Boost.Spirit URL parsing

I'm trying to parse an URL with Boost.Spirit based on this [w3schools.com] format. The problem is that when I type the domain on its own (like google.com) it doesn't work. My guess is that because the host is defined as a word followed by a dot, the parser thinks I've written the host and half the domain name. How can I fix this?

Code

GeSHi (cpp):
#include <iostream>
#include <string>
#include <boost/spirit.hpp>
 
using namespace std;
using namespace boost::spirit;
 
bool parseUrl(const string& str)
{
    rule<> word_p = +alpha_p;
    rule<> scheme_p = word_p >> str_p("://");    // http://
    rule<> host_p = word_p >> ch_p('.');             // www.
    rule<> domain_p = word_p >> ch_p('.') >> word_p;   // google.com
    rule<> port_p = ch_p(':') >> uint_p;               // :80
    rule<> path_p = ch_p('/') % word_p;               // /path/to/file/
    rule<> filename_p = word_p >> !(ch_p('.') >> word_p);   // logo.gif (extension optional)
 
    // Optional scheme, optional host, domain, optional port, path and filename option. Can have path without filename, but not filename without path.
    rule<> url_p = !scheme_p >> !host_p >> domain_p >> !port_p >> !(path_p >> !filename_p);
 
    return parse(str.c_str(), url_p, space_p).full;
}
 
int main()
{
    bool quit = false;
 
    while(!quit)
    {
        string str;
        cin >> str;
 
        if(str == "quit")
            quit = true;
        else
            cout << parseUrl(str) << endl;
    }
 
    return 0;
}Created by GeSHI 1.0.7.18

Thanks.

Edit:
If you've done BNF grammar before, but not used Spirit, the rule<>'s are regular grammar rules. The = operator is used instead of ::=, the ! operator means the rule following it is optional, >> means sequence (a>>b in Spirit is a b in BNF), ch_p represents a character and +alpha_p means one or more of any alphabetical character.