"Cannot decode string with wide characters" appears on a weird place - perl

Question

I am trying to use XML::RAI perl module on UTF8 coded text and I still have error I don't really understand... here is the code (it shouldn't do anything useful yet):
use HTTP::Request;
use LWP::UserAgent;
use XML::RAI;
use Encode;
my $ua = LWP::UserAgent->new;
sub readFromWeb{
my $address = shift;
my $request = HTTP::Request->new( GET => $address );
my $response = $ua->request( $request );
return unless $response->code == 200;
return decode("utf8", $response->content());
}
sub readFromRSS{
my $address=shift;
my $content = readFromWeb $address;
my $rai = XML::RAI->parse_string($content);
#this line "causes" the error
}
readFromRSS("http://aktualne.centrum.cz/export/rss-hp.phtml");
#I am testing it on this particular RSS
the error is:
Cannot decode string with wide characters at /usr/lib/perl5/5.8.8/i686-linux/Encode.pm line 166.
I don't have a clue if that's my fault or the fault of XML::RAI. I don't see where these wide characters can be, if $content is already decoded from utf8...
edit: for some reason I still don't understand, removing the "decode" part actually solved the problem.

Answer 1

The problem is double-decoding. XML::RAI::parse_string() apparently
expects an UTF-8 encoded document and does the decoding itself. If you
pass in a string that is already decoded, decoding it a second time will fail,
of course:
#!/usr/bin/perl
use strict;
use warnings;
use Encode qw( decode );
use LWP::Simple qw( get );
my $xml = get("http://aktualne.centrum.cz/export/rss-hp.phtml");
$xml = decode('UTF-8', $xml);
$xml = decode('UTF-8', $xml); # dies: Cannot decode string with wide characters ...
So just skip the decode() step and you'll be fine.