From: Levin Alexander <levin@...>
Date: 2005-12-18T21:54:27+09:00
Subject: Better way to read data from IO into packets?

Hi,
I have a small program, that reads data from a serial port and chopsit into packets.  A Packet has the following format:
  [0x65, 0xEB, <type:8>, <counter:8>, <length:8>, data:length>, <crc:16>]
I have a thread that reads the data from an IO object:
  @receiver_thread = Thread.new do 	    Thread.abort_on_exception = true    loop do	      begin	        char = @io.readchar	        add_char_to_packet(char) if char	      rescue EOFError	        Thread.pass # there is currently nothing to read      end	    end
and a state machine, that decodes the format:
    def add_char_to_packet(char)      @state = :first_checksum if (@state == 0)      case @state      when :first_startbyte        @data = ""        @state = ((char == STARTBYTES[0]) ? :second_startbyte ::first_startbyte)      when :second_startbyte        @state = (char == STARTBYTES[1]) ? :type :          # special case: first startbyte is repeated          (char == STARTBYTES[0] ? :second_startbyte : :first_startbyte)      when :type        @type = TYPE.invert[char]        @state = :counter      when :counter        @counter = char        @state = :length      when :length        @length = char        @state = @length      when Integer        @data << char        @state -= 1      when :first_checksum        @checksum = (char << 8)        @state = :second_checksum     [...]
This works, but the code is ugly and also a little slow because I haveto process each byte seperately.  Is there a better way?
Thank you,Levin