#lang racket/base

(define (main port)
  (define listener (tcp-listen port 4 #t))
  (let loop ()
    (define-values (cin cout) (tcp-accept listener))
    (thread (connection-handler cin cout))
    (loop)))

(define ((connection-handler cin cout))
  (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))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(main 5999)

(require racket/tcp)