prop224: Add time period functions and unittests

This will be used by the build blinded key functions.

Signed-off-by: David Goulet <dgoulet@torproject.org>

3 files changed, 107 insertions, 1 deletions

diff --git a/src/or/hs_common.c b/src/or/hs_common.c
index 4af3081502..42508126f8 100644
--- a/src/or/hs_common.c
+++ b/src/or/hs_common.c
@@ -9,6 +9,8 @@
  *        protocol.
  **/
 
+#define HS_COMMON_PRIVATE
+
 #include "or.h"
 
 #include "config.h"
@@ -50,6 +52,46 @@ hs_check_service_private_dir(const char *username, const char *path,
   return 0;
 }
 
+/** Get the default HS time period length in minutes from the consensus. */
+STATIC uint64_t
+get_time_period_length(void)
+{
+  int32_t time_period_length = networkstatus_get_param(NULL, "hsdir-interval",
+                                             HS_TIME_PERIOD_LENGTH_DEFAULT,
+                                             HS_TIME_PERIOD_LENGTH_MIN,
+                                             HS_TIME_PERIOD_LENGTH_MAX);
+  /* Make sure it's a positive value. */
+  tor_assert(time_period_length >= 0);
+  /* uint64_t will always be able to contain a int32_t */
+  return (uint64_t) time_period_length;
+}
+
+/** Get the HS time period number at time <b>now</b> */
+STATIC uint64_t
+get_time_period_num(time_t now)
+{
+  uint64_t time_period_num;
+  uint64_t time_period_length = get_time_period_length();
+  uint64_t minutes_since_epoch = now / 60;
+
+  /* Now subtract half a day to fit the prop224 time period schedule (see
+   * section [TIME-PERIODS]). */
+  tor_assert(minutes_since_epoch > HS_TIME_PERIOD_ROTATION_OFFSET);
+  minutes_since_epoch -= HS_TIME_PERIOD_ROTATION_OFFSET;
+
+  /* Calculate the time period */
+  time_period_num = minutes_since_epoch / time_period_length;
+  return time_period_num;
+}
+
+/** Get the number of the _upcoming_ HS time period, given that the current
+ *  time is <b>now</b>. */
+uint64_t
+hs_get_next_time_period_num(time_t now)
+{
+  return get_time_period_num(now) + 1;
+}
+
 /* Create a new rend_data_t for a specific given <b>version</b>.
  * Return a pointer to the newly allocated data structure. */
 static rend_data_t *
diff --git a/src/or/hs_common.h b/src/or/hs_common.h
index d7d4228da2..a8fded652a 100644
--- a/src/or/hs_common.h
+++ b/src/or/hs_common.h
@@ -40,6 +40,15 @@
 /* String prefix for the signature of ESTABLISH_INTRO */
 #define ESTABLISH_INTRO_SIG_PREFIX "Tor establish-intro cell v1"
 
+/* The default HS time period length */
+#define HS_TIME_PERIOD_LENGTH_DEFAULT 1440 /* 1440 minutes == one day */
+/* The minimum time period length as seen in prop224 section [TIME-PERIODS] */
+#define HS_TIME_PERIOD_LENGTH_MIN 30 /* minutes */
+/* The minimum time period length as seen in prop224 section [TIME-PERIODS] */
+#define HS_TIME_PERIOD_LENGTH_MAX (60 * 24 * 10) /* 10 days or 14400 minutes */
+/* The time period rotation offset as seen in prop224 section [TIME-PERIODS] */
+#define HS_TIME_PERIOD_ROTATION_OFFSET (12 * 60) /* minutes */
+
 int hs_check_service_private_dir(const char *username, const char *path,
                                  unsigned int dir_group_readable,
                                  unsigned int create);
@@ -60,5 +69,18 @@ const char *rend_data_get_desc_id(const rend_data_t *rend_data,
 const uint8_t *rend_data_get_pk_digest(const rend_data_t *rend_data,
                                        size_t *len_out);
 
+uint64_t hs_get_next_time_period_num(time_t now);
+
+#ifdef HS_COMMON_PRIVATE
+
+#ifdef TOR_UNIT_TESTS
+
+STATIC uint64_t get_time_period_length(void);
+STATIC uint64_t get_time_period_num(time_t now);
+
+#endif /* TOR_UNIT_TESTS */
+
+#endif /* HS_COMMON_PRIVATE */
+
 #endif /* TOR_HS_COMMON_H */
 
diff --git a/src/test/test_hs_service.c b/src/test/test_hs_service.c
index ec9cc4579b..8207ddc160 100644
--- a/src/test/test_hs_service.c
+++ b/src/test/test_hs_service.c
@@ -6,6 +6,7 @@
  * \brief Test hidden service functionality.
  */
 
+#define HS_COMMON_PRIVATE
 #define HS_SERVICE_PRIVATE
 #define HS_INTROPOINT_PRIVATE
 
@@ -14,6 +15,7 @@
 #include "crypto.h"
 
 #include "hs/cell_establish_intro.h"
+#include "hs_common.h"
 #include "hs_service.h"
 #include "hs_intropoint.h"
 
@@ -196,12 +198,52 @@ test_hs_ntor(void *arg)
   ;
 }
 
+/** Test that our HS time period calculation functions work properly */
+static void
+test_time_period(void *arg)
+{
+  (void) arg;
+  unsigned int tn;
+  int retval;
+  time_t fake_time;
+
+  /* Let's do the example in prop224 section [TIME-PERIODS] */
+  retval = parse_rfc1123_time("Wed, 13 Apr 2016 11:00:00 UTC",
+                              &fake_time);
+  tt_int_op(retval, ==, 0);
+
+  /* Check that the time period number is right */
+  tn = get_time_period_num(fake_time);
+  tt_int_op(tn, ==, 16903);
+
+  /* Increase current time to 11:59:59 UTC and check that the time period
+     number is still the same */
+  fake_time += 3599;
+  tn = get_time_period_num(fake_time);
+  tt_int_op(tn, ==, 16903);
+
+  /* Now take time to 12:00:00 UTC and check that the time period rotated */
+  fake_time += 1;
+  tn = get_time_period_num(fake_time);
+  tt_int_op(tn, ==, 16904);
+
+  /* Now also check our hs_get_next_time_period_num() function */
+  tn = hs_get_next_time_period_num(fake_time);
+  tt_int_op(tn, ==, 16905);
+
+ done:
+  ;
+}
+
 struct testcase_t hs_service_tests[] = {
   { "gen_establish_intro_cell", test_gen_establish_intro_cell, TT_FORK,
     NULL, NULL },
   { "gen_establish_intro_cell_bad", test_gen_establish_intro_cell_bad, TT_FORK,
     NULL, NULL },
-  { "hs_ntor", test_hs_ntor, TT_FORK, NULL, NULL },
+  { "hs_ntor", test_hs_ntor, TT_FORK,
+    NULL, NULL },
+  { "time_period", test_time_period, TT_FORK,
+    NULL, NULL },
 
   END_OF_TESTCASES
 };