Subject: Re: [bug#36919] [PATCH 1/2] gnu-maintenance: KDE updater no longer relies on FTP access.

From: Ludovic Courtès <[email-masked]>
Date: Sat, 17 Aug 2019 23:01:11 +0200

Hi Hartmut,

Hartmut Goebel <[email-masked]> skribis:

> * guix/gnu-maintenance.scm (%kde-file-list-uri): New variable.
>   (download.kde.org-files): New procedure.
>   (latest-kde-release): Change to use DOWNLOAD.KDE.ORG-FILES and search
>   for files in this list.

Nice!

How about moving this code to (guix import kde) as was done for (guix
import gnome) when we discussed it back then?  (See
<https://issues.guix.gnu.org/issue/28159>.)

> +(define download.kde.org-files
> +  (mlambda ()
> +    "Return the list of files available at download.kde.org."
> +    ;; XXX: Memoize the whole procedure to work around the fact that
> +    ;; 'http-fetch/cached' caches the bzip2-compressed version.
> +
> +    (define (canonicalize-path path)
> +      (if (string-prefix? "/srv/archives/ftp/" path)
> +          (set! path (string-drop path 17)))
> +      (if (string-suffix? ":" path)
> +          (set! path (string-drop-right path 1)))
> +      (if (not (string-suffix? "/" path))
> +          (set! path (string-append path "/")))
> +      path)

As a rule of thumb we don’t use ‘set!’ in Guix, except in special
circumstances.  In this case you can write:

  (define (canonicalize-path path)
    (cond ((string-prefix? …)
           (string-drop path 17))
          ((string-suffix? …)
           (string-drop-right path 1))
          …))

> +    (define (ls-lR-line->filename path line)
> +      ;; remove mode, blocks, user, group, size, date, time and one space
> +      (regexp-substitute
> +       #f (string-match "^(\\S+\\s+){6}\\S+\\s" line) path 'post))
> +
> +    (let ((entries `())
> +          (port (decompressed-port
> +                 'bzip2
> +                 (http-fetch/cached %kde-file-list-uri #:ttl 3600))))

What about passing ‘http-fetch/cached’ a custom #:write-cache, as is
done in (guix cve)?  That would allow us to store the cached file list
in a pre-processed (and possibly decompressed) format, speeding up
operation on cache hits.

> +      (do ((path (read-line port) (read-line port)))
> +          ((or (eof-object? path) (string= path "")))
> +        (set! path (canonicalize-path path))

I also recommend against ‘do’.  You can use a “named let” loop instead,
as in:

  (let loop ((files '()))
    (match (read-line port)
      ((? eof-object?)
       (reverse files))
      (line
       (loop (cons … files)))))

That’s about it.

Thanks!

Ludo’.