w32dlfcn.h

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/*
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#ifndef COMPAT_W32DLFCN_H
#define COMPAT_W32DLFCN_H

#ifdef _WIN32
#include <windows.h>
#if _WIN32_WINNT < 0x0602
#include "libavutil/wchar_filename.h"
#endif
/**
 * Safe function used to open dynamic libs. This attempts to improve program security
 * by removing the current directory from the dll search path. Only dll's found in the
 * executable or system directory are allowed to be loaded.
 * @param name  The dynamic lib name.
 * @return A handle to the opened lib.
 */
static inline HMODULE win32_dlopen(const char *name)
{
#if _WIN32_WINNT < 0x0602
    // Need to check if KB2533623 is available
    if (!GetProcAddress(GetModuleHandleW(L"kernel32.dll"), "SetDefaultDllDirectories")) {
        HMODULE module = NULL;
        wchar_t *path = NULL, *name_w = NULL;
        DWORD pathlen;
        if (utf8towchar(name, &name_w))
            goto exit;
        path = (wchar_t *)av_mallocz_array(MAX_PATH, sizeof(wchar_t));
        // Try local directory first
        pathlen = GetModuleFileNameW(NULL, path, MAX_PATH);
        pathlen = wcsrchr(path, '\\') - path;
        if (pathlen == 0 || pathlen + wcslen(name_w) + 2 > MAX_PATH)
            goto exit;
        path[pathlen] = '\\';
        wcscpy(path + pathlen + 1, name_w);
        module = LoadLibraryExW(path, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
        if (module == NULL) {
            // Next try System32 directory
            pathlen = GetSystemDirectoryW(path, MAX_PATH);
            if (pathlen == 0 || pathlen + wcslen(name_w) + 2 > MAX_PATH)
                goto exit;
            path[pathlen] = '\\';
            wcscpy(path + pathlen + 1, name_w);
            module = LoadLibraryExW(path, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
        }
exit:
        av_free(path);
        av_free(name_w);
        return module;
    }
#endif
#ifndef LOAD_LIBRARY_SEARCH_APPLICATION_DIR
#   define LOAD_LIBRARY_SEARCH_APPLICATION_DIR 0x00000200
#endif
#ifndef LOAD_LIBRARY_SEARCH_SYSTEM32
#   define LOAD_LIBRARY_SEARCH_SYSTEM32        0x00000800
#endif
    return LoadLibraryExA(name, NULL, LOAD_LIBRARY_SEARCH_APPLICATION_DIR | LOAD_LIBRARY_SEARCH_SYSTEM32);
}
#define dlopen(name, flags) win32_dlopen(name)
#define dlclose FreeLibrary
#define dlsym GetProcAddress
#else
#include <dlfcn.h>
#endif

#endif /* COMPAT_W32DLFCN_H */