private static bool TryValidateUtf8(ArraySegment<byte> arraySegment, bool endOfMessage, Utf8MessageState state)
{
for (int i = arraySegment.Offset; i < arraySegment.Offset + arraySegment.Count;)
{
// Have we started a character sequence yet?
if (!state.SequenceInProgress)
{
// The first byte tells us how many bytes are in the sequence.
state.SequenceInProgress = true;
byte b = arraySegment.Array[i];
i++;
if ((b & 0x80) == 0) // 0bbbbbbb, single byte
{
state.AdditionalBytesExpected = 0;
state.CurrentDecodeBits = b & 0x7F;
state.ExpectedValueMin = 0;
}
else if ((b & 0xC0) == 0x80)
{
// Misplaced 10bbbbbb continuation byte. This cannot be the first byte.
return false;
}
else if ((b & 0xE0) == 0xC0) // 110bbbbb 10bbbbbb
{
state.AdditionalBytesExpected = 1;
state.CurrentDecodeBits = b & 0x1F;
state.ExpectedValueMin = 0x80;
}
else if ((b & 0xF0) == 0xE0) // 1110bbbb 10bbbbbb 10bbbbbb
{
state.AdditionalBytesExpected = 2;
state.CurrentDecodeBits = b & 0xF;
state.ExpectedValueMin = 0x800;
}
else if ((b & 0xF8) == 0xF0) // 11110bbb 10bbbbbb 10bbbbbb 10bbbbbb
{
state.AdditionalBytesExpected = 3;
state.CurrentDecodeBits = b & 0x7;
state.ExpectedValueMin = 0x10000;
}
else // 111110bb & 1111110b & 11111110 && 11111111 are not valid
{
return false;
}
}
while (state.AdditionalBytesExpected > 0 && i < arraySegment.Offset + arraySegment.Count)
{
byte b = arraySegment.Array[i];
if ((b & 0xC0) != 0x80)
{
return false;
}
i++;
state.AdditionalBytesExpected--;
// Each continuation byte carries 6 bits of data 0x10bbbbbb.
state.CurrentDecodeBits = (state.CurrentDecodeBits << 6) | (b & 0x3F);
if (state.AdditionalBytesExpected == 1 && state.CurrentDecodeBits >= 0x360 && state.CurrentDecodeBits <= 0x37F)
{
// This is going to end up in the range of 0xD800-0xDFFF UTF-16 surrogates that are not allowed in UTF-8;
return false;
}
if (state.AdditionalBytesExpected == 2 && state.CurrentDecodeBits >= 0x110)
{
// This is going to be out of the upper Unicode bound 0x10FFFF.
return false;
}
}
if (state.AdditionalBytesExpected == 0)
{
state.SequenceInProgress = false;
if (state.CurrentDecodeBits < state.ExpectedValueMin)
{
// Overlong encoding (e.g. using 2 bytes to encode something that only needed 1).
return false;
}
}
}
if (endOfMessage && state.SequenceInProgress)
{
return false;
}
return true;
}
