vrt_var: Make req.ttl and req.grace unsettable

req.ttl and req.grace are NAN when unset

bin/varnishd/cache/cache_expire.c

@@ -73,8 +73,10 @@ EXP_Ttl(const struct req *req, const struct objcore *oc)
 	CHECK_OBJ_NOTNULL(oc, OBJCORE_MAGIC);
 
 	r = oc->ttl;
-	if (req != NULL && req->d_ttl >= 0. && req->d_ttl < r)
+	if (req != NULL && !isnan(req->d_ttl) && req->d_ttl < r) {
+		assert(req->d_ttl >= 0.);
 		r = req->d_ttl;
+	}
 	return (oc->t_origin + r);
 }
 
@@ -91,8 +93,10 @@ EXP_Ttl_grace(const struct req *req, const struct objcore *oc)
 	CHECK_OBJ_NOTNULL(oc, OBJCORE_MAGIC);
 
 	g = oc->grace;
-	if (req != NULL && req->d_grace >= 0. && req->d_grace < g)
+	if (req != NULL && !isnan(req->d_grace) && req->d_grace < g) {
+		assert(req->d_grace >= 0.);
 		g = req->d_grace;
+	}
 	return (EXP_Ttl(req, oc) + g);
 }
 

bin/varnishd/cache/cache_req_fsm.c

@@ -893,8 +893,8 @@ cnt_recv_prep(struct req *req, const char *ci)
 		VRT_Assign_Backend(&req->director_hint,
 		    VCL_DefaultDirector(req->vcl));
 
-		req->d_ttl = -1;
-		req->d_grace = -1;
+		req->d_ttl = NAN;
+		req->d_grace = NAN;
 		req->disable_esi = 0;
 		req->hash_always_miss = 0;
 		req->hash_ignore_busy = 0;

bin/varnishd/cache/cache_vrt_var.c

@@ -576,12 +576,24 @@ VRT_r_req_##nm(VRT_CTX)							\
 	return (ctx->req->elem);					\
 }
 
+#define REQ_VAR_U(nm, elem, val)					\
+									\
+VCL_VOID								\
+VRT_u_req_##nm(VRT_CTX)							\
+{									\
+	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);				\
+	CHECK_OBJ_NOTNULL(ctx->req, REQ_MAGIC);				\
+	ctx->req->elem = val;						\
+}
+
 REQ_VAR_R(backend_hint, director_hint, VCL_BACKEND)
 
 REQ_VAR_L(ttl, d_ttl, VCL_DURATION, if (!(arg>0.0)) arg = 0;)
 REQ_VAR_R(ttl, d_ttl, VCL_DURATION)
+REQ_VAR_U(ttl, d_ttl, NAN)
 REQ_VAR_L(grace, d_grace, VCL_DURATION, if (!(arg>0.0)) arg = 0;)
 REQ_VAR_R(grace, d_grace, VCL_DURATION)
+REQ_VAR_U(grace, d_grace, NAN)
 
 VCL_VOID
 VRT_l_req_backend_hint(VRT_CTX, VCL_BACKEND be)

bin/varnishtest/tests/b00064.vtc

@@ -84,7 +84,7 @@ client c2 {
 	expect resp.status == 200
 	expect resp.body == "1"
 	expect resp.http.X-grace == "60.000"
-	expect resp.http.X-req-grace < 0.
+	expect resp.http.X-req-grace == "NAN"
 	expect resp.http.X-was-bgfetch == <undef>
 } -run
 
@@ -118,7 +118,7 @@ client c4 {
 	# We should get what c1 got in the very beginning
 	expect resp.body == "1"
 	expect resp.http.X-grace == "60.000"
-	expect resp.http.X-req-grace < 0.
+	expect resp.http.X-req-grace == "NAN"
 	expect resp.http.X-was-bgfetch == <undef>
 } -start
 

bin/varnishtest/tests/b00093.vtc

@@ -0,0 +1,37 @@
+varnishtest "unset req.ttl and req.grace"
+
+server s1 {
+	rxreq
+	expect req.http.ttl-initial == "NAN"
+	expect req.http.grace-initial == "NAN"
+	expect req.http.ttl-set == 0.000
+	expect req.http.grace-set == 0.000
+	expect req.http.ttl-unset == "NAN"
+	expect req.http.grace-unset == "NAN"
+	txresp
+} -start
+
+varnish v1 -vcl+backend {
+	sub vcl_recv {
+		set req.http.ttl-initial = req.ttl;
+		set req.http.grace-initial = req.grace;
+
+		set req.ttl = 0s;
+		set req.grace = 0s;
+
+		set req.http.ttl-set = req.ttl;
+		set req.http.grace-set = req.grace;
+
+		unset req.ttl;
+		unset req.grace;
+
+		set req.http.ttl-unset = req.ttl;
+		set req.http.grace-unset = req.grace;
+	}
+} -start
+
+client c1 -repeat 2 {
+	txreq
+	rxresp
+	expect resp.status == 200
+} -run

doc/sphinx/reference/vcl_var.rst

@@ -272,11 +272,14 @@ req.grace
 
 	Writable from: client
 
+	Unsettable from: client
 
 	Upper limit on the object grace.
 
 	During lookup the minimum of req.grace and the object's stored
-	grace value will be used as the object's grace.
+	grace value will be used as the object's grace. Setting req.grace
+	to 0s prevents hits on stale objects. Negative values are treated
+	as 0s.
 
 
 .. _req.hash:
@@ -536,8 +539,13 @@ req.ttl
 
 	Writable from: client
 
+	Unsettable from: client
 
 	Upper limit on the object age for cache lookups to return hit.
+	Setting ``req.ttl = 0s`` forces a cache MISS, but unlike
+	``req.hash_always_miss = true``, the request may go on the
+	waitinglist for an ongoing fetch. Negative values are treated
+	as 0s.
 
 
 .. _req.url: