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7 <h1>zstd 1.1.4 Manual</h1>
9 <a name="Contents"></a><h2>Contents</h2>
11 <li><a href="#Chapter1">Introduction</a></li>
12 <li><a href="#Chapter2">Version</a></li>
13 <li><a href="#Chapter3">Simple API</a></li>
14 <li><a href="#Chapter4">Explicit memory management</a></li>
15 <li><a href="#Chapter5">Simple dictionary API</a></li>
16 <li><a href="#Chapter6">Fast dictionary API</a></li>
17 <li><a href="#Chapter7">Streaming</a></li>
18 <li><a href="#Chapter8">Streaming compression - HowTo</a></li>
19 <li><a href="#Chapter9">Streaming decompression - HowTo</a></li>
20 <li><a href="#Chapter10">START OF ADVANCED AND EXPERIMENTAL FUNCTIONS</a></li>
21 <li><a href="#Chapter11">Advanced types</a></li>
22 <li><a href="#Chapter12">Compressed size functions</a></li>
23 <li><a href="#Chapter13">Decompressed size functions</a></li>
24 <li><a href="#Chapter14">Advanced compression functions</a></li>
25 <li><a href="#Chapter15">Advanced decompression functions</a></li>
26 <li><a href="#Chapter16">Advanced streaming functions</a></li>
27 <li><a href="#Chapter17">Buffer-less and synchronous inner streaming functions</a></li>
28 <li><a href="#Chapter18">Buffer-less streaming compression (synchronous mode)</a></li>
29 <li><a href="#Chapter19">Buffer-less streaming decompression (synchronous mode)</a></li>
30 <li><a href="#Chapter20">Block functions</a></li>
33 <a name="Chapter1"></a><h2>Introduction</h2><pre>
34 zstd, short for Zstandard, is a fast lossless compression algorithm, targeting real-time compression scenarios
35 at zlib-level and better compression ratios. The zstd compression library provides in-memory compression and
36 decompression functions. The library supports compression levels from 1 up to ZSTD_maxCLevel() which is 22.
37 Levels >= 20, labeled `--ultra`, should be used with caution, as they require more memory.
38 Compression can be done in:
39 - a single step (described as Simple API)
40 - a single step, reusing a context (described as Explicit memory management)
41 - unbounded multiple steps (described as Streaming compression)
42 The compression ratio achievable on small data can be highly improved using compression with a dictionary in:
43 - a single step (described as Simple dictionary API)
44 - a single step, reusing a dictionary (described as Fast dictionary API)
46 Advanced experimental functions can be accessed using #define ZSTD_STATIC_LINKING_ONLY before including zstd.h.
47 These APIs shall never be used with a dynamic library.
48 They are not "stable", their definition may change in the future. Only static linking is allowed.
51 <a name="Chapter2"></a><h2>Version</h2><pre></pre>
53 <pre><b>unsigned ZSTD_versionNumber(void); </b>/**< library version number; to be used when checking dll version */<b>
55 <a name="Chapter3"></a><h2>Simple API</h2><pre></pre>
57 <pre><b>size_t ZSTD_compress( void* dst, size_t dstCapacity,
58 const void* src, size_t srcSize,
59 int compressionLevel);
60 </b><p> Compresses `src` content as a single zstd compressed frame into already allocated `dst`.
61 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
62 @return : compressed size written into `dst` (<= `dstCapacity),
63 or an error code if it fails (which can be tested using ZSTD_isError()).
66 <pre><b>size_t ZSTD_decompress( void* dst, size_t dstCapacity,
67 const void* src, size_t compressedSize);
68 </b><p> `compressedSize` : must be the _exact_ size of some number of compressed and/or skippable frames.
69 `dstCapacity` is an upper bound of originalSize.
70 If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data.
71 @return : the number of bytes decompressed into `dst` (<= `dstCapacity`),
72 or an errorCode if it fails (which can be tested using ZSTD_isError()).
75 <pre><b>unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
76 </b><p> NOTE: This function is planned to be obsolete, in favour of ZSTD_getFrameContentSize.
77 ZSTD_getFrameContentSize functions the same way, returning the decompressed size of a single
78 frame, but distinguishes empty frames from frames with an unknown size, or errors.
80 Additionally, ZSTD_findDecompressedSize can be used instead. It can handle multiple
81 concatenated frames in one buffer, and so is more general.
82 As a result however, it requires more computation and entire frames to be passed to it,
83 as opposed to ZSTD_getFrameContentSize which requires only a single frame's header.
85 'src' is the start of a zstd compressed frame.
86 @return : content size to be decompressed, as a 64-bits value _if known_, 0 otherwise.
87 note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
88 When `return==0`, data to decompress could be any size.
89 In which case, it's necessary to use streaming mode to decompress data.
90 Optionally, application can still use ZSTD_decompress() while relying on implied limits.
91 (For example, data may be necessarily cut into blocks <= 16 KB).
92 note 2 : decompressed size is always present when compression is done with ZSTD_compress()
93 note 3 : decompressed size can be very large (64-bits value),
94 potentially larger than what local system can handle as a single memory segment.
95 In which case, it's necessary to use streaming mode to decompress data.
96 note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified.
97 Always ensure result fits within application's authorized limits.
98 Each application can set its own limits.
99 note 5 : when `return==0`, if precise failure cause is needed, use ZSTD_getFrameParams() to know more.
102 <h3>Helper functions</h3><pre></pre><b><pre>int ZSTD_maxCLevel(void); </b>/*!< maximum compression level available */<b>
103 size_t ZSTD_compressBound(size_t srcSize); </b>/*!< maximum compressed size in worst case scenario */<b>
104 unsigned ZSTD_isError(size_t code); </b>/*!< tells if a `size_t` function result is an error code */<b>
105 const char* ZSTD_getErrorName(size_t code); </b>/*!< provides readable string from an error code */<b>
107 <a name="Chapter4"></a><h2>Explicit memory management</h2><pre></pre>
109 <h3>Compression context</h3><pre> When compressing many times,
110 it is recommended to allocate a context just once, and re-use it for each successive compression operation.
111 This will make workload friendlier for system's memory.
112 Use one context per thread for parallel execution in multi-threaded environments.
113 </pre><b><pre>typedef struct ZSTD_CCtx_s ZSTD_CCtx;
114 ZSTD_CCtx* ZSTD_createCCtx(void);
115 size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx);
117 <pre><b>size_t ZSTD_compressCCtx(ZSTD_CCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize, int compressionLevel);
118 </b><p> Same as ZSTD_compress(), requires an allocated ZSTD_CCtx (see ZSTD_createCCtx()).
121 <h3>Decompression context</h3><pre> When decompressing many times,
122 it is recommended to allocate a context just once, and re-use it for each successive compression operation.
123 This will make workload friendlier for system's memory.
124 Use one context per thread for parallel execution in multi-threaded environments.
125 </pre><b><pre>typedef struct ZSTD_DCtx_s ZSTD_DCtx;
126 ZSTD_DCtx* ZSTD_createDCtx(void);
127 size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx);
129 <pre><b>size_t ZSTD_decompressDCtx(ZSTD_DCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
130 </b><p> Same as ZSTD_decompress(), requires an allocated ZSTD_DCtx (see ZSTD_createDCtx()).
133 <a name="Chapter5"></a><h2>Simple dictionary API</h2><pre></pre>
135 <pre><b>size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx,
136 void* dst, size_t dstCapacity,
137 const void* src, size_t srcSize,
138 const void* dict,size_t dictSize,
139 int compressionLevel);
140 </b><p> Compression using a predefined Dictionary (see dictBuilder/zdict.h).
141 Note : This function loads the dictionary, resulting in significant startup delay.
142 Note : When `dict == NULL || dictSize < 8` no dictionary is used.
145 <pre><b>size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx,
146 void* dst, size_t dstCapacity,
147 const void* src, size_t srcSize,
148 const void* dict,size_t dictSize);
149 </b><p> Decompression using a predefined Dictionary (see dictBuilder/zdict.h).
150 Dictionary must be identical to the one used during compression.
151 Note : This function loads the dictionary, resulting in significant startup delay.
152 Note : When `dict == NULL || dictSize < 8` no dictionary is used.
155 <a name="Chapter6"></a><h2>Fast dictionary API</h2><pre></pre>
157 <pre><b>ZSTD_CDict* ZSTD_createCDict(const void* dictBuffer, size_t dictSize, int compressionLevel);
158 </b><p> When compressing multiple messages / blocks with the same dictionary, it's recommended to load it just once.
159 ZSTD_createCDict() will create a digested dictionary, ready to start future compression operations without startup delay.
160 ZSTD_CDict can be created once and used by multiple threads concurrently, as its usage is read-only.
161 `dictBuffer` can be released after ZSTD_CDict creation, as its content is copied within CDict
164 <pre><b>size_t ZSTD_freeCDict(ZSTD_CDict* CDict);
165 </b><p> Function frees memory allocated by ZSTD_createCDict().
168 <pre><b>size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx,
169 void* dst, size_t dstCapacity,
170 const void* src, size_t srcSize,
171 const ZSTD_CDict* cdict);
172 </b><p> Compression using a digested Dictionary.
173 Faster startup than ZSTD_compress_usingDict(), recommended when same dictionary is used multiple times.
174 Note that compression level is decided during dictionary creation.
177 <pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dictBuffer, size_t dictSize);
178 </b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
179 dictBuffer can be released after DDict creation, as its content is copied inside DDict
182 <pre><b>size_t ZSTD_freeDDict(ZSTD_DDict* ddict);
183 </b><p> Function frees memory allocated with ZSTD_createDDict()
186 <pre><b>size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
187 void* dst, size_t dstCapacity,
188 const void* src, size_t srcSize,
189 const ZSTD_DDict* ddict);
190 </b><p> Decompression using a digested Dictionary.
191 Faster startup than ZSTD_decompress_usingDict(), recommended when same dictionary is used multiple times.
194 <a name="Chapter7"></a><h2>Streaming</h2><pre></pre>
196 <pre><b>typedef struct ZSTD_inBuffer_s {
197 const void* src; </b>/**< start of input buffer */<b>
198 size_t size; </b>/**< size of input buffer */<b>
199 size_t pos; </b>/**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
202 <pre><b>typedef struct ZSTD_outBuffer_s {
203 void* dst; </b>/**< start of output buffer */<b>
204 size_t size; </b>/**< size of output buffer */<b>
205 size_t pos; </b>/**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
208 <a name="Chapter8"></a><h2>Streaming compression - HowTo</h2><pre>
209 A ZSTD_CStream object is required to track streaming operation.
210 Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources.
211 ZSTD_CStream objects can be reused multiple times on consecutive compression operations.
212 It is recommended to re-use ZSTD_CStream in situations where many streaming operations will be achieved consecutively,
213 since it will play nicer with system's memory, by re-using already allocated memory.
214 Use one separate ZSTD_CStream per thread for parallel execution.
216 Start a new compression by initializing ZSTD_CStream.
217 Use ZSTD_initCStream() to start a new compression operation.
218 Use ZSTD_initCStream_usingDict() or ZSTD_initCStream_usingCDict() for a compression which requires a dictionary (experimental section)
220 Use ZSTD_compressStream() repetitively to consume input stream.
221 The function will automatically update both `pos` fields.
222 Note that it may not consume the entire input, in which case `pos < size`,
223 and it's up to the caller to present again remaining data.
224 @return : a size hint, preferred nb of bytes to use as input for next function call
225 or an error code, which can be tested using ZSTD_isError().
226 Note 1 : it's just a hint, to help latency a little, any other value will work fine.
227 Note 2 : size hint is guaranteed to be <= ZSTD_CStreamInSize()
229 At any moment, it's possible to flush whatever data remains within internal buffer, using ZSTD_flushStream().
230 `output->pos` will be updated.
231 Note that some content might still be left within internal buffer if `output->size` is too small.
232 @return : nb of bytes still present within internal buffer (0 if it's empty)
233 or an error code, which can be tested using ZSTD_isError().
235 ZSTD_endStream() instructs to finish a frame.
236 It will perform a flush and write frame epilogue.
237 The epilogue is required for decoders to consider a frame completed.
238 Similar to ZSTD_flushStream(), it may not be able to flush the full content if `output->size` is too small.
239 In which case, call again ZSTD_endStream() to complete the flush.
240 @return : nb of bytes still present within internal buffer (0 if it's empty, hence compression completed)
241 or an error code, which can be tested using ZSTD_isError().
246 <h3>ZSTD_CStream management functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream(void);
247 size_t ZSTD_freeCStream(ZSTD_CStream* zcs);
249 <h3>Streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel);
250 size_t ZSTD_compressStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
251 size_t ZSTD_flushStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
252 size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
254 <pre><b>size_t ZSTD_CStreamInSize(void); </b>/**< recommended size for input buffer */<b>
256 <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>
258 <a name="Chapter9"></a><h2>Streaming decompression - HowTo</h2><pre>
259 A ZSTD_DStream object is required to track streaming operations.
260 Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources.
261 ZSTD_DStream objects can be re-used multiple times.
263 Use ZSTD_initDStream() to start a new decompression operation,
264 or ZSTD_initDStream_usingDict() if decompression requires a dictionary.
265 @return : recommended first input size
267 Use ZSTD_decompressStream() repetitively to consume your input.
268 The function will update both `pos` fields.
269 If `input.pos < input.size`, some input has not been consumed.
270 It's up to the caller to present again remaining data.
271 If `output.pos < output.size`, decoder has flushed everything it could.
272 @return : 0 when a frame is completely decoded and fully flushed,
273 an error code, which can be tested using ZSTD_isError(),
274 any other value > 0, which means there is still some decoding to do to complete current frame.
275 The return value is a suggested next input size (a hint to improve latency) that will never load more than the current frame.
279 <h3>ZSTD_DStream management functions</h3><pre></pre><b><pre>ZSTD_DStream* ZSTD_createDStream(void);
280 size_t ZSTD_freeDStream(ZSTD_DStream* zds);
282 <h3>Streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_initDStream(ZSTD_DStream* zds);
283 size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
285 <pre><b>size_t ZSTD_DStreamInSize(void); </b>/*!< recommended size for input buffer */<b>
287 <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>
289 <a name="Chapter10"></a><h2>START OF ADVANCED AND EXPERIMENTAL FUNCTIONS</h2><pre> The definitions in this section are considered experimental.
290 They should never be used with a dynamic library, as they may change in the future.
291 They are provided for advanced usages.
292 Use them only in association with static linking.
296 <a name="Chapter11"></a><h2>Advanced types</h2><pre></pre>
298 <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>
300 <pre><b>typedef struct {
301 unsigned windowLog; </b>/**< largest match distance : larger == more compression, more memory needed during decompression */<b>
302 unsigned chainLog; </b>/**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */<b>
303 unsigned hashLog; </b>/**< dispatch table : larger == faster, more memory */<b>
304 unsigned searchLog; </b>/**< nb of searches : larger == more compression, slower */<b>
305 unsigned searchLength; </b>/**< match length searched : larger == faster decompression, sometimes less compression */<b>
306 unsigned targetLength; </b>/**< acceptable match size for optimal parser (only) : larger == more compression, slower */<b>
307 ZSTD_strategy strategy;
308 } ZSTD_compressionParameters;
310 <pre><b>typedef struct {
311 unsigned contentSizeFlag; </b>/**< 1: content size will be in frame header (when known) */<b>
312 unsigned checksumFlag; </b>/**< 1: generate a 32-bits checksum at end of frame, for error detection */<b>
313 unsigned noDictIDFlag; </b>/**< 1: no dictID will be saved into frame header (if dictionary compression) */<b>
314 } ZSTD_frameParameters;
316 <pre><b>typedef struct {
317 ZSTD_compressionParameters cParams;
318 ZSTD_frameParameters fParams;
321 <h3>Custom memory allocation functions</h3><pre></pre><b><pre>typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size);
322 typedef void (*ZSTD_freeFunction) (void* opaque, void* address);
323 typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem;
325 <a name="Chapter12"></a><h2>Compressed size functions</h2><pre></pre>
327 <pre><b>size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize);
328 </b><p> `src` should point to the start of a ZSTD encoded frame or skippable frame
329 `srcSize` must be at least as large as the frame
330 @return : the compressed size of the frame pointed to by `src`, suitable to pass to
331 `ZSTD_decompress` or similar, or an error code if given invalid input.
334 <a name="Chapter13"></a><h2>Decompressed size functions</h2><pre></pre>
336 <pre><b>unsigned long long ZSTD_getFrameContentSize(const void *src, size_t srcSize);
337 </b><p> `src` should point to the start of a ZSTD encoded frame
338 `srcSize` must be at least as large as the frame header. A value greater than or equal
339 to `ZSTD_frameHeaderSize_max` is guaranteed to be large enough in all cases.
340 @return : decompressed size of the frame pointed to be `src` if known, otherwise
341 - ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined
342 - ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small)
345 <pre><b>unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize);
346 </b><p> `src` should point the start of a series of ZSTD encoded and/or skippable frames
347 `srcSize` must be the _exact_ size of this series
348 (i.e. there should be a frame boundary exactly `srcSize` bytes after `src`)
349 @return : the decompressed size of all data in the contained frames, as a 64-bit value _if known_
350 - if the decompressed size cannot be determined: ZSTD_CONTENTSIZE_UNKNOWN
351 - if an error occurred: ZSTD_CONTENTSIZE_ERROR
353 note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
354 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size.
355 In which case, it's necessary to use streaming mode to decompress data.
356 Optionally, application can still use ZSTD_decompress() while relying on implied limits.
357 (For example, data may be necessarily cut into blocks <= 16 KB).
358 note 2 : decompressed size is always present when compression is done with ZSTD_compress()
359 note 3 : decompressed size can be very large (64-bits value),
360 potentially larger than what local system can handle as a single memory segment.
361 In which case, it's necessary to use streaming mode to decompress data.
362 note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified.
363 Always ensure result fits within application's authorized limits.
364 Each application can set its own limits.
365 note 5 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to
366 read each contained frame header. This is efficient as most of the data is skipped,
367 however it does mean that all frame data must be present and valid.
370 <a name="Chapter14"></a><h2>Advanced compression functions</h2><pre></pre>
372 <pre><b>size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams);
373 </b><p> Gives the amount of memory allocated for a ZSTD_CCtx given a set of compression parameters.
374 `frameContentSize` is an optional parameter, provide `0` if unknown
377 <pre><b>ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem);
378 </b><p> Create a ZSTD compression context using external alloc and free functions
381 <pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
382 </b><p> Gives the amount of memory used by a given ZSTD_CCtx
385 <pre><b>typedef enum {
386 ZSTD_p_forceWindow, </b>/* Force back-references to remain < windowSize, even when referencing Dictionary content (default:0) */<b>
387 ZSTD_p_forceRawDict </b>/* Force loading dictionary in "content-only" mode (no header analysis) */<b>
388 } ZSTD_CCtxParameter;
390 <pre><b>size_t ZSTD_setCCtxParameter(ZSTD_CCtx* cctx, ZSTD_CCtxParameter param, unsigned value);
391 </b><p> Set advanced parameters, selected through enum ZSTD_CCtxParameter
392 @result : 0, or an error code (which can be tested with ZSTD_isError())
395 <pre><b>ZSTD_CDict* ZSTD_createCDict_byReference(const void* dictBuffer, size_t dictSize, int compressionLevel);
396 </b><p> Create a digested dictionary for compression
397 Dictionary content is simply referenced, and therefore stays in dictBuffer.
398 It is important that dictBuffer outlives CDict, it must remain read accessible throughout the lifetime of CDict
401 <pre><b>ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize, unsigned byReference,
402 ZSTD_parameters params, ZSTD_customMem customMem);
403 </b><p> Create a ZSTD_CDict using external alloc and free, and customized compression parameters
406 <pre><b>size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
407 </b><p> Gives the amount of memory used by a given ZSTD_sizeof_CDict
410 <pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
411 </b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize.
412 `estimatedSrcSize` value is optional, select 0 if not known
415 <pre><b>ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
416 </b><p> same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`.
417 All fields of `ZSTD_frameParameters` are set to default (0)
420 <pre><b>size_t ZSTD_checkCParams(ZSTD_compressionParameters params);
421 </b><p> Ensure param values remain within authorized range
424 <pre><b>ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize);
425 </b><p> optimize params for a given `srcSize` and `dictSize`.
426 both values are optional, select `0` if unknown.
429 <pre><b>size_t ZSTD_compress_advanced (ZSTD_CCtx* ctx,
430 void* dst, size_t dstCapacity,
431 const void* src, size_t srcSize,
432 const void* dict,size_t dictSize,
433 ZSTD_parameters params);
434 </b><p> Same as ZSTD_compress_usingDict(), with fine-tune control of each compression parameter
437 <a name="Chapter15"></a><h2>Advanced decompression functions</h2><pre></pre>
439 <pre><b>unsigned ZSTD_isFrame(const void* buffer, size_t size);
440 </b><p> Tells if the content of `buffer` starts with a valid Frame Identifier.
441 Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0.
442 Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled.
443 Note 3 : Skippable Frame Identifiers are considered valid.
446 <pre><b>size_t ZSTD_estimateDCtxSize(void);
447 </b><p> Gives the potential amount of memory allocated to create a ZSTD_DCtx
450 <pre><b>ZSTD_DCtx* ZSTD_createDCtx_advanced(ZSTD_customMem customMem);
451 </b><p> Create a ZSTD decompression context using external alloc and free functions
454 <pre><b>size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);
455 </b><p> Gives the amount of memory used by a given ZSTD_DCtx
458 <pre><b>ZSTD_DDict* ZSTD_createDDict_byReference(const void* dictBuffer, size_t dictSize);
459 </b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
460 Dictionary content is simply referenced, and therefore stays in dictBuffer.
461 It is important that dictBuffer outlives DDict, it must remain read accessible throughout the lifetime of DDict
464 <pre><b>ZSTD_DDict* ZSTD_createDDict_advanced(const void* dict, size_t dictSize,
465 unsigned byReference, ZSTD_customMem customMem);
466 </b><p> Create a ZSTD_DDict using external alloc and free, optionally by reference
469 <pre><b>size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
470 </b><p> Gives the amount of memory used by a given ZSTD_DDict
473 <pre><b>unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize);
474 </b><p> Provides the dictID stored within dictionary.
475 if @return == 0, the dictionary is not conformant with Zstandard specification.
476 It can still be loaded, but as a content-only dictionary.
479 <pre><b>unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict);
480 </b><p> Provides the dictID of the dictionary loaded into `ddict`.
481 If @return == 0, the dictionary is not conformant to Zstandard specification, or empty.
482 Non-conformant dictionaries can still be loaded, but as content-only dictionaries.
485 <pre><b>unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
486 </b><p> Provides the dictID required to decompressed the frame stored within `src`.
487 If @return == 0, the dictID could not be decoded.
488 This could for one of the following reasons :
489 - The frame does not require a dictionary to be decoded (most common case).
490 - The frame was built with dictID intentionally removed. Whatever dictionary is necessary is a hidden information.
491 Note : this use case also happens when using a non-conformant dictionary.
492 - `srcSize` is too small, and as a result, the frame header could not be decoded (only possible if `srcSize < ZSTD_FRAMEHEADERSIZE_MAX`).
493 - This is not a Zstandard frame.
494 When identifying the exact failure cause, it's possible to used ZSTD_getFrameParams(), which will provide a more precise error code.
497 <a name="Chapter16"></a><h2>Advanced streaming functions</h2><pre></pre>
499 <h3>Advanced Streaming compression functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
500 size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize must be correct, a size of 0 means unknown. for a frame size of 0 use initCStream_advanced */<b>
501 size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); </b>/**< note: a dict will not be used if dict == NULL or dictSize < 8 */<b>
502 size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize,
503 ZSTD_parameters params, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize is optional and can be 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0 */<b>
504 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>
505 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. note: pledgedSrcSize must be correct, a size of 0 means unknown. for a frame size of 0 use initCStream_advanced */<b>
506 size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs);
508 <h3>Advanced Streaming decompression functions</h3><pre></pre><b><pre>typedef enum { DStream_p_maxWindowSize } ZSTD_DStreamParameter_e;
509 ZSTD_DStream* ZSTD_createDStream_advanced(ZSTD_customMem customMem);
510 size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize); </b>/**< note: a dict will not be used if dict == NULL or dictSize < 8 */<b>
511 size_t ZSTD_setDStreamParameter(ZSTD_DStream* zds, ZSTD_DStreamParameter_e paramType, unsigned paramValue);
512 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>
513 size_t ZSTD_resetDStream(ZSTD_DStream* zds); </b>/**< re-use decompression parameters from previous init; saves dictionary loading */<b>
514 size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds);
516 <a name="Chapter17"></a><h2>Buffer-less and synchronous inner streaming functions</h2><pre>
517 This is an advanced API, giving full control over buffer management, for users which need direct control over memory.
518 But it's also a complex one, with many restrictions (documented below).
519 Prefer using normal streaming API for an easier experience
523 <a name="Chapter18"></a><h2>Buffer-less streaming compression (synchronous mode)</h2><pre>
524 A ZSTD_CCtx object is required to track streaming operations.
525 Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource.
526 ZSTD_CCtx object can be re-used multiple times within successive compression operations.
528 Start by initializing a context.
529 Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression,
530 or ZSTD_compressBegin_advanced(), for finer parameter control.
531 It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx()
533 Then, consume your input using ZSTD_compressContinue().
534 There are some important considerations to keep in mind when using this advanced function :
535 - ZSTD_compressContinue() has no internal buffer. It uses externally provided buffer only.
536 - Interface is synchronous : input is consumed entirely and produce 1+ (or more) compressed blocks.
537 - Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario.
538 Worst case evaluation is provided by ZSTD_compressBound().
539 ZSTD_compressContinue() doesn't guarantee recover after a failed compression.
540 - ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog).
541 It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks)
542 - ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps.
543 In which case, it will "discard" the relevant memory section from its history.
545 Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum.
546 It's possible to use srcSize==0, in which case, it will write a final empty block to end the frame.
547 Without last block mark, frames will be considered unfinished (corrupted) by decoders.
549 `ZSTD_CCtx` object can be re-used (ZSTD_compressBegin()) to compress some new frame.
552 <h3>Buffer-less streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel);
553 size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel);
554 size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_parameters params, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize is optional and can be 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0 */<b>
555 size_t ZSTD_copyCCtx(ZSTD_CCtx* cctx, const ZSTD_CCtx* preparedCCtx, unsigned long long pledgedSrcSize); </b>/**< note: if pledgedSrcSize can be 0, indicating unknown size. if it is non-zero, it must be accurate. for 0 size frames, use compressBegin_advanced */<b>
556 size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict, unsigned long long pledgedSrcSize); </b>/**< note: if pledgedSrcSize can be 0, indicating unknown size. if it is non-zero, it must be accurate. for 0 size frames, use compressBegin_advanced */<b>
557 size_t ZSTD_compressContinue(ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
558 size_t ZSTD_compressEnd(ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
560 <a name="Chapter19"></a><h2>Buffer-less streaming decompression (synchronous mode)</h2><pre>
561 A ZSTD_DCtx object is required to track streaming operations.
562 Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it.
563 A ZSTD_DCtx object can be re-used multiple times.
565 First typical operation is to retrieve frame parameters, using ZSTD_getFrameParams().
566 It fills a ZSTD_frameParams structure which provide important information to correctly decode the frame,
567 such as the minimum rolling buffer size to allocate to decompress data (`windowSize`),
568 and the dictionary ID used.
569 (Note : content size is optional, it may not be present. 0 means : content size unknown).
570 Note that these values could be wrong, either because of data malformation, or because an attacker is spoofing deliberate false information.
571 As a consequence, check that values remain within valid application range, especially `windowSize`, before allocation.
572 Each application can set its own limit, depending on local restrictions. For extended interoperability, it is recommended to support at least 8 MB.
573 Frame parameters are extracted from the beginning of the compressed frame.
574 Data fragment must be large enough to ensure successful decoding, typically `ZSTD_frameHeaderSize_max` bytes.
575 @result : 0 : successful decoding, the `ZSTD_frameParams` structure is correctly filled.
576 >0 : `srcSize` is too small, please provide at least @result bytes on next attempt.
577 errorCode, which can be tested using ZSTD_isError().
579 Start decompression, with ZSTD_decompressBegin() or ZSTD_decompressBegin_usingDict().
580 Alternatively, you can copy a prepared context, using ZSTD_copyDCtx().
582 Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively.
583 ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue().
584 ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail.
586 @result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity).
587 It can be zero, which is not an error; it just means ZSTD_decompressContinue() has decoded some metadata item.
588 It can also be an error code, which can be tested with ZSTD_isError().
590 ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize`.
591 They should preferably be located contiguously, prior to current block.
592 Alternatively, a round buffer of sufficient size is also possible. Sufficient size is determined by frame parameters.
593 ZSTD_decompressContinue() is very sensitive to contiguity,
594 if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place,
595 or that previous contiguous segment is large enough to properly handle maximum back-reference.
597 A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero.
598 Context can then be reset to start a new decompression.
600 Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType().
601 This information is not required to properly decode a frame.
603 == Special case : skippable frames
605 Skippable frames allow integration of user-defined data into a flow of concatenated frames.
606 Skippable frames will be ignored (skipped) by a decompressor. The format of skippable frames is as follows :
607 a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F
608 b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits
609 c) Frame Content - any content (User Data) of length equal to Frame Size
610 For skippable frames ZSTD_decompressContinue() always returns 0.
611 For skippable frames ZSTD_getFrameParams() returns fparamsPtr->windowLog==0 what means that a frame is skippable.
612 Note : If fparamsPtr->frameContentSize==0, it is ambiguous: the frame might actually be a Zstd encoded frame with no content.
613 For purposes of decompression, it is valid in both cases to skip the frame using
614 ZSTD_findFrameCompressedSize to find its size in bytes.
615 It also returns Frame Size as fparamsPtr->frameContentSize.
618 <pre><b>typedef struct {
619 unsigned long long frameContentSize;
622 unsigned checksumFlag;
625 <h3>Buffer-less streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_getFrameParams(ZSTD_frameParams* fparamsPtr, const void* src, size_t srcSize); </b>/**< doesn't consume input, see details below */<b>
626 size_t ZSTD_decompressBegin(ZSTD_DCtx* dctx);
627 size_t ZSTD_decompressBegin_usingDict(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
628 void ZSTD_copyDCtx(ZSTD_DCtx* dctx, const ZSTD_DCtx* preparedDCtx);
629 size_t ZSTD_nextSrcSizeToDecompress(ZSTD_DCtx* dctx);
630 size_t ZSTD_decompressContinue(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
631 typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e;
632 ZSTD_nextInputType_e ZSTD_nextInputType(ZSTD_DCtx* dctx);
634 <a name="Chapter20"></a><h2>Block functions</h2><pre>
635 Block functions produce and decode raw zstd blocks, without frame metadata.
636 Frame metadata cost is typically ~18 bytes, which can be non-negligible for very small blocks (< 100 bytes).
637 User will have to take in charge required information to regenerate data, such as compressed and content sizes.
639 A few rules to respect :
640 - Compressing and decompressing require a context structure
641 + Use ZSTD_createCCtx() and ZSTD_createDCtx()
642 - It is necessary to init context before starting
643 + compression : ZSTD_compressBegin()
644 + decompression : ZSTD_decompressBegin()
645 + variants _usingDict() are also allowed
646 + copyCCtx() and copyDCtx() work too
647 - Block size is limited, it must be <= ZSTD_getBlockSizeMax()
648 + If you need to compress more, cut data into multiple blocks
649 + Consider using the regular ZSTD_compress() instead, as frame metadata costs become negligible when source size is large.
650 - When a block is considered not compressible enough, ZSTD_compressBlock() result will be zero.
651 In which case, nothing is produced into `dst`.
652 + User must test for such outcome and deal directly with uncompressed data
653 + ZSTD_decompressBlock() doesn't accept uncompressed data as input !!!
654 + In case of multiple successive blocks, decoder must be informed of uncompressed block existence to follow proper history.
655 Use ZSTD_insertBlock() in such a case.
658 <h3>Raw zstd block functions</h3><pre></pre><b><pre>size_t ZSTD_getBlockSizeMax(ZSTD_CCtx* cctx);
659 size_t ZSTD_compressBlock (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
660 size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
661 size_t ZSTD_insertBlock(ZSTD_DCtx* dctx, const void* blockStart, size_t blockSize); </b>/**< insert block into `dctx` history. Useful for uncompressed blocks */<b>
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