From: jason@... (Jason Voegele)
Date: 2001-10-05T01:07:26+09:00
Subject: [ruby-talk:22091] Help with Array#pack

I'm working with a network protocol that uses messages in the
following format:

BYTE 1 | BYTE 2 | BYTES 3&4 | BYTES 5-8 | BYTES 9-12 | BYTES 13-16
------ | ------ | --------- | --------- | ---------- | -----------
 cmd   |   var  |    flags  |    id     |    var     |     var

Where "cmd" is a number 0-27, flags is a bitwise "or" of flag values,
and "id" is a 4 byte identifier.  "var" is a varying value of the
appropriate size/range.

I'd like to be able to specify an array that consists of 6 numbers,
and pack them into the binary format specified above, for example:

command = [1, 0, 1|2, 0x1000, 99, 0]

These six entries in the array should correspond to the six fields in
the message header above.  So the above array should be converted to
the binary string:
 
BYTE 1 | BYTE 2 | BYTES 3&4 | BYTES 5-8 | BYTES 9-12 | BYTES 13-16
------ | ------ | --------- | --------- | ---------- | -----------
   1   |   0    |    3      |    4096   |     99     |     0

(Or the 16 byte number 1329228233469478973560546180437377024 ;-)

I've tried to use Array#pack to do this, but I can't figure out the
proper format string for the pack method that makes this work, and the
documentation is somewhat vague.

Any pointers?

Thanks,
Jason Voegele