...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Establishes a connection by trying each endpoint in a sequence asynchronously.
template< class EndpointSequence, class ConnectCondition, class RangeConnectHandler = net::default_completion_token_t<executor_type>> DEDUCED async_connect( EndpointSequence const& endpoints, ConnectCondition connect_condition, RangeConnectHandler&& handler = net::default_completion_token_t< executor_type >{});
This function attempts to connect the stream to one of a sequence of endpoints by trying each endpoint until a connection is successfully established. The underlying socket is automatically opened if needed. An automatically opened socket is not returned to the closed state upon failure.
The algorithm, known as a composed asynchronous operation,
is implemented in terms of calls to the underlying socket's async_connect
function.
If the timeout timer expires while the operation is outstanding, the
current connection attempt will be canceled and the completion handler
will be invoked with the error error::timeout
.
Name |
Description |
---|---|
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A sequence of endpoints. This this object must meet the requirements of EndpointSequence. |
|
A function object that is called prior to each connection attempt. The signature of the function object must be: bool connect_condition( error_code const & ec, typename Protocol::endpoint const & next);
The |
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The completion handler to invoke when the operation completes. The implementation takes ownership of the handler by performing a decay-copy. The equivalent function signature of the handler must be: void handler( // Result of operation. if the sequence is empty, set to // net::error::not_found. Otherwise, contains the // error from the last connection attempt. error_code const & error, // On success, the successfully connected endpoint. // Otherwise, a default-constructed endpoint. typename Protocol::endpoint const & endpoint );
If the handler has an associated immediate executor, an immediate
completion will be dispatched to it. Otherwise, the handler
will not be invoked from within this function. Invocation of
the handler will be performed by dispatching to the immediate
executor. If no immediate executor is specified, this is equivalent
to using |
The following connect condition function object can be used to output information about the individual connection attempts:
struct my_connect_condition { bool operator()( error_code const & ec, net::ip::tcp::endpoint const & next) { if (ec) std::cout << "Error: " << ec.message() << std::endl; std::cout << "Trying: " << next << std::endl; return true ; } };
This asynchronous operation supports cancellation for the following net::cancellation_type values:
net::cancellation_type::terminal
net::cancellation_type::partial
net::cancellation_type::total
if they are also supported by the socket's async_connect
operation.