How to iterate boost::beast HTTP response headers

// Read & parse the response
beast::flat_buffer buffer;
http::response<http::dynamic_body> res;
http::read(stream, buffer, res);

// Iterate response headers
for (auto it = res.begin(); it != res.end(); ++it) {
    std::cout << it->name_string() << ": " << it->value() << "\n";
}

// ... or get one specific header
cout << res["Content-Length"] << endl;