(cherry-picked by nickm, with changes file from isis.)

changes/bug18920

@@ -0,0 +1,5 @@
+  o Minor bugfixes (controller, microdescriptors):
+    - Make GETINFO dir/status-vote/current/consensus conform to the control
+      specification by returning "551 Could not open cached consensus..."
+      when not caching consensuses.
+      Fixes bug 18920; bugfix on 0.2.2.6-alpha.

src/or/control.c

@@ -2011,6 +2011,11 @@ getinfo_helper_dir(control_connection_t *control_conn,
       char *filename = get_datadir_fname("cached-consensus");
       *answer = read_file_to_str(filename, RFTS_IGNORE_MISSING, NULL);
       tor_free(filename);
+      if (!*answer) { /* generate an error */
+        *errmsg = "Could not open cached consensus. "
+          "Make sure FetchUselessDescriptors is set to 1.";
+        return -1;
+      }
     }
   } else if (!strcmp(question, "network-status")) { /* v1 */
     routerlist_t *routerlist = router_get_routerlist();