DNSControl does not allow valid SRV target "."

[pro-sumer]

Describe the bug
I'm trying to set up Fastmail's recommended configuration via DNSControl and therefore use SRV records with a . as target for domain example.com:

SRV('_submission._tcp.example.com', 0, 0, 0, '.')

However, DNSControl's preview fails with this error:

2026/01/21 22:15:01 ERROR: BUNNY_DNS rejects domain example.com: srv has null target

To Reproduce
Steps to reproduce the behavior:

1. Configure an SRV record with target .
2. Run dnscontrol preview

Expected behavior
Record is considered valid, as per RFC2052:

A Target of "." means that the service is decidedly not available at this domain.

DNS Provider
Bunny DNS

Additional context
Bunny finally supports the target . as of this week (on my request).

However, DNSControl seems to always reject such targets?

https://github.com/StackExchange/dnscontrol/blob/main/pkg/rejectif/srv.go

[tlimoncelli]

Good to hear that BunnyDNS changed bad on your request!

Now that they support it, remove the restriction in the provider:

dnscontrol/providers/bunnydns/auditrecords.go

Line 14 in 8470260

a.Add("SRV", rejectif.SrvHasNullTarget) // Last verified 2024-01-02

[pro-sumer]

Thanks!

I have never written Go, but might try to make a PR.

[pro-sumer]

@tlimoncelli I might need some guidance...

Removed the suggested line; preview works, but push fails:

#1: + CREATE __submission._tcp.example.com SRV 0 0 0 . ttl=86400
[BUNNY_DNS: Bad API response for PUT /dnszone/007/records: {"ErrorKey":"validation_error","Field":"Value","Message":" is not a valid hostname.\r"}]
FAILURE! bad status code from BUNNY_DNS: 400 not in [201]

Proxyman reveals that this is being sent:

{"Type":8,"Name":"_submission._tcp","Value":"","Disabled":false,"Ttl":86400,"Flags":0,"Priority":0,"Weight":0,"Port":0,"Tag":""}

I checked with someone from Bunny on their Discord and they confirmed that they only allow "." and not "" (empty string).

Is this (using ".") something that can be done with the current DNSControl architecture? How?

[pro-sumer]

Maybe add SRV records to nullTypes in convert.go?

[tlimoncelli]

I don't have access to a BunnyDNS account, but try what I put in tlim_b3997_bunnysrv

That is... rewrite the code near convert.go:50 to be:

	switch r.Type {
	case recordTypeSVCB, recordTypeHTTPS:
		// In the case of SVCB/HTTPS records, the Target is part of the Value.
		// After removing trailing dots for said target, we can add the params to the value.
		r.Value = fmt.Sprintf("%s %s", r.Value, rc.SvcParams)
	case recordTypeSRV:
		// SRV empty target is represented as "."
		if r.Value == "" {
			r.Value = "."
		}
	}

[pro-sumer]

Yes, that could also work, but don't you then first remove the period a few lines above and add it back on line 50?

My suggestion also works, but since you already have that branch I don't need to create a PR?

[tlimoncelli]

Yes, it removes the "." then re-adds it. We could get more fancy but... unless you are processing millions of SRV records I don't think its going to matter much.

Yes, I'll turn that branch into a PR.

[tlimoncelli]

Here ya go... #4003

Could you please confirm that that PR fixes the problem?

[pro-sumer]

Could you please confirm that that PR fixes the problem?

Sure. Yes it does (as did mine):

CONCURRENTLY checking for 0 zone(s)
SERIALLY checking for 1 zone(s)
Serially checking for zone: "example.com"
CONCURRENTLY gathering records of 0 zone(s)
SERIALLY gathering records of 1 zone(s)
Serially Gathering: "example.com"
******************** Domain: example.com
1 correction (bunny_dns)
#1: + CREATE __submission._tcp.example.com SRV 0 0 0 . ttl=86400
SUCCESS!
Done. 1 corrections.

Thank you for creating this PR! Looking forward to the release that contains it.