Socket fields
:id - The string id of the socket
:assigns - The map of socket assigns, default: %{}
:channel - The current channel module
:channel_pid - The channel pid
:endpoint - The endpoint module where this socket originated, for example: MyApp.Endpoint
:handler - The socket module where this socket originated, for example: MyApp.UserSocket
:joined - If the socket has effectively joined the channel
:join_ref - The ref sent by the client when joining
:ref - The latest ref sent by the client
:pubsub_server - The registered name of the socket’s pubsub server
:topic - The string topic, for example "room:123"
:transport - An identifier for the transport, used for logging
:transport_pid - The pid of the socket’s transport process
:serializer - The serializer for socket messages