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

> On 6 May 2025, at 10:53 PM, Aditya Garg <gargaditya08@live.com> wrote:
> 
> 
> 
>> On 06/05/25 10:41 pm, Junio C Hamano wrote:
>> Aditya Garg <gargaditya08@live.com> writes:
>> 
>>> I think we can add a minimal check to ensure that there are no two dots together.
>>> Does that sound fair?
>> 
>> Is it a common misconfiguration in the first place that singling out
>> a name ending with double dots (which indeed is very likely that
>> nobody should be relying on getting accepted by sensible SMTP
>> servers, hence very safe tightening) is worth doing?  If MacBooks as
>> shipped would by default claim to be "MacBook.." like your example
>> had (I do not know if that is the case, as I do not live in Apple
>> ecosystem), it may give us a reason to special case the trailing
>> double-dots, for example.
> 
> Its not an Apple thing. I am not even using macOS at the first place
> when I tested this, I was on Ubuntu running on my Mac.
> 
> Its a problem with Net::Domain. In systems without a domainname, and
> without a period in the hostname, Net::Domain will always output
> "hostname..". You probably should check your machine with smtp-debug?
> Btw, the output of `hostname -f` on these machines will be "hostname".
> 
> Now gmail does not reject this, probably the reason it is unnoticed?
> Since Outlook support is new, such problems are being observed.
> 
> 
>> 
>> I personally feel that "run of at most 63 alnum or dash separated by
>> a single dot in between" is easy enough to explain, so if I were
>> doing this change, I would just use the regexp used in posted patch
>> [*] and if nobody complains, stop right there.  If we get any
>> complaint, then I'd detect and reject the case where the string ends
>> with double-dots.
> 
> The regexp used in the original patch covers the double dots case as well.
> Its basically following the RFC guidelines, which a sensible SMTP server
> should follow, and so must a user.
> 
>> 
>> [Footnote]
>> 
>> * ... 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