From: Daniel Martin <martin@...>
Date: 2006-07-18T05:48:47+09:00
Subject: Re: How can I parse binary files?

Fabio Vitale <fabio@sferaconsulting.it> writes:

> And now: how to populate the mrk instance just created from the imap.mrk 
> binary file?

First off, the other message's advice about your field sizes should be
taken (you want to use "32", not "4").  Also, you almost certainly
want to add :endian => :native to your structure.  Finally, you'll
want to adjust the bit_length method of your MRKHeader class since it
won't construct the appropriate length just from the field info.

  class MRKHeader < BitStruct
    unsigned :version,            32, "Version",     :endian => :native
    unsigned :uid_Validity,       32, "UIDValidity", :endian => :native
    unsigned :uid_next,           32, "UIDNext",     :endian => :native
    unsigned :last_write_counter, 32, "LastWriteCounter", :endian => :native
    rest     :unused,                 "Unused"
    def MRKHeader.bit_length
      super
      36*8
    end
  end

Okay, now let's assume that you also define the per-message structure
using BitStruct as MRKMessage. (For the message code, you don't need
to redefine bit_length since it can be computed straight from the
fields.  Do however use the endianness option on all the integers)

Then:

File.open("imap.mrk") {|f|
  head_string = f.read(MRKHeader.round_byte_length)
  raise "No header!" unless head_string
  mrk_header = MRKHeader.new(head_string)
  puts mrk_header.inspect
  while msg_string = f.read(MRKMessage.round_byte_length) do
    puts MRKMessage.new(msg_string)
  end
}