net: TestLookupCNAME sometimes failing on Plan 9

[0intro]

Sometimes, TestLookupCNAME is failing on Plan 9.

--- FAIL: TestLookupCNAME (0.24s)
	lookup_test.go:266: write /net/dns: dns: resource does not exist; negrcode 0
FAIL
FAIL	net	19.087s

Indeed, resolving an nonexistent CNAME can result in either the "dns failure" or the "resource does not exist" error. This behavior can be reproduced with ndb/dnsquery:

cpu% ndb/dnsquery
> www.iana.org cname
www.iana.org cname	ianawww.vip.icann.org
> www.iana.org. cname
www.iana.org cname	ianawww.vip.icann.org
> www.google.com cname
!dns: dns failure
> www.google.com cname
!dns: dns failure
> www.google.com cname
!dns: dns failure
> google.com
google.com ip	216.58.198.206
> www.google.fr cname
!dns: resource does not exist; negrcode 0
> www.google.fr cname
!dns: resource does not exist; negrcode 0
> 

This is related to (closed) issue #18391.

[gopherbot]

Change https://golang.org/cl/53670 mentions this issue: net: fix LookupCNAME on Plan 9