From: Joel VanderWerf <vjoel@...>
Date: 2009-07-01T01:22:17+09:00
Subject: Re: Question on networking with custom binary interface.

Greg Chambers wrote:
> Joel VanderWerf wrote:
>> Greg Chambers wrote:
>>> Any advice for doing this type of binary IO?
>> Array#pack, String#unpack are your friends.
> 
> I am looking at the documentation of these methods and this covers a LOT 
> of what I need to do, but I am worried in a couple areas.  For example, 
> part of the binary string I will be getting will contain an eight byte 
> unsigned long long.  How should I approach custom byte structures like 
> this?

Ok, Array#pack, String#unpack are your _relatives_. BitStruct is your 
_friend_.

require 'bit-struct'

class MyPacket < BitStruct
   unsigned :x, 8*8, "The x field", :endian => :network
     # :network is the default, and it's the same as :big
   unsigned :y, 8*8, "The y field", :endian => :little
end

pkt = MyPacket.new
pkt.x = 59843759843759843
pkt.y = 59843759843759843

p pkt.x  # 59843759843759843
p pkt.y  # 59843759843759843

p pkt.inspect
# "#<MyPacket x=59843759843759843, y=59843759843759843>"
p pkt.to_s.inspect
# 
"\"\\000\\324\\233\\225\\037\\202\\326\\343\\343\\326\\202\\037\\225\\233\\324\\000\""

puts pkt.inspect_detailed
# MyPacket:
#                    The x field = 59843759843759843
#                    The y field = 59843759843759843

puts MyPacket.describe
#     byte: type         name          [size] description
# ----------------------------------------------------------------------
#       @0: unsigned     x             [  8B] The x field
#       @8: unsigned     y             [  8B] The y field

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407