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* bug#22901: drain-input doesn't decode
@ 2016-03-04  3:09 Zefram
  2016-06-20 16:12 ` Andy Wingo
                   ` (3 more replies)
  0 siblings, 4 replies; 6+ messages in thread
From: Zefram @ 2016-03-04  3:09 UTC (permalink / raw)
  To: 22901

The documentation for drain-input says that it returns a string of
characters, implying that the result is equivalent to what you'd get
from calling read-char some number of times.  In fact it differs in a
significant respect: whereas read-char decodes input octets according to
the port's selected encoding, drain-input ignores the selected encoding
and always decodes according to ISO-8859-1 (thus preserving the octet
values in character form).

$ echo -n $'\1a\2b\3c' | guile-2.0 -c '(set-port-encoding! (current-input-port) "UCS-2BE") (write (port-encoding (current-input-port))) (newline) (write (map char->integer (let r ((l '\''())) (let ((c (read-char (current-input-port)))) (if (eof-object? c) (reverse l) (r (cons c l))))))) (newline)'
"UCS-2BE"
(353 610 867)
$ echo -n $'\1a\2b\3c' | guile-2.0 -c '(set-port-encoding! (current-input-port) "UCS-2BE") (write (port-encoding (current-input-port))) (newline) (peek-char (current-input-port)) (write (map char->integer (string->list (drain-input (current-input-port))))) (newline)'
"UCS-2BE"
(1 97 2 98 3 99)

The practical upshot is that the input returned by drain-input can't
be used in the same way as regular input from read-char.  It can still
be used if the code doing the reading is totally aware of the encoding,
so that it can perform the decoding manually, but this seems a failure
of abstraction.  The value returned by drain-input ought to be coherent
with the abstraction level at which it is specified.

I can see that there is a reason for drain-input to avoid performing
decoding: the problem that occurs if the buffer ends in the middle
of a character.  If drain-input is to return decoded characters then
presumably in this case it would have to read further octets beyond the
buffer contents, in an unbuffered manner, until it reaches a character
boundary.  If this is too unpalatable, perhaps drain-input should be
permitted only on ports configured for single-octet character encodings.

If, on the other hand, it is decided to endorse the current non-decoding
behaviour, then the break of abstraction needs to be documented.

-zefram





^ permalink raw reply	[flat|nested] 6+ messages in thread

* bug#22901: drain-input doesn't decode
  2016-03-04  3:09 bug#22901: drain-input doesn't decode Zefram
@ 2016-06-20 16:12 ` Andy Wingo
  2017-02-26 17:46 ` Matt Wette
                   ` (2 subsequent siblings)
  3 siblings, 0 replies; 6+ messages in thread
From: Andy Wingo @ 2016-06-20 16:12 UTC (permalink / raw)
  To: Zefram; +Cc: 22901

On Fri 04 Mar 2016 04:09, Zefram <zefram@fysh.org> writes:

> The documentation for drain-input says that it returns a string of
> characters, implying that the result is equivalent to what you'd get
> from calling read-char some number of times.  In fact it differs in a
> significant respect: whereas read-char decodes input octets according to
> the port's selected encoding, drain-input ignores the selected encoding
> and always decodes according to ISO-8859-1 (thus preserving the octet
> values in character form).
>
> $ echo -n $'\1a\2b\3c' | guile-2.0 -c '(set-port-encoding!
> (current-input-port) "UCS-2BE") (write (port-encoding
> (current-input-port))) (newline) (write (map char->integer (let r ((l
> '\''())) (let ((c (read-char (current-input-port)))) (if (eof-object?
> c) (reverse l) (r (cons c l))))))) (newline)'
> "UCS-2BE"
> (353 610 867)
> $ echo -n $'\1a\2b\3c' | guile-2.0 -c '(set-port-encoding!
> (current-input-port) "UCS-2BE") (write (port-encoding
> (current-input-port))) (newline) (peek-char (current-input-port))
> (write (map char->integer (string->list (drain-input
> (current-input-port))))) (newline)'
> "UCS-2BE"
> (1 97 2 98 3 99)

Thanks for the test case!  FWIW, this is fixed in Guile 2.1.3.  I am not
sure what we should do about Guile 2.0.  I guess we should make it do
the documented thing though!

Andy





^ permalink raw reply	[flat|nested] 6+ messages in thread

* bug#22901: drain-input doesn't decode
  2016-03-04  3:09 bug#22901: drain-input doesn't decode Zefram
  2016-06-20 16:12 ` Andy Wingo
@ 2017-02-26 17:46 ` Matt Wette
  2017-02-26 17:58   ` Matt Wette
  2021-05-16 17:55 ` Taylan Kammer
  2021-05-19 11:41 ` Taylan Kammer
  3 siblings, 1 reply; 6+ messages in thread
From: Matt Wette @ 2017-02-26 17:46 UTC (permalink / raw)
  To: 22901

[-- Attachment #1: Type: text/plain, Size: 543 bytes --]

I put together a test and tried on 2.1.7 - my test fails.  See attached.

  (pass-if "encoded input"
    (let ((fn (test-file))
	  (nc "utf-8")
	  (st "\u03b2\u03b1\u03b4 \u03b1\u03c3\u03c3 am I.")
	  ;;(st "hello, world\n")
	  )
      (let ((p1 (open-output-file fn #:encoding nc)))
	;;(display st p1)
	(string-for-each (lambda (ch) (write-char ch p1)) st)
	(close p1))
      (let* ((p0 (open-input-file fn #:encoding nc))
	     (s0 (begin (unread-char (read-char p0) p0) (drain-input p0))))
	(simple-format #t "~S\n" s0)
	(equal? s0 st))))


[-- Attachment #2: port-di.test --]
[-- Type: application/octet-stream, Size: 712 bytes --]

;; port-di.text  -*- scheme -*-

(add-to-load-path "guile-2.1.7-dev3/test-suite")

(use-modules (test-suite lib))

(define (test-file)
  (string-append (getcwd) "/ports-test.tmp"))

(with-test-prefix "drain-input"
  
  (pass-if "encoded input"
    (let ((fn (test-file))
	  (nc "utf-8")
	  (st "\u03b2\u03b1\u03b4 \u03b1\u03c3\u03c3 am I.")
	  ;;(st "hello, world\n")
	  )
      (let ((p1 (open-output-file fn #:encoding nc)))
	;;(display st p1)
	(string-for-each (lambda (ch) (write-char ch p1)) st)
	(close p1))
      (let* ((p0 (open-input-file fn #:encoding nc))
	     (s0 (begin (unread-char (read-char p0) p0) (drain-input p0))))
	(simple-format #t "~S\n" s0)
	(equal? s0 st))))

  )

;; --- last line ---

^ permalink raw reply	[flat|nested] 6+ messages in thread

* bug#22901: drain-input doesn't decode
  2017-02-26 17:46 ` Matt Wette
@ 2017-02-26 17:58   ` Matt Wette
  0 siblings, 0 replies; 6+ messages in thread
From: Matt Wette @ 2017-02-26 17:58 UTC (permalink / raw)
  To: 22901

[-- Attachment #1: Type: text/plain, Size: 859 bytes --]


> On Feb 26, 2017, at 9:46 AM, Matt Wette <matt.wette@gmail.com> wrote:
> 
> I put together a test and tried on 2.1.7 - my test fails.  See attached.
> 
>  (pass-if "encoded input"
>    (let ((fn (test-file))
> 	  (nc "utf-8")
> 	  (st "\u03b2\u03b1\u03b4 \u03b1\u03c3\u03c3 am I.")
> 	  ;;(st "hello, world\n")
> 	  )
>      (let ((p1 (open-output-file fn #:encoding nc)))
> 	;;(display st p1)
> 	(string-for-each (lambda (ch) (write-char ch p1)) st)
> 	(close p1))
>      (let* ((p0 (open-input-file fn #:encoding nc))
> 	     (s0 (begin (unread-char (read-char p0) p0) (drain-input p0))))
> 	(simple-format #t "~S\n" s0)
> 	(equal? s0 st))))
> 

My bad.  The failure was on guile-2.0.13.  It seems to work on guile-2.1.7:

mwette$ guile-2.1.7-dev3/meta/guile port-di.test
"βαδ ασσ am I."
PASS: drain-input: encoded input


[-- Attachment #2: Type: text/html, Size: 2931 bytes --]

^ permalink raw reply	[flat|nested] 6+ messages in thread

* bug#22901: drain-input doesn't decode
  2016-03-04  3:09 bug#22901: drain-input doesn't decode Zefram
  2016-06-20 16:12 ` Andy Wingo
  2017-02-26 17:46 ` Matt Wette
@ 2021-05-16 17:55 ` Taylan Kammer
  2021-05-19 11:41 ` Taylan Kammer
  3 siblings, 0 replies; 6+ messages in thread
From: Taylan Kammer @ 2021-05-16 17:55 UTC (permalink / raw)
  To: 22901, Zefram, Andy Wingo

Are we still maintaining 2.0, or can this issue be closed?

-- 
Taylan





^ permalink raw reply	[flat|nested] 6+ messages in thread

* bug#22901: drain-input doesn't decode
  2016-03-04  3:09 bug#22901: drain-input doesn't decode Zefram
                   ` (2 preceding siblings ...)
  2021-05-16 17:55 ` Taylan Kammer
@ 2021-05-19 11:41 ` Taylan Kammer
  3 siblings, 0 replies; 6+ messages in thread
From: Taylan Kammer @ 2021-05-19 11:41 UTC (permalink / raw)
  To: 22901-done

Closing this since it's 5 years old and fixed in Guile 2.1 and higher.

-- 
Taylan





^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2021-05-19 11:41 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-03-04  3:09 bug#22901: drain-input doesn't decode Zefram
2016-06-20 16:12 ` Andy Wingo
2017-02-26 17:46 ` Matt Wette
2017-02-26 17:58   ` Matt Wette
2021-05-16 17:55 ` Taylan Kammer
2021-05-19 11:41 ` Taylan Kammer

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