// Reads attributes specific to the GNU format.
// Throws if any conversion fails.
private void ReadGnuAttributes(Span <byte> buffer)
{
// Convert byte arrays
long aTime = (long)TarHelpers.ParseOctal <ulong>(buffer.Slice(FieldLocations.ATime, FieldLengths.ATime));
_aTime = TarHelpers.GetDateTimeOffsetFromSecondsSinceEpoch(aTime);
long cTime = (long)TarHelpers.ParseOctal <ulong>(buffer.Slice(FieldLocations.CTime, FieldLengths.CTime));
_cTime = TarHelpers.GetDateTimeOffsetFromSecondsSinceEpoch(cTime);
// TODO: Read the bytes of the currently unsupported GNU fields, in case user wants to write this entry into another GNU archive, they need to be preserved. https://github.com/dotnet/runtime/issues/68230
}
// Reads the attributes shared by the POSIX and GNU formats.
// Throws if converting the bytes to their expected data type fails.
private void ReadPosixAndGnuSharedAttributes(Span <byte> buffer)
{
// Convert the byte arrays
_uName = TarHelpers.GetTrimmedAsciiString(buffer.Slice(FieldLocations.UName, FieldLengths.UName));
_gName = TarHelpers.GetTrimmedAsciiString(buffer.Slice(FieldLocations.GName, FieldLengths.GName));
// DevMajor and DevMinor only have values with character devices and block devices.
// For all other typeflags, the values in these fields are irrelevant.
if (_typeFlag is TarEntryType.CharacterDevice or TarEntryType.BlockDevice)
{
// Major number for a character device or block device entry.
_devMajor = (int)TarHelpers.ParseOctal <uint>(buffer.Slice(FieldLocations.DevMajor, FieldLengths.DevMajor));
// Minor number for a character device or block device entry.
_devMinor = (int)TarHelpers.ParseOctal <uint>(buffer.Slice(FieldLocations.DevMinor, FieldLengths.DevMinor));
}
}
// Attempts to read the fields shared by all formats and stores them in their expected data type.
// Throws if any data type conversion fails.
// Returns true on success, false if checksum is zero.
private static TarHeader?TryReadCommonAttributes(Span <byte> buffer, TarEntryFormat initialFormat)
{
// Start by collecting fields that need special checks that return early when data is wrong
// Empty checksum means this is an invalid (all blank) entry, finish early
Span <byte> spanChecksum = buffer.Slice(FieldLocations.Checksum, FieldLengths.Checksum);
if (TarHelpers.IsAllNullBytes(spanChecksum))
{
return(null);
}
int checksum = (int)TarHelpers.ParseOctal <uint>(spanChecksum);
// Zero checksum means the whole header is empty
if (checksum == 0)
{
return(null);
}
long size = (int)TarHelpers.ParseOctal <uint>(buffer.Slice(FieldLocations.Size, FieldLengths.Size));
if (size < 0)
{
throw new FormatException(string.Format(SR.TarSizeFieldNegative));
}
// Continue with the rest of the fields that require no special checks
TarHeader header = new(initialFormat,
name : TarHelpers.GetTrimmedUtf8String(buffer.Slice(FieldLocations.Name, FieldLengths.Name)),
mode : (int)TarHelpers.ParseOctal <uint>(buffer.Slice(FieldLocations.Mode, FieldLengths.Mode)),
mTime : TarHelpers.GetDateTimeOffsetFromSecondsSinceEpoch((long)TarHelpers.ParseOctal <ulong>(buffer.Slice(FieldLocations.MTime, FieldLengths.MTime))),
typeFlag : (TarEntryType)buffer[FieldLocations.TypeFlag])
{
_checksum = checksum,
_size = size,
_uid = (int)TarHelpers.ParseOctal <uint>(buffer.Slice(FieldLocations.Uid, FieldLengths.Uid)),
_gid = (int)TarHelpers.ParseOctal <uint>(buffer.Slice(FieldLocations.Gid, FieldLengths.Gid)),
_linkName = TarHelpers.GetTrimmedUtf8String(buffer.Slice(FieldLocations.LinkName, FieldLengths.LinkName))
};
if (header._format == TarEntryFormat.Unknown)
{
header._format = header._typeFlag switch
{
TarEntryType.ExtendedAttributes or
TarEntryType.GlobalExtendedAttributes => TarEntryFormat.Pax,
TarEntryType.DirectoryList or
TarEntryType.LongLink or
TarEntryType.LongPath or
TarEntryType.MultiVolume or
TarEntryType.RenamedOrSymlinked or
TarEntryType.TapeVolume => TarEntryFormat.Gnu,
// V7 is the only one that uses 'V7RegularFile'.
TarEntryType.V7RegularFile => TarEntryFormat.V7,
TarEntryType.SparseFile => throw new NotSupportedException(string.Format(SR.TarEntryTypeNotSupported, header._typeFlag)),
// We can quickly determine the *minimum* possible format if the entry type
// is the POSIX 'RegularFile', although later we could upgrade it to PAX or GNU
_ => (header._typeFlag == TarEntryType.RegularFile) ? TarEntryFormat.Ustar : TarEntryFormat.V7
};
}
return(header);
}
