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Subject: Re: Serverside SNI support in libpq
From: Daniel Gustafsson <daniel@yesql.se>
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Date: Thu, 18 Dec 2025 01:07:41 +0100
Cc: Jelte Fennema-Nio <postgres@jeltef.nl>,
 Heikki Linnakangas <hlinnaka@iki.fi>,
 Dewei Dai <daidewei1970@163.com>,
 "li.evan.chao" <li.evan.chao@gmail.com>,
 Michael Paquier <michael@paquier.xyz>,
 Andres Freund <andres@anarazel.de>,
 Pgsql Hackers <pgsql-hackers@lists.postgresql.org>
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To: Jacob Champion <jacob.champion@enterprisedb.com>
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 <https://www.postgresql.org/message-id/01412917-C42E-4238-97E2-707C32940DDD%40yesql.se>
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> On 18 Dec 2025, at 00:58, Jacob Champion =
<jacob.champion@enterprisedb.com> wrote:
>=20
> On Fri, Dec 12, 2025 at 3:41=E2=80=AFAM Daniel Gustafsson =
<daniel@yesql.se> wrote:
>>> The comment for HostsLine.ssl_ca, and the code that assigns it,
>>> implies to me that host->ssl_ca should never be NULL. Am I missing a
>>> case where it could be?
>>=20
>> The attached version allows ssl_ca to be omitted from the pg_host =
config to
>> match the ssl_ca GUC.
>=20
> Aha! I think ssl_ca should be moved into the "Optional fields" section
> of `struct HostsLine` now.

Ah, yes.

>> I'm still not sure why they pass for me locally with that error, but =
I've
>> updated to patch to match CI.
>=20
> There's one diff remaining from my old tests patch: the example.org
> line doesn't set ssl_ca, so I expect
>=20
>> -       expected_stderr =3D> qr/unknown ca/);
>> +       expected_stderr =3D> qr/client certificates can only be =
checked if a root certificate store is available/);
>=20
> because host_context->ssl_loaded_verify_locations should be false. But
> that doesn't happen... Why?

I'll have a look.

> Just checking my understanding: is the use case for no_sni primarily
> that you should be able to strictly refuse clients who say they're
> talking to someone else -- so you don't want a wildcard -- but you
> still want to gracefully handle clients who don't speak SNI at all?

Yeah, pretty much.

>> +           else if (strcmp(host->hostname, "no_sni") =3D=3D 0)
>> +               no_sni_context =3D host_context;
>=20
> Will anyone be mad at us for camping on the "no_sni" identifier? I
> know technically underscore isn't allowed in DNS hostnames, buuuut [1,
> 2]

Maybe, but I think that regardless of what we do someone will be mad.  =
The
other option would be to use another single character like '?' or =
something.
Not sure that will improve readability though.

>> +   /* Hostname */
>> +   field =3D list_head(tok_line->fields);
>> +   tokens =3D lfirst(field);
>> +   token =3D linitial(tokens);
>> +   parsedline->hostname =3D pstrdup(token->string);
>=20
> We should probably check tokens->length to make sure that the user
> hasn't passed more than one token for each field, similar to how
> parse_hba_line() does it.

Good point, will do that.

> Should we support multiple hostname tokens in a single line, though,
> and just copy the settings that follow across all of them?

I've been hesitant to add too much complexity, but perhaps just allowing =
a
comma separated list is a good middle ground to avoid going full regex?

--
Daniel Gustafsson