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Re: are ALPN values desirable command line options?

From: Stephen Farrell <>
Date: Mon, 23 Oct 2023 23:32:58 +0100


On 23/10/2023 07:51, Daniel Stenberg wrote:
> Are there actually cases where sending in a custom ALPN is likely to
> be the right thing for a user to get a transfer going? I have not
> heard of any such cases before.

On 23/10/2023 08:44, Stefan Eissing wrote:
> For this to work, curl needs to know the ALPN protocol. Because
> otherwise, it does not know how to talk to the server or understand
> the answer. If one would specify "--alpn xyz" what should curl do
> when "xyz" as negotiated?
I'm sensing skepticism:-) But that's fine. I don't actually know if
there are many sites that really need an ALPN ID that's not tied to
the HTTP version. I looked at the registry [1] and not many IDs seem
to me to be both relevant to curl and where there's likely a benefit
for the client in sending - maybe "acme-tls/1" but not sure.

I do agree that the niche use-case I mentioned in the original mail
wouldn't really justify adding such an option all by itself.

That said, I'll ask a few people at the IETF meeting in a couple of
weeks and see if there's more to it than that.

If not, it's fine that this topic also fades away like the other
from today (have to say, I liked Mark's phrasing of that one:-)



Received on 2023-10-24