try ipv6 connections even after udp timeout

Also adds a test (auto_reconnect_test) which fails without this change.

CMakeLists.txt

@@ -427,6 +427,7 @@ auto_test(network)
 auto_test(onion)
 auto_test(overflow_recvq)
 auto_test(overflow_sendq)
+auto_test(reconnect)
 auto_test(save_friend)
 auto_test(save_load)
 auto_test(send_message)

auto_tests/Makefile.inc

@@ -24,6 +24,7 @@ TESTS = \
 	onion_test \
 	overflow_recvq_test \
 	overflow_sendq_test \
+	reconnect_test \
 	save_compatibility_test \
 	save_friend_test \
 	save_load_test \
@@ -154,6 +155,10 @@ overflow_sendq_test_SOURCES = ../auto_tests/overflow_sendq_test.c
 overflow_sendq_test_CFLAGS = $(AUTOTEST_CFLAGS)
 overflow_sendq_test_LDADD = $(AUTOTEST_LDADD)
 
+reconnect_test_SOURCES = ../auto_tests/reconnect_test.c
+reconnect_test_CFLAGS = $(AUTO_TEST_CFLAGS)
+reconnect_test_LDADD = $(AUTOTEST_LDADD)
+
 save_compatibility_test_SOURCES = ../auto_tests/save_compatibility_test.c
 save_compatibility_test_CFLAGS = $(AUTOTEST_CFLAGS)
 save_compatibility_test_LDADD = $(AUTOTEST_LDADD)

auto_tests/reconnect_test.c

@@ -0,0 +1,108 @@
+/* Auto Tests: Reconnection.
+ *
+ * This test checks that when a tox instance is suspended for long enough that
+ * its friend connections time out, those connections are promptly
+ * re-established when the instance is resumed.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#include "../testing/misc_tools.h"
+#include "../toxcore/friend_connection.h"
+#include "../toxcore/tox.h"
+#include "../toxcore/util.h"
+#include "check_compat.h"
+
+#define TOX_COUNT 2
+#define RECONNECT_TIME_MAX (FRIEND_CONNECTION_TIMEOUT + 3)
+
+typedef struct State {
+    uint32_t index;
+} State;
+
+#include "run_auto_test.h"
+
+static uint32_t tox_connected_count(uint32_t tox_count, Tox **toxes, State *state, uint32_t index)
+{
+    const size_t friend_count = tox_self_get_friend_list_size(toxes[index]);
+    uint32_t connected_count = 0;
+
+    for (size_t j = 0; j < friend_count; j++) {
+        if (tox_friend_get_connection_status(toxes[index], j, nullptr) != TOX_CONNECTION_NONE) {
+            ++connected_count;
+        }
+    }
+
+    return connected_count;
+}
+
+static bool all_disconnected_from(uint32_t tox_count, Tox **toxes, State *state, uint32_t index)
+{
+    for (uint32_t i = 0; i < tox_count; i++) {
+        if (i == index) {
+            continue;
+        }
+
+        if (tox_connected_count(tox_count, toxes, state, i) >= tox_count - 1) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+static void test_reconnect(Tox **toxes, State *state)
+{
+    const time_t test_start_time = time(nullptr);
+
+    printf("letting connections settle\n");
+
+    do {
+        iterate_all(TOX_COUNT, toxes, state);
+
+        c_sleep(ITERATION_INTERVAL);
+    } while (time(nullptr) - test_start_time < 2);
+
+    uint16_t disconnect = random_u16() % TOX_COUNT;
+    printf("disconnecting #%u\n", state[disconnect].index);
+
+    do {
+        for (uint16_t i = 0; i < TOX_COUNT; ++i) {
+            if (i != disconnect) {
+                tox_iterate(toxes[i], &state[i]);
+            }
+        }
+
+        c_sleep(ITERATION_INTERVAL);
+    } while (!all_disconnected_from(TOX_COUNT, toxes, state, disconnect));
+
+    const time_t reconnect_start_time = time(nullptr);
+
+    printf("reconnecting\n");
+
+    do {
+        iterate_all(TOX_COUNT, toxes, state);
+
+        c_sleep(ITERATION_INTERVAL);
+    } while (!all_friends_connected(TOX_COUNT, toxes));
+
+    const int reconnect_time = (int)(time(nullptr) - reconnect_start_time);
+    ck_assert_msg(reconnect_time <= RECONNECT_TIME_MAX, "reconnection took %d seconds; expected at most %d seconds",
+                  reconnect_time, RECONNECT_TIME_MAX);
+
+    printf("test_reconnect succeeded, took %d seconds\n", (int)(time(nullptr) - test_start_time));
+}
+
+int main(void)
+{
+    setvbuf(stdout, nullptr, _IONBF, 0);
+
+    run_auto_test(TOX_COUNT, test_reconnect);
+    return 0;
+}

toxcore/net_crypto.c

@@ -634,6 +634,9 @@ static IP_Port return_ip_port_connection(Net_Crypto *c, int crypt_connection_id)
         v6 = 1;
     }
 
+    /* Prefer IP_Ports which haven't timed out to those which have.
+     * To break ties, prefer ipv4 lan, then ipv6, then non-lan ipv4.
+     */
     if (v4 && ip_is_lan(conn->ip_portv4.ip)) {
         return conn->ip_portv4;
     }
@@ -642,6 +645,18 @@ static IP_Port return_ip_port_connection(Net_Crypto *c, int crypt_connection_id)
         return conn->ip_portv6;
     }
 
+    if (v4 && net_family_is_ipv4(conn->ip_portv4.ip.family)) {
+        return conn->ip_portv4;
+    }
+
+    if (ip_is_lan(conn->ip_portv4.ip)) {
+        return conn->ip_portv4;
+    }
+
+    if (net_family_is_ipv6(conn->ip_portv6.ip.family)) {
+        return conn->ip_portv6;
+    }
+
     if (net_family_is_ipv4(conn->ip_portv4.ip.family)) {
         return conn->ip_portv4;
     }