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Clarify dstCapacity requirements #3531

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Mar 9, 2023
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Clarify dstCapacity requirements #3531

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6 changes: 4 additions & 2 deletions lib/zstd.h
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Original file line number Diff line number Diff line change
Expand Up @@ -148,7 +148,8 @@ ZSTDLIB_API const char* ZSTD_versionString(void);
***************************************/
/*! ZSTD_compress() :
* Compresses `src` content as a single zstd compressed frame into already allocated `dst`.
* Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
* NOTE: Providing `dstCapacity >= ZSTD_compressBound(srcSize)` guarantees that zstd will have
* enough space to successfully compress the data.
* @return : compressed size written into `dst` (<= `dstCapacity),
* or an error code if it fails (which can be tested using ZSTD_isError()). */
ZSTDLIB_API size_t ZSTD_compress( void* dst, size_t dstCapacity,
Expand Down Expand Up @@ -578,7 +579,8 @@ ZSTDLIB_API size_t ZSTD_CCtx_reset(ZSTD_CCtx* cctx, ZSTD_ResetDirective reset);
* Should cctx hold data from a previously unfinished frame, everything about it is forgotten.
* - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*()
* - The function is always blocking, returns when compression is completed.
* Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
* NOTE: Providing `dstCapacity >= ZSTD_compressBound(srcSize)` guarantees that zstd will have
* enough space to successfully compress the data, though it is possible it fails for other reasons.
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though it is possible it fails for other reasons

What other reasons do you have in mind ?
Memory allocation failures ?
Providing dstCapacity >= ZSTD_compressBound(srcSize) should be enough to avoid #3524.

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I mean ZSTD_compress2() can let you specify a lot of options. E.g. compression could fail to allocate a thread. We could run out of memory.

I only mentioned this in ZSTD_compress2(), and skipped it in ZSTD_compress(), but I just mean that you still have to check the error code.

* @return : compressed size written into `dst` (<= `dstCapacity),
* or an error code if it fails (which can be tested using ZSTD_isError()).
*/
Expand Down