name : dictionary_decompression.c /* * Copyright (c) Meta Platforms, Inc. and affiliates. * 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; }