var parser = new UnmanagedJsonParser(state);
while(true)
{
       if(parser.Read() == false)
       {
           var read = stream.Read(buffer, 0, buffer.Length);
           if (read == 0)
              throw new EndOfStreamException();
           parser.SetBuffer(buffer, 0, read);
           continue;
       }
       if(state.CurrentTokenType != JsonParserToken.String)
          throw new InvalidStateException();

       // do something with the string
}