream(ZSTD_CStream* zcs);
size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel);
size_t ZSTD_compressStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
size_t ZSTD_flushStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
< / b > < / pre > < BR >
< pre > < b > size_t ZSTD_CStreamInSize(void); < / b > /**< recommended size for input buffer * / < b >
< / b > < / pre > < BR >
< pre > < b > size_t ZSTD_CStreamOutSize(void); < / b > /**< recommended size for output buffer . Guarantee to successfully flush at least one complete compressed block in all circumstances . * / < b >
< / b > < / pre > < BR >
< a name = "Chapter9" > < / a > < h2 > Streaming decompression - HowTo< / h2 > < pre >
A ZSTD_DStream object is required to track streaming operations.
Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources.
ZSTD_DStream objects can be re-used multiple times.
Use ZSTD_initDStream() to start a new decompression operation,
or ZSTD_initDStream_usingDict() if decompression requires a dictionary.
@return : recommended first input size
Use ZSTD_decompressStream() repetitively to consume your input.
The function will update both `pos` fields.
If `input.pos < input.size ` , some input has not been consumed .
It's up to the caller to present again remaining data.
If `output.pos < output.size ` , decoder has flushed everything it could .
@return : 0 when a frame is completely decoded and fully flushed,
an error code, which can be tested using ZSTD_isError(),
any other value > 0, which means there is still some work to do to complete the frame.
The return value is a suggested next input size (just an hint, to help latency).
< BR > < / pre >
< h3 > Streaming decompression functions< / h3 > < pre > < b > typedef struct ZSTD_DStream_s ZSTD_DStream;
ZSTD_DStream* ZSTD_createDStream(void);
size_t ZSTD_freeDStream(ZSTD_DStream* zds);
size_t ZSTD_initDStream(ZSTD_DStream* zds);
size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
< / b > < / pre > < BR >
< pre > < b > size_t ZSTD_DStreamInSize(void); < / b > /*!< recommended size for input buffer * / < b >
< / b > < / pre > < BR >
< pre > < b > size_t ZSTD_DStreamOutSize(void); < / b > /*!< recommended size for output buffer . Guarantee to successfully flush at least one complete block in all circumstances . * / < b >
< / b > < / pre > < BR >
< a name = "Chapter10" > < / a > < h2 > START OF ADVANCED AND EXPERIMENTAL FUNCTIONS< / h2 > < pre > The definitions in this section are considered experimental.
They should never be used with a dynamic library, as they may change in the future.
They are provided for advanced usages.
Use them only in association with static linking.
< BR > < / pre >
< a name = "Chapter11" > < / a > < h2 > Advanced types< / h2 > < pre > < / pre >
2016-10-31 09:44:44 +00:00
< pre > < b > typedef enum { ZSTD_fast, ZSTD_dfast, ZSTD_greedy, ZSTD_lazy, ZSTD_lazy2, ZSTD_btlazy2, ZSTD_btopt, ZSTD_btopt2 } ZSTD_strategy; < / b > /* from faster to stronger */< b >
2016-10-24 14:07:53 +00:00
< / b > < / pre > < BR >
< pre > < b > typedef struct {
unsigned windowLog; < / b > /**< largest match distance : larger = = more compression , more memory needed during decompression * / < b >
unsigned chainLog; < / b > /**< fully searched segment : larger = = more compression , slower , more memory ( useless for fast ) * / < b >
unsigned hashLog; < / b > /**< dispatch table : larger = = faster , more memory * / < b >
unsigned searchLog; < / b > /**< nb of searches : larger = = more compression , slower * / < b >
unsigned searchLength; < / b > /**< match length searched : larger = = faster decompression , sometimes less compression * / < b >
unsigned targetLength; < / b > /**< acceptable match size for optimal parser ( only ) : larger = = more compression , slower * / < b >
ZSTD_strategy strategy;
} ZSTD_compressionParameters;
< / b > < / pre > < BR >
< pre > < b > typedef struct {
unsigned contentSizeFlag; < / b > /**< 1: content size will be in frame header ( if known ) . * / < b >
unsigned checksumFlag; < / b > /**< 1: will generate a 22-bits checksum at end of frame , to be used for error detection by decompressor * / < b >
unsigned noDictIDFlag; < / b > /**< 1: no dict ID will be saved into frame header ( if dictionary compression ) * / < b >
} ZSTD_frameParameters;
< / b > < / pre > < BR >
< pre > < b > typedef struct {
ZSTD_compressionParameters cParams;
ZSTD_frameParameters fParams;
} ZSTD_parameters;
< / b > < / pre > < BR >
< h3 > Custom memory allocation functions< / h3 > < pre > < b > typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size);
typedef void (*ZSTD_freeFunction) (void* opaque, void* address);
typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem;
< / b > < / pre > < BR >
< a name = "Chapter12" > < / a > < h2 > Advanced compression functions< / h2 > < pre > < / pre >
< pre > < b > size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams);
< / b > < p > Gives the amount of memory allocated for a ZSTD_CCtx given a set of compression parameters.
`frameContentSize` is an optional parameter, provide `0` if unknown
< / p > < / pre > < BR >
< pre > < b > ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem);
< / b > < p > Create a ZSTD compression context using external alloc and free functions
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
< / b > < p > Gives the amount of memory used by a given ZSTD_CCtx
< / p > < / pre > < BR >
< pre > < b > ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize,
ZSTD_parameters params, ZSTD_customMem customMem);
< / b > < p > Create a ZSTD_CDict using external alloc and free, and customized compression parameters
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
< / b > < p > Gives the amount of memory used by a given ZSTD_sizeof_CDict
< / p > < / pre > < BR >
< pre > < b > ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long srcSize, size_t dictSize);
< / b > < p > same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of a `ZSTD_compressionParameters`.
All fields of `ZSTD_frameParameters` are set to default (0)
< / p > < / pre > < BR >
< pre > < b > ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long srcSize, size_t dictSize);
< / b > < p > @return ZSTD_compressionParameters structure for a selected compression level and srcSize.
`srcSize` value is optional, select 0 if not known
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_checkCParams(ZSTD_compressionParameters params);
< / b > < p > Ensure param values remain within authorized range
< / p > < / pre > < BR >
< pre > < b > ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize);
< / b > < p > optimize params for a given `srcSize` and `dictSize`.
both values are optional, select `0` if unknown.
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_compress_advanced (ZSTD_CCtx* ctx,
void* dst, size_t dstCapacity,
const void* src, size_t srcSize,
const void* dict,size_t dictSize,
ZSTD_parameters params);
< / b > < p > Same as ZSTD_compress_usingDict(), with fine-tune control of each compression parameter
< / p > < / pre > < BR >
< a name = "Chapter13" > < / a > < h2 > Advanced decompression functions< / h2 > < pre > < / pre >
< pre > < b > size_t ZSTD_estimateDCtxSize(void);
< / b > < p > Gives the potential amount of memory allocated to create a ZSTD_DCtx
< / p > < / pre > < BR >
< pre > < b > ZSTD_DCtx* ZSTD_createDCtx_advanced(ZSTD_customMem customMem);
< / b > < p > Create a ZSTD decompression context using external alloc and free functions
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);
< / b > < p > Gives the amount of memory used by a given ZSTD_DCtx
< / p > < / pre > < BR >
< pre > < b > size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
< / b > < p > Gives the amount of memory used by a given ZSTD_DDict
< / p > < / pre > < BR >
< a name = "Chapter14" > < / a > < h2 > Advanced streaming functions< / h2 > < pre > < / pre >
< h3 > Advanced Streaming compression functions< / h3 > < pre > < b > ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel);
size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize,
ZSTD_parameters params, unsigned long long pledgedSrcSize); < / b > /**< pledgedSrcSize is optional and can be zero = = unknown * / < b >
2016-10-31 09:44:44 +00:00
size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict); < / b > /**< note : cdict will just be referenced , and must outlive compression session * / < b >
size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize); < / b > /**< re-use compression parameters from previous init ; skip dictionary loading stage ; zcs must be init at least once before * / < b >
2016-10-24 14:07:53 +00:00
size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs);
< / b > < / pre > < BR >
< h3 > Advanced Streaming decompression functions< / h3 > < pre > < b > typedef enum { ZSTDdsp_maxWindowSize } ZSTD_DStreamParameter_e;
ZSTD_DStream* ZSTD_createDStream_advanced(ZSTD_customMem customMem);
size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize);
size_t ZSTD_setDStreamParameter(ZSTD_DStream* zds, ZSTD_DStreamParameter_e paramType, unsigned paramValue);
2016-10-31 09:44:44 +00:00
size_t ZSTD_initDStream_usingDDict(ZSTD_DStream* zds, const ZSTD_DDict* ddict); < / b > /**< note : ddict will just be referenced , and must outlive decompression session * / < b >
2016-10-24 14:07:53 +00:00
size_t ZSTD_resetDStream(ZSTD_DStream* zds); < / b > /**< re-use decompression parameters from previous init ; saves dictionary loading * / < b >
size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds);
< / b > < / pre > < BR >
< a name = "Chapter15" > < / a > < h2 > Buffer-less and synchronous inner streaming functions< / h2 > < pre >
This is an advanced API, giving full control over buffer management, for users which need direct control over memory.
But it's also a complex one, with many restrictions (documented below).
2016-10-31 09:44:44 +00:00
Prefer using normal streaming API for an easier experience
2016-10-24 14:07:53 +00:00
< BR > < / pre >
< a name = "Chapter16" > < / a > < h2 > Buffer-less streaming compression (synchronous mode)< / h2 > < pre >
A ZSTD_CCtx object is required to track streaming operations.
Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource.
ZSTD_CCtx object can be re-used multiple times within successive compression operations.
Start by initializing a context.
Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression,
or ZSTD_compressBegin_advanced(), for finer parameter control.
It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx()
Then, consume your input using ZSTD_compressContinue().
There are some important considerations to keep in mind when using this advanced function :
- ZSTD_compressContinue() has no internal buffer. It uses externally provided buffer only.
- Interface is synchronous : input is consumed entirely and produce 1+ (or more) compressed blocks.
- Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario.
Worst case evaluation is provided by ZSTD_compressBound().
ZSTD_compressContinue() doesn't guarantee recover after a failed compression.
- ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog).
It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks)
- ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps.
In which case, it will "discard" the relevant memory section from its history.
Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum.
It's possible to use a NULL,0 src content, in which case, it will write a final empty block to end the frame,
Without last block mark, frames will be considered unfinished (broken) by decoders.
You can then reuse `ZSTD_CCtx` (ZSTD_compressBegin()) to compress some new frame.
< BR > < / pre >
< h3 > Buffer-less streaming compression functions< / h3 > < pre > < b > size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel);
size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel);
size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_parameters params, unsigned long long pledgedSrcSize);
size_t ZSTD_copyCCtx(ZSTD_CCtx* cctx, const ZSTD_CCtx* preparedCCtx, unsigned long long pledgedSrcSize);
size_t ZSTD_compressContinue(ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
size_t ZSTD_compressEnd(ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
< / b > < / pre > < BR >
< a name = "Chapter17" > < / a > < h2 > Buffer-less streaming decompression (synchronous mode)< / h2 > < pre >
A ZSTD_DCtx object is required to track streaming operations.
Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it.
A ZSTD_DCtx object can be re-used multiple times.
First typical operation is to retrieve frame parameters, using ZSTD_getFrameParams().
It fills a ZSTD_frameParams structure which provide important information to correctly decode the frame,
such as the minimum rolling buffer size to allocate to decompress data (`windowSize`),
and the dictionary ID used.
(Note : content size is optional, it may not be present. 0 means : content size unknown).
Note that these values could be wrong, either because of data malformation, or because an attacker is spoofing deliberate false information.
As a consequence, check that values remain within valid application range, especially `windowSize`, before allocation.
Each application can set its own limit, depending on local restrictions. For extended interoperability, it is recommended to support at least 8 MB.
Frame parameters are extracted from the beginning of the compressed frame.
Data fragment must be large enough to ensure successful decoding, typically `ZSTD_frameHeaderSize_max` bytes.
@result : 0 : successful decoding, the `ZSTD_frameParams` structure is correctly filled.
>0 : `srcSize` is too small, please provide at least @result bytes on next attempt.
errorCode, which can be tested using ZSTD_isError().
Start decompression, with ZSTD_decompressBegin() or ZSTD_decompressBegin_usingDict().
Alternatively, you can copy a prepared context, using ZSTD_copyDCtx().
Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively.
ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue().
ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail.
@result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily < = dstCapacity).
It can be zero, which is not an error; it just means ZSTD_decompressContinue() has decoded some metadata item.
It can also be an error code, which can be tested with ZSTD_isError().
ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize`.
They should preferably be located contiguously, prior to current block.
Alternatively, a round buffer of sufficient size is also possible. Sufficient size is determined by frame parameters.
ZSTD_decompressContinue() is very sensitive to contiguity,
if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place,
or that previous contiguous segment is large enough to properly handle maximum back-reference.
A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero.
Context can then be reset to start a new decompression.
Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType().
This information is not required to properly decode a frame.
== Special case : skippable frames ==
Skippable frames allow integration of user-defined data into a flow of concatenated frames.
Skippable frames will be ignored (skipped) by a decompressor. The format of skippable frames is as follows :
a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F
b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits
c) Frame Content - any content (User Data) of length equal to Frame Size
For skippable frames ZSTD_decompressContinue() always returns 0.
For skippable frames ZSTD_getFrameParams() returns fparamsPtr->windowLog==0 what means that a frame is skippable.
It also returns Frame Size as fparamsPtr->frameContentSize.
< BR > < / pre >
< pre > < b > typedef struct {
unsigned long long frameContentSize;
unsigned windowSize;
unsigned dictID;
unsigned checksumFlag;
} ZSTD_frameParams;
< / b > < / pre > < BR >
< h3 > Buffer-less streaming decompression functions< / h3 > < pre > < b > size_t ZSTD_getFrameParams(ZSTD_frameParams* fparamsPtr, const void* src, size_t srcSize); < / b > /**< doesn ' t consume input , see details below * / < b >
size_t ZSTD_decompressBegin(ZSTD_DCtx* dctx);
size_t ZSTD_decompressBegin_usingDict(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
void ZSTD_copyDCtx(ZSTD_DCtx* dctx, const ZSTD_DCtx* preparedDCtx);
size_t ZSTD_nextSrcSizeToDecompress(ZSTD_DCtx* dctx);
size_t ZSTD_decompressContinue(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e;
ZSTD_nextInputType_e ZSTD_nextInputType(ZSTD_DCtx* dctx);
< / b > < / pre > < BR >
< a name = "Chapter18" > < / a > < h2 > Block functions< / h2 > < pre >
Block functions produce and decode raw zstd blocks, without frame metadata.
Frame metadata cost is typically ~18 bytes, which can be non-negligible for very small blocks (< 100 bytes ) .
User will have to take in charge required information to regenerate data, such as compressed and content sizes.
A few rules to respect :
- Compressing and decompressing require a context structure
+ Use ZSTD_createCCtx() and ZSTD_createDCtx()
- It is necessary to init context before starting
+ compression : ZSTD_compressBegin()
+ decompression : ZSTD_decompressBegin()
+ variants _usingDict() are also allowed
+ copyCCtx() and copyDCtx() work too
- Block size is limited, it must be < = ZSTD_getBlockSizeMax()
+ If you need to compress more, cut data into multiple blocks
+ Consider using the regular ZSTD_compress() instead, as frame metadata costs become negligible when source size is large.
- When a block is considered not compressible enough, ZSTD_compressBlock() result will be zero.
In which case, nothing is produced into `dst`.
+ User must test for such outcome and deal directly with uncompressed data
+ ZSTD_decompressBlock() doesn't accept uncompressed data as input !!!
+ In case of multiple successive blocks, decoder must be informed of uncompressed block existence to follow proper history.
Use ZSTD_insertBlock() in such a case.
< BR > < / pre >
< h3 > Raw zstd block functions< / h3 > < pre > < b > size_t ZSTD_getBlockSizeMax(ZSTD_CCtx* cctx);
size_t ZSTD_compressBlock (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
size_t ZSTD_insertBlock(ZSTD_DCtx* dctx, const void* blockStart, size_t blockSize); < / b > /**< insert block into ` dctx ` history . Useful for uncompressed blocks * / < b >
< / b > < / pre > < BR >
< / html >
< / body >
