Hi Guix,

this patch adds an inetd-service.  The service is configured using a list of <inetd-entry> records, which correspond to lines in the inetd.conf file (documented in the inetutils info manual).  The following example will start inetd with the built-in “echo” service, and with an smtp service, which uses ssh to tunnel smtp traffic to a server “smtp-server” behind a gateway “hostname”:

(service inetd-service-type
                            (list
                             (inetd-entry
                              (name "echo")
                              (socket-type 'stream)
                              (protocol "tcp")
                              (wait? #t)
                              (user "root")) ; no program and arguments fields required for inetd's "internal" services such as echo
                             (inetd-entry
                              (node "127.0.0.1")
                              (name "smtp")
                              (socket-type 'stream)
                              (protocol "tcp")
                              (wait? #f)
                              (user "root")
                              (program (file-append openssh "/bin/ssh"))
                              (arguments "-q -T -i /path/to/key -W smtp-server:25 user@hostname"))))

This will run inetd with a config file containing these 2 lines::
<---------------------------------------------------------------------------->
echo stream tcp wait root internal internal
127.0.0.1:smtp stream tcp nowait root /gnu/store/kdn1099drrdd2xbypg8x006a0aknskx8-openssh-7.4p1/bin/ssh -q -T -i /path/to/key -W smtp-server:25 user@hostname
<---------------------------------------------------------------------------->

The configuration doesn't include an “escape hatch” option where the user can specify an arbitrary inetd.conf, but I think the current configuration method captures all possibilities, and inetd's configuration format is unlikely to change radically?  Or perhaps the (inetd-config-file) procedure can be exported, so users can either use the procedure with a list of <inetd-entry>'s, or directly pass a (mixed-text-file) or any other file-like.

Obviously documentation is still missing, but I wanted to wait for a first round of comments before writing the docs.  Let me know if I should already include them anyway.

Thomas