add filter-read-input-port' to racket/port'

original commit: ce2d6030c73e0a04a2a5661a035c0e0d86d9c999

collects/mzlib/port.rkt

@@ -478,6 +478,35 @@
      count-lines!-proc
      pos)))
 
+(define filter-read-input-port
+  (lambda (p wrap-read wrap-peek [close? #t])
+    (make-input-port
+     (object-name p)
+     (lambda (s)
+       (let ([v (read-bytes-avail!* s p)])
+         (wrap-read
+          s
+          (if (eq? v 0) (wrap-evt p (lambda (x) 0)) v))))
+     (lambda (s skip evt)
+       (let ([v (peek-bytes-avail!* s skip evt p)])
+         (wrap-peek
+          s skip evt
+          (if (eq? v 0)
+              (choice-evt
+               (wrap-evt p (lambda (x) 0))
+               (if evt (wrap-evt evt (lambda (x) #f)) never-evt))
+              v))))
+     (lambda ()
+       (when close? (close-input-port p)))
+     (and (port-provides-progress-evts? p)
+          (lambda () (port-progress-evt p)))
+     (and (port-provides-progress-evts? p)
+          (lambda (n evt target-evt) (port-commit-peeked n evt target-evt p)))
+     (lambda () (port-next-location p))
+     (lambda () (port-count-lines! p))
+     (let-values ([(line col pos) (port-next-location p)])
+       (or pos (file-position p))))))
+
 ;; Not kill-safe.
 (define make-pipe-with-specials
   ;; This implementation of pipes is almost CML-style, with a manager thread
@@ -1732,6 +1761,7 @@
          peeking-input-port
          relocate-input-port
          transplant-input-port
+         filter-read-input-port
          special-filter-input-port
          relocate-output-port
          transplant-output-port