module IO::Stream::Readable

@returns [String] The data read from the stream, or the provided buffer filled with data.
@parameter buffer [String | Nil] An optional buffer to fill with data instead of allocating a new string.
@parameter size [Integer | Nil] The number of bytes to read. If nil, read all available data.
Read at most `size` bytes from the stream. Will avoid reading from the underlying stream if possible.

def read_partial(size = nil, buffer = nil)
	if size == 0
		if buffer
			buffer.clear
			buffer.force_encoding(Encoding::BINARY)
			return buffer
		else
			return String.new(encoding: Encoding::BINARY)
		end
	end
	
	if !@finished and @read_buffer.empty?
		fill_read_buffer
	end
	
	return consume_read_buffer(size, buffer)
end