add directors.resolve() and test it

bin/varnishtest/tests/d00021.vtc

@@ -1,16 +1,16 @@
 varnishtest "shard director LAZY and layering"
 
-server s1 -repeat 2 {
+server s1 -repeat 3 {
 	rxreq
 	txresp -body "ech3Ooj"
 } -start
 
-server s2 -repeat 2 {
+server s2 -repeat 3 {
 	rxreq
 	txresp -body "ieQu2qua"
 } -start
 
-server s3 -repeat 2 {
+server s3 -repeat 3 {
 	rxreq
 	txresp -body "xiuFi3Pe"
 } -start
@@ -54,6 +54,10 @@ varnish v1 -vcl+backend {
 	}
 
 	sub vcl_recv {
+	    # coverage
+	    set req.backend_hint = directors.resolve(vd.backend());
+	    set req.backend_hint = directors.resolve(l.backend());
+	    set req.backend_hint = directors.resolve(ll.backend());
 	    return(pass);
 	}
 
@@ -86,7 +90,10 @@ varnish v1 -vcl+backend {
 	}
 
 	sub vcl_backend_fetch {
-	    if (bereq.http.layered) {
+	    if (bereq.http.resolve) {
+		call backend_fetch_layered;
+		set bereq.backend = directors.resolve(bereq.backend);
+	    } else if (bereq.http.layered) {
 		call backend_fetch_layered;
 	    } else {
 		call backend_fetch_direct;
@@ -148,4 +155,25 @@ client c1 {
 	expect resp.http.healthy == "true"
 	expect resp.http.director == "ll"
 	expect resp.http.backend == "s3"
+
+	txreq -url /1 -hdr "resolve: true"
+	rxresp
+	expect resp.body == "ech3Ooj"
+	expect resp.http.healthy == "true"
+	expect resp.http.director == "s1"
+	expect resp.http.backend == "s1"
+
+	txreq -url /2 -hdr "resolve: true"
+	rxresp
+	expect resp.body == "ieQu2qua"
+	expect resp.http.healthy == "true"
+	expect resp.http.director == "s2"
+	expect resp.http.backend == "s2"
+
+	txreq -url /3 -hdr "resolve: true"
+	rxresp
+	expect resp.body == "xiuFi3Pe"
+	expect resp.http.healthy == "true"
+	expect resp.http.director == "s3"
+	expect resp.http.backend == "s3"
 } -run

lib/libvmod_directors/misc.c

@@ -33,6 +33,8 @@
 #include "vdef.h"
 #include "vrt.h"
 #include "vcl.h"
+#include "vas.h"
+#include "miniobj.h"
 
 #include "vcc_if.h"
 
@@ -47,3 +49,11 @@ VPFX(lookup)(VRT_CTX, VCL_STRING name)
 
 	return (VRT_LookupDirector(ctx, name));
 }
+
+VCL_BACKEND
+VPFX(resolve)(VRT_CTX, VCL_BACKEND d)
+{
+	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
+
+	return (VRT_DirectorResolve(ctx, d));
+}

lib/libvmod_directors/vmod.vcc

@@ -711,6 +711,28 @@ Lookup a backend by its name.
 
 This function can only be used from ``vcl_init{}`` and  ``vcl_fini{}``.
 
+$Function BACKEND resolve(BACKEND)
+
+Return a backend which any layer of directors resolves to.
+
+Most ``.backend()`` methods of varnish directors return a reference to
+the director itself (basically, all except ``shard`` with
+``resolve=NOW``). Only when it is time to make an actual connection is
+the decision on which backend to contact made.
+
+This function allows to have that decision made early, it returns a
+final ("real") backend which the given director argument would
+return.
+
+Notice that this decision is not saved, in other words, repeated calls
+to `directors.resolve()`_ may return different values, and the implicit
+resolution may use a different value yet again.
+
+To make a resolution decision permanent, it has to be saved
+explicitly, for example by assignment to ``(be)req.backend`` as in::
+
+	set bereq.backend = directors.resolve(bereq.backend);
+
 ACKNOWLEDGEMENTS
 ================