cmp two HTML fragments

I had a need to compare two fragments of HTML to see if they were equivalent.

This snippet builds two HTML::TreeBuilder representations of the fragments, then recursively compares the contents of the fragments.

To use the snippet call cmpHtml passing the two fragments as strings:

print cmpHtml(
    '<p><font foo="bar" bar="1">bar 1</font></p>',
    '<p><font bar="2" foo="bar">bar 1</font></p>'
);
[download]

or if you already have two HTML::Elements that you want to compare you can:

print cmpHtmlElt ($elt1, $elt2);
[download]

sub cmpHtml {
    my ($html1, $html2) = @_;
    my $root1 = HTML::TreeBuilder->new;
    my $root2 = HTML::TreeBuilder->new;

    $root1->parse_content ($html1);
    $root1->elementify    ();
    $root2->parse_content ($html2);
    $root2->elementify    ();

    return cmpHtmlElt ($root1, $root2);
}

sub cmpHtmlElt {
    my ($elt1, $elt2) = @_;

    my $cmp = defined $elt1 cmp defined $elt2;
    return $cmp if $cmp;
    return 0 unless defined $elt1;

    $cmp = ref $elt1 cmp ref $elt2;
    return $cmp if $cmp;
    return $elt1 cmp $elt2 unless ref $elt1;

    $cmp = $elt1->tag () cmp $elt2->tag ();
    return $cmp if $cmp;

    my %attribs1 = $elt1->all_attr ();
    my %attribs2 = $elt2->all_attr ();

    $cmp = keys %attribs1 <=> keys %attribs2;
    return $cmp if $cmp;

    for my $key (keys %attribs1) {
        return 1 unless exists $attribs2{$key};
        next if $key =~ /^_/;

        $cmp = $attribs1{$key} cmp $attribs2{$key};
        return $cmp if $cmp;
    }

    my @children1 = $elt1->content_list ();
    my @children2 = $elt2->content_list ();

    $cmp = @children1 <=> @children2;
    return $cmp if $cmp;

    for my $index (0 .. $#children1) {
        $cmp = cmpHtmlElt ($children1[$index], $children2[$index]);
        return $cmp if $cmp;
    }
}
[download]

Comment on cmp two HTML fragments Select or Download Code

Replies are listed 'Best First'.
Re: cmp two HTML fragments by lodin (Hermit) on Feb 10, 2008 at 14:51 UTC
Nice. Have you considered turning this into a module? Another way to do this is to use HTML::PrettyPrinter or somesuch and do a string-wise comparision. That way it's easier to find how the code differes (using string diff tools) if needed, but it's probably a lot slower. There's an (inherited) bug in your code. It leaks memory. You need to free the circular references in the tree by using the `delete` method: `sub cmpHtml { ... my $cmp = cmpHtmlElt ($root1, $root2); $_->delete for $root1, $root2; return $cmp; }` [download] As a parenthesis I'd like to share this little trick: `$cmp = EXPR; return $cmp if $cmp;` [download] which you use make plenty use of can be replaced with `{ return EXPR \|\| next }` [download] (assuming scalar context) though that may be a bit too obfuscated to use in public code. :-) lodin	[reply] [d/l] [select]
Re^2: cmp two HTML fragments by GrandFather (Saint) on Feb 10, 2008 at 22:37 UTC
as it happens the code shown was pretty transient anyway. For the module test suite that I wrote the code for, I replaced it with: `my $root1 = HTML::TreeBuilder->new (); my $root2 = HTML::TreeBuilder->new (); $root1->parse_content ($rendered)->elementify () ->delete_ignorable_whitespace (); $root2->parse_content ($expected)->elementify () ->delete_ignorable_whitespace (); is ($root1->as_HTML (undef, ' ', {}), $root2->as_HTML (undef, ' ', {}), $testName);` [download] in any case so that I'd get better diagnostics (I see the two HTML fragments when the test fails). However, with a little tweaking to give a traceback the original code would be even better in the test context because it would highlight the difference by reducing the clutter. That version might almost be worth generating a module for. Perl is environmentally friendly - it saves trees	[reply] [d/l]
Re: cmp two HTML fragments by planetscape (Chancellor) on Mar 22, 2008 at 21:09 UTC
A much older thread, yet containing some interesting ideas: HTML Document Comparison HTH, planetscape	[reply]


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