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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.html *
// * Copyright (C) Zenju (zenju AT gmx DOT de) - All Rights Reserved *
// **************************************************************************
#ifndef SYMLINK_WIN_H_INCLUDED
#define SYMLINK_WIN_H_INCLUDED
#include "scope_guard.h"
#include "file_error.h"
#ifdef FFS_WIN
#include "win.h" //includes "windows.h"
#include "WinIoCtl.h"
#include "privilege.h"
#include "long_path_prefix.h"
#elif defined FFS_LINUX
#include <unistd.h>
#endif
namespace zen
{
#ifdef FFS_WIN
bool isSymlink(const WIN32_FIND_DATA& data); //*not* a simple FILE_ATTRIBUTE_REPARSE_POINT check!
bool isSymlink(DWORD fileAttributes, DWORD reparseTag);
#endif
Zstring getSymlinkRawTargetString(const Zstring& linkPath); //throw FileError
}
//################################ implementation ################################
#ifdef _MSC_VER //I don't have Windows Driver Kit at hands right now, so unfortunately we need to redefine this structures 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 FFS_WIN
//FSCTL_GET_REPARSE_POINT: http://msdn.microsoft.com/en-us/library/aa364571(VS.85).aspx
//reading certain symlinks/junctions requires admin rights!
try
{ activatePrivilege(SE_BACKUP_NAME); } //throw FileError
catch (FileError&) {} //This shall not cause an error in user mode!
const HANDLE hLink = ::CreateFile(applyLongPathPrefix(linkPath).c_str(),
GENERIC_READ,
FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
nullptr,
OPEN_EXISTING,
FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT,
nullptr);
if (hLink == INVALID_HANDLE_VALUE)
throw FileError(replaceCpy(_("Cannot resolve symbolic link %x."), L"%x", fmtFileName(linkPath)) + L"\n\n" + getLastErrorFormatted());
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 FileError(replaceCpy(_("Cannot resolve symbolic link %x."), L"%x", fmtFileName(linkPath)) + L"\n\n" + getLastErrorFormatted());
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", fmtFileName(linkPath)) + L"\n\n" + L"Not a symbolic link or junction!");
//absolute symlinks and junctions technically start with \??\ while relative ones do not
if (startsWith(output, Zstr("\\??\\")))
output = Zstring(output.c_str() + 4, output.length() - 4);
return output;
#elif defined FFS_LINUX
const int BUFFER_SIZE = 10000;
std::vector<char> buffer(BUFFER_SIZE);
const int bytesWritten = ::readlink(linkPath.c_str(), &buffer[0], BUFFER_SIZE);
if (bytesWritten < 0 || bytesWritten >= BUFFER_SIZE)
{
std::wstring errorMessage = replaceCpy(_("Cannot resolve symbolic link %x."), L"%x", fmtFileName(linkPath));
if (bytesWritten < 0)
errorMessage += L"\n\n" + getLastErrorFormatted();
throw FileError(errorMessage);
}
buffer[bytesWritten] = 0; //set null-terminating char
return Zstring(&buffer[0], bytesWritten);
#endif
}
}
namespace zen
{
inline
Zstring getSymlinkRawTargetString(const Zstring& linkPath) { return getSymlinkRawTargetString_impl(linkPath); }
#ifdef FFS_WIN
/*
Reparse Point Tags
http://msdn.microsoft.com/en-us/library/windows/desktop/aa365511(v=vs.85).aspx
WIN32_FIND_DATA structure
http://msdn.microsoft.com/en-us/library/windows/desktop/aa365740(v=vs.85).aspx
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_WIN_H_INCLUDED
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