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Re: Re: hash collision DOS

by QwertyD (Pilgrim)
on Jun 02, 2003 at 04:53 UTC ( #262303=note: print w/ replies, xml ) Need Help??


in reply to Re: hash collision DOS
in thread hash collision DOS

But doesn't CGI store fields internally as a hash?

From CGI 2.81:

sub param { my($self,@p) = self_or_default(@_); return $self->all_parameters unless @p; my($name,$value,@other); #~~~~~Snip~~~~~ ($name,$value,@other) = rearrange([NAME,[DEFAULT,VALUE,VALUES]],@p +); #~~~~~Snip~~~~~ return wantarray ? @{$self->{$name}} : $self->{$name}->[0]; }

It also looks like CGI::Simple does the same:

From CGI::Simple 0.06

sub param { my ( $self, $param, @p ) = @_; #~~~~~Snip~~~~~ return wantarray ? @{$self->{$param}} : $self->{$param}->[0]; }

How do I love -d? Let me count the ways...


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Re: Re: Re: hash collision DOS
by crazyinsomniac (Prior) on Jun 02, 2003 at 13:50 UTC
      It doesn't have anything to do with the Vars() method. The worst-case performance of the hash slows down insertion of elements. CGI.pm inserts parameter names as keys when parsing the query string.
        Look at this
        C:\>perl -MData::Dumper -MCGI -e"die Dumper( CGI->new( { 1..10 }) ) " $VAR1 = bless( { '.charset' => 'ISO-8859-1', '1' => [ 2 ], '3' => [ 4 ], 'escape' => 1, '5' => [ 6 ], '7' => [ 8 ], '.parameters' => [ '7', '9', '1', '3', '5' ], '9' => [ 10 ], '.fieldnames' => {} }, 'CGI' ); C:\>
        Do all the keys map to one bucket? I'm pretty sure they don't.
        C:\>perl -MData::Dumper -MCGI -e"warn Dumper( $a=CGI->new );die Dumper +(scalar $a->Vars() ) " a= b= c= d= e= f= g= $VAR1 = bless( { '.charset' => 'ISO-8859-1', 'a' => [ '' ], 'escape' => 1, 'b' => [ '' ], 'c' => [ '' ], 'd' => [ '' ], 'e' => [ '' ], 'f' => [ '' ], 'g' => [ '' ], '.parameters' => [ 'a', 'b', 'c', 'd', 'e', 'f', 'g' ], '.fieldnames' => {} }, 'CGI' ); $VAR1 = { 'a' => '', 'b' => '', 'c' => '', 'd' => '', 'e' => '', 'f' => '', 'g' => '' };
        The only way all the various keys would map to one bucket would be when you construct a hash by calling Vars. Do you see what I'm saying, or did I miss something crucial.
        update: I improved the 2nd snippet. Now it shows all the various keys going to a single bucket.

        update: Why not just post the example?

         
        ______crazyinsomniac_____________________________
        Of all the things I've lost, I miss my mind the most.
        perl -e "$q=$_;map({chr unpack qq;H*;,$_}split(q;;,q*H*));print;$q/$q;"

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