C4/SIP/Sip/Checksum.pm

   1 package C4::SIP::Sip::Checksum;
   2
   3 use Exporter;
   4 use strict;
   5 use warnings;
   6
   7 our @ISA = qw(Exporter);
   8 our @EXPORT_OK = qw(checksum verify_cksum);
   9 our $debug = 0;
  10
  11 sub checksum {
  12     my $pkt = shift;
  13     return (-unpack('%16C*', $pkt) & 0xFFFF);
  14 }
  15
  16 sub verify_cksum {
  17     my $pkt = shift;
  18     my $cksum;
  19     my $shortsum;
  20
  21         if ($pkt =~ /AZ(....)$/) {
  22                 $debug and warn "verify_cksum: sum ($1) detected";
  23         } else {
  24                 warn "verify_cksum: no sum detected";
  25                 return 0; # No checksum at end
  26         }
  27     # return 0 if (substr($pkt, -6, 2) ne "AZ");
  28
  29     # Convert the checksum back to hex and calculate the sum of the
  30     # pack without the checksum.
  31     $cksum = hex($1);
  32     $shortsum = unpack("%16C*", substr($pkt, 0, -4));
  33
  34     # The checksum is valid if the hex sum, plus the checksum of the
  35     # base packet short when truncated to 16 bits.
  36     return (($cksum + $shortsum) & 0xFFFF) == 0;
  37 }
  38
  39 1;
  40 __END__
  41
  42 #
  43 # Some simple test data
  44 #
  45 sub test {
  46     my $testpkt = shift;
  47     my $cksum = checksum($testpkt);
  48     my $fullpkt = sprintf("%s%4X", $testpkt, $cksum);
  49
  50     print $fullpkt, "\n";
  51 }
  52
  53 while (<>) {
  54     chomp;
  55     test($_);
  56 }
  57
  58 1;