Phoenix.LiveView.get_connect_info

You're seeing just the function get_connect_info, go back to Phoenix.LiveView module for more information.
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get_connect_info(socket)

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Accesses the connect info from the socket to use on connected mount.

Connect info are only sent when the client connects to the server and only remain available during mount. nil is returned when called in a disconnected state and a RuntimeError is raised if called after mount.

Examples

First, when invoking the LiveView socket, you need to declare the connect_info you want to receive. Typically, it includes at least the session but it may include other keys, such as :peer_data. See Phoenix.Endpoint.socket/3:

socket "/live", Phoenix.LiveView.Socket,
  websocket: [connect_info: [:peer_data, session: @session_options]]

Those values can now be accessed on the connected mount as get_connect_info/1:

def mount(_params, _session, socket) do
  if info = get_connect_info(socket) do
    {:ok, assign(socket, ip: info.peer_data.address)}
  else
    {:ok, assign(socket, ip: nil)}
  end
end