typedef resolver::iterator resolver_iterator;

typedef std::function<void (const boost::system::error_code&,

resolver_iterator)> callback_fn;

voidasync_resolve(const std::string &host, std::uint16_t port,callback_fn callback) {

voidasync_resolve(const std::string &host, std::uint16_t port,Handler&& handler) {

if (cache_resolved_) {

endpoint_cache::iterator it = endpoint_cache_.find(boost::to_lower_copy(host));

if (it != endpoint_cache_.end()) {

boost::system::error_code ec;

callback(ec, it->second);

handler(ec, it->second);

return;

}

}

resolver::queryquery(host,std::to_string(port));

resolver_.async_resolve(query,

resolver_strand_->wrap(

[&host, &callback,this](const boost::system::error_code &ec,

[&host, &handler,this](const boost::system::error_code &ec,

resolver_iterator endpoint_iterator) {

if (ec) {

callback(ec,resolver_iterator());

handler(ec,resolver_iterator());

}

else {

if (cache_resolved_) {

endpoint_cache_.insert(std::make_pair(host, endpoint_iterator));

}

callback(ec, endpoint_iterator);

handler(ec, endpoint_iterator);

}

}));

}

virtualvoidasync_connect(boost::asio::ip::tcp::endpoint &endpoint,

const std::string &host, connect_callback callback) = 0;