Distinguish true clock jumps from idleness

Since we're going to be disabling the second-elapsed callback, we're
going to sometimes have long periods when no events file, and so the
current second is not updated.  Handle that by having a better means
to detect "clock jumps" as opposed to "being idle for a while".
Tolerate far more of the latter.

Part of #26009.

src/test/test_mainloop.c

@@ -12,13 +12,19 @@
 #include "or.h"
 #include "main.h"
 
+static const uint64_t BILLION = 1000000000;
+
 static void
 test_mainloop_update_time_normal(void *arg)
 {
   (void)arg;
 
+  monotime_enable_test_mocking();
+  /* This is arbitrary */
+  uint64_t mt_now = U64_LITERAL(7493289274986);
   /* This time is in the past as of when this test was written. */
   time_t now = 1525272090;
+  monotime_coarse_set_mock_time_nsec(mt_now);
   reset_uptime();
   update_current_time(now);
   tt_int_op(approx_time(), OP_EQ, now);
@@ -28,12 +34,16 @@ test_mainloop_update_time_normal(void *arg)
   tt_int_op(get_uptime(), OP_EQ, 0);
 
   now += 1;
+  mt_now += BILLION;
+  monotime_coarse_set_mock_time_nsec(mt_now);
   update_current_time(now);
   tt_int_op(approx_time(), OP_EQ, now);
   tt_int_op(get_uptime(), OP_EQ, 1);
 
   now += 2; // two-second jump is unremarkable.
+  mt_now += 2*BILLION;
   update_current_time(now);
+  monotime_coarse_set_mock_time_nsec(mt_now);
   tt_int_op(approx_time(), OP_EQ, now);
   tt_int_op(get_uptime(), OP_EQ, 3);
 
@@ -43,7 +53,7 @@ test_mainloop_update_time_normal(void *arg)
   tt_int_op(get_uptime(), OP_EQ, 3); // but it doesn't roll back our uptime
 
  done:
-  ;
+  monotime_disable_test_mocking();
 }
 
 static void
@@ -51,8 +61,12 @@ test_mainloop_update_time_jumps(void *arg)
 {
   (void)arg;
 
+  monotime_enable_test_mocking();
+  /* This is arbitrary */
+  uint64_t mt_now = U64_LITERAL(7493289274986);
   /* This time is in the past as of when this test was written. */
   time_t now = 220897152;
+  monotime_coarse_set_mock_time_nsec(mt_now);
   reset_uptime();
   update_current_time(now);
   tt_int_op(approx_time(), OP_EQ, now);
@@ -60,16 +74,19 @@ test_mainloop_update_time_jumps(void *arg)
 
   /* Put some uptime on the clock.. */
   now += 3;
+  mt_now += 3*BILLION;
+  monotime_coarse_set_mock_time_nsec(mt_now);
   update_current_time(now);
   tt_int_op(approx_time(), OP_EQ, now);
   tt_int_op(get_uptime(), OP_EQ, 3);
 
-  /* Now try jumping forward. */
+  /* Now try jumping forward and backward, without updating the monotonic
+   * clock.  */
   setup_capture_of_logs(LOG_NOTICE);
-  now += 3600;
+  now += 1800;
   update_current_time(now);
   expect_single_log_msg_containing(
-               "Your system clock just jumped 3600 seconds forward");
+               "Your system clock just jumped 1800 seconds forward");
   tt_int_op(approx_time(), OP_EQ, now);
   tt_int_op(get_uptime(), OP_EQ, 3); // no uptime change.
   mock_clean_saved_logs();
@@ -80,15 +97,38 @@ test_mainloop_update_time_jumps(void *arg)
                "Your system clock just jumped 600 seconds backward");
   tt_int_op(approx_time(), OP_EQ, now);
   tt_int_op(get_uptime(), OP_EQ, 3); // no uptime change.
+  mock_clean_saved_logs();
 
   /* uptime tracking should go normally now if the clock moves sensibly. */
   now += 2;
+  mt_now += 2*BILLION;
   update_current_time(now);
   tt_int_op(approx_time(), OP_EQ, now);
   tt_int_op(get_uptime(), OP_EQ, 5);
 
+  /* If we skip forward by a few minutes but the monotonic clock agrees,
+   * we've just been idle: that counts as not worth warning about. */
+  now += 1800;
+  mt_now += 1800*BILLION;
+  monotime_coarse_set_mock_time_nsec(mt_now);
+  update_current_time(now);
+  expect_no_log_entry();
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 5); // this doesn't count to uptime, though.
+
+  /* If we skip forward by a long time, even if the clock agrees, it's
+   * idnless that counts. */
+  now += 4000;
+  mt_now += 4000*BILLION;
+  monotime_coarse_set_mock_time_nsec(mt_now);
+  update_current_time(now);
+  expect_single_log_msg_containing("Tor has been idle for 4000 seconds");
+  tt_int_op(approx_time(), OP_EQ, now);
+  tt_int_op(get_uptime(), OP_EQ, 5);
+
  done:
   teardown_capture_of_logs();
+  monotime_disable_test_mocking();
 }
 
 #define MAINLOOP_TEST(name) \