Reads into an existing List<int> from the socket into the range:
[start,end).
Reads into an existing List<int> from the socket. If start is present,
the bytes will be filled into buffer from index start, otherwise index
end is present, end - start bytes will be read into buffer,
otherwise up to buffer.length. If end == start, no bytes are read.
Returns the number of bytes read.int readIntoSync(List<int> buffer, [int start = 0, int end]);