introduce fbclock_gettime_utc

Summary: Add method to get time in UTC. For now, simply apply known offset.

Reviewed By: leoleovich

Differential Revision: D51116026

fbshipit-source-id: 8ad1e08eb9b0f7cb0c103c6cfc4becc98575cb81

fbclock/cpp_test/test.cpp

@@ -193,6 +193,18 @@ TEST(fbclock_test, test_fbclock_calculate_time) {
   EXPECT_EQ(truetime.latest_ns, 1647290691804195223);
 }
 
+TEST(fbclock_test, test_fbclock_apply_utc_offset) {
+  int err;
+  fbclock_truetime truetime;
+  truetime.earliest_ns = 1647269091803102338;
+  truetime.latest_ns = 1647269091803103576;
+
+  fbclock_apply_utc_offset(&truetime);
+
+  EXPECT_EQ(truetime.earliest_ns, 1647269054803102338);
+  EXPECT_EQ(truetime.latest_ns, 1647269054803103576);
+}
+
 int main(int argc, char** argv) {
   ::testing::InitGoogleTest(&argc, argv);
   return RUN_ALL_TESTS();

fbclock/fbclock.c

@@ -221,6 +221,24 @@ int fbclock_gettime(fbclock_lib* lib, fbclock_truetime* truetime) {
       error_bound, h_value, state.ingress_time_ns, res.ts, truetime);
 }
 
+void fbclock_apply_utc_offset(fbclock_truetime* truetime) {
+  truetime->earliest_ns += UTC_TAI_OFFSET;
+  truetime->latest_ns += UTC_TAI_OFFSET;
+}
+
+// When/if new leap second is announced, we would need to update this function
+// to do smearing, and fetch offset from fbclock daemon.
+// For now, we apply the offset, as leap seconds will be abandoned by 2035
+// and it is possible we won't have any at all.
+int fbclock_gettime_utc(fbclock_lib* lib, fbclock_truetime* truetime) {
+  int rcode = fbclock_gettime(lib, truetime);
+  if (rcode != 0) {
+    return rcode;
+  }
+  fbclock_apply_utc_offset(truetime);
+  return 0;
+}
+
 const char* fbclock_strerror(int err_code) {
   const char* err_info = "unknown error";
   switch (err_code) {

fbclock/fbclock.go

@@ -87,3 +87,17 @@ func (f *FBClock) GetTime() (*TrueTime, error) {
 
 	return &TrueTime{Earliest: earliest, Latest: latest}, nil
 }
+
+// GetTimeUTC returns TrueTime in UTC
+func (f *FBClock) GetTimeUTC() (*TrueTime, error) {
+	tt := &C.fbclock_truetime{}
+	errCode := C.fbclock_gettime_utc(f.cFBClock, tt)
+	if errCode != 0 {
+		return nil, fmt.Errorf("reading FBClock TrueTime UTC: %s", strerror(errCode))
+	}
+
+	earliest := time.Unix(0, int64(tt.earliest_ns))
+	latest := time.Unix(0, int64(tt.latest_ns))
+
+	return &TrueTime{Earliest: earliest, Latest: latest}, nil
+}

fbclock/fbclock.h

@@ -35,6 +35,9 @@ typedef atomic_uint_fast64_t atomic_uint64;
 #define FBCLOCK_E_WOU_TOO_BIG -6
 #define FBCLOCK_E_PHC_IN_THE_PAST -7
 
+// until new leap second is introduced, UTC is exactly 37 seconds behind TAI
+#define UTC_TAI_OFFSET (int64_t)(-37e9)
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -85,11 +88,13 @@ int fbclock_calculate_time(
     int64_t ingress_time_ns,
     int64_t phctime_ns,
     fbclock_truetime* truetime);
+void fbclock_apply_utc_offset(fbclock_truetime* truetime);
 
 // methods we provide to end users
 int fbclock_init(fbclock_lib* lib, const char* shm_path);
 int fbclock_destroy(fbclock_lib* lib);
 int fbclock_gettime(fbclock_lib* lib, fbclock_truetime* truetime);
+int fbclock_gettime_utc(fbclock_lib* lib, fbclock_truetime* truetime);
 // turn error code into err msg
 const char* fbclock_strerror(int err_code);