bring back beresp.storage_hint for vcl 4.0

see doc/changes.rst for details

Closes #2509

bin/varnishd/cache/cache_vrt_var.c

@@ -365,6 +365,53 @@ VRT_l_beresp_storage(VRT_CTX, VCL_STEVEDORE stv)
 	ctx->bo->storage = stv;
 }
 
+/*--------------------------------------------------------------------
+ * VCL <= 4.0 ONLY
+ */
+
+#include "storage/storage.h"
+
+const char *
+VRT_r_beresp_storage_hint(VRT_CTX)
+{
+	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
+	CHECK_OBJ_NOTNULL(ctx->bo, BUSYOBJ_MAGIC);
+	if (ctx->bo->storage == NULL)
+		return (NULL);
+	CHECK_OBJ_NOTNULL(ctx->bo->storage, STEVEDORE_MAGIC);
+	return (ctx->bo->storage->vclname);
+}
+
+void
+VRT_l_beresp_storage_hint(VRT_CTX, const char *str, ...)
+{
+	const char *p;
+	va_list ap;
+	uintptr_t sn;
+	VCL_STEVEDORE stv;
+
+	CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
+	CHECK_OBJ_NOTNULL(ctx->bo, BUSYOBJ_MAGIC);
+
+	sn = WS_Snapshot(ctx->ws);
+	va_start(ap, str);
+	p = VRT_String(ctx->ws, NULL, str, ap);
+	va_end(ap);
+
+	if (p == NULL) {
+		VSLb(ctx->vsl, SLT_LostHeader, "storage_hint");
+		WS_MarkOverflow(ctx->ws);
+		WS_Reset(ctx->ws, sn);
+		return;
+	}
+
+	stv = VRT_stevedore(p);
+	if (stv != NULL)
+		ctx->bo->storage = stv;
+
+	WS_Reset(ctx->ws, sn);
+}
+
 /*--------------------------------------------------------------------*/
 
 VCL_STEVEDORE

bin/varnishtest/tests/c00078.vtc

 varnishtest "Stevedores RR, beresp.storage"
 
-server s1 -repeat 6 {
+server s1 -repeat 7 {
 	rxreq
 	txresp
 } -start
@@ -17,8 +17,11 @@ varnish v1 \
 			set beresp.storage = storage.s1;
 		} else if (bereq.url == "/6") {
 			set beresp.storage = vtc.no_stevedore();
+		} else if (bereq.url == "/deprecated") {
+			set beresp.storage_hint = "s1";
 		}
 		set beresp.http.storage = beresp.storage;
+		set beresp.http.storage-hint = beresp.storage_hint;
 	}
 } -start
 
@@ -26,19 +29,38 @@ client c1 {
 	txreq -url /1
 	rxresp
 	expect resp.http.storage == "storage.s1"
+	expect resp.http.storage == resp.http.storage-hint
 	txreq -url /2
 	rxresp
 	expect resp.http.storage == "storage.s1"
+	expect resp.http.storage == resp.http.storage-hint
 	txreq -url /3
 	rxresp
 	expect resp.http.storage == "storage.s0"
+	expect resp.http.storage == resp.http.storage-hint
 	txreq -url /4
 	rxresp
 	expect resp.http.storage == "storage.s1"
+	expect resp.http.storage == resp.http.storage-hint
 	txreq -url /5
 	rxresp
 	expect resp.http.storage == "storage.s2"
+	expect resp.http.storage == resp.http.storage-hint
 	txreq -url /6
 	rxresp
 	expect resp.http.storage == <undef>
+	expect resp.http.storage == resp.http.storage-hint
+	txreq -url /deprecated
+	rxresp
+	expect resp.http.storage == "storage.s1"
+	expect resp.http.storage == resp.http.storage-hint
 } -run
+
+varnish v1 \
+    -syntax 4.1 \
+    -errvcl "Only available when VCL syntax <= 4.0" {
+	import vtc;
+	sub vcl_backend_response {
+		set beresp.storage_hint = "foo";
+	}
+}

doc/changes.rst

@@ -41,7 +41,17 @@ VCL and bundled VMODs
   ``req.hash_always_miss`` are now accessible from all of the client
   side subs, not just ``vcl_recv{}``
 
-* Removed ``beresp.storage_hint`` (was deprecated since Varnish 5.1)
+* Removed ``beresp.storage_hint`` for VCL 4.1 (was deprecated since
+  Varnish 5.1)
+
+  For VCL 4.0, compatibility is preserved, but the implementation is
+  changed slightly: ``beresp.storage_hint`` is now referring to the
+  same internal data structure as ``beresp.storage``.
+
+  In particular, it was previously possible to set
+  ``beresp.storage_hint`` to an invalid storage name and later
+  retrieve it back. Doing so will now yield the last successfully set
+  stevedore or the undefined (``NULL``) string.
 
 * workspace overflows in ``std.log()`` now trigger a VCL failure
 

doc/sphinx/reference/vcl_var.rst

@@ -868,6 +868,21 @@ beresp.storage
 	
 	The storage backend to use to save this object.
 
+beresp.storage_hint	``VCL <= 4.0``
+
+	Type: STRING
+
+	Readable from: vcl_backend_response, vcl_backend_error
+
+	Writable from: vcl_backend_response, vcl_backend_error
+
+	
+	Deprecated since varnish 5.1 and discontinued since VCL
+	4.1 (varnish 6.0). Use beresp.storage instead.
+	
+	Hint to Varnish that you want to save this object to a
+	particular storage backend.
+
 obj
 ~~~
 

include/vrt.h

@@ -61,8 +61,8 @@
  *	VRT_VSC_Overhead() added
  *	struct director.event added
  *	struct director.destroy added
- *	VRT_r_beresp_storage_hint() removed - under discussion #2509
- *	VRT_l_beresp_storage_hint() removed - under discussion #2509
+ *	VRT_r_beresp_storage_hint() VCL <= 4.0  #2509
+ *	VRT_l_beresp_storage_hint() VCL <= 4.0  #2509
  *	VRT_blob() added
  *	VCL_STRANDS added
  * 6.1 (2017-09-15 aka 5.2)