added : ZSTD_getDecompressedSize()

NEWS

@@ -1,5 +1,6 @@
 v0.7.3
 added : `--` separator, stating that all following arguments are file names. Suggested by Chip Turner.
+added : `ZSTD_getDecompressedSize()`
 added : OpenBSD target, by Juan Francisco Cantero Hurtado
 fixed : dictBuilder using HC levels, reported by Bartosz Taudul
 fixed : legacy support from ZSTD_decompress_usingDDict(), reported by Felix Handte

lib/common/zstd.h

@@ -296,6 +296,15 @@ ZSTDLIB_API size_t ZSTD_compress_advanced (ZSTD_CCtx* ctx,
 
 /*--- Advanced Decompression functions ---*/
 
+/** ZSTD_getDecompressedSize() :
+*   compatible with legacy mode
+*   @return : decompressed size if known, 0 otherwise
+              note : 0 can mean any of the following :
+                   - decompressed size is not provided within frame header
+                   - frame header unknown / not supported
+                   - frame header not completely provided (`srcSize` too small) */
+unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
+
 /*! ZSTD_createDCtx_advanced() :
  *  Create a ZSTD decompression context using external alloc and free functions */
 ZSTDLIB_API ZSTD_DCtx* ZSTD_createDCtx_advanced(ZSTD_customMem customMem);

lib/decompress/zstd_decompress.c

@@ -391,6 +391,28 @@ size_t ZSTD_getFrameParams(ZSTD_frameParams* fparamsPtr, const void* src, size_t
 }
 
 
+/** ZSTD_getDecompressedSize() :
+*   compatible with legacy mode
+*   @return : decompressed size if known, 0 otherwise
+              note : 0 can mean any of the following :
+                   - decompressed size is not provided within frame header
+                   - frame header unknown / not supported
+                   - frame header not completely provided (`srcSize` too small) */
+unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize) {
+#if ZSTD_LEGACY_SUPPORT
+    if (srcSize < 4) return 0;
+    {   U32 const magic = MEM_readLE32(src);
+        if (ZSTD_isLegacy(magic)) return ZSTD_getDecompressedSize_legacy(src, srcSize);
+    }
+#endif
+    {   ZSTD_frameParams fparams;
+        size_t const frResult = ZSTD_getFrameParams(&fparams, src, srcSize);
+        if (frResult!=0) return 0;
+        return fparams.frameContentSize;
+    }
+}
+
+
 /** ZSTD_decodeFrameHeader() :
 *   `srcSize` must be the size provided by ZSTD_frameHeaderSize().
 *   @return : 0 if success, or an error code, which can be tested using ZSTD_isError() */

lib/legacy/zstd_legacy.h

@@ -69,6 +69,30 @@ MEM_STATIC unsigned ZSTD_isLegacy (U32 magicNumberLE)
 }
 
 
+MEM_STATIC unsigned long long ZSTD_getDecompressedSize_legacy(const void* src, size_t srcSize)
+{
+    if (srcSize < 4) return 0;
+
+    {   U32 const magic = MEM_readLE32(src);
+        U32 const version = ZSTD_isLegacy(magic);
+        if (!version) return 0;   /* not a supported legacy format */
+        if (version < 5) return 0;  /* no decompressed size in frame header */
+        if (version==5) {
+            ZSTDv05_parameters fParams;
+            size_t const frResult = ZSTDv05_getFrameParams(&fParams, src, srcSize);
+            if (frResult != 0) return 0;
+            return fParams.srcSize;
+        }
+        if (version==6) {
+            ZSTDv06_frameParams fParams;
+            size_t const frResult = ZSTDv06_getFrameParams(&fParams, src, srcSize);
+            if (frResult != 0) return 0;
+            return fParams.frameContentSize;
+        }
+        return 0;   /* should not be possible */
+    }
+}
+
 MEM_STATIC size_t ZSTD_decompressLegacy(
                      void* dst, size_t dstCapacity,
                const void* src, size_t compressedSize,

lib/legacy/zstd_v06.c

@@ -36,7 +36,7 @@
 #include "zstd_v06.h"
 #include <stddef.h>    /* size_t, ptrdiff_t */
 #include <string.h>    /* memcpy */
-#include <stdlib.h>    /* malloc, free, qsort */ 
+#include <stdlib.h>    /* malloc, free, qsort */
 
 
 
@@ -535,8 +535,6 @@ ZSTDLIB_API size_t ZSTDv06_decompress_usingPreparedDCtx(
 
 
 
-struct ZSTDv06_frameParams_s { U64 frameContentSize; U32 windowLog; };
-
 #define ZSTDv06_FRAMEHEADERSIZE_MAX 13    /* for static allocation */
 static const size_t ZSTDv06_frameHeaderSize_min = 5;
 static const size_t ZSTDv06_frameHeaderSize_max = ZSTDv06_FRAMEHEADERSIZE_MAX;

lib/legacy/zstd_v06.h

@@ -107,7 +107,7 @@ ZSTDLIB_API size_t ZSTDv06_decompress_usingDict(ZSTDv06_DCtx* dctx,
 /*-************************
 *  Advanced Streaming API
 ***************************/
-
+struct ZSTDv06_frameParams_s { unsigned long long frameContentSize; unsigned windowLog; };
 typedef struct ZSTDv06_frameParams_s ZSTDv06_frameParams;
 
 ZSTDLIB_API size_t ZSTDv06_getFrameParams(ZSTDv06_frameParams* fparamsPtr, const void* src, size_t srcSize);   /**< doesn't consume input */

programs/fuzzer.c

@@ -137,6 +137,12 @@ static int basicUnitTests(U32 seed, double compressibility)
               cSize=r );
     DISPLAYLEVEL(4, "OK (%u bytes : %.2f%%)\n", (U32)cSize, (double)cSize/CNBuffSize*100);
 
+    DISPLAYLEVEL(4, "test%3i : decompressed size test : ", testNb++);
+    {   unsigned long long const rSize = ZSTD_getDecompressedSize(compressedBuffer, cSize);
+        if (rSize != CNBuffSize) goto _output_error;
+    }
+    DISPLAYLEVEL(4, "OK \n");
+
     DISPLAYLEVEL(4, "test%3i : decompress %u bytes : ", testNb++, (U32)CNBuffSize);
     CHECKPLUS( r , ZSTD_decompress(decodedBuffer, CNBuffSize, compressedBuffer, cSize),
                if (r != CNBuffSize) goto _output_error);
@@ -390,19 +396,21 @@ static int basicUnitTests(U32 seed, double compressibility)
         U32 rSeed = 1;
 
         /* create batch of 3-bytes sequences */
-        { int i; for (i=0; i < NB3BYTESSEQ; i++) {
+        {   int i;
-            _3BytesSeqs[i][0] = (BYTE)(FUZ_rand(&rSeed) & 255);
+            for (i=0; i < NB3BYTESSEQ; i++) {
-            _3BytesSeqs[i][1] = (BYTE)(FUZ_rand(&rSeed) & 255);
+                _3BytesSeqs[i][0] = (BYTE)(FUZ_rand(&rSeed) & 255);
-            _3BytesSeqs[i][2] = (BYTE)(FUZ_rand(&rSeed) & 255);
+                _3BytesSeqs[i][1] = (BYTE)(FUZ_rand(&rSeed) & 255);
-        }}
+                _3BytesSeqs[i][2] = (BYTE)(FUZ_rand(&rSeed) & 255);
+        }   }
 
         /* randomly fills CNBuffer with prepared 3-bytes sequences */
-        { int i; for (i=0; i < _3BYTESTESTLENGTH; i += 3) {   /* note : CNBuffer size > _3BYTESTESTLENGTH+3 */
+        {   int i;
-            U32 const id = FUZ_rand(&rSeed) & NB3BYTESSEQMASK;
+            for (i=0; i < _3BYTESTESTLENGTH; i += 3) {   /* note : CNBuffer size > _3BYTESTESTLENGTH+3 */
-            ((BYTE*)CNBuffer)[i+0] = _3BytesSeqs[id][0];
+                U32 const id = FUZ_rand(&rSeed) & NB3BYTESSEQMASK;
-            ((BYTE*)CNBuffer)[i+1] = _3BytesSeqs[id][1];
+                ((BYTE*)CNBuffer)[i+0] = _3BytesSeqs[id][0];
-            ((BYTE*)CNBuffer)[i+2] = _3BytesSeqs[id][2];
+                ((BYTE*)CNBuffer)[i+1] = _3BytesSeqs[id][1];
-    }   }}
+                ((BYTE*)CNBuffer)[i+2] = _3BytesSeqs[id][2];
+    }   }   }
     DISPLAYLEVEL(4, "test%3i : compress lots 3-bytes sequences : ", testNb++);
     { CHECK_V(r, ZSTD_compress(compressedBuffer, ZSTD_compressBound(_3BYTESTESTLENGTH),
                                  CNBuffer, _3BYTESTESTLENGTH, 19) );
@@ -556,6 +564,11 @@ static int fuzzerTests(U32 seed, U32 nbTests, unsigned startTest, U32 const maxD
                   CHECK(endCheck != endMark, "ZSTD_compressCCtx : dst buffer overflow"); }
         }   }
 
+        /* Decompressed size test */
+        {   unsigned long long const rSize = ZSTD_getDecompressedSize(cBuffer, cSize);
+            CHECK(rSize != sampleSize, "decompressed size incorrect");
+        }
+
         /* frame header decompression test */
         {   ZSTD_frameParams dParams;
             size_t const check = ZSTD_getFrameParams(&dParams, cBuffer, cSize);