ipv4 and ipv6 from any valid address

Question

I'm trying to get both the ipv4 and ipv6 address from any string address, be it by ipv4, ipv6, or DNS address.

I can create my own function to do so, but I'm trying to take expert advice and utilize built-in capabilities.

Is there a way to input an address string of any format, and have both ipv4 and ipv6 boost addresses returned?

Answer 1

Getting an address from the DNS name involves... querying a naming server (DNS!). If you want to enumerate the results, use a resolver in asio:

• http://www.boost.org/doc/libs/1_55_0/doc/html/boost_asio/reference/ip__tcp/resolver.html

Simple example:

#include <boost/asio.hpp>
#include <boost/function_output_iterator.hpp>
#include <set>

using boost::asio::ip::address;

std::set<address> unique_endpoints(std::string const& ip)
{
    using resolver = boost::asio::ip::tcp::resolver;
    boost::asio::io_service ios; // TODO use existing service / resolver
    resolver r(ios);

    std::set<address> unique;
    for (auto it = r.resolve({ip, ""}); it != resolver::iterator {}; ++it)
    {
        //std::cout << "Resolved: " << it->host_name() << " -> " << it->endpoint() << " " << it->service_name() << "\n";
        address a = it->endpoint().address();
        if (a.is_v4())
            unique.insert(boost::asio::ip::address_v6::v4_mapped(a.to_v4()));
        else
            unique.insert(a);
    }

    return unique;
}

template <typename S>
bool endpoints_overlap(S const& a, S const& b)
{
    bool matching_found = false;

    std::set_intersection(
            a.begin(), a.end(), b.begin(), b.end(),
            boost::make_function_output_iterator([&](address const&) { matching_found = true; }));

    return matching_found;
}

int main()
{
    auto h = unique_endpoints("bbs2.fritz.box");
    auto a = unique_endpoints("192.168.2.111");
    auto b = unique_endpoints("::ffff:192.168.2.111");
    auto c = unique_endpoints("::ffff:c0a8:026f");

    assert(endpoints_overlap(a, b));
    assert(endpoints_overlap(a, c));
    assert(endpoints_overlap(b, c));

    assert(endpoints_overlap(h, a));
    assert(endpoints_overlap(h, b));
    assert(endpoints_overlap(h, c));
}

Note that this test will decide that endpoints overlap when one of the DNS responses matches. This might not always be true in a cluster setting (? no expert there) and you might also want to detect broadcast addresses before using this algorithm (not tested).

Note also, I don't think there's a way to detect equivalence of actual hosts (meaning, if a host has several physical/logical NICs, they will appear as separate servers on the transport level).

Finally, in a real-world application you will want to do the resolving asynchronously (use async_resolve)