async_connect (1 of 4 overloads)

Asynchronously establishes a socket connection by trying each endpoint in a sequence.

template<
    typename Protocol,
    typename SocketService,
    typename Iterator,
    typename ComposedConnectHandler>
void-or-deduced async_connect(
    basic_socket< Protocol, SocketService > & s,
    Iterator begin,
    ComposedConnectHandler handler);

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.

Parameters

s

The socket to be connected. If the socket is already open, it will be closed.

begin

An iterator pointing to the start of a sequence of endpoints.

handler

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
  // asio::error::not_found. Otherwise, contains the
  // error from the last connection attempt.
  const asio::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. Invocation of the handler will be performed in a manner equivalent to using asio::io_service::post().

Remarks

This overload assumes that a default constructed object of type Iterator represents the end of the sequence. This is a valid assumption for iterator types such as asio::ip::tcp::resolver::iterator.

Example

tcp::resolver r(io_service);
tcp::resolver::query q("host", "service");
tcp::socket s(io_service);

// ...

r.async_resolve(q, resolve_handler);

// ...

void resolve_handler(
    const asio::error_code& ec,
    tcp::resolver::iterator i)
{
  if (!ec)
  {
    asio::async_connect(s, i, connect_handler);
  }
}

// ...

void connect_handler(
    const asio::error_code& ec,
    tcp::resolver::iterator i)
{
  // ...
}