I got the socket after following your instruction.

:sys.get_state(conn)

returned the following:

{:connected, 
    %Redix.Connection{
        backoff_current: nil, 
        client_reply: :on, 
        connected_address: "127.0.0.1:6379", 
        counter: 0, 
        opts: [
                socket_opts: [], 
                ssl: false, 
                sync_connect: false, 
                backoff_initial: 500, 
                backoff_max: 30000, 
                log: [
                    disconnection: :error, 
                    failed_connection: :error,
                    reconnection: :info
                    ], 
                exit_on_disconnection: false, 
                timeout: 5000, 
                host: '127.0.0.1', 
                port: 6379
            ], 
        socket: #Port<0.9>, 
        socket_owner: #PID<0.180.0>, 
        table: #Reference<0.3121165064.4228775937.104953>, 
        transport: :gen_tcp
    }
}

socket is a Port<0.9>
Then after

:gen_tcp.recv(socket, 0)

It get a error, the socket did not work

{:error, :einval}

But you figured me out, it is not the right way. It should be done in the redis lib.

I should fork Redix or find other redis lib.
(similar to redigo lib in golang, there is a Receive function in such situation.)

Thank you very much.