[Varnish 4] Respecting client's Cache-Control: max-age= as TTL

[Martynas Jusevičius]

Sorry, sent too soon. Here it goes:

Thanks Guillaume.

First I tried return(fetch) as you suggested

sub vcl_hit {
    if (req.http.Cache-Control ~ "max-age=[0-9]*") {
        set req.http.Max-Age = regsub(req.http.Cache-Control,
"max-age=([0-9]*)", "\1");
        if (obj.age > std.duration(req.http.Max-Age + "s", 1000000s)) {
            std.log("obj.age: " + obj.age + " req.http.Max-Age: " +
req.http.Max-Age);
            return(fetch);
        }
    }
    ...

but I got an error:

-   VCL_call       HIT
-   ReqHeader      Max-Age: 69
-   VCL_Log        obj.age: 102.306 req.http.Max-Age: 69
-   VCL_return     fetch
-   VCL_Error      change return(fetch) to return(miss) in vcl_hit{}
-   VCL_Error      vcl_hit{} returns miss without busy object.  Doing pass.
-   VCL_call       PASS
-   VCL_return     fetch

I did as told and I tried return(miss)

sub vcl_hit {
    if (req.http.Cache-Control ~ "max-age=[0-9]*") {
        set req.http.Max-Age = regsub(req.http.Cache-Control,
"max-age=([0-9]*)", "\1");
        if (obj.age > std.duration(req.http.Max-Age + "s", 1000000s)) {
            std.log("obj.age: " + obj.age + " req.http.Max-Age: " +
req.http.Max-Age);
            return(miss);
        }
    }
    ...

but then I got another error:

-   VCL_call       HIT
-   ReqHeader      Max-Age: 69
-   VCL_Log        obj.age: 195.391 req.http.Max-Age: 69
-   VCL_return     miss
-   VCL_Error      vcl_hit{} returns miss without busy object.  Doing pass.
-   VCL_call       PASS
-   VCL_return     fetch

So it looks like the max-age logic is triggered correctly, but what is
wrong with the return values?

On Tue, Aug 1, 2017 at 12:01 AM, Martynas Jusevičius <martynas at atomgraph.com
> wrote:

> Thanks Guillaume.
>
> First I tried
>
> sub vcl_hit {
>     if (req.http.Cache-Control ~ "max-age=[0-9]*") {
>         set req.http.Max-Age = regsub(req.http.Cache-Control,
> "max-age=([0-9]*)", "\1");
>         if (obj.age > std.duration(req.http.Max-Age + "s", 1000000s)) {
>             std.log("obj.age: " + obj.age + " req.http.Max-Age: " +
> req.http.Max-Age);
>             return(fetch);
>         }
>     }
>     ...
>
> but I got an error:
>
> -   VCL_call       HIT
> -   ReqHeader      Max-Age: 69
> -   VCL_Log        obj.age: 102.306 req.http.Max-Age: 69
> -   VCL_return     fetch
> -   VCL_Error      change return(fetch) to return(miss) in vcl_hit{}
> -   VCL_Error      vcl_hit{} returns miss without busy object.  Doing pass.
> -   VCL_call       PASS
> -   VCL_return     fetch
>
> I did as told and I tried
>
>
> On Mon, Jul 31, 2017 at 9:11 PM, Guillaume Quintard <
> guillaume at varnish-software.com> wrote:
>
>> man vcl
>>
>> bereq is filtered to avoid side effects of the client forcing the ttl to
>> the backed.
>>
>> Anyway, by the time you have access to bereq, it's too late for you since
>> the decision to go to the backend has already been been made.
>>
>> --
>> Guillaume Quintard
>>
>>
>> On Jul 31, 2017 19:56, "Martynas Jusevičius" <martynas at atomgraph.com>
>> wrote:
>>
>> Thanks. What was mostly unclear to me is passing the req header value all
>> the way to where it's used to set TTL.
>>
>> Why doesn't bereq contain the req headers? At least Cache-Control is gone.
>>
>> But I guess that can be done using obj.ttl, which I didn't know about.
>> Any documentation on that?
>>
>> On Mon, 31 Jul 2017 at 18.38, Guillaume Quintard <
>> guillaume at varnish-software.com> wrote:
>>
>>> On github I pointed to the doc explaining how you can return(fetch) to
>>> ignore a cached object, possibly based on ttl, so you already have half the
>>> answer.
>>>
>>> The other part of the equation is just converting req.http.cache-control
>>> to a duration and comparing that to obj.ttl. It will be similar to what you
>>> have done on v3.
>>>
>>> --
>>> Guillaume Quintard
>>>
>>> On Jul 31, 2017 18:25, "Martynas Jusevičius" <martynas at atomgraph.com>
>>> wrote:
>>>
>>>> Hi,
>>>>
>>>> I have been reading quite a bit about Varnish and VCL but found almost
>>>> no examples with Cache-Control coming from the client request [1].
>>>>
>>>> What I want to achieve: if the client sends Cache-Control: max-age=60,
>>>> TTL becomes 60 s. If the cache hit is fresher than 60 s, deliver it,
>>>> otherwise fetch a new response from backend (I hope I'm not misusing the
>>>> VCL terms here) *and* cache it.
>>>>
>>>> I had hacked this together in the vcl_fetch section in Varnish 3.x by
>>>> setting the req.http.Cache-Control max-age value as beresp.ttl, but
>>>> vcl_fetch is gone in Varnish 4.x.
>>>>
>>>> I have received a suggestion to use vcl_hit and/or grace [2], but again
>>>> -- no examples...
>>>>
>>>> Could anyone provide some VCL pseudo-code that
>>>> uses req.http.Cache-Control value to override TTL? max-age number parsing
>>>> not necessary, I have figure that out.
>>>>
>>>> Thanks,
>>>>
>>>> Martynas
>>>>
>>>> [1] https://developer.mozilla.org/en-US/docs/Web/HTTP/Header
>>>> s/Cache-Control#Cache_request_directives
>>>> [2] https://github.com/varnishcache/varnish-cache/issues/201
>>>> 4#issuecomment-319096566
>>>>
>>>> _______________________________________________
>>>> varnish-misc mailing list
>>>> varnish-misc at varnish-cache.org
>>>> https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc
>>>>
>>>
>>
>
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