64 lines
1.2 KiB
Perl
64 lines
1.2 KiB
Perl
package Sip::Checksum;
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use Exporter;
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use strict;
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use warnings;
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our @ISA = qw(Exporter);
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our @EXPORT_OK = qw(checksum verify_cksum);
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our $debug = 0;
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sub checksum {
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my $pkt = shift;
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return (-unpack('%16U*', $pkt) & 0xFFFF);
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}
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sub verify_cksum {
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my $pkt = shift;
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my $cksum;
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my $shortsum;
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if ($pkt =~ /AZ(....)$/) {
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$debug and warn "verify_cksum: sum ($1) detected";
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} else {
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warn "verify_cksum: no sum detected";
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return 0; # No checksum at end
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}
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# return 0 if (substr($pkt, -6, 2) ne "AZ");
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# Convert the checksum back to hex and calculate the sum of the
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# pack without the checksum.
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$cksum = hex($1);
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$shortsum = unpack("%16U*", substr($pkt, 0, -4));
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# The checksum is valid if the hex sum, plus the checksum of the
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# base packet short when truncated to 16 bits.
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return (($cksum + $shortsum) & 0xFFFF) == 0;
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}
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{
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no warnings qw(once);
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eval join('',<main::DATA>) || die $@ unless caller();
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# FIXME: what the heck is this?
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}
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1;
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__END__
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#
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# Some simple test data
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#
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sub test {
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my $testpkt = shift;
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my $cksum = checksum($testpkt);
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my $fullpkt = sprintf("%s%4X", $testpkt, $cksum);
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print $fullpkt, "\n";
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}
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while (<>) {
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chomp;
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test($_);
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}
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1;
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