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HttpUtils.pm: Handle in-name compression in DNS answer (Forum #87840)

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git-svn-id: https://svn.fhem.de/fhem/trunk@16759 2b470e98-0d58-463d-a4d8-8e2adae1ed80
This commit is contained in:
rudolfkoenig 2018-05-19 07:24:56 +00:00
parent 99854ea608
commit cb8ad22eef
1 changed files with 15 additions and 7 deletions
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22
fhem/FHEM/HttpUtils.pm
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@ -136,30 +136,38 @@ ip2str($)
return "[$h]"; return "[$h]";
} }
# http://www.ccs.neu.edu/home/amislove/teaching/cs4700/fall09/handouts/project1-primer.pdf # https://mislove.org/teaching/cs4700/spring11/handouts/project1-primer.pdf
my %HU_dnsCache; my %HU_dnsCache;
sub sub
HttpUtils_dnsParse($$$) HttpUtils_dnsParse($$$)
{ {
my ($a, $ql,$try6) = @_; # $ql: avoid hardcoding query length my ($a,$ql,$try6) = @_; # $ql: query length
my $ml = length($a);
return "short DNS answer" if(length($a) <= $ql);
return "wrong message ID" if(unpack("H*",substr($a,0,2)) ne "7072"); return "wrong message ID" if(unpack("H*",substr($a,0,2)) ne "7072");
while(length($a) >= $ql+16) { return "Cant find host" if(unpack("n",substr($a,6,2)) == 0);
while($ml >= $ql+16) { # there is a header
my $l = unpack("C",substr($a,$ql, 1)); my $l = unpack("C",substr($a,$ql, 1));
if(($l & 0xC0) == 0xC0) { # DNS packed compression if(($l & 0xC0) == 0xC0) { # DNS packed compression
$ql += 2; $ql += 2;
} else { } else {
while($l != 0) { while($l != 0 && ($ql+$l+1)<$ml) { # skip a name
$ql += $l+1; $ql += $l+1;
$l = unpack("C",substr($a,$ql,2)); $l = unpack("C",substr($a,$ql,2));
if(($l & 0xC0) == 0xC0) { # DNS packed compression
$ql++;
last;
}
} }
$ql++; $ql++;
} }
return (undef, substr($a,$ql+10,16),unpack("N",substr($a,$ql+4,4))) return (undef, substr($a,$ql+10,16),unpack("N",substr($a,$ql+4,4)))
if(unpack("N",substr($a,$ql,4)) == 0x1c0001 && $try6); if($ql+4<= $ml && unpack("N",substr($a,$ql,4)) == 0x1c0001 && $try6);
return (undef, substr($a,$ql+10,4), unpack("N",substr($a,$ql+4,4))) return (undef, substr($a,$ql+10,4), unpack("N",substr($a,$ql+4,4)))
if(unpack("N",substr($a,$ql,4)) == 0x10001 && !$try6); if($ql+4 <= $ml && unpack("N",substr($a,$ql,4)) == 0x10001 && !$try6);
$ql += 10+unpack("n",substr($a,$ql+8)) if(length($a) >= $ql+10); $ql += 10+unpack("n",substr($a,$ql+8)) if($ql+10 <= $ml);
} }
return "No A record found"; return "No A record found";
} }