1 files changed, 99 insertions, 0 deletions
diff --git a/src/zstd/examples/dictionary_decompression.c b/src/zstd/examples/dictionary_decompression.c
new file mode 100644
index 000000000..7e50986e3
--- /dev/null
+++ b/src/zstd/examples/dictionary_decompression.c
@@ -0,0 +1,99 @@
+/*
+ * Copyright (c) 2016-2020, Yann Collet, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under both the BSD-style license (found in the
+ * LICENSE file in the root directory of this source tree) and the GPLv2 (found
+ * in the COPYING file in the root directory of this source tree).
+ * You may select, at your option, one of the above-listed licenses.
+ */
+
+
+#include <stdio.h>     // printf
+#include <stdlib.h>    // free
+#include <zstd.h>      // presumes zstd library is installed
+#include "common.h"    // Helper functions, CHECK(), and CHECK_ZSTD()
+
+/* createDict() :
+   `dictFileName` is supposed to have been created using `zstd --train` */
+static ZSTD_DDict* createDict_orDie(const char* dictFileName)
+{
+    size_t dictSize;
+    printf("loading dictionary %s \n", dictFileName);
+    void* const dictBuffer = mallocAndLoadFile_orDie(dictFileName, &dictSize);
+    ZSTD_DDict* const ddict = ZSTD_createDDict(dictBuffer, dictSize);
+    CHECK(ddict != NULL, "ZSTD_createDDict() failed!");
+    free(dictBuffer);
+    return ddict;
+}
+
+static void decompress(const char* fname, const ZSTD_DDict* ddict)
+{
+    size_t cSize;
+    void* const cBuff = mallocAndLoadFile_orDie(fname, &cSize);
+    /* Read the content size from the frame header. For simplicity we require
+     * that it is always present. By default, zstd will write the content size
+     * in the header when it is known. If you can't guarantee that the frame
+     * content size is always written into the header, either use streaming
+     * decompression, or ZSTD_decompressBound().
+     */
+    unsigned long long const rSize = ZSTD_getFrameContentSize(cBuff, cSize);
+    CHECK(rSize != ZSTD_CONTENTSIZE_ERROR, "%s: not compressed by zstd!", fname);
+    CHECK(rSize != ZSTD_CONTENTSIZE_UNKNOWN, "%s: original size unknown!", fname);
+    void* const rBuff = malloc_orDie((size_t)rSize);
+
+    /* Check that the dictionary ID matches.
+     * If a non-zstd dictionary is used, then both will be zero.
+     * By default zstd always writes the dictionary ID into the frame.
+     * Zstd will check if there is a dictionary ID mismatch as well.
+     */
+    unsigned const expectedDictID = ZSTD_getDictID_fromDDict(ddict);
+    unsigned const actualDictID = ZSTD_getDictID_fromFrame(cBuff, cSize);
+    CHECK(actualDictID == expectedDictID,
+          "DictID mismatch: expected %u got %u",
+          expectedDictID,
+          actualDictID);
+
+    /* Decompress using the dictionary.
+     * If you need to control the decompression parameters, then use the
+     * advanced API: ZSTD_DCtx_setParameter(), ZSTD_DCtx_refDDict(), and
+     * ZSTD_decompressDCtx().
+     */
+    ZSTD_DCtx* const dctx = ZSTD_createDCtx();
+    CHECK(dctx != NULL, "ZSTD_createDCtx() failed!");
+    size_t const dSize = ZSTD_decompress_usingDDict(dctx, rBuff, rSize, cBuff, cSize, ddict);
+    CHECK_ZSTD(dSize);
+    /* When zstd knows the content size, it will error if it doesn't match. */
+    CHECK(dSize == rSize, "Impossible because zstd will check this condition!");
+
+    /* success */
+    printf("%25s : %6u -> %7u \n", fname, (unsigned)cSize, (unsigned)rSize);
+
+    ZSTD_freeDCtx(dctx);
+    free(rBuff);
+    free(cBuff);
+}
+
+
+int main(int argc, const char** argv)
+{
+    const char* const exeName = argv[0];
+
+    if (argc<3) {
+        printf("wrong arguments\n");
+        printf("usage:\n");
+        printf("%s [FILES] dictionary\n", exeName);
+        return 1;
+    }
+
+    /* load dictionary only once */
+    const char* const dictName = argv[argc-1];
+    ZSTD_DDict* const dictPtr = createDict_orDie(dictName);
+
+    int u;
+    for (u=1; u<argc-1; u++) decompress(argv[u], dictPtr);
+
+    ZSTD_freeDDict(dictPtr);
+    printf("All %u files correctly decoded (in memory) \n", argc-2);
+    return 0;
+}