[bug#67842,4/4] services: mympd: Refactor serialization process.

* gnu/services/audio.scm: (string-or-symbol?): Remove unused predicate.
<mympd-configuration>[acl, covercache-ttl, http?, host, log-to, uri,
script-acl, ssl?, ssl-port, ssl-cert, ssl-key, pin-hash, save-caches?]: Pass
file-names via custom serializer procedure.
[port, log-level, ssl-port]: Use exact-integer (resp. maybe-exact-integer).
(mympd-field-serializer): New procedure, extracted from …
(mympd-serialize-configuration): … this. Refactor and rename it to
(mympd-configuration->files): … this.
(mympd-log-rotation): Restyle.
(mympd-service-type): Adjust service-extension to renamed procedure.
Use @acronym for description.
* doc/guix.texi: Update it.
---
 doc/guix.texi          |   8 +--
 gnu/services/audio.scm | 153 ++++++++++++++++++++---------------------
 2 files changed, 78 insertions(+), 83 deletions(-)
  

Am Freitag, dem 15.12.2023 um 21:02 +0000 schrieb Bruno Victal:
> -(define-maybe/no-serialization integer)
> +(define-maybe/no-serialization exact-integer)
At the risk of asking a silly question, what's the difference between
an integer and an exact integer?

>  (define-maybe/no-serialization mympd-ip-acl)
>  
>  (define %mympd-user
> @@ -749,11 +747,28 @@ (define (mympd-log-to-sanitizer value)
>       value)
>      (_ (configuration-field-error #f 'log-to value))))
>  
> -;; XXX: The serialization procedures are insufficient since we
> require
> -;; access to multiple fields at once.
> -;; Fields marked with empty-serializer are never serialized and are
> -;; used for command-line arguments or by the service definition.
> -(define-configuration/no-serialization mympd-configuration
> +(define (mympd-field-serializer file-name)
> +  "Return a procedure that partially serializes the fields of
> +mympd-configuration as pairs of file-names and file-like objects
> whose
> +contents are the serialized values of the fields."
> +  (define serialize-value
> +    (match-lambda
> +      ((? boolean? val) (if val "true" "false"))
> +      ((? integer? val) (number->string val))
> +      ((? mympd-ip-acl? val) (ip-acl-serialize-configuration val))
> +      ((? string? val) val)))
> +
> +  (define (ip-acl-serialize-configuration config)
> +    (string-join
> +     (append
> +      (map (cut string-append "+" <>) (mympd-ip-acl-allow config))
> +      (map (cut string-append "-" <>) (mympd-ip-acl-deny config)))
> ","))
> +
> +  (lambda (_ field-value)
> +    (cons file-name
> +          (plain-file file-name (serialize-value field-value)))))
> +
> +(define-configuration mympd-configuration
>    (package
>      (file-like mympd)
>      "The package object of the myMPD server."
> @@ -789,27 +804,33 @@ (define-configuration/no-serialization mympd-
> configuration
>  
>    (acl
>     maybe-mympd-ip-acl
> -   "ACL to access the myMPD webserver.")
> +   "ACL to access the myMPD webserver."
> +   (serializer (mympd-field-serializer "acl")))
>  
>    (covercache-ttl
> -   (maybe-integer 31)
> -   "How long to keep cached covers, @code{0} disables cover
> caching.")
> +   (maybe-exact-integer 31)
> +   "How long to keep cached covers, @code{0} disables cover
> caching."
> +   (serializer (mympd-field-serializer "covercache_keep_days")))
>  
>    (http?
>     (boolean #t)
> -   "HTTP support.")
> +   "HTTP support."
> +   (serializer (mympd-field-serializer "http")))
>  
>    (host
>     (string "[::]")
> -   "Host name to listen on.")
> +   "Host name to listen on."
> +   (serializer (mympd-field-serializer "http_host")))
>  
>    (port
> -   (maybe-port 80)
> -   "HTTP port to listen on.")
> +   (maybe-exact-integer 80)
Losing the information that this is a port (i.e. only integers that fit
into a uint16 are valid) is imho not great.
> +   "HTTP port to listen on."
> +   (serializer (mympd-field-serializer "http_port")))
>  
>    (log-level
> -   (integer 5)
> -   "How much detail to include in logs, possible values: @code{0} to
> @code{7}.")
> +   (exact-integer 5)
> +   "How much detail to include in logs, possible values: @code{0} to
> @code{7}."
> +   (serializer (mympd-field-serializer "loglevel")))
>  
>    (log-to
>     maybe-string
> @@ -822,89 +843,64 @@ (define-configuration/no-serialization mympd-
> configuration
>    (lualibs
>     (maybe-string "all")
>     "See
> -
> @url{https://jcorporation.github.io/myMPD/scripting/#lua-standard-libr
> aries}.")
> +@url{
> https://jcorporation.github.io/myMPD/scripting/#lua-standard-librarie
> s}."
> +   (serializer (mympd-field-serializer "lualibs")))
>  
>    (uri
>     maybe-string
>     "Override URI to myMPD.
> -See @url{https://github.com/jcorporation/myMPD/issues/950}.")
> +See @url{https://github.com/jcorporation/myMPD/issues/950}."
> +   (serializer (mympd-field-serializer "mympd_uri")))
>  
>    (script-acl
>     (maybe-mympd-ip-acl (mympd-ip-acl
>                          (allow '("127.0.0.1"))))
> -   "ACL to access the myMPD script backend.")
> +   "ACL to access the myMPD script backend."
> +   (serializer (mympd-field-serializer "scriptacl")))
>  
>    (ssl?
>     (boolean #f)
> -   "SSL/TLS support.")
> +   "SSL/TLS support."
> +   (serializer (mympd-field-serializer "ssl")))
>  
>    (ssl-port
> -   (maybe-port 443)
> -   "Port to listen for HTTPS.")
> +   (maybe-exact-integer 443)
> +   "Port to listen for HTTPS."
> +   (serializer (mympd-field-serializer "ssl_port")))
>  
>    (ssl-cert
>     maybe-string
> -   "Path to PEM encoded X.509 SSL/TLS certificate (public key).")
> +   "Path to PEM encoded X.509 SSL/TLS certificate (public key)."
> +   (serializer (mympd-field-serializer "ssl_cert")))
>  
>    (ssl-key
>     maybe-string
> -   "Path to PEM encoded SSL/TLS private key.")
> +   "Path to PEM encoded SSL/TLS private key."
> +   (serializer (mympd-field-serializer "ssl_key")))
>  
>    (pin-hash
>     maybe-string
>     "SHA-256 hashed pin used by myMPD to control settings access by
> -prompting a pin from the user.")
> +prompting a pin from the user."
> +   (serializer (mympd-field-serializer "pin_hash")))
>  
>    (save-caches?
>     maybe-boolean
> -   "Whether to preserve caches between service restarts."))
> -
> -(define (mympd-serialize-configuration config)
> -  (define serialize-value
> -    (match-lambda
> -      ((? boolean? val) (if val "true" "false"))
> -      ((? integer? val) (number->string val))
> -      ((? mympd-ip-acl? val) (ip-acl-serialize-configuration val))
> -      ((? string? val) val)))
> -
> -  (define (ip-acl-serialize-configuration config)
> -    (define (serialize-list-of-strings prefix lst)
> -      (map (cut format #f "~a~a" prefix <>) lst))
> -    (string-join
> -     (append
> -      (serialize-list-of-strings "+" (mympd-ip-acl-allow config))
> -      (serialize-list-of-strings "-" (mympd-ip-acl-deny config)))
> ","))
> -
> -  ;; myMPD configuration fields are serialized as individual files
> under
> -  ;; <work-directory>/config/.
> -  (match-record config <mympd-configuration> (work-directory acl
> -                                              covercache-ttl http?
> host port
> -                                              log-level lualibs uri
> script-acl
> -                                              ssl? ssl-port ssl-cert
> ssl-key
> -                                              pin-hash save-caches?)
> -    (define (serialize-field filename value)
> -      (when (maybe-value-set? value)
> -        (list (format #f "~a/config/~a" work-directory filename)
> -              (mixed-text-file filename (serialize-value value)))))
> -
> -    (let ((filename-to-field `(("acl" . ,acl)
> -                               ("covercache_keep_days" .
> ,covercache-ttl)
> -                               ("http"                 . ,http?)
> -                               ("http_host"            . ,host)
> -                               ("http_port"            . ,port)
> -                               ("loglevel"             . ,log-level)
> -                               ("lualibs"              . ,lualibs)
> -                               ("mympd_uri"            . ,uri)
> -                               ("scriptacl"            . ,script-
> acl)
> -                               ("ssl"                  . ,ssl?)
> -                               ("ssl_port"             . ,ssl-port)
> -                               ("ssl_cert"             . ,ssl-cert)
> -                               ("ssl_key"              . ,ssl-key)
> -                               ("pin_hash"             . ,pin-hash)
> -                               ("save_caches"          . ,save-
> caches?))))
> -      (filter list?
> -              (generic-serialize-alist list serialize-field
> -                                       filename-to-field)))))
> +   "Whether to preserve caches between service restarts."
> +   (serializer (mympd-field-serializer "save_caches"))))
> +
> +(define (mympd-configuration->files config)
> +  (match-record config <mympd-configuration> (work-directory)
> +    (list-transduce
> +     (compose (base-transducer config)
> +              (tmap (match-lambda
> +                      ((file-name . file)
> +                       ;; myMPD configuration fields are serialized
> as
> +                       ;; individual files under <work-
> directory>/config/….
> +                       (list (string-append work-directory
> "/config/"
> +                                            file-name)
> +                             file)))))
> +     rcons mympd-configuration-fields)))
>  
>  (define (mympd-shepherd-service config)
>    (match-record config <mympd-configuration>
> @@ -957,8 +953,7 @@ (define (mympd-accounts config)
>        (list user group))))
>  
>  (define (mympd-log-rotation config)
> -  (match-record config <mympd-configuration>
> -    (log-to)
> +  (match-record config <mympd-configuration> (log-to)
>      (if (maybe-value-set? log-to)
>          (list (log-rotation
>                 (files (list log-to))))
> @@ -973,8 +968,8 @@ (define mympd-service-type
>             (service-extension account-service-type
>                                mympd-accounts)
>             (service-extension special-files-service-type
> -                              mympd-serialize-configuration)
> +                              mympd-configuration->files)
>             (service-extension rottlog-service-type
>                                mympd-log-rotation)))
> -   (description "Run myMPD, a frontend for MPD. (Music Player
> Daemon)")
> +   (description "Run myMPD, a frontend for @acronym{MPD, Music
> Player Daemon}.")
>     (default-value (mympd-configuration))))
Cheers
  

Hi Liliana,

On 2023-12-16 01:44, Liliana Marie Prikler wrote:
> Am Freitag, dem 15.12.2023 um 21:02 +0000 schrieb Bruno Victal:
>> -(define-maybe/no-serialization integer)
>> +(define-maybe/no-serialization exact-integer)
> At the risk of asking a silly question, what's the difference between
> an integer and an exact integer?

IIUC it has to do with whether a decimal point is present or not,
which influences the serialization process. (e.g. having port set
to 8080.0 doesn't make much sense even though it is an integer)

--8<---------------cut here---------------start------------->8---
$ cat integer-dem.scm
#!/usr/bin/env -S guile --no-auto-compile
!#

(for-each
 (lambda (s)
   (format #t "Formatted output: ~a~%" s)
   (format #t "number->string: ~a~%" (number->string s))
   (format #t "Integer? ~a~%" (integer? s))
   (format #t "Exact-integer? ~a~%" (exact-integer? s))
   (newline))
 (list 64 128.0))

$ ./integer-dem.scm
Formatted output: 64
number->string: 64
Integer? #t
Exact-integer? #t

Formatted output: 128.0
number->string: 128.0
Integer? #t
Exact-integer? #f
--8<---------------cut here---------------end--------------->8---

>>    (port
>> -   (maybe-port 80)
>> -   "HTTP port to listen on.")
>> +   (maybe-exact-integer 80)
> Losing the information that this is a port (i.e. only integers that fit
> into a uint16 are valid) is imho not great.

I'm not too happy with this either, though in hindsight I think
redefining 'port?' (from Guile Ports) was a bad idea. At the moment
the (re)defined port? predicate only checks whether the value is an
integer, so switching it to exact-integer doesn't seem to change things
much. (other than being stricter in criteria)

Alternatively we could have a proper predicate, perhaps named ip-port?
that would not only perform the exact-integer? check, but also test
whether it fits within a uint16. I'm more inclined to introduce this
kind of change in a separate series that would define it in a reusable
manner and perform a cleanup run across the existing services though.
  

Am Samstag, dem 16.12.2023 um 19:36 +0000 schrieb Bruno Victal:
> Hi Liliana,
> 
> On 2023-12-16 01:44, Liliana Marie Prikler wrote:
> > Am Freitag, dem 15.12.2023 um 21:02 +0000 schrieb Bruno Victal:
> > > -(define-maybe/no-serialization integer)
> > > +(define-maybe/no-serialization exact-integer)
> > At the risk of asking a silly question, what's the difference
> > between an integer and an exact integer?
> 
> IIUC it has to do with whether a decimal point is present or not,
> which influences the serialization process. (e.g. having port set
> to 8080.0 doesn't make much sense even though it is an integer)
I don't think we have to make this distinction that often, though; and
if we do, there are more fitting descriptions like signed-integer and
unsigned-integer.  Even if it's to guard against silly inputs, most
folks wouldn't write 8080.0 there.

> --8<---------------cut here---------------start------------->8---
> $ cat integer-dem.scm
> #!/usr/bin/env -S guile --no-auto-compile
> !#
> 
> (for-each
>  (lambda (s)
>    (format #t "Formatted output: ~a~%" s)
>    (format #t "number->string: ~a~%" (number->string s))
>    (format #t "Integer? ~a~%" (integer? s))
>    (format #t "Exact-integer? ~a~%" (exact-integer? s))
>    (newline))
>  (list 64 128.0))
> 
> $ ./integer-dem.scm
> Formatted output: 64
> number->string: 64
> Integer? #t
> Exact-integer? #t
> 
> Formatted output: 128.0
> number->string: 128.0
> Integer? #t
> Exact-integer? #f
> --8<---------------cut here---------------end--------------->8---
> 
> > >    (port
> > > -   (maybe-port 80)
> > > -   "HTTP port to listen on.")
> > > +   (maybe-exact-integer 80)
> > Losing the information that this is a port (i.e. only integers that
> > fit
> > into a uint16 are valid) is imho not great.
> 
> I'm not too happy with this either, though in hindsight I think
> redefining 'port?' (from Guile Ports) was a bad idea. At the moment
> the (re)defined port? predicate only checks whether the value is an
> integer, so switching it to exact-integer doesn't seem to change
> things much. (other than being stricter in criteria)
Maybe port-number? is clearer?

> Alternatively we could have a proper predicate, perhaps named ip-
> port? that would not only perform the exact-integer? check, but also
> test whether it fits within a uint16. I'm more inclined to introduce
> this kind of change in a separate series that would define it in a
> reusable manner and perform a cleanup run across the existing
> services though.
From my point of view you are already introducing "this kind of change"
as not a separate series :)

Cheers