So basically it works. I've just been undusting the patch
before it becomes bitrot.
To be useful in automation I'll finish my service at some
point, but the point of this small application is that
it can be run from the commandline without requiring
lots of tricky options.
It must be run as root. Example test that follows geomyidae(8):

user@abyayala ~ mkdir /tmp/gopherd ; cp ~/Downloads/geomyidae-0.29/index.gph /tmp/gopherd/
user@abyayala /gnu/store/j8q61m2wfqg2akl4y0lqacmyds9i7vc7-geomyidae-0.29/bin$ ./geomyidae -d -b /tmp/gopherd -p 70
getlistenfd4: Permission denied
user@abyayala /gnu/store/j8q61m2wfqg2akl4y0lqacmyds9i7vc7-geomyidae-0.29/bin$ sudo ./geomyidae -d -b /tmp/gopherd -p 70

# now point lynx (or another browser) to the server, in other words: lynx gopher://localhost
# output in the console where the server was started:

[Tue Nov 28 18:48:24 UTC 2017|::ffff:127.0.0.1:34650]  (serving)
-- 
GnuPG: A88C8ADD129828D7EAC02E52E22F9BBFEE348588
GnuPG: https://c.n0.is/ng0_pubkeys/tree/keys
  WWW: https://n0.is