Re: Upgrade, hmmm...

Eric J Bowman <> Sat, 01 August 2020 00:34 UTC

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Date: Fri, 31 Jul 2020 17:31:06 -0700
From: Eric J Bowman <>
To: "Nick Harper" <>
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Subject: Re: Upgrade, hmmm...
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Not how current browsers work, no. But, a client asking for that upgrade and getting an affirmative response via TCP, can feel free to repeat the request via UDP. At the cost of a round-trip. I'm taking under consideration your interpretation of Upgrade as being meant for the same connection, my way would be a different connection, you're right. What's the downside?


(sorry for the double-post if I forgot to reply all, oops)

---- On Fri, 31 Jul 2020 16:59:20 -0700 Nick Harper <> wrote ----

On Fri, Jul 31, 2020 at 4:51 PM Eric J Bowman <> wrote:

Please refer me to previous discussions about why h2 and h2c, but no h1, h1c, or h3.

I'm coding a webserver from scratch, with the goal of serving an index.html file and its ancillaries, over any of HTTP/1.1, HTTP/2, HTTP/3, FTP, WAKA (if Roy ever publishes it), or "ERIC" because I have my own ideas. Encrypted or not (I realize "not" isn't an option with HTTP/3). So the main loop is protocol-negotiation hell worse than any conneg/langneg I've ever coded.

If I'm hosting multiple websites on my service, I might want to default to h2, at this time. But if one of those client websites is a law firm, they don't care about serving legal definitions over "h1c" to incarcerated clients, who aren't allowed to use encryption unless it's attorney-client privileged communication. So, how does a gateway at the prison wall connect using h2 but request "Downgrade: h1c"? Or maybe there could be a "Protocol" header with a weighted list (lol).

(Taking a presentation I watched on YouTube by PHK, to heart -- some sovereign states disallow encryption, and heck, America's own FBI wants to kill it. But I agree it's important to be able to downgrade to cleartext.)

Or, why can't an h2c connection request Upgrade: h3? Coding my webserver to shift those gears, turns out to be trivial, all things considered at this point. So, why are only h2/h2c standardized as Upgrade tokens?

The Upgrade header is used to suggest switching protocols on the *same* connection. Given that an h2 (or h2c) connection runs on TCP and HTTP/3 runs on UDP, there's no way to upgrade the existing connection to HTTP/3.