neinp is a toolkit to implement 9p servers.
go get git.sr.ht/rbn/neinp
a example of how to use this can be found here: https://git.sr.ht/rbn/rssfs
furthermore, the documentation of this package should cover most things. additional information about the 9p protocol can be found in the plan9 manual (should be available online at cat-v.org for example).