FreeBSD/Linux Kernel Cross Reference
sys/contrib/zstd/examples/dictionary_decompression.c

     /*
      * Copyright (c) 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;
    }

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