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Re: Socket Newbie (perl newbie, too...)

by btrott (Parson)
on Jun 18, 2001 at 22:29 UTC ( #89392=note: print w/replies, xml ) Need Help??

in reply to Socket Newbie (perl newbie, too...)

I think you're misunderstanding the packet format. When you say that the representation is in "binary", it doesn't mean the binary representation that you get by doing unpack "B*"; it means that your data is packed as if it's in a binary structure. So you have the right operator (pack), you just have the wrong pack template.

I think that this will work for you:

my $data = "LOGON USERNAME=NAME PASSWORD=PASS\0"; my $packet = pack "CnCCNnn", 2, ## sync byte length($data)+13, ## message size 13, ## header size hex("4c"), ## message type 1, ## sequence ID 0, ## protocol ID 1; ## version number $packet .= $data;
That pack template ("CnCCNnn") says to pack the list of values (the rest of the arguments to pack) in the following way:
  • unsigned char value (1 byte)
  • short in network order (2 bytes)
  • unsigned char value (1 byte)
  • unsigned char value (1 byte)
  • long in network order (4 bytes)
  • short in network order (2 bytes)
  • short in network order (2 bytes)
This varies from your use of pack in two important ways. First, we no longer use 'unpack "B*"', because the point of that is to take a binary structure and make it into a human-readable string that looks like a sequence of bits. That's not what you want: you want to send the data to the server as a binary structure.

Second, you can't just use 'pack "N"'; that packs everything as a network-order long, which is 4 bytes. You don't want everything to be 4 bytes; some things are 1 byte, some are 2, some are 4. You have to vary you pack template depending on that.

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