Rewrite the example to be a hello world vmod

src/tests/test01.vtc

@@ -9,14 +9,14 @@ varnish v1 -vcl+backend {
 	import example from "${vmod_topbuild}/src/.libs/libvmod_example.so";
 
 	sub vcl_deliver {
-		set resp.http.val = example.abs(2-3);
+		set resp.http.hello = example.hello("World!");
 	}
 } -start
 
 client c1 {
 	txreq -url "/"
 	rxresp
-	expect resp.http.val == "1"
+	expect resp.http.hello == "Hello, World!"
 }
 
 client c1 -run

src/vmod_example.c

@@ -11,8 +11,22 @@ init_function(struct vmod_priv *priv, const struct VCL_conf *conf)
 	return (0);
 }
 
-int
-vmod_abs(struct sess *sp, int val)
+const char *
+vmod_hello(struct sess *sp, const char *name)
 {
-	return (abs(val));
+	char *p;
+	unsigned u, v;
+
+	u = WS_Reserve(sp->wrk->ws, 0); /* Reserve some work space */
+	p = sp->wrk->ws->f;		/* Front of workspace area */
+	v = snprintf(p, u, "Hello, %s", name);
+	v++;
+	if (v > u) {
+		/* No space, reset and leave */
+		WS_Release(sp->wrk->ws, 0);
+		return (NULL);
+	}
+	/* Update work space with what we've used */
+	WS_Release(sp->wrk->ws, v);
+	return (p);
 }

src/vmod_example.vcc

 Module example
 Init init_function
-Function INT abs(INT)
+Function STRING hello(STRING)