[Chicken-janitors] #1339: char-ready? returns #f even when input is available

[Chicken Trac]

#1339: char-ready? returns #f even when input is available
----------------------------+-------------------------------
 Reporter:  kooda           |                 Owner:
     Type:  defect          |                Status:  new
 Priority:  minor           |             Milestone:  5.0
Component:  core libraries  |               Version:  4.11.0
 Keywords:                  |  Estimated difficulty:  insane
----------------------------+-------------------------------
 The current implementation of char-ready? on stdio files returns #f if you
 have buffering enabled, didn’t consume the whole buffer and no more input
 is available from the system’s point of view, as it only asks the system
 via select or poll (see C_char_ready_p and C_check_fd_ready).

 I’m afraid there’s no way to do better than this with stdio files, as
 there is no way of checking the state of the buffer.

 The workaround I found was to simply disable buffering altogether, like
 so:

 {{{
 (set-buffering-mode! (current-input-port) #:none)
 }}}

 This bug probably requires a pretty big rework of ports.

 Here is a little program that '''might''' show the erroneous behaviour:

 {{{
 (use posix)

 (call-with-input-pipe "echo coucou"
   (lambda (p)
     (let loop ((c (read-char p)))
       (unless (eof-object? c)
         (print c)
         (when (char-ready? p) (loop (read-char p)))))))
 }}}

--
Ticket URL: <https://bugs.call-cc.org/ticket/1339>
CHICKEN Scheme <https://www.call-cc.org/>
CHICKEN Scheme is a compiler for the Scheme programming language.