How do I cleanly reconnect a boost::socket following a disconnect?

You need to create a new boost::asio::ip::tcp::socket each time you reconnect. The easiest way to do this is probably to just allocate the socket on the heap using a boost::shared_ptr (you could probably also get away with scoped_ptr if your socket is entirely encapsulated within a class). E.g.:

bool MyClient::myconnect()
{
    bool isConnected = false;

    // Attempt connection
    // socket is of type boost::shared_ptr<boost::asio::ip::tcp::socket>
    socket.reset(new boost::asio::ip::tcp::socket(...));
    socket->connect(server_endpoint, errorcode);
    // ...
}

Then, when mydisconnect is called, you could deallocate the socket:

void MyClient::mydisconnect(void)
{
    // ...
    // deallocate socket.  will close any open descriptors
    socket.reset();
}

The error you’re seeing is probably a result of the OS cleaning up the file descriptor after you’ve called close. When you call close and then try to connect on the same socket, you’re probably trying to connect an invalid file descriptor. At this point you should see an error message starting with “Connection failed: …” based on your logic, but you then call mydisconnect which is probably then attempting to call shutdown on an invalid file descriptor. Vicious cycle!