private static async ValueTask <String> ReadJSONStringAsync(
CharacterReader reader,
StreamReaderWithResizableBuffer stream,
Boolean startQuoteRead
)
{
Char charRead;
var proceed = startQuoteRead;
if (!startQuoteRead)
{
stream.EraseReadBytesFromBuffer();
charRead = await reader.ReadNextCharacterAsync(stream, c => !Char.IsWhiteSpace(c));
proceed = charRead == STR_START;
}
String str;
var encoding = reader.Encoding;
var eencoding = encoding.Encoding;
if (proceed)
{
// At this point, we have read the starting quote, now read the contents.
var asciiSize = encoding.BytesPerASCIICharacter;
var startIdx = stream.ReadBytesCount;
async ValueTask <Int32> DecodeUnicodeEscape()
{
var decodeIdx = stream.ReadBytesCount;
await stream.ReadMoreOrThrow(4 *asciiSize);
return((encoding.ReadHexDecimal(stream.Buffer, ref decodeIdx) << 8) | (encoding.ReadHexDecimal(stream.Buffer, ref decodeIdx)));
}
// Read string, but mind the escapes
Int32 curIdx;
do
{
curIdx = stream.ReadBytesCount;
charRead = await reader.TryReadNextCharacterAsync(stream) ?? STR_END;
if (charRead == STR_ESCAPE_PREFIX)
{
// Escape handling - next character decides what we will do
charRead = await reader.TryReadNextCharacterAsync(stream) ?? STR_END;
Byte replacementByte = 0;
switch (charRead)
{
case STR_END:
case STR_ESCAPE_PREFIX:
case '/':
// Actual value is just just read char minus the '\'
replacementByte = (Byte)charRead;
break;
case 'b':
// Backspace
replacementByte = (Byte)'\b';
break;
case 'f':
// Form feed
replacementByte = (Byte)'\f';
break;
case 'n':
// New line
replacementByte = (Byte)'\n';
break;
case 'r':
// Carriage return
replacementByte = (Byte)'\r';
break;
case 't':
// Horizontal tab
replacementByte = (Byte)'\t';
break;
case 'u':
// Unicode sequence - followed by four hexadecimal digits
var code = await DecodeUnicodeEscape();
if (code <= Char.MaxValue && code >= Char.MinValue && Char.IsSurrogate((charRead = (Char)code)))
{
var idxAfterDecode = stream.ReadBytesCount;
Char?nullableChar;
if (
(nullableChar = await reader.TryReadNextCharacterAsync(stream)).HasValue && nullableChar.Value == STR_ESCAPE_PREFIX &&
(nullableChar = await reader.TryReadNextCharacterAsync(stream)).HasValue && nullableChar.Value == 'u'
)
{
var code2 = await DecodeUnicodeEscape();
reader.GetBytes(charRead, (Char)code2, stream.Buffer, ref curIdx);
}
else
{
// Orphaned surrogate character...
stream.UnreadBytes(stream.ReadBytesCount - idxAfterDecode);
reader.GetBytes(charRead, stream.Buffer, ref curIdx);
}
}
else
{
var codeStr = Char.ConvertFromUtf32(code);
// Overwrite '\uXXXX' with actual character
curIdx += eencoding.GetBytes(codeStr, 0, codeStr.Length, stream.Buffer, curIdx);
}
break;
default:
// Just let it slide
curIdx = stream.ReadBytesCount;
break;
}
if (replacementByte > 0)
{
// We just read ASCII char, which should be now replaced
encoding.WriteASCIIByte(stream.Buffer, ref curIdx, replacementByte);
}
// Erase anything extra
stream.EraseReadBufferSegment(curIdx, stream.ReadBytesCount - curIdx);
// Always read next char
charRead = (Char)0;
}
} while (charRead != STR_END);
var strByteCount = stream.ReadBytesCount - startIdx - asciiSize;
str = strByteCount <= 0 ? "" : eencoding.GetString(stream.Buffer, startIdx, strByteCount);
}
else
{
str = null;
}
return(str);
}