Copy the status code, proto, status string and response message on

backend IMS.

When revalidating using backend IMS, copy the status code, status
code, status string and response message from the original object into
the new revalidated object. This makes sure that none of the 304
message fields gets applied to the new revalidated object.

Fixes: #1485

bin/varnishd/cache/cache_fetch.c

@@ -356,9 +356,9 @@ vbf_stp_startfetch(struct worker *wrk, struct busyobj *bo)
 	AZ(bo->do_esi);
 
 	if (bo->ims_obj != NULL && bo->beresp->status == 304) {
-		bo->beresp->status = 200;
 		http_Merge(bo->ims_obj->http, bo->beresp,
 		    bo->ims_obj->changed_gzip);
+		assert(bo->beresp->status == 200);
 		do_ims = 1;
 	} else
 		do_ims = 0;

bin/varnishd/cache/cache_http.c

@@ -637,7 +637,9 @@ http_FilterResp(const struct http *fm, struct http *to, unsigned how)
 }
 
 /*--------------------------------------------------------------------
- * Merge two HTTP headers the "wrong" way.
+ * Merge two HTTP headers the "wrong" way. Used by backend IMS to
+ * merge in the headers of the validated object with the headers of
+ * the 304 response.
  */
 
 void
@@ -646,6 +648,11 @@ http_Merge(const struct http *fm, struct http *to, int not_ce)
 	unsigned u, v;
 	const char *p;
 
+	to->status = fm->status;
+	http_SetH(to, HTTP_HDR_PROTO, fm->hd[HTTP_HDR_PROTO].b);
+	http_SetH(to, HTTP_HDR_STATUS, fm->hd[HTTP_HDR_STATUS].b);
+	http_SetH(to, HTTP_HDR_RESPONSE, fm->hd[HTTP_HDR_RESPONSE].b);
+
 	for (u = HTTP_HDR_FIRST; u < fm->nhd; u++)
 		fm->hdf[u] |= HDF_MARKER;
 	if (not_ce) {

bin/varnishtest/tests/r01485.vtc

+varnishtest "#1485: Wrong response reason phrase"
+
+server s1 {
+	rxreq
+	txresp -hdr "Etag: foo"
+
+	rxreq
+	expect req.http.If-None-Match == "foo"
+	txresp -status 304 -msg "Not Modified"
+} -start
+
+varnish v1 -vcl+backend {
+	sub vcl_backend_response {
+		set beresp.ttl = 1ms;
+		set beresp.grace = 0s;
+		set beresp.keep = 1h;
+	}
+} -start
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == 200
+	expect resp.msg == "OK"
+
+	delay 0.1
+
+	txreq
+	rxresp
+	expect resp.status == 200
+	expect resp.msg == "OK"
+} -run