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// *****************************************************************************
// * This file is part of the FreeFileSync project. It is distributed under *
// * GNU General Public License: http://www.gnu.org/licenses/gpl-3.0 *
// * Copyright (C) Zenju (zenju AT freefilesync DOT org) - All Rights Reserved *
// *****************************************************************************
#ifndef SYMLINK_TARGET_H_801783470198357483
#define SYMLINK_TARGET_H_801783470198357483
#include "scope_guard.h"
#include "file_error.h"
#ifdef ZEN_WIN
#include "win.h" //includes "windows.h"
#include "privilege.h"
#include "long_path_prefix.h"
#include "dll.h"
#elif defined ZEN_LINUX || defined ZEN_MAC
#include <unistd.h>
#include <stdlib.h> //realpath
#endif
namespace zen
{
#ifdef ZEN_WIN
bool isSymlink(const WIN32_FIND_DATA& data); //checking FILE_ATTRIBUTE_REPARSE_POINT is insufficient!
bool isSymlink(DWORD fileAttributes, DWORD reparseTag);
#endif
Zstring getResolvedSymlinkPath(const Zstring& linkPath); //throw FileError; Win: requires Vista or later!
Zstring getSymlinkTargetRaw (const Zstring& linkPath); //throw FileError
}
//################################ implementation ################################
#ifdef ZEN_WIN
//I don't have Windows Driver Kit at hands right now, so unfortunately we need to redefine this structure and cross fingers...
typedef struct _REPARSE_DATA_BUFFER //from ntifs.h
{
ULONG ReparseTag;
USHORT ReparseDataLength;
USHORT Reserved;
union
{
struct
{
USHORT SubstituteNameOffset;
USHORT SubstituteNameLength;
USHORT PrintNameOffset;
USHORT PrintNameLength;
ULONG Flags;
WCHAR PathBuffer[1];
} SymbolicLinkReparseBuffer;
struct
{
USHORT SubstituteNameOffset;
USHORT SubstituteNameLength;
USHORT PrintNameOffset;
USHORT PrintNameLength;
WCHAR PathBuffer[1];
} MountPointReparseBuffer;
struct
{
UCHAR DataBuffer[1];
} GenericReparseBuffer;
};
} REPARSE_DATA_BUFFER, *PREPARSE_DATA_BUFFER;
#define REPARSE_DATA_BUFFER_HEADER_SIZE FIELD_OFFSET(REPARSE_DATA_BUFFER, GenericReparseBuffer)
#endif
namespace
{
//retrieve raw target data of symlink or junction
Zstring getSymlinkRawTargetString_impl(const Zstring& linkPath) //throw FileError
{
using namespace zen;
#ifdef ZEN_WIN
//FSCTL_GET_REPARSE_POINT: https://msdn.microsoft.com/en-us/library/aa364571
//reading certain symlinks/junctions requires admin rights!
try
{ activatePrivilege(PrivilegeName::BACKUP); } //throw FileError
catch (FileError&) {} //This shall not cause an error in user mode!
const HANDLE hLink = ::CreateFile(applyLongPathPrefix(linkPath).c_str(), //_In_ LPCTSTR lpFileName,
//it seems we do not even need GENERIC_READ!
0, //_In_ DWORD dwDesiredAccess,
FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, //_In_ DWORD dwShareMode,
nullptr, //_In_opt_ LPSECURITY_ATTRIBUTES lpSecurityAttributes,
OPEN_EXISTING, //_In_ DWORD dwCreationDisposition,
FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT, //_In_ DWORD dwFlagsAndAttributes,
nullptr); //_In_opt_ HANDLE hTemplateFile
if (hLink == INVALID_HANDLE_VALUE)
THROW_LAST_FILE_ERROR(replaceCpy(_("Cannot resolve symbolic link %x."), L"%x", fmtPath(linkPath)), L"CreateFile");
ZEN_ON_SCOPE_EXIT(::CloseHandle(hLink));
//respect alignment issues...
const DWORD bufferSize = REPARSE_DATA_BUFFER_HEADER_SIZE + MAXIMUM_REPARSE_DATA_BUFFER_SIZE;
std::vector<char> buffer(bufferSize);
DWORD bytesReturned = 0; //dummy value required by FSCTL_GET_REPARSE_POINT!
if (!::DeviceIoControl(hLink, //__in HANDLE hDevice,
FSCTL_GET_REPARSE_POINT, //__in DWORD dwIoControlCode,
nullptr, //__in_opt LPVOID lpInBuffer,
0, //__in DWORD nInBufferSize,
&buffer[0], //__out_opt LPVOID lpOutBuffer,
bufferSize, //__in DWORD nOutBufferSize,
&bytesReturned, //__out_opt LPDWORD lpBytesReturned,
nullptr)) //__inout_opt LPOVERLAPPED lpOverlapped
THROW_LAST_FILE_ERROR(replaceCpy(_("Cannot resolve symbolic link %x."), L"%x", fmtPath(linkPath)), L"DeviceIoControl, FSCTL_GET_REPARSE_POINT");
REPARSE_DATA_BUFFER& reparseData = *reinterpret_cast<REPARSE_DATA_BUFFER*>(&buffer[0]); //REPARSE_DATA_BUFFER needs to be artificially enlarged!
Zstring output;
if (reparseData.ReparseTag == IO_REPARSE_TAG_SYMLINK)
{
output = Zstring(reparseData.SymbolicLinkReparseBuffer.PathBuffer + reparseData.SymbolicLinkReparseBuffer.SubstituteNameOffset / sizeof(WCHAR),
reparseData.SymbolicLinkReparseBuffer.SubstituteNameLength / sizeof(WCHAR));
}
else if (reparseData.ReparseTag == IO_REPARSE_TAG_MOUNT_POINT)
{
output = Zstring(reparseData.MountPointReparseBuffer.PathBuffer + reparseData.MountPointReparseBuffer.SubstituteNameOffset / sizeof(WCHAR),
reparseData.MountPointReparseBuffer.SubstituteNameLength / sizeof(WCHAR));
}
else
throw FileError(replaceCpy(_("Cannot resolve symbolic link %x."), L"%x", fmtPath(linkPath)), L"Not a symbolic link or junction.");
//absolute symlinks and junctions use NT namespace naming convention while relative ones do not:
//https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247#NT_Namespaces
return ntPathToWin32Path(output);
#elif defined ZEN_LINUX || defined ZEN_MAC
const size_t BUFFER_SIZE = 10000;
std::vector<char> buffer(BUFFER_SIZE);
const ssize_t bytesWritten = ::readlink(linkPath.c_str(), &buffer[0], BUFFER_SIZE);
if (bytesWritten < 0)
THROW_LAST_FILE_ERROR(replaceCpy(_("Cannot resolve symbolic link %x."), L"%x", fmtPath(linkPath)), L"readlink");
if (bytesWritten >= static_cast<ssize_t>(BUFFER_SIZE)) //detect truncation, not an error for readlink!
throw FileError(replaceCpy(_("Cannot resolve symbolic link %x."), L"%x", fmtPath(linkPath)), L"readlink: buffer truncated.");
return Zstring(&buffer[0], bytesWritten); //readlink does not append 0-termination!
#endif
}
Zstring getResolvedSymlinkPath_impl(const Zstring& linkPath) //throw FileError
{
using namespace zen;
#ifdef ZEN_WIN
//GetFinalPathNameByHandle() is not available before Vista!
using GetFinalPathNameByHandleWFunc = DWORD (WINAPI*)(HANDLE hFile, LPTSTR lpszFilePath, DWORD cchFilePath, DWORD dwFlags);
const SysDllFun<GetFinalPathNameByHandleWFunc> getFinalPathNameByHandle(L"kernel32.dll", "GetFinalPathNameByHandleW");
if (!getFinalPathNameByHandle)
throw FileError(replaceCpy(_("Cannot determine final path for %x."), L"%x", fmtPath(linkPath)), replaceCpy(_("Cannot find system function %x."), L"%x", L"\"GetFinalPathNameByHandleW\""));
const HANDLE hFile = ::CreateFile(applyLongPathPrefix(linkPath).c_str(), //_In_ LPCTSTR lpFileName,
0, //_In_ DWORD dwDesiredAccess,
FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, //_In_ DWORD dwShareMode,
nullptr, //_In_opt_ LPSECURITY_ATTRIBUTES lpSecurityAttributes,
OPEN_EXISTING, //_In_ DWORD dwCreationDisposition,
//needed to open a directory:
FILE_FLAG_BACKUP_SEMANTICS, //_In_ DWORD dwFlagsAndAttributes,
nullptr); //_In_opt_ HANDLE hTemplateFile
if (hFile == INVALID_HANDLE_VALUE)
THROW_LAST_FILE_ERROR(replaceCpy(_("Cannot determine final path for %x."), L"%x", fmtPath(linkPath)), L"CreateFile");
ZEN_ON_SCOPE_EXIT(::CloseHandle(hFile));
const DWORD bufferSize = getFinalPathNameByHandle(hFile, nullptr, 0, 0);
if (bufferSize == 0)
THROW_LAST_FILE_ERROR(replaceCpy(_("Cannot determine final path for %x."), L"%x", fmtPath(linkPath)), L"GetFinalPathNameByHandle");
std::vector<wchar_t> targetPath(bufferSize);
const DWORD charsWritten = getFinalPathNameByHandle(hFile, //__in HANDLE hFile,
&targetPath[0], //__out LPTSTR lpszFilePath,
bufferSize, //__in DWORD cchFilePath,
0); //__in DWORD dwFlags
if (charsWritten == 0)
THROW_LAST_FILE_ERROR(replaceCpy(_("Cannot determine final path for %x."), L"%x", fmtPath(linkPath)), L"GetFinalPathNameByHandle");
if (charsWritten >= bufferSize)
throw FileError(replaceCpy(_("Cannot determine final path for %x."), L"%x", fmtPath(linkPath)), L"GetFinalPathNameByHandle: insufficient buffer size.");
return removeLongPathPrefix(Zstring(&targetPath[0], charsWritten)); //MSDN: GetFinalPathNameByHandle() always prepends "\\?\"
#elif defined ZEN_LINUX || defined ZEN_MAC
char* targetPath = ::realpath(linkPath.c_str(), nullptr);
if (!targetPath)
THROW_LAST_FILE_ERROR(replaceCpy(_("Cannot determine final path for %x."), L"%x", fmtPath(linkPath)), L"realpath");
ZEN_ON_SCOPE_EXIT(::free(targetPath));
return targetPath;
#endif
}
}
namespace zen
{
inline
Zstring getSymlinkTargetRaw(const Zstring& linkPath) { return getSymlinkRawTargetString_impl(linkPath); }
inline
Zstring getResolvedSymlinkPath(const Zstring& linkPath) { return getResolvedSymlinkPath_impl(linkPath); }
#ifdef ZEN_WIN
/*
Reparse Point Tags
https://msdn.microsoft.com/en-us/library/windows/desktop/aa365511
WIN32_FIND_DATA structure
https://msdn.microsoft.com/en-us/library/windows/desktop/aa365740
The only surrogate reparse points are;
IO_REPARSE_TAG_MOUNT_POINT
IO_REPARSE_TAG_SYMLINK
*/
inline
bool isSymlink(DWORD fileAttributes, DWORD reparseTag)
{
return (fileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) != 0 &&
IsReparseTagNameSurrogate(reparseTag);
}
inline
bool isSymlink(const WIN32_FIND_DATA& data)
{
return isSymlink(data.dwFileAttributes, data.dwReserved0);
}
#endif
}
#endif //SYMLINK_TARGET_H_801783470198357483
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