bug#21829: guix import hackage failures

[Federico Beffa <beffa@ieee.org>]

On Thu, Nov 12, 2015 at 9:21 PM, Ludovic Courtès <ludo@gnu.org> wrote:
> If we go for the CRLF conversion port, we should avoid the pipe and
> extra thread.  Instead, I would suggest something like:
>
>   (define (canonical-newline-port port)
>     "Return an input port that wraps PORT such that all newlines consist
>   of a single carriage return."
>     (make-custom-binary-input-port …))

I like this suggestion :-)

I never used custom ports. Is something like this OK? (Seems to work
in the REPL.)

---------------------------------------------------------------
(define (canonical-newline-port port)
  "Return an input port that wraps PORT such that all newlines consist
  of a single carriage return."
  (define (get-position)
    (if (port-has-port-position? port) (port-position port) #f))
  (define (set-position! position)
    (if (port-has-set-port-position!? port)
        (set-port-position! position port)
        #f))
  (define (close) (close-port port))
  (define (read! bv start n)
    (let loop ((count 0)
               (byte (get-u8 port)))
      (cond ((or (eof-object? byte) (= count n)) count)
            ((eqv? byte (char->integer #\return)) (loop count (get-u8 port)))
            (else
             (bytevector-u8-set! bv (+ start count) byte)
             (loop (+ count 1) (get-u8 port))))))
  (make-custom-binary-input-port "canonical-newline-port"
                                 read!
                                 get-position
                                 set-position!
                                 close))
---------------------------------------------------------------

IMO this is general enough that it could go into "guix/utils.scm". Are
you OK with this?

Regards,
Fede