Hello all. I'm using 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!

Here's my 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 $@;
}

[download]

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:

http://sam.tregar.com/libxml-fail.html

BEWARE: 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.

I've never had alarm() fail like this. Is there an alternative I can try? Any other ideas about how to handle this?

Thanks!

-sam

UPDATE: 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.

In reply to Problem timing out XML::LibXML parsing by samtregar

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