Implement support for per-circuit guard restrictions.

This is an important thing I hadn't considered when writing prop271:
sometimes you have to restrict what guard you use for a particular
circuit.  Most frequently, that would be because you plan to use a
certain node as your exit, and so you can't choose that for your
guard.

This change means that the upgrade-waiting-circuits algorithm needs
a slight tweak too: circuit A cannot block circuit B from upgrading
if circuit B needs to follow a restriction that circuit A does not
follow.

1 files changed, 13 insertions, 2 deletions

diff --git a/src/or/circuitbuild.c b/src/or/circuitbuild.c
index c7e116e853..07903092b5 100644
--- a/src/or/circuitbuild.c
+++ b/src/or/circuitbuild.c
@@ -2515,8 +2515,8 @@ extend_info_dup(extend_info_t *info)
   return newinfo;
 }
 
-/** Return the routerinfo_t for the chosen exit router in <b>state</b>.
- * If there is no chosen exit, or if we don't know the routerinfo_t for
+/** Return the node_t for the chosen exit router in <b>state</b>.
+ * If there is no chosen exit, or if we don't know the node_t for
  * the chosen exit, return NULL.
  */
 const node_t *
@@ -2527,6 +2527,17 @@ build_state_get_exit_node(cpath_build_state_t *state)
   return node_get_by_id(state->chosen_exit->identity_digest);
 }
 
+/** Return the RSA ID digest for the chosen exit router in <b>state</b>.
+ * If there is no chosen exit, return NULL.
+ */
+const uint8_t *
+build_state_get_exit_rsa_id(cpath_build_state_t *state)
+{
+  if (!state || !state->chosen_exit)
+    return NULL;
+  return (const uint8_t *) state->chosen_exit->identity_digest;
+}
+
 /** Return the nickname for the chosen exit router in <b>state</b>. If
  * there is no chosen exit, or if we don't know the routerinfo_t for the
  * chosen exit, return NULL.