// Reads fields only found in ustar format or above and converts them to their expected data type.
// Throws if any conversion fails.
private void ReadMagicAttribute(Span <byte> buffer)
{
Span <byte> magic = buffer.Slice(FieldLocations.Magic, FieldLengths.Magic);
// If at this point the magic value is all nulls, we definitely have a V7
if (TarHelpers.IsAllNullBytes(magic))
{
_format = TarEntryFormat.V7;
return;
}
// When the magic field is set, the archive is newer than v7.
if (magic.SequenceEqual(GnuMagicBytes))
{
_magic = GnuMagic;
_format = TarEntryFormat.Gnu;
}
else if (magic.SequenceEqual(UstarMagicBytes))
{
_magic = UstarMagic;
if (_format == TarEntryFormat.V7)
{
// Important: Only change to ustar if we had not changed the format to pax already
_format = TarEntryFormat.Ustar;
}
}
else
{
_magic = Encoding.ASCII.GetString(magic);
}
}
// 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);
}
// 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 bool TryReadCommonAttributes(Span <byte> buffer)
{
// 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(false);
}
_checksum = TarHelpers.GetTenBaseNumberFromOctalAsciiChars(spanChecksum);
// Zero checksum means the whole header is empty
if (_checksum == 0)
{
return(false);
}
_size = TarHelpers.GetTenBaseNumberFromOctalAsciiChars(buffer.Slice(FieldLocations.Size, FieldLengths.Size));
if (_size < 0)
{
throw new FormatException(string.Format(SR.TarSizeFieldNegative, _name));
}
// Continue with the rest of the fields that require no special checks
_name = TarHelpers.GetTrimmedUtf8String(buffer.Slice(FieldLocations.Name, FieldLengths.Name));
_mode = TarHelpers.GetTenBaseNumberFromOctalAsciiChars(buffer.Slice(FieldLocations.Mode, FieldLengths.Mode));
_uid = TarHelpers.GetTenBaseNumberFromOctalAsciiChars(buffer.Slice(FieldLocations.Uid, FieldLengths.Uid));
_gid = TarHelpers.GetTenBaseNumberFromOctalAsciiChars(buffer.Slice(FieldLocations.Gid, FieldLengths.Gid));
int mTime = TarHelpers.GetTenBaseNumberFromOctalAsciiChars(buffer.Slice(FieldLocations.MTime, FieldLengths.MTime));
_mTime = TarHelpers.GetDateTimeFromSecondsSinceEpoch(mTime);
_typeFlag = (TarEntryType)buffer[FieldLocations.TypeFlag];
_linkName = TarHelpers.GetTrimmedUtf8String(buffer.Slice(FieldLocations.LinkName, FieldLengths.LinkName));
if (_format == TarFormat.Unknown)
{
_format = _typeFlag switch
{
TarEntryType.ExtendedAttributes or
TarEntryType.GlobalExtendedAttributes => TarFormat.Pax,
TarEntryType.DirectoryList or
TarEntryType.LongLink or
TarEntryType.LongPath or
TarEntryType.MultiVolume or
TarEntryType.RenamedOrSymlinked or
TarEntryType.SparseFile or
TarEntryType.TapeVolume => TarFormat.Gnu,
// V7 is the only one that uses 'V7RegularFile'.
TarEntryType.V7RegularFile => TarFormat.V7,
// 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
_ => (_typeFlag == TarEntryType.RegularFile) ? TarFormat.Ustar : TarFormat.V7
};
}
return(true);
}
