Make it possible to get the length from WS_VSB_finish() (ie: H2 headers).

bin/varnishd/cache/cache.h

@@ -796,7 +796,7 @@ int WS_Inside(const struct ws *, const void *, const void *);
 void WS_Assert_Allocated(const struct ws *ws, const void *ptr, ssize_t len);
 
 void WS_VSB_new(struct vsb *, struct ws *);
-char *WS_VSB_finish(struct vsb *, struct ws *);
+char *WS_VSB_finish(struct vsb *, struct ws *, size_t *);
 
 static inline char*
 WS_Front(const struct ws *ws)

bin/varnishd/cache/cache_vrt.c

@@ -474,7 +474,7 @@ VRT_StrandsWS(struct ws *ws, const char *h, VCL_STRANDS s)
 		if (s->p[i] != NULL && *s->p[i] != '\0')
 			VSB_cat(vsb, s->p[i]);
 	}
-	return (WS_VSB_finish(vsb, ws));
+	return (WS_VSB_finish(vsb, ws, NULL));
 }
 
 /*--------------------------------------------------------------------

bin/varnishd/cache/cache_ws.c

@@ -352,7 +352,7 @@ WS_Overflowed(const struct ws *ws)
  *
  *	WS_VSB_new(vsb, ctx->ws);
  *	VSB_printf(vsb, "blablabla");
- *	p = WS_VSB_finish(vsb);
+ *	p = WS_VSB_finish(vsb, NULL);
  *	if (p == NULL)
  *		return (FAILURE);
  */
@@ -375,7 +375,7 @@ WS_VSB_new(struct vsb *vsb, struct ws *ws)
 }
 
 char *
-WS_VSB_finish(struct vsb *vsb, struct ws *ws)
+WS_VSB_finish(struct vsb *vsb, struct ws *ws, size_t *szp)
 {
 	char *p;
 
@@ -384,11 +384,15 @@ WS_VSB_finish(struct vsb *vsb, struct ws *ws)
 		p = VSB_data(vsb);
 		if (p == WS_Front(ws)) {
 			WS_Release(ws, VSB_len(vsb) + 1);
+			if (szp != NULL)
+				*szp = VSB_len(vsb);
 			VSB_delete(vsb);
 			return (p);
 		}
 	}
 	VSB_delete(vsb);
 	WS_Release(ws, 0);
+	if (szp)
+		*szp = 0;
 	return (NULL);
 }