Any chance to support "max-stale" request header in Varnish?

[Michael Lee]

Hi Guys,

I am working on a tutorial of HTTP/1.1 caching and I'd like to use 
Varnish as the reverse proxy to demonstrate how HTTP/1.1 caching works. 
However, I found there is no way to support the max-stale request header 
("Cache-Control: max-stale=...").

The problem is that "a call to return(deliver)" always triggers a 
backend fetch, explicitly, if the object's ttl has been exceeded, so 
it's impossible to deliver a staled object for a single request.

The workaround might be shutting down the backend server to force a 
failure of the backend fetch, thus to get the staled object delivered. 
But besides that, is there any better solution to support the max-stale 
header?

In fact, the "max-stale" header is almost identical to "grace", except 
that the "max-stale" header is controlled by the client, while the 
"grace" is controlled by varnish. But still, unless we shut down the 
backend server, there is no way to demonstrate the "grace" for single 
request either.

Kind regards,

Michael

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