perlquestion
samtregar
Hello all. I'm using [cpan://XML::LibXML] to parse some HTML. Mostly it's working great - fast and very useful XPath support. My problem is that it's choking on some very bad HTML in a very bad way - it's sitting on the CPU until killed manually. I expected some HTML wouldn't parse, so this isn't such a tragedy. What is a big problem is that my attempt to work around this with alarm() aren't working!
<p>
Here's my code:
<p>
<code>use strict;
use warnings;
use XML::LibXML;
my $html = do { local $/; <> };
my $libxml = XML::LibXML->new();
#$libxml->recover(2);
eval {
local $SIG{ALRM} = sub { die "TIMEOUT\n" };
alarm(10);
$libxml->parse_html_string($html);
alarm(0);
};
if ($@ and $@ eq "TIMEOUT\n") {
warn "Timed out ok.\n";
} elsif ($@) {
die $@;
}
</code>
<p>
If I replace the parse call with sleep(20) then it works as expected - the alarm triggers and the timeout is caught. If I run it as-is with my sample HTML then it never stops until killed. If you want to play along at home here's the test file:
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<a href="http://sam.tregar.com/libxml-fail.html">http://sam.tregar.com/libxml-fail.html</a>
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<b>BEWARE:</b> that's some really bad HTML and it not only breaks XML::LibXML but it also crashed Firefox while I was writing this post the first time! You probably don't want to load it in your browser.
<p>
I've never had alarm() fail like this. Is there an alternative I can try? Any other ideas about how to handle this?
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Thanks!
<P>
-sam
<p>
<b>UPDATE:</b> [perrin] reminded me about how safe-signals work in recent perls. That is indeed the problem - setting PERL_SIGNALS=unsafe makes my code DWIM, at the cost of a certain degree of safety. Ideas for alternatives are still welcome of course.