private static bool IsFormatV1(ReadOnlySpan <byte> buffer, out Endianness endianness)
{
endianness = Endianness.Little;
// Need at least 256 bytes
if (buffer.Length < 256)
{
return(false);
}
if (buffer[0] == 0)
{
// First byte is zero.
// V1 not an option, as it would make for an invalid entry name
// V2-3 are not an option either, as it would mean the entry count is 0
// Either invalid, or big endian
return(false);
}
bool nameTerminated = false;
for (int i = 0; i < 252; i++)
{
if (buffer[i] == 0)
{
nameTerminated = true;
}
// If the name has already been terminated but there's still data in the reserved space,
// fail the test
if (nameTerminated && buffer[i] != 0)
{
return(false);
}
}
var length = BinaryPrimitives.ReadInt32LittleEndian(buffer.Slice(252));
if (length < 0 || length >= MAX_LENGTH_SANITY_VALUE)
{
BinaryOperations <int> .Reverse(ref length);
if (length < 0 || length >= MAX_LENGTH_SANITY_VALUE)
{
return(false);
}
endianness = Endianness.Big;
}
return(true);
}
private static bool IsFormatV2OrV3(ReadOnlySpan <byte> buffer, int entrySize, out Endianness endianness)
{
endianness = Endianness.Little;
// Need at least a full entry
if (buffer.Length < 4 + entrySize)
{
return(false);
}
var entryCount = BinaryPrimitives.ReadInt32LittleEndian(buffer);
if (entryCount <= 0 || entryCount > 1024)
{
BinaryOperations <int> .Reverse(ref entryCount);
if (entryCount <= 0 || entryCount > 1024)
{
return(false);
}
endianness = Endianness.Big;
}
// check if the name field is correct
if (buffer[4] == 0)
{
return(false);
}
var nameTerminated = false;
for (int i = 0; i < (entrySize - 4); i++)
{
if (buffer[4 + i] == 0x00)
{
nameTerminated = true;
}
else if (nameTerminated)
{
return(false);
}
}
// Data length sanity check
var length = BinaryPrimitives.ReadInt32LittleEndian(buffer.Slice(4 + entrySize - 4));
if (length < 0 || length >= MAX_LENGTH_SANITY_VALUE)
{
BinaryOperations <int> .Reverse(ref length);
if (length < 0 || length >= MAX_LENGTH_SANITY_VALUE)
{
return(false);
}
endianness = Endianness.Big;
}
return(true);
}