If the match subject is NULL, then match as if it is the empty string.

For compatibility with native VCL regexen.

src/tests/match.vtc

@@ -83,45 +83,6 @@ client c1 -repeat 2 {
 	expect resp.http.bar1 == "2"
 } -run
 
-# server s1 -wait
-
-# server s1 -repeat 2 {
-#         rxreq
-#         txresp -body "foobar"
-# } -start
-
-# varnish v1 -vcl+backend {
-# 	import pcre2 from "${vmod_topbuild}/src/.libs/libvmod_pcre2.so";
-
-# 	sub vcl_init {
-#                 new end = pcre2.regex("$");
-#                 new empty = pcre2.regex("");
-#         }
-
-#         sub vcl_backend_response {
-# 		if (beresp.http.bar ~ "$") {
-# 			set beresp.http.foo-native = "XXX";
-# 		}
-# 		if (beresp.http.foo ~ "") {
-# 			set beresp.http.bar-native = "YYY";
-# 		}
-#                 if (end.match(beresp.http.bar)) {
-#                         set beresp.http.foo = "XXX";
-#                 }
-#                 if (empty.match(beresp.http.foo)) {
-#                         set beresp.http.bar = "YYY";
-#                 }
-#         }
-# }
-
-# client c1 -repeat 2 {
-#         txreq
-#         rxresp
-#         expect resp.status == 200
-#         expect resp.http.foo == "XXX"
-#         expect resp.http.bar == "YYY"
-# } -run
-
 # test matches from pcre2 testinput1
 varnish v1 -vcl {
 	import pcre2 from "${vmod_topbuild}/src/.libs/libvmod_pcre2.so";

src/tests/match_null.vtc

+# looks like -*- vcl -*-
+
+varnishtest "match null subjects"
+
+# Confirm that if the subject is NULL, for example when set from an
+# unset header, it is matched as if it is the empty string. For
+# compatibility with native VCL regexen.
+
+# cf. varnish r00913.vtc
+server s1 -repeat 2 {
+	rxreq
+	txresp -body "foobar"
+} -start
+
+varnish v1 -vcl+backend {
+	import pcre2 from "${vmod_topbuild}/src/.libs/libvmod_pcre2.so";
+
+	sub vcl_init {
+		new end = pcre2.regex("$");
+		new empty = pcre2.regex("");
+	}
+
+	sub vcl_backend_response {
+		if (beresp.http.bar ~ "$") {
+			set beresp.http.foo-native = "XXX";
+		}
+		if (beresp.http.foo ~ "") {
+			set beresp.http.bar-native = "YYY";
+		}
+		if (end.match(beresp.http.bar)) {
+			set beresp.http.foo = "XXX";
+		}
+		if (empty.match(beresp.http.foo)) {
+			set beresp.http.bar = "YYY";
+		}
+	}
+} -start
+
+client c1 -repeat 2 {
+	txreq
+	rxresp
+	expect resp.status == 200
+	expect resp.http.foo-native == "XXX"
+	expect resp.http.bar-native == "YYY"
+	expect resp.http.foo == "XXX"
+	expect resp.http.bar == "YYY"
+} -run

src/vmod_pcre2.c

@@ -403,10 +403,8 @@ vmod_regex_match(VRT_CTX, struct vmod_pcre2_regex *regex,
 	CHECK_OBJ_NOTNULL(regex, VMOD_PCRE2_REGEX_MAGIC);
 	AN(gctx_task);
 	AN(mctx_call);
-	if (subject == NULL) {
-		VERR(ctx, "subject is NULL in %s.match()", regex->vcl_name);
-		return 0;
-	}
+	if (subject == NULL)
+		subject = "";
 
 	/*
 	 * The general context is task-scoped and shared by all objects