r3019 - trunk/varnish-cache/bin/varnishd
phk at projects.linpro.no
phk at projects.linpro.no
Fri Jul 25 00:12:42 CEST 2008
Author: phk
Date: 2008-07-25 00:12:41 +0200 (Fri, 25 Jul 2008)
New Revision: 3019
Modified:
trunk/varnish-cache/bin/varnishd/heritage.h
trunk/varnish-cache/bin/varnishd/mgt_param.c
trunk/varnish-cache/bin/varnishd/rfc2616.c
Log:
Don my peril sensitive sun-glasses, and go over the TTL calculation
routine.
Follow RFC2616 more closely, and make relative (ie: max-age) specifications
take precedence over absolute specifications (Expires:)
Add an explicit clock-skew window (parameter: clock_skew) and only
interpret Expires: in absolute terms if the Date: header is inside
this window.
Explicit check for the case where the backend sends an Expires: which
is before the Date:, even if the Date: is out side our window.
Modified: trunk/varnish-cache/bin/varnishd/heritage.h
===================================================================
--- trunk/varnish-cache/bin/varnishd/heritage.h 2008-07-24 22:09:25 UTC (rev 3018)
+++ trunk/varnish-cache/bin/varnishd/heritage.h 2008-07-24 22:12:41 UTC (rev 3019)
@@ -175,6 +175,9 @@
/* Prefer IPv6 connections to backend*/
unsigned prefer_ipv6;
+
+ /* Acceptable clockskew with backends */
+ unsigned clock_skew;
};
extern volatile struct params *params;
Modified: trunk/varnish-cache/bin/varnishd/mgt_param.c
===================================================================
--- trunk/varnish-cache/bin/varnishd/mgt_param.c 2008-07-24 22:09:25 UTC (rev 3018)
+++ trunk/varnish-cache/bin/varnishd/mgt_param.c 2008-07-24 22:12:41 UTC (rev 3019)
@@ -745,6 +745,11 @@
"VCL can override this default value for each backend.",
0,
"400", "ms" },
+ { "clock_skew", tweak_uint, &master.clock_skew, 0, UINT_MAX,
+ "How much clockskew we are willing to accept between the "
+ "backend and our own clock.",
+ 0,
+ "10", "s" },
{ "prefer_ipv6", tweak_bool, &master.prefer_ipv6, 0, 0,
"Prefer IPv6 address when connecting to backends which "
"have both IPv4 and IPv6 addresses.",
Modified: trunk/varnish-cache/bin/varnishd/rfc2616.c
===================================================================
--- trunk/varnish-cache/bin/varnishd/rfc2616.c 2008-07-24 22:09:25 UTC (rev 3018)
+++ trunk/varnish-cache/bin/varnishd/rfc2616.c 2008-07-24 22:12:41 UTC (rev 3019)
@@ -60,106 +60,101 @@
* choice.
*
* Varnish implements a policy which is RFC2616 compliant when there
- * is no clockskew, and falls back to a new "clockless cache" mode otherwise.
+ * is no clockskew, and falls as gracefully as possible otherwise.
* Our "clockless cache" model is syntehsized from the bits of RFC2616
* that talks about how a cache should react to a clockless origin server,
- * and more or uses the inverse logic for the opposite relationship.
+ * and more or less uses the inverse logic for the opposite relationship.
*
*/
-#if PSEUDO_CODE
- /* Marker for no retirement age determined */
- retirement_age = INT_MAX
+static double
+RFC2616_Ttl(const struct sess *sp, const struct http *hp, struct object *obj)
+{
+ int ttl;
+ unsigned max_age, age;
+ double h_date, h_expires, ttd;
+ char *p;
- /* If we have a max-age directive, respect it */
- if (max-age)
- retirement_age = max(0,min(retirement_age, max-age - Age:))
+ /* If all else fails, cache using default ttl */
+ ttl = params->default_ttl;
- /* If Date: is not in future and Expires: looks sensible, use it */
- if ((!date || date < our_clock) && expires > our_clock) {
- ttd = min(our_clock + retirement_age, Expires:)
+ max_age = age = 0;
+ ttd = 0;
+ h_expires = 0;
+ h_date = 0;
- /* Otherwise we have clock-skew */
- } else {
- /* If we have both date and expires, infer max-age */
- if (date && expires)
- retirement_age =
- max(0, min(retirement_age, Expires: - Date:)
+ do { /* Allows us to break when we want out */
- /* Apply default_ttl if nothing better found */
- if (retirement_age == INT_MAX)
- retirement_age = default_ttl
+ /*
+ * First find any relative specification from the backend
+ * These take precedence according to RFC2616, 13.2.4
+ */
- /* Apply the max-age we can up with */
- ttd = our_clock + retirement_age
- }
+ if ((http_GetHdrField(hp, H_Cache_Control, "s-maxage", &p) ||
+ http_GetHdrField(hp, H_Cache_Control, "max-age", &p)) &&
+ p != NULL) {
- /* Apply hard limits */
- ttd = max(ttd, our_clock + hard_lower_ttl)
- ttd = min(ttd, our_clock + hard_upper_ttl)
-#endif
+ max_age = strtoul(p, NULL, 0);
+ if (http_GetHdr(hp, H_Age, &p)) {
+ age = strtoul(p, NULL, 0);
+ obj->age = age;
+ }
-static double
-RFC2616_Ttl(const struct sess *sp, const struct http *hp, struct object *obj)
-{
- int retirement_age;
- unsigned u1, u2;
- double h_date, h_expires, ttd;
- char *p;
+ if (age > max_age)
+ ttl = 0;
+ else
+ ttl = max_age - age;
+ break;
+ }
- retirement_age = INT_MAX;
+ /* Next look for absolute specifications from backend */
- u1 = u2 = 0;
- if ((http_GetHdrField(hp, H_Cache_Control, "s-maxage", &p) ||
- http_GetHdrField(hp, H_Cache_Control, "max-age", &p)) &&
- p != NULL) {
- u1 = strtoul(p, NULL, 0);
- u2 = 0;
- if (http_GetHdr(hp, H_Age, &p)) {
- u2 = strtoul(p, NULL, 0);
- obj->age = u2;
- }
- if (u2 <= u1)
- retirement_age = u1 - u2;
- }
+ if (http_GetHdr(hp, H_Expires, &p))
+ h_expires = TIM_parse(p);
+ if (h_expires == 0)
+ break;
- /*
- * XXX: if the backends time is too skewed relative to our own
- * XXX: we should blacklist the backend, to avoid getting totally
- * XXX: bogus results further down. Exactly what "too skewed" means
- * XXX: in this context is a good question. It could be determined
- * XXX: out according to the backends headers, but a simple fixed
- * XXX: tolerance of a minute either way would be more predictable.
- */
- h_date = 0;
- if (http_GetHdr(hp, H_Date, &p))
- h_date = TIM_parse(p);
+ if (http_GetHdr(hp, H_Date, &p))
+ h_date = TIM_parse(p);
- h_expires = 0;
- if (http_GetHdr(hp, H_Expires, &p))
- h_expires = TIM_parse(p);
+ /* If backend told us it is expired already, don't cache. */
+ if (h_expires < h_date) {
+ ttl = 0;
+ break;
+ }
- if (h_date < obj->entered && h_expires > obj->entered) {
- ttd = h_expires;
- if (retirement_age != INT_MAX &&
- obj->entered + retirement_age < ttd)
- ttd = obj->entered + retirement_age;
- } else {
- if (h_date != 0 && h_expires != 0) {
- if (h_date < h_expires &&
- h_expires - h_date < retirement_age)
- retirement_age = h_expires - h_date;
+ if (h_date == 0 ||
+ (h_date < obj->entered + params->clock_skew &&
+ h_date + params->clock_skew > obj->entered)) {
+ /*
+ * If we have no Date: header or if it is
+ * sufficiently close to our clock we will
+ * trust Expires: relative to our own clock.
+ */
+ if (h_expires < obj->entered)
+ ttl = 0;
+ else
+ ttd = h_expires;
+ break;
}
- if (retirement_age == INT_MAX)
- retirement_age = params->default_ttl;
- ttd = obj->entered + retirement_age;
- }
+ /*
+ * But even if the clocks are out of whack we can still
+ * derive a relative time from the two headers.
+ * (the negative ttl case is caught above)
+ */
+ ttl = (h_expires - h_date);
+ } while (0);
+
+ if (ttl > 0 && ttd == 0)
+ ttd = obj->entered + ttl;
+
/* calculated TTL, Our time, Date, Expires, max-age, age */
- WSP(sp, SLT_TTL, "%u RFC %d %d %d %d %d %d", sp->xid,
- (int)(ttd - obj->entered), (int)obj->entered, (int)h_date,
- (int)h_expires, (int)u1, (int)u2);
+ WSP(sp, SLT_TTL, "%u RFC %d %d %d %d %u %u", sp->xid,
+ ttd ? (int)(ttd - obj->entered) : 0,
+ (int)obj->entered, (int)h_date,
+ (int)h_expires, max_age, age);
return (ttd);
}
@@ -194,9 +189,8 @@
}
sp->obj->ttl = RFC2616_Ttl(sp, hp, sp->obj);
- if (sp->obj->ttl == 0) {
+ if (sp->obj->ttl == 0)
sp->obj->cacheable = 0;
- }
return (body);
}
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