Add underscore to allowed service type names

[WeeJeWel]

Some services have an _ in their service. This PR allows for those kinds of services.

[agnat]

Thanks for looking into this.

Some services have an _ in their service.

Yet they shouldn't. From http://files.dns-sd.org/draft-cheshire-dnsext-dns-sd.txt ...

   As defined the rules for service names [RFC 6335], Application
   Protocol Names may be no more than fifteen characters (not counting
   the mandatory underscore), consisting of only letters, digits, and
   hyphens, must begin and end with a letter or digit, must not contain
   consecutive hyphens, and must contain at least one letter.

node_mdns does not implement the full rule set, but the character set seems correct. How about adding an option to disable or override the check?

[WeeJeWel]

An opt-in flag seems good to me :)

[agnat]

Hehe, yeah... that’s not going to happen. ;)

On 29. Nov 2021, at 00:05, Emile Nijssen @.***> wrote:

An opt-in flag seems good to me :)

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[WeeJeWel]

Sorry, i thought that was what you were proposing?

[agnat]

Ah, so sorry... I thought you meant an opt-in for the conformance check. But you meant an opt-in for underscores.

Yes, that'll work.