diff options
Diffstat (limited to 'shared/dst_hack.cpp')
| -rw-r--r-- | shared/dst_hack.cpp | 312 |
1 files changed, 312 insertions, 0 deletions
diff --git a/shared/dst_hack.cpp b/shared/dst_hack.cpp new file mode 100644 index 00000000..87ed6c2f --- /dev/null +++ b/shared/dst_hack.cpp @@ -0,0 +1,312 @@ +#include "dst_hack.h" +#include "system_constants.h" +#include <wx/intl.h> +#include "long_path_prefix.h" +#include "string_conv.h" +#include "system_func.h" +#include <wx/longlong.h> +#include "assert_static.h" +#include <bitset> +#include "global_func.h" +#include <limits> + + +bool dst::isFatDrive(const Zstring& fileName) //throw() +{ + using namespace ffs3; + + const size_t BUFFER_SIZE = MAX_PATH + 1; + wchar_t buffer[BUFFER_SIZE]; + +//this call is expensive: ~1.5 ms! +// if (!::GetVolumePathName(applyLongPathPrefix(fileName).c_str(), //__in LPCTSTR lpszFileName, +// buffer, //__out LPTSTR lpszVolumePathName, +// BUFFER_SIZE)) //__in DWORD cchBufferLength +// ... +// Zstring volumePath = buffer; +// if (!volumePath.EndsWith(common::FILE_NAME_SEPARATOR)) //a trailing backslash is required +// volumePath += common::FILE_NAME_SEPARATOR; + + //fast ::GetVolumePathName() clone: let's hope it's not too simple (doesn't honor mount points) + const Zstring nameFmt = removeLongPathPrefix(fileName); //throw() + const size_t pos = nameFmt.find(Zstr(":\\")); + if (pos != 1) //expect single letter volume + return false; + const Zstring volumePath(nameFmt.c_str(), 3); + + //suprisingly fast: ca. 0.03 ms per call! + if (!::GetVolumeInformation(volumePath.c_str(), //__in_opt LPCTSTR lpRootPathName, + NULL, //__out LPTSTR lpVolumeNameBuffer, + 0, //__in DWORD nVolumeNameSize, + NULL, //__out_opt LPDWORD lpVolumeSerialNumber, + NULL, //__out_opt LPDWORD lpMaximumComponentLength, + NULL, //__out_opt LPDWORD lpFileSystemFlags, + buffer, //__out LPTSTR lpFileSystemNameBuffer, + BUFFER_SIZE)) //__in DWORD nFileSystemNameSize + { + assert(false); //shouldn't happen + return false; + } + const Zstring fileSystem = buffer; + + //DST hack seems to be working equally well for FAT and FAT32 (in particular creation time has 10^-2 s precision as advertised) + return fileSystem == Zstr("FAT") || + fileSystem == Zstr("FAT32"); +} + + +namespace +{ +FILETIME utcToLocal(const FILETIME& utcTime) //throw (std::runtime_error) +{ + //treat binary local time representation (which is invariant under DST time zone shift) as logical UTC: + FILETIME localTime = {}; + if (!::FileTimeToLocalFileTime( + &utcTime, //__in const FILETIME *lpFileTime, + &localTime)) //__out LPFILETIME lpLocalFileTime + { + const wxString errorMessage = wxString(_("Conversion error:")) + wxT(" FILETIME -> local FILETIME: ") + + wxT("(") + wxULongLong(utcTime.dwHighDateTime, utcTime.dwLowDateTime).ToString() + wxT(") ") + wxT("\n\n") + ffs3::getLastErrorFormatted(); + throw std::runtime_error(std::string((errorMessage).ToUTF8())); + } + return localTime; +} + + +FILETIME localToUtc(const FILETIME& localTime) //throw (std::runtime_error) +{ + //treat binary local time representation (which is invariant under DST time zone shift) as logical UTC: + FILETIME utcTime = {}; + if (!::LocalFileTimeToFileTime( + &localTime, //__in const FILETIME *lpLocalFileTime, + &utcTime)) //__out LPFILETIME lpFileTime + { + const wxString errorMessage = wxString(_("Conversion error:")) + wxT(" local FILETIME -> FILETIME: ") + + wxT("(") + wxULongLong(localTime.dwHighDateTime, localTime.dwLowDateTime).ToString() + wxT(") ") + wxT("\n\n") + ffs3::getLastErrorFormatted(); + throw std::runtime_error(std::string((errorMessage).ToUTF8())); + } + return utcTime; +} + + +int cmpFileTime(const FILETIME& a, const FILETIME& b) +{ + if (a.dwHighDateTime != b.dwHighDateTime) + return a.dwHighDateTime - b.dwHighDateTime; + return a.dwLowDateTime - b.dwLowDateTime; +} + + +template <class T> //convert wxULongLong and wxLongLong to FILETIME +inline +FILETIME toFiletime(const T& number) +{ + assert_static(sizeof(DWORD) == sizeof(long)); + assert_static(sizeof(long) == 4); + assert(number.GetHi() >= 0); //for wxLongLong + + FILETIME output = {}; + output.dwHighDateTime = number.GetHi(); + output.dwLowDateTime = number.GetLo(); + return output; +} + + +inline +wxULongLong toULonglong(const FILETIME& fileTime) +{ + assert_static(sizeof(DWORD) == sizeof(long)); + assert_static(sizeof(long) == 4); + + return wxULongLong(fileTime.dwHighDateTime, fileTime.dwLowDateTime); +} + + +inline +wxLongLong toLonglong(const FILETIME& fileTime) +{ + assert_static(sizeof(DWORD) == sizeof(long)); + assert_static(sizeof(long) == 4); + assert(fileTime.dwHighDateTime <= static_cast<unsigned long>(std::numeric_limits<long>::max())); + + return wxLongLong(fileTime.dwHighDateTime, fileTime.dwLowDateTime); +} + + +//struct FILETIME {DWORD dwLowDateTime; DWORD dwHighDateTime;}; +const FILETIME FAT_MIN_TIME = {13374976, 27846544}; //1980 \ both are valid max/min FAT dates for 2 second precision +const FILETIME FAT_MAX_TIME = {14487552, 37251238}; //2107 / + +//http://en.wikipedia.org/wiki/File_Allocation_Table +const size_t PRECISION_WRITE_TIME = 20000000; //number of 100 ns per step -> 2 s +const size_t PRECISION_CREATE_TIME = 100000; // -> 1/100 s + +/* +Number of bits of information in create time: ln_2((FAT_MAX_TIME - FAT_MIN_TIME) / PRECISION_CREATE_TIME) = 38.55534023 +Number of bits of information in write time: 30.91148404 +*/ +//total size available to store data: +const size_t CREATE_TIME_INFO_BITS = 38; +// I. indicator that offset in II) is present +const size_t INDICATOR_EXISTING_BITS = 1; +// II. local<->UTC time offset +const size_t UTC_LOCAL_OFFSET_BITS = 7; +// III. indicator that offset in II) corresponds to current local write time (this could be a hash of the write time) +const size_t WRITE_TIME_HASH_BITS = CREATE_TIME_INFO_BITS - INDICATOR_EXISTING_BITS - UTC_LOCAL_OFFSET_BITS; + + +template <size_t precision> +FILETIME encodeRawInformation(wxULongLong rawInfo) +{ + rawInfo *= precision; + rawInfo += toULonglong(FAT_MIN_TIME); + + assert(rawInfo <= toULonglong(FAT_MAX_TIME)); + return toFiletime(rawInfo); +} + + +template <size_t precision> +wxULongLong extractRawInformation(const FILETIME& createTime) +{ + assert(cmpFileTime(FAT_MIN_TIME, createTime) <= 0); + assert(cmpFileTime(createTime, FAT_MAX_TIME) <= 0); + + //FAT create time ranges from 1980 - 2107 (2^7 years) with 1/100 seconds precision + wxULongLong rawInfo = toULonglong(createTime); + assert_static(sizeof(DWORD) == sizeof(long)); + assert_static(sizeof(long) == 4); + + rawInfo -= toULonglong(FAT_MIN_TIME); + rawInfo /= precision; //reduce precision (FILETIME has unit 10^-7 s) + + assert(cmpFileTime(encodeRawInformation<precision>(rawInfo), createTime) == 0); //must be reversible + return rawInfo; +} + + +//convert write time to it's minimal representation (no restriction to FAT range "1980 - 2107") +wxULongLong extractRawWriteTime(const FILETIME& writeTime) +{ + wxULongLong rawInfo = toULonglong(writeTime); + assert(rawInfo % PRECISION_WRITE_TIME == 0); + rawInfo /= PRECISION_WRITE_TIME; //reduce precision (FILETIME has unit 10^-7 s) + return rawInfo; +} + + +//files with different resolution than 2 seconds are rounded up when written to FAT +FILETIME roundToFatWriteTime(const FILETIME& writeTime) +{ + wxULongLong rawData = toULonglong(writeTime); + + if (rawData % PRECISION_WRITE_TIME != 0) + rawData += PRECISION_WRITE_TIME; + + rawData /= PRECISION_WRITE_TIME; + rawData *= PRECISION_WRITE_TIME; + return toFiletime(rawData); +} + + +//get 7-bit value representing time shift in number of quarter-hours +std::bitset<UTC_LOCAL_OFFSET_BITS> getUtcLocalShift() +{ + FILETIME utcTime = FAT_MIN_TIME; + utcTime.dwHighDateTime += 5000000; //some arbitrary valid time + + const FILETIME localTime = utcToLocal(utcTime); + + const int timeShiftSec = ((toLonglong(localTime) - toLonglong(utcTime)) / 10000000).ToLong(); //time shift in seconds + + const int timeShiftQuarter = timeShiftSec / (60 * 15); //time shift in quarter-hours + + const int absValue = common::abs(timeShiftQuarter); //MSVC C++0x bug: std::bitset<>(unsigned long) is ambiguous + + if (std::bitset<UTC_LOCAL_OFFSET_BITS - 1>(absValue).to_ulong() != static_cast<unsigned long>(absValue) || //time shifts that big shouldn't be possible! + timeShiftSec % (60 * 15) != 0) //all known time shift have at least 15 minute granularity! + { + const wxString errorMessage = wxString(_("Conversion error:")) + wxT(" Unexpected UTC <-> local time shift: ") + + wxT("(") + wxLongLong(timeShiftSec).ToString() + wxT(") ") + wxT("\n\n") + ffs3::getLastErrorFormatted(); + throw std::runtime_error(std::string((errorMessage).ToUTF8())); + } + + std::bitset<UTC_LOCAL_OFFSET_BITS> output(absValue); + output[UTC_LOCAL_OFFSET_BITS - 1] = timeShiftQuarter < 0; //sign bit + return output; +} + + +//get time-zone shift in seconds +inline +int convertUtcLocalShift(std::bitset<UTC_LOCAL_OFFSET_BITS> rawShift) +{ + const bool hasSign = rawShift[UTC_LOCAL_OFFSET_BITS - 1]; + rawShift[UTC_LOCAL_OFFSET_BITS - 1] = false; + + assert_static(UTC_LOCAL_OFFSET_BITS <= sizeof(unsigned long) * 8); + return hasSign ? + rawShift.to_ulong() * 15 * 60 * -1 : + rawShift.to_ulong() * 15 * 60; +} +} + + +bool dst::fatHasUtcEncoded(const RawTime& rawTime) //"createTimeRaw" as retrieved by ::FindFirstFile() and ::GetFileAttributesEx(); throw (std::runtime_error) +{ + if ( cmpFileTime(rawTime.createTimeRaw, FAT_MIN_TIME) < 0 || + cmpFileTime(FAT_MAX_TIME, rawTime.createTimeRaw) < 0) + { + assert(false); //shouldn't be possible according to FAT specification + return false; + } + + const wxULongLong rawInfo = extractRawInformation<PRECISION_CREATE_TIME>(utcToLocal(rawTime.createTimeRaw)); + + assert_static(WRITE_TIME_HASH_BITS == 30); + return (extractRawWriteTime(utcToLocal(rawTime.writeTimeRaw)) & 0x3FFFFFFF) == (rawInfo & 0x3FFFFFFF) && //ensure write time wasn't changed externally + rawInfo >> (CREATE_TIME_INFO_BITS - INDICATOR_EXISTING_BITS) == 1; //extended data available +} + + +dst::RawTime dst::fatEncodeUtcTime(const FILETIME& writeTimeRealUtc) //throw (std::runtime_error) +{ + const FILETIME fatWriteTimeUtc = roundToFatWriteTime(writeTimeRealUtc); //writeTimeRealUtc may have incompatible precision (NTFS) + + //create time lets us store 40 bit of information + + //indicator that utc time is encoded -> hopefully results in a date long way in the future; but even if this bit is accidentally set, we still have the hash! + wxULongLong data = 1; + + const std::bitset<UTC_LOCAL_OFFSET_BITS> utcShift = getUtcLocalShift(); + data <<= UTC_LOCAL_OFFSET_BITS; + data |= utcShift.to_ulong(); + + data <<= WRITE_TIME_HASH_BITS; + data |= extractRawWriteTime(utcToLocal(fatWriteTimeUtc)) & 0x3FFFFFFF; //trim to last 30 bit of information + assert_static(WRITE_TIME_HASH_BITS == 30); + + const FILETIME encodedData = localToUtc(encodeRawInformation<PRECISION_CREATE_TIME>(data)); //localToUtc: make sure data is physically saved as FAT local time + assert(cmpFileTime(FAT_MIN_TIME, encodedData) <= 0); + assert(cmpFileTime(encodedData, FAT_MAX_TIME) <= 0); + + return RawTime(encodedData, fatWriteTimeUtc); //keep compatible with other applications, at least until DST shift actually occurs +} + + +FILETIME dst::fatDecodeUtcTime(const RawTime& rawTime) //return real UTC time; throw (std::runtime_error) +{ + if (!fatHasUtcEncoded(rawTime)) + return rawTime.writeTimeRaw; + + const wxULongLong rawInfo = extractRawInformation<PRECISION_CREATE_TIME>(utcToLocal(rawTime.createTimeRaw)); + + const std::bitset<UTC_LOCAL_OFFSET_BITS> rawShift(static_cast<int>(((rawInfo >> WRITE_TIME_HASH_BITS) & 0x7F).ToULong())); //static_cast<int>: a shame MSC... + assert_static(UTC_LOCAL_OFFSET_BITS == 7); + + const int timeShiftSec = convertUtcLocalShift(rawShift); + const FILETIME writeTimeLocal = utcToLocal(rawTime.writeTimeRaw); + + const wxLongLong realUTC = toLonglong(writeTimeLocal) - wxLongLong(timeShiftSec) * 10000000; + return toFiletime(realUTC); +} |