Implement backend_fetch_response( return (retry); )

bin/varnishd/cache/cache_fetch.c

@@ -58,7 +58,8 @@ vbf_release_req(struct req ***reqpp)
  */
 
 static enum fetch_step
-vbf_stp_mkbereq(struct worker *wrk, struct busyobj *bo, const struct req *req)
+vbf_stp_mkbereq(const struct worker *wrk, struct busyobj *bo,
+    const struct req *req)
 {
 
 	CHECK_OBJ_NOTNULL(wrk, WORKER_MAGIC);
@@ -205,6 +206,14 @@ vbf_stp_fetchhdr(struct worker *wrk, struct busyobj *bo, struct req ***reqpp)
 
 	if (wrk->handling == VCL_RET_DELIVER)
 		return (F_STP_FETCH);
+	if (wrk->handling == VCL_RET_RETRY) {
+		bo->retries++;
+		if (bo->retries <= cache_param->max_retries) {
+			VDI_CloseFd(&bo->vbc);
+			return (F_STP_STARTFETCH);
+		}
+		// XXX: wrk->handling = VCL_RET_SYNTH;
+	}
 
 	return (F_STP_NOTYET);
 }

bin/varnishd/common/params.h

@@ -143,6 +143,9 @@ struct params {
 	/* Maximum restarts allowed */
 	unsigned		max_restarts;
 
+	/* Maximum backend retriesallowed */
+	unsigned		max_retries;
+
 	/* Maximum esi:include depth allowed */
 	unsigned		max_esi_depth;
 

bin/varnishd/mgt/mgt_param_tbl.c

@@ -319,6 +319,10 @@ const struct parspec mgt_parspec[] = {
 		"the backend, so don't increase thoughtlessly.\n",
 		0,
 		"4", "restarts" },
+	{ "max_retries", tweak_uint, &mgt_param.max_retries, 0, UINT_MAX,
+		"Upper limit on how many times a backend fetch can retry.\n",
+		0,
+		"4", "retries" },
 	{ "esi_syntax",
 		tweak_uint, &mgt_param.esi_syntax, 0, UINT_MAX,
 		"Bitmap controlling ESI parsing code:\n"

bin/varnishtest/tests/c00056.vtc

+varnishtest	"vcl_backend_response{} retry"
+
+server s1 {
+	rxreq
+	txresp -hdr "foo: 1"
+	accept
+	rxreq
+	txresp -hdr "foo: 2"
+} -start
+
+varnish v1 -vcl+backend {
+	sub vcl_recv { return (pass); }
+	sub vcl_backend_response {
+		set beresp.http.bar = bereq.retries;
+		if (beresp.http.foo != bereq.http.stop) {
+			return (retry);
+		}
+	}
+} -start
+
+varnish v1 -cliok "param.set debug +syncvsl"
+
+client c1 {
+	txreq -hdr "stop: 2"
+	rxresp
+	expect resp.http.foo == 2
+} -run
+
+delay .1
+
+server s1 {
+	rxreq
+	txresp -hdr "foo: 1"
+	accept
+	rxreq
+	txresp -hdr "foo: 2"
+	accept
+	rxreq
+	txresp -hdr "foo: 3"
+} -start
+
+varnish v1 -cliok "param.set max_retries 2"
+
+client c1 {
+	txreq -hdr "stop: 3"
+	rxresp
+	expect resp.http.foo == 3
+} -run
+
+# XXX: Add a test which exceeds max_retries and gets 503 back

bin/varnishtest/tests/v00017.vtc

@@ -67,7 +67,7 @@ varnish v1 -vcl {
 varnish v1 -vcl {
 	backend b { .host = "127.0.0.1"; }
 	sub vcl_recv { if (client.ip == "127.0.0.1") { return(pass); } }
-	sub vcl_backend_response { if (client.ip != "127.0.0.1") { return(restart); } }
+	sub vcl_backend_response { if (client.ip != "127.0.0.1") { return(retry); } }
 }
 
 varnish v1 -errvcl {Operator > not possible on IP} {

lib/libvcl/generate.py

@@ -86,7 +86,7 @@ returns =(
 	('miss',		"C", ('error', 'restart', 'pass', 'fetch',)),
 	('lookup',		"C", ('error', 'restart', 'pass', 'deliver',)),
 	('backend_fetch',	"B", ('fetch', 'abandon')),
-	('backend_response',	"B", ('deliver', 'restart', 'error')),
+	('backend_response',	"B", ('deliver', 'retry', 'abandon')),
 	('deliver',		"C", ('restart', 'deliver',)),
 	('error',		"C", ('restart', 'deliver',)),
 	('init',		"", ('ok',)),