// During server setup:
s.limiter = NewLimiter(Config{
  MaxConnsPerClientIP: 10,
})

// handleConn is called in its own goroutine for each net.Conn accepted by
// a net.Listener.
func (s *Server) handleConn(conn net.Conn) {
  defer conn.Close()

  // Track the connection
  free, err := s.limiter.Accept(conn)
  if err != nil {
    // Not accepted as limit has been reached (or some other error), log error
    // or warning and close.

    // The standard err.Error() message when limit is reached is generic so it
    // doesn't leak information which may potentially be sensitive (e.g. current
    // limits set or number of connections). This also allows comparison to
    // ErrPerClientIPLimitReached if it's important to handle it differently
    // from an internal library or io error (currently not possible but might be
    // in the future if additional functionality is added).

    // If you would like to log more information about the current limit that
    // can be obtained with s.limiter.Config().
    return
  }
  // Defer a call to free to decrement the counter for this client IP once we
  // are done with this conn.
  defer free()


  // Handle the conn
}

lim := NewLimiter(Config{
  MaxConnsPerClientIP: 10,
})
s := http.Server{
  // Other config here
  ConnState: lim.HTTPConnStateFunc(),
}