2 files changed, 17 insertions, 2 deletions

diff --git a/src/core/or/policies.c b/src/core/or/policies.c
index 0eda93c5f3..123fc8566e 100644
--- a/src/core/or/policies.c
+++ b/src/core/or/policies.c
@@ -29,6 +29,7 @@
 #include "feature/relay/routermode.h"
 #include "lib/geoip/geoip.h"
 #include "ht.h"
+#include "lib/crypt_ops/crypto_rand.h"
 #include "lib/encoding/confline.h"
 
 #include "core/or/addr_policy_st.h"
@@ -461,7 +462,8 @@ fascist_firewall_use_ipv6(const or_options_t *options)
    * ClientPreferIPv6DirPort is deprecated, but check it anyway. */
   return (options->ClientUseIPv6 == 1 || options->ClientUseIPv4 == 0 ||
           options->ClientPreferIPv6ORPort == 1 ||
-          options->ClientPreferIPv6DirPort == 1 || options->UseBridges == 1);
+          options->ClientPreferIPv6DirPort == 1 || options->UseBridges == 1 ||
+          options->ClientAutoIPv6ORPort == 1);
 }
 
 /** Do we prefer to connect to IPv6, ignoring ClientPreferIPv6ORPort and
@@ -488,6 +490,15 @@ fascist_firewall_prefer_ipv6_impl(const or_options_t *options)
   return -1;
 }
 
+/* Choose whether we prefer IPv4 or IPv6 by randomly choosing an address
+ * family. Return 0 for IPv4, and 1 for IPv6. */
+MOCK_IMPL(int,
+fascist_firewall_rand_prefer_ipv6_addr, (void))
+{
+  /* TODO: Check for failures, and infer our preference based on this. */
+  return crypto_rand_int(2);
+}
+
 /** Do we prefer to connect to IPv6 ORPorts?
  * Use node_ipv6_or_preferred() whenever possible: it supports bridge client
  * per-node IPv6 preferences.
@@ -502,7 +513,10 @@ fascist_firewall_prefer_ipv6_orport(const or_options_t *options)
   }
 
   /* We can use both IPv4 and IPv6 - which do we prefer? */
-  if (options->ClientPreferIPv6ORPort == 1) {
+  if (options->ClientAutoIPv6ORPort == 1) {
+    /* If ClientAutoIPv6ORPort is 1, we prefer IPv4 or IPv6 at random. */
+    return fascist_firewall_rand_prefer_ipv6_addr();
+  } else if (options->ClientPreferIPv6ORPort == 1) {
     return 1;
   }
 
diff --git a/src/core/or/policies.h b/src/core/or/policies.h
index 7da3ba031f..0c64ecf378 100644
--- a/src/core/or/policies.h
+++ b/src/core/or/policies.h
@@ -70,6 +70,7 @@ typedef struct short_policy_t {
 int firewall_is_fascist_or(void);
 int firewall_is_fascist_dir(void);
 int fascist_firewall_use_ipv6(const or_options_t *options);
+MOCK_DECL(int, fascist_firewall_rand_prefer_ipv6_addr, (void));
 int fascist_firewall_prefer_ipv6_orport(const or_options_t *options);
 int fascist_firewall_prefer_ipv6_dirport(const or_options_t *options);