Add minimum allowable client library version configuration block

[phho]

Feature Request

Provide minimum allowable client library version configuration block feature, so that NATS server can deny outdated client library connections to avoid unexpected server and client behaviors.

Use Case:

NATS server administrator can configure programming language and minimum allowable client library version to protect NATS servers.

Proposed Change:

As slack discussion with Derek, Byron, Todd and Jeremy. All NATS client libraries should already follow semver rule. It will be helpful to provide configuration block feature like below.

allow_client_lang_verions :[
{ lang: "java" , min_version: "2.15.0"},
{ lang: "go" , min_version: "1.15.0"},
...
]

Who Benefits From The Change(s)?

All NATS user

Alternative Approaches

Slack thread link and attach discussion snapshot.

[tbeets]

This is a good ER @phho . Thank you for submitting. I will be creating an ADR for some design discuss of syntax and functionality.

I believe there is probably room for a non-inclusive "max" option as well, e.g. As an operator I want to specify that a client of type Java must be of version 1.15.6 or greater but in any case less than version 2.0.0.

[phho]

Thank @tbeets for your reply.
Your design is indeed more complete. The max options can avoid the unexpected behavior of the client when the server is running in a previous stable version, but the client uses the new version of libray to connect to the server and wants to use the latest server functionality.

[tbeets]

@phho I have started ADR-27.

[h20220025]

hi @derekcollison i am looking forward to work in order to resolve the issue.

[derekcollison]

We like the idea, won't make it into 2.9 but is on our radar.