I just found that on very specific web pages parsed by my scripts, that setting a UserAgent value through LWP::UserAgent seems to crash XML::LibXML, and I can't figure out why.

Here's a snippet to exhibit this behavior. Run this, then uncomment the $browser->agent($ua); call to see the crash:

use strict;
use LWP::UserAgent;
use XML::LibXML;

# Or http://www.cboe.com/Chinese/
my $url         =    'http://www.cboe.com/Spanish/';

my $ua          = 
   'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)';

my $browser     = LWP::UserAgent->new();  

# Uncomment this line to crash libxml's parser
# $browser->agent($ua);

my $response    = $browser->get($url);
my $content     = $response->content; 
my $type        = $response->content_type;

print "Cleaning $url ($type)...\n";
clean_html($content);

sub clean_html {
        my $input       = shift;
        my $parser      = XML::LibXML->new();

        $parser->recover(1);
  
        my $cleaned     =
           $parser->parse_html_string($input)->toStringHTML;

}

[download]

It only happens on some pages, and I can't find a pattern in the actual HTML content itself that causes it. Here's the error I get when it dies (a few hundred of these for this particular page parsed): 

output conversion failed due to conv error
Bytes: 0xE4 0xE5 0xE6 0xE8
xmlOutputBufferWrite: encoder error
output conversion failed due to conv error
Bytes: 0xE5 0xE6 0xE8 0x26
xmlOutputBufferWrite: encoder error
...

[download]

Comment out the UserAgent value, and it seems to work perfectly, without any errors. What could be causing this?

Update: Further investigation shows that the '/' in the UserAgent value is stuffing up XML::LibXML here. Changing the '/' to anything else will cause the page to work.

Why would a slash character in the UserAgent string dump libxml?

In reply to Crashing XML::LibXML by setting UserAgent by hacker

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