varnish (plus) http/2 and websockets, server sent events

[Tom Anheyer | BerlinOnline]

Good morning,

OK, one more. Server-Sent-Events are streaming GET requests. I've tried

sub vcl_recv {
	…
	return(pass);
}

sub vcl_backend_fetch {
	set bereq.first_byte_timeout = 30s;
	set bereq.between_bytes_timeout = 30s;
}

sub vcl_backend_response {
	set beresp.do_esi = false;
	set beresp.do_stream = true;
}

without success. The request is forwarded to the SSE server but comes never back
and does not show up in varnishlog. Is there any chance to get this work without
`pipe`? 

thanks in advance 
tom

Am Freitag, dem 20.06.2025 um 15:05 +0200 schrieb Guillaume Quintard:
> Always a pleasure! Let us know if you have any further questions!
> 
> -- 
> Guillaume Quintard
> 
> On Fri, Jun 20, 2025, 13:30 Tom Anheyer | BerlinOnline
> <Tom.Anheyer at berlinonline.de> wrote:
> > 
> > Hi Guillaume,
> > 
> > thank you for your very quick (as always) and clear answer.
> > 
> > tom
> > 
> > Am Freitag, dem 20.06.2025 um 11:37 +0200 schrieb Guillaume Quintard:
> > > Hi Tom,
> > > This is a base behavior, so Varnish Enterprise inherits it, but it's
> > present
> > > in Varnish Cache too.
> > > Piping involves foregoing HTTP parsing and just passing all the connection
> > > bytes back and forth. It's possible on HTTP 1.x since there's only at most
> > one
> > > request per connection, but this breaks with HTTP2 multiplexing, so
> > Varnish
> > > does the best thing it can and uses a pass instead.
> > > Interestingly, H/2 didn't plan an upgrade path to websockets (or to
> > anything
> > > else, really) for a relatively sane reason: H/2 requires TLS and TLS has
> > ALPN
> > > that allows you to go to websockets directly, without the upgrade hop.
> > > So, to my (maybe outdated) knowledge of H/2, upgrading to websockets isn't
> > > possible.
> > > Please let me know if I'm not being clear.
> > > -- 
> > > Guillaume Quintard
> > > 
> > > On Fri, Jun 20, 2025, 11:15 Tom Anheyer | BerlinOnline
> > > <Tom.Anheyer at berlinonline.de> wrote:
> > > > Hello,
> > > > 
> > > > I don't know if this is specific to varnish plus:
> > > > 
> > > > 
> > > > If I enable pipe-mode for server sent events in vcl_recv this way:
> > > > 
> > > > if (…) {
> > > >     set req.http.connection = "close";
> > > >     return(pipe);
> > > > }
> > > > 
> > > > the log shows:
> > > > 
> > > > -   VCL_return     pipe
> > > > -   VCL_call       HASH
> > > > -   VCL_return     lookup
> > > > -   VCL_Error      vcl_recv{} returns pipe/connect for HTTP/2 request. 
> > > > Doing pass.
> > > > -   VCL_call       PASS
> > > > 
> > > > 
> > > > Is it possible to use server sent events, websockets with http/2
> > requests?
> > > > 
> > > > 
> > > > I've opened a varnish software ticket but I thin [1]k that's public
> > interest.
> > > > 
> > > > tom  
> > > > 
> > 

-- 
Tom Anheyer
Senior Developer

BerlinOnline GmbH
Stefan-Heym-Platz 1
10367 Berlin
Germany

Tel.: +49-30-5771180-62
Fax: +49 30 5771180-95
E-Mail: tom.anheyer at berlinonline.de

berlin.de | berlinonline.net

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[1] pened a varnish software ticket but I thin
    https://www.google.com/maps/search/pened+a+varnish+software+ticket+but+I+thin?entry=gmail&source=g
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