Indy Client ReadLn on Data Available Question

I am switching my client to the indy client  from the Turbopower client.

I want to execute readln when data is available from the server, and don't
want to site there and test it.

In Turbopower there is an event procedure that fires when there is data in
the client buffer, which makes this simple.  I can't find anything similar
in TidTCPClient.  What am I missing?