Fix bufferless API with attached dictionary

Fixes #3102.

lib/compress/zstd_compress_internal.h

@@ -1172,10 +1172,15 @@ ZSTD_checkDictValidity(const ZSTD_window_t* window,
                     (unsigned)blockEndIdx, (unsigned)maxDist, (unsigned)loadedDictEnd);
         assert(blockEndIdx >= loadedDictEnd);
 
-        if (blockEndIdx > loadedDictEnd + maxDist) {
+        if (blockEndIdx > loadedDictEnd + maxDist || loadedDictEnd != window->dictLimit) {
             /* On reaching window size, dictionaries are invalidated.
              * For simplification, if window size is reached anywhere within next block,
              * the dictionary is invalidated for the full block.
+             *
+             * We also have to invalidate the dictionary if ZSTD_window_update() has detected
+             * non-contiguous segments, which means that loadedDictEnd != window->dictLimit.
+             * loadedDictEnd may be 0, if forceWindow is true, but in that case we never use
+             * dictMatchState, so setting it to NULL is not a problem.
              */
             DEBUGLOG(6, "invalidating dictionary for current block (distance > windowSize)");
             *loadedDictEndPtr = 0;

tests/fuzzer.c

@@ -2592,6 +2592,27 @@ static int basicUnitTests(U32 const seed, double compressibility)
         }
         DISPLAYLEVEL(3, "OK \n");
 
+        DISPLAYLEVEL(3, "test%3d : bufferless api with cdict : ", testNb++);
+        {   ZSTD_CDict* const cdict = ZSTD_createCDict(dictBuffer, dictSize, 1);
+            ZSTD_DCtx* const dctx = ZSTD_createDCtx();
+            ZSTD_frameParameters const fParams = { 0, 1, 0 };
+            size_t cBlockSize;
+            cSize = 0;
+            CHECK_Z(ZSTD_compressBegin_usingCDict_advanced(cctx, cdict, fParams, ZSTD_CONTENTSIZE_UNKNOWN));
+            cBlockSize = ZSTD_compressContinue(cctx, (char*)compressedBuffer + cSize, compressedBufferSize - cSize, CNBuffer, 1000);
+            CHECK_Z(cBlockSize);
+            cSize += cBlockSize;
+            cBlockSize = ZSTD_compressEnd(cctx, (char*)compressedBuffer + cSize, compressedBufferSize - cSize, (char const*)CNBuffer + 2000, 1000);
+            CHECK_Z(cBlockSize);
+            cSize += cBlockSize;
+
+            CHECK_Z(ZSTD_decompress_usingDict(dctx, decodedBuffer, CNBuffSize, compressedBuffer, cSize, dictBuffer, dictSize));
+
+            ZSTD_freeCDict(cdict);
+            ZSTD_freeDCtx(dctx);
+        }
+        DISPLAYLEVEL(3, "OK \n");
+
         DISPLAYLEVEL(3, "test%3i : Building cdict w/ ZSTD_dct_fullDict on a good dictionary : ", testNb++);
         {   ZSTD_compressionParameters const cParams = ZSTD_getCParams(1, CNBuffSize, dictSize);
             ZSTD_CDict* const cdict = ZSTD_createCDict_advanced(dictBuffer, dictSize, ZSTD_dlm_byRef, ZSTD_dct_fullDict, cParams, ZSTD_defaultCMem);