HTML syntax checker with Nu Validator

nu-validator.pl

#!/usr/bin/env perl

use strict;
use warnings;

use JSON;
use LWP::UserAgent;

my $file = shift;

my $ua = LWP::UserAgent->new();
my $res = $ua->post("http://validator.w3.org/nu/",
  Content_type => "form-data",
  Content      => [
    out  => "json",
    file => [$file],
  ]
);

if ($res->is_success) {
  my $result = from_json($res->decoded_content);
  my $messages = $result->{messages};

  if (scalar(@$messages) > 0) {
    foreach my $m (@$messages) {
      if ($m->{type} eq 'error') {
        print join(":", $file, $m->{lastLine}, $m->{lastColumn}, $m->{message}), "\n";
      }
    }
  }
} else {
  die $res->status_line;
}

exit;

nu-validator.vim

if exists('current_compiler')
  finish
endif
let current_compiler = 'nu-validator'

if exists(":CompilerSet") != 2 " older Vim always used :setlocal
  command -nargs=* CompilerSet setlocal <args>
endif

let s:cpo_save = &cpo
set cpo-=C

CompilerSet makeprg=nu-validator.pl\ %
CompilerSet errorformat=%f:%l:%c:%m

let &cpo = s:cpo_save
unlet s:cpo_save