Re: Best practices for writing services

[Joshua Branson]

Xinglu Chen <public@yoctocell.xyz> writes:

> Hi Guix,
>
> I am going to write an mcron service for `guix home`[1][2] and before
> proceding, I would like to get some suggestions on what the best
> practices are for writing services in Guix.

Please note that I am a guix documentation contributor, and I am not
quite a guix developer yet.  :)  Though I do have a patch pending on
http://issues.guix.gnu.org/39136  (not certain why the 2/2 patch does
not show, 'cause I saw that come through in my inbox).

>
> Currently there seems to be two main ways to do this, the first one
> is the define one or more records for the configuration field of a
> service using `define-record-type*`, see the tor service in (gnu
> services networking) for example.  The other method is to use
> `define-configuration` to declare the configuration fields of a service,
> see the transmission service in (gnu services file-sharing) for example.

I believe that the first method via define-record-type* seems to be the
recommended method to do this.  I only say that because I feel like more
services are defined that way now.  :)

> The second method removes quite a lot of boilerplate and the developer
> will define different serializers that convert scheme syntax like lists,
> alist, boolean... to the "real" configuration syntax of the program.  It
> also does some automatic typechecking to some degree and allows the
> developer to write docstrings for each configuration field.  There is
> then a procedure called `generate-documentation` which can automatically
> generate texinfo documenation from the docstrings.

I do like that generate-documentation procedure.  Perhaps we could add
that for the define-record-type*  somehow...

>
> I couldn't find any information in the manual regarding what conventions
> should be used when writing services for Guix and would like to hear
> from more experienced Guix hackers what the best practices are.

You might try asking in irc in #guix too!

I've been working on a sway service and an endlessh service in my
hacking videos
(https://video.hardlimit.com/accounts/joshua_branson/video-channels).  I
was running into issues, where I could compile the service, but trying
to reconfigure my system would result in errors.  The errors messages
were a little vague.  I will also say that the better method I have
found in writing a guix service is to

1) write the service as simply as possible first.  I personally would
copy the simplest service that you can find in gnu/services/  and modify
that via a M-x anzu-query-replace-regexp.  If re-configuring works, make a 
commit.

2) If possible, containerize the service.  If it works, make a commit.

3) Now start adding in all the features you left out before.

--
Joshua Branson (joshuaBPMan in #guix)
Sent from Emacs and Gnus
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enough other people get what they want." - Zig Ziglar