(define (open-input-fd fd)
  (make-input-port
   (lambda ()
     (thread-wait-for-i/o! fd #:input)
     (string-ref (car (file-read fd 1)) 0))
   (lambda ()
     (nth-value 0 (file-select fd #f 0)))
   (lambda ()
     (file-close fd))))

(define (open-output-fd fd)
  (let ((port (open-output-file* fd)))
    (make-output-port
     (lambda (buffer)
       (let loop ((buffer buffer) (len (string-length buffer)))
         (thread-wait-for-i/o! fd #:output)
         (let ((written (file-write fd buffer)))
           (unless (= written len)
             (loop (substring written len) (- len written))))))
     (lambda ()
       (close-output-port port))
     (lambda ()
       (flush-output port)))))