private string ReadString (Stream input) {
int byteCount = ReadVarint(input, true);
switch (byteCount) {
case 0:
return null;
case 1:
return "";
}
byteCount--;
byte[] buffer = this.buffer;
if (buffer.Length < byteCount) buffer = new byte[byteCount];
ReadFully(input, buffer, 0, byteCount);
return System.Text.Encoding.UTF8.GetString(buffer, 0, byteCount);
}