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Provide an API function to estimate decompressed size.

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Introduces a new utility function `ZSTD_findFrameCompressedSize_internal` which
is equivalent to `ZSTD_findFrameCompressSize`, but accepts an additional output
parameter `bound` that computes an upper-bound for the compressed data in the frame.

The new API function is named `ZSTD_decompressBound` to be consistent with
`zstd_compressBound` (the inverse operation). Clients will now be able to compute an upper-bound for
their compressed payloads instead of guessing a large size.

Implements https://github.com/facebook/zstd/issues/1536.
This commit is contained in:
shakeelrao
2019-02-28 00:42:49 -08:00
parent be3bd70c57
commit 820af1e078
5 changed files with 101 additions and 14 deletions
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lib/decompress/zstd_decompress.c
+71 -6
View File
@@ -434,12 +434,7 @@ static size_t ZSTD_decodeFrameHeader(ZSTD_DCtx* dctx, const void* src, size_t he
}
/** ZSTD_findFrameCompressedSize() :
* compatible with legacy mode
* `src` must point to the start of a ZSTD frame, ZSTD legacy frame, or skippable frame
* `srcSize` must be at least as large as the frame contained
* @return : the compressed size of the frame starting at `src` */
size_t ZSTD_findFrameCompressedSize(const void *src, size_t srcSize)
static size_t ZSTD_findFrameCompressedSize_internal(const void *src, size_t srcSize, size_t* bound)
{
#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT >= 1)
if (ZSTD_isLegacy(src, srcSize))
@@ -464,6 +459,7 @@ size_t ZSTD_findFrameCompressedSize(const void *src, size_t srcSize)
remainingSize -= zfh.headerSize;
/* Loop on each block */
unsigned nbBlocks = 0;
while (1) {
blockProperties_t blockProperties;
size_t const cBlockSize = ZSTD_getcBlockSize(ip, remainingSize, &blockProperties);
@@ -474,6 +470,7 @@ size_t ZSTD_findFrameCompressedSize(const void *src, size_t srcSize)
ip += ZSTD_blockHeaderSize + cBlockSize;
remainingSize -= ZSTD_blockHeaderSize + cBlockSize;
nbBlocks++;
if (blockProperties.lastBlock) break;
}
@@ -483,10 +480,78 @@ size_t ZSTD_findFrameCompressedSize(const void *src, size_t srcSize)
ip += 4;
}
if (bound != NULL) *bound = (nbBlocks * zfh.blockSizeMax); /* set to block-based bound */
return ip - ipstart;
}
}
/** ZSTD_findFrameCompressedSize() :
* compatible with legacy mode
* `src` must point to the start of a ZSTD frame, ZSTD legacy frame, or skippable frame
* `srcSize` must be at least as large as the frame contained
* @return : the compressed size of the frame starting at `src` */
size_t ZSTD_findFrameCompressedSize(const void *src, size_t srcSize)
{
return ZSTD_findFrameCompressedSize_internal(src, srcSize, NULL);
}
/** ZSTD_decompressBound() :
* currently incompatible with legacy mode
* `src` must point to the start of a ZSTD frame or a skippeable frame
* `srcSize` must be at least as large as the frame contained
* @return : maximum decompressed size of the compressed source
*/
size_t ZSTD_decompressBound(const void* src, size_t srcSize)
{
#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT >= 1)
if (ZSTD_isLegacy(src, srcSize))
return ERROR(version_unsupported);
#endif
size_t totalDstSize = 0;
/* Loop over each frame */
while (srcSize >= ZSTD_FRAMEHEADERSIZE_PREFIX) {
U32 const magicNumber = MEM_readLE32(src);
if ((magicNumber & ZSTD_MAGIC_SKIPPABLE_MASK) == ZSTD_MAGIC_SKIPPABLE_START) {
size_t const skippableSize = readSkippableFrameSize(src, srcSize);
if (ZSTD_isError(skippableSize))
return skippableSize;
if (srcSize < skippableSize) {
return ZSTD_CONTENTSIZE_ERROR;
}
src = (const BYTE *)src + skippableSize;
srcSize -= skippableSize;
continue;
}
{ unsigned long long const ret = ZSTD_getFrameContentSize(src, srcSize);
if (ret == ZSTD_CONTENTSIZE_ERROR) return ret;
size_t bound;
size_t const frameSrcSize = ZSTD_findFrameCompressedSize_internal(src, srcSize, &bound);
if (ZSTD_isError(frameSrcSize)) {
return ZSTD_CONTENTSIZE_ERROR;
}
size_t frameBound = (ret == ZSTD_CONTENTSIZE_UNKNOWN) ? bound : ret;
/* check for overflow */
if (totalDstSize + frameBound < totalDstSize) return ZSTD_CONTENTSIZE_ERROR;
totalDstSize += frameBound;
src = (const BYTE *)src + frameSrcSize;
srcSize -= frameSrcSize;
}
} /* while (srcSize >= ZSTD_frameHeaderSize_prefix) */
if (srcSize) return ZSTD_CONTENTSIZE_ERROR;
return totalDstSize;
}
/*-*************************************************************