Home | Libraries | People | FAQ | More |
Asynchronously establishes a socket connection by trying each endpoint in a sequence.
template< typename Protocol, typename Executor, typename EndpointSequence, typename ConnectCondition, typename RangeConnectHandler = DEFAULT> DEDUCED async_connect( basic_socket< Protocol, Executor > & s, const EndpointSequence & endpoints, ConnectCondition connect_condition, RangeConnectHandler && handler = DEFAULT, typename enable_if< is_endpoint_sequence< EndpointSequence >::value >::type * = 0);
This function attempts to connect a socket to one of a sequence of endpoints.
It does this by repeated calls to the socket's async_connect
member function, once for each endpoint in the sequence, until a connection
is successfully established.
The socket to be connected. If the socket is already open, it will be closed.
A sequence of endpoints.
A function object that is called prior to each connection attempt. The signature of the function object must be:
bool connect_condition( const boost::system::error_code& ec, const typename Protocol::endpoint& next);
The ec
parameter contains the result from the most recent
connect operation. Before the first connection attempt, ec
is always set to indicate success. The next
parameter
is the next endpoint to be tried. The function object should return
true if the next endpoint should be tried, and false if it should
be skipped.
The handler to be called when the connect operation completes. Copies will be made of the handler as required. The function signature of the handler must be:
void handler( // Result of operation. if the sequence is empty, set to // boost::asio::error::not_found. Otherwise, contains the // error from the last connection attempt. const boost::system::error_code& error, // On success, an iterator denoting the successfully // connected endpoint. Otherwise, the end iterator. Iterator iterator );
Regardless of whether the asynchronous operation completes immediately
or not, the handler will not be invoked from within this function.
On immediate completion, invocation of the handler will be performed
in a manner equivalent to using post
.
The following connect condition function object can be used to output information about the individual connection attempts:
struct my_connect_condition { bool operator()( const boost::system::error_code& ec, const::tcp::endpoint& next) { if (ec) std::cout << "Error: " << ec.message() << std::endl; std::cout << "Trying: " << next << std::endl; return true; } };
It would be used with the boost::asio::connect
function as
follows:
tcp::resolver r(my_context); tcp::resolver::query q("host", "service"); tcp::socket s(my_context); // ... r.async_resolve(q, resolve_handler); // ... void resolve_handler( const boost::system::error_code& ec, tcp::resolver::results_type results) { if (!ec) { boost::asio::async_connect(s, results, my_connect_condition(), connect_handler); } } // ... void connect_handler( const boost::system::error_code& ec, const tcp::endpoint& endpoint) { if (ec) { // An error occurred. } else { std::cout << "Connected to: " << endpoint << std::endl; } }