use URI;
my $uri = URI->new($path);
die "bad schema" unless is_safe_schema($uri->schema);
die "bad domain" unless is_safe_domain($uri->host);
die "bad path" unless is_safe_path($uri->path);

sub is_safe_schema {
    # left as excersize to reader
}

sub is_safe_domain {
    # left as excersize to reader
}

sub is_safe_path {
    my $path = shift;
    my @comps = split '/', $path;
    for my $comp (@comps) {
        return 0 unless is_safe_path_comp
    }
    return 1;
}

sub is_safe_path_comp {
    my $comp = shift;
    return 0 if $comp =~ /\0\\/;
    return 0 if $comp eq '..';
    # other unsafe patterns
    ....
    return 1;
}