we've found an issue recently while developing an add-on for one of our customers.
our add-on is an agenda that includes days and appointments; for days we implemented a view that shows all appointments on that day and a calendar to make navigating the agenda easy.
the calendar is build on the fly using
application/json calls to other days on the same month to mark all days with appointments and to make fast updates when a user selects another day.
resuming: if I traverse to the default view of a day, I get normal HTML; if I request
application/json using an AJAX call to the same default view, I get JSON.
everything was more or less working until we deployed it and then we discovered that Varnish was caching only one of the versions breaking the whole thing.
Vary header; according to Varnish documentation:
If the origin server sends
Varyin a response, Varnish does not use this response to satisfy a later request unless the later request has the same values for the listed fields in
Varyas the original request. As a consequence,
Varyexpands the cache key required to match a new request to the stored cache entry.
so, according to this I can fix the issue adding the
Vary header to my response.
my next step was testing the following on our code:
def __call__(self): self.setup() self.request.response.appendHeader('Vary', 'Accept') return self.index()
and it works fine, except for one detail: it's only applied to the HTML response.
does anybody else has found this issue? how do you deal with it?
I'm wondering why this header is not included by default in plone.restapi (any comments, @tisto?)
tomorrow I'm going to test a workaround using plone.app.caching; I'll post my results after that.