[racket] Creating protocols

Suppose I wanted to make a client/server application that communicates via a 
protocol which has to be designed for that application. A neat way of doing it 
would be for the client to send s-exprs to the server via TCP, which were then 
evaluated. This is a huge security risk, though, because naturally you don't 
want a malicious client injecting all sorts non-protocol commands to the 
evaluator, or maybe exploiting some quirk to do some damage. I don't know much 
about Tcl, but I hear that it has a bullet-proof customisable interpreter for 
just such a scenario. Is there an equivalent for DrRacket (ideally with some 
simple examples) to do this kind of thing?