[racket] Doubt about the 'More: Systems Programming with Racket'

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Hello list.
I was playing around the quoted tutorial, and found a strange behavior
in the following code:

;;code
#lang racket

(require racket/tcp)
(provide serve)

(define (serve port-no)
  (define listener (tcp-listen port-no 5 #t))
  (define (loop)
    (accept-and-handle listener)
    (loop))
  (define t (thread loop))
  (lambda ()
    (kill-thread t)
    (tcp-close listener)))

(define (accept-and-handle listener)
  (define-values (in out) (tcp-accept listener))
  (thread
   (lambda ()
     (handle in out)
     (close-input-port in)
     (close-output-port out))))

(define (handle in out)
  (display (port->string in))) ;; it locks here

;; test

(define-test-suite small-suite
  (let*-values ([(stopper) (serve 8080)]
              [(tcp-input-port tcp-output-port)
               (tcp-connect "127.0.0.1" 8080)])
    (display "stuff" tcp-output-port)
    (flush-output tcp-output-port)
    (sleep 0.1)
    (check-equal? (port->string tcp-input-port)
                  "stuff")
    (stopper)))

(run-tests small-suite)

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The code above works very well if I read the input port with
read-line, but won't budge if I use something like port->string.
Can somebody shed a light on this?
Thanks for the time.
- -- 
Eduardo Bellani

omnia mutantur, nihil interit.
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