#lang racket/base

(require racket/tcp)

(define (main port)
  (define listener (tcp-listen port 4 #t))
  (let loop ()
    (define-values (cin cout) (tcp-accept listener))
    (thread
     (lambda ()
       (let connection-loop ()
	 (define v (read-byte cin))
	 (unless (or (eof-object? v)
		     (equal? v #"\4"))
	   (write-byte v cout)
	   (flush-output cout)
	   (connection-loop)))
       (close-input-port cin)
       (close-output-port cout)))
    (loop)))

(main 5999)