import succeeds with a Varnish 4.0.3 source tree:

- VMOD function vxid commented out, because 4.0.3 doesn't have PRIV_TASK
- VRT_selecthttp is also not exposed in 4.0.3

src/tests/a01.vtc

+varnishtest "vtstor-vmod: Test basic import"
+
+server s1 {
+	timeout 10
+	rxreq
+	expect req.url == "/"
+	txresp -status 200 -hdr "foo: 1"
+} -start
+
+varnish v1 -vcl+backend {
+	import vtstor from "${vmod_topbuild}/src/.libs/libvmod_vtstor.so";
+} -start
+
+client c1 {
+	txreq -url "/"
+	rxresp
+	expect resp.status == 200
+	expect resp.http.foo == 1
+} -run
+

src/vmod_vtstor.c

@@ -32,6 +32,34 @@
 
 #include "vtstor.h"
 
+/*
+ * VRT_selecthttp is not public in Varnish <= 4.0.3.
+ */
+static struct http *
+selecthttp(VRT_CTX, enum gethdr_e where)
+{
+        struct http *hp;
+
+        CHECK_OBJ_NOTNULL(ctx, VRT_CTX_MAGIC);
+        switch (where) {
+        case HDR_REQ:
+                hp = ctx->http_req;
+                break;
+        case HDR_BEREQ:
+                hp = ctx->http_bereq;
+                break;
+        case HDR_BERESP:
+                hp = ctx->http_beresp;
+                break;
+        case HDR_RESP:
+                hp = ctx->http_resp;
+                break;
+        default:
+                WRONG("selecthttp 'where' invalid");
+        }
+        return (hp);
+}
+
 VCL_VOID __match_proto__(td_vmod_vtstor__init)
 vmod_vtstor__init(VRT_CTX,
     struct vmod_vtstor_vtstor **vmip, const char *vcl_name)
@@ -76,7 +104,7 @@ vmod_vtstor_store(VRT_CTX, struct vmod_vtstor_vtstor *vmi,
 	AN(hdr);
 	AN(hdr->what);
 
-	hp = VRT_selecthttp(ctx, hdr->where);
+	hp = selecthttp(ctx, hdr->where);
 	CHECK_OBJ_NOTNULL(hp, HTTP_MAGIC);
 
 	unsigned u, l = hdr->what[0];
@@ -96,7 +124,7 @@ vmod_vtstor_get(VRT_CTX, struct vmod_vtstor_vtstor *vmi, VCL_HEADER hdr)
 
 	AN(hdr);
 	AN(hdr->what);
-	hp = VRT_selecthttp(ctx, hdr->where);
+	hp = selecthttp(ctx, hdr->where);
 	CHECK_OBJ_NOTNULL(hp, HTTP_MAGIC);
 
 	unsigned u, l = hdr->what[0];
@@ -117,7 +145,7 @@ vmod_vtstor_delete(VRT_CTX, struct vmod_vtstor_vtstor *vmi, VCL_HEADER hdr)
 	AN(hdr);
 	AN(hdr->what);
 
-	hp = VRT_selecthttp(ctx, hdr->where);
+	hp = selecthttp(ctx, hdr->where);
 	CHECK_OBJ_NOTNULL(hp, HTTP_MAGIC);
 
 	unsigned u, l = hdr->what[0];
@@ -128,6 +156,7 @@ vmod_vtstor_delete(VRT_CTX, struct vmod_vtstor_vtstor *vmi, VCL_HEADER hdr)
 	}
 }
 
+#if 0
 VCL_STRING __match_proto__(td_vmod_vxid)
 vmod_vxid(VRT_CTX, struct vmod_priv *priv)
 {
@@ -140,3 +169,4 @@ vmod_vxid(VRT_CTX, struct vmod_priv *priv)
 	}
 	return(priv->priv);
 }
+#endif

src/vmod_vtstor.vcc

@@ -33,4 +33,4 @@ $Method VOID .store(STRING, HEADER)
 $Method STRING .get(HEADER)
 $Method VOID .delete(HEADER)
 
-$Function STRING vxid(PRIV_TASK)
+# $Function STRING vxid(PRIV_TASK)