Summary

The spec for "Configurable DNS domain validation for SRV records" (https://jira.mongodb.org/browse/DRIVERS-3632) does not fully answer the following 2 questions:
1. How should the Driver respond if the type of use callback is not the expected type? For static languages, this is not possible, but for Node it's entirely possible that the user will pass in a constant expression, or a callback that returns the wrong type. How should this issue be surfaced to the user?
2. srvAllowedHostsSuffix is described as "a valid DNS hostname suffix", but there is no RFC specified, so different Drivers have implemented this differently. Java implemented RFC 1035 (which does not allow underscores), while Python/Node/C# are going against RFC 2181 (which does allow underscores). This difference in implementations means that Java Driver users may be unable to connect to servers that other Driver are able to connect to.

Motivation

Who is the affected end user?

Drivers maintainers.

How does this affect the end user?

Will be confused when some servers are unreachable in broken Drivers.

How likely is it that this problem or use case will occur?

Edge case.

If the problem does occur, what are the consequences and how severe are they?

Impacted Driver won't be able to connect to some hosts.

Is this issue urgent?

No timeline.

Is this ticket required by a downstream team?

No.

Is this ticket only for tests?

No, spec update as well.

Acceptance Criteria

Both issues are addressed in the spec:
1. Error behavior when the callback is of the wrong type
2. Specific RFC chosen for DNS host suffix validation