Bootstrap: try harder to get descriptors in non-exit test networks

Use the mid weight for the third hop when there are no exits.

Fixes bug 27237; bugfix on 0.2.6.2-alpha.

1 files changed, 8 insertions, 3 deletions

diff --git a/src/feature/nodelist/nodelist.c b/src/feature/nodelist/nodelist.c
index bf298337ae..07edc5abab 100644
--- a/src/feature/nodelist/nodelist.c
+++ b/src/feature/nodelist/nodelist.c
@@ -2361,9 +2361,14 @@ compute_frac_paths_available(const networkstatus_t *consensus,
       f_exit = f_myexit;
   }
 
-  /* if the consensus has no exits, treat the exit fraction as 100% */
+  /* if the consensus has no exits, we can only build onion service paths,
+   * which are G - M - M. So use the middle fraction for the exit fraction. */
   if (router_have_consensus_path() != CONSENSUS_PATH_EXIT) {
-    f_exit = 1.0;
+    /* If there are no exits in the consensus, then f_exit is always 0, so
+     * it is safe to replace f_exit with f_mid. */
+    if (!BUG(f_exit > 0.0)) {
+      f_exit = f_mid;
+    }
   }
 
   f_path = f_guard * f_mid * f_exit;
@@ -2379,7 +2384,7 @@ compute_frac_paths_available(const networkstatus_t *consensus,
                  (int)(f_exit*100),
                  (router_have_consensus_path() == CONSENSUS_PATH_EXIT ?
                   "" :
-                  " (no exits in consensus)"),
+                  " (no exits in consensus, using mid)"),
                  (int)(f_path*100));
 
   return f_path;