Re: [PATCH v3 1/3] send-mail: improve checks for valid_fqdn

From: Junio C Hamano <gitster@pobox.com>
Date: May 6, 2025, 22:07 UTC
Message-ID: <xmqqzffpfl57.fsf@gitster.g>
In-Reply-To: <PN3PR01MB959731081532150F5FE54875B889A@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>

Aditya Garg <gargaditya08@live.com> writes:

Show 10 quoted lines

>>  * ... but I don't know if your use of negative lookaround
>>    assersions is correct.  Shouldn't the "a label cannot begin or
>>    end with dash" be applied not just to the first label but
>>    consistently to all of the dot-separated labels?
>
> I think you are talking about this case:
>
> someone.-example.com
>
> No, its not valid.a

I was not talking about any "case"; I was talking more about your regexp to catch invalid addresses. From RFC 5321,

    helo       = "HELO" SP Domain CRLF
    Domain     = sub-domain *("." sub-domain)
    sub-domain = Let-dig [Ldh-str]
    Let-dig    = ALPHA / DIGIT
    Ldh-str    = *( ALPHA / DIGIT / "-" ) Let-dig

so the syntax for first "sub-domain" applies equally to the other "sub-domain". If "-example" cannot be the third-level subdomain, then it equally cannot be the second-level, either, but IIRC, the patch had regexp that treated the first level differently from the rest.