Merge bitcoin#21110: util: remove Boost posix_time usage from GetTime*

9266f74 util: Use std::chrono for time getters (MarcoFalke)
3c2e16b time: add runtime sanity check (Cory Fields)

Pull request description:

  I have a followup that should remove the last of our `boost:posix_time` usage in `ParseISO8601DateTime`, but that will likely need more cross-platform testing/discussion, so have just split them up as this change is straight forward.

ACKs for top commit:
  practicalswift:
    Tested ACK 9266f74
  laanwj:
    Code review ACK 9266f74

Tree-SHA512: 5471a60e65e9fa8ef48320743ef637f1d162724e717e0f5509118e1e5732fc0844656a9c09d3d1300eb657dcc7a1e1e67305d8c9ef959c63be67393607dd4ceb

Author: laanwj

src/init.cpp

@@ -773,6 +773,10 @@ static bool InitSanityCheck()
         return InitError(Untranslated("OS cryptographic RNG sanity check failure. Aborting."));
     }
 
+    if (!ChronoSanityCheck()) {
+        return InitError(Untranslated("Clock epoch mismatch. Aborting."));
+    }
+
     return true;
 }
 

src/test/sanity_tests.cpp

@@ -5,6 +5,7 @@
 #include <compat/sanity.h>
 #include <key.h>
 #include <test/util/setup_common.h>
+#include <util/time.h>
 
 #include <boost/test/unit_test.hpp>
 
@@ -15,6 +16,7 @@ BOOST_AUTO_TEST_CASE(basic_sanity)
   BOOST_CHECK_MESSAGE(glibc_sanity_test() == true, "libc sanity test");
   BOOST_CHECK_MESSAGE(glibcxx_sanity_test() == true, "stdlib sanity test");
   BOOST_CHECK_MESSAGE(ECC_InitSanityCheck() == true, "secp256k1 sanity test");
+  BOOST_CHECK_MESSAGE(ChronoSanityCheck() == true, "chrono epoch test");
 }
 
 BOOST_AUTO_TEST_SUITE_END()

src/util/time.cpp

@@ -33,6 +33,49 @@ int64_t GetTime()
     return now;
 }
 
+bool ChronoSanityCheck()
+{
+    // std::chrono::system_clock.time_since_epoch and time_t(0) are not guaranteed
+    // to use the Unix epoch timestamp, prior to C++20, but in practice they almost
+    // certainly will. Any differing behavior will be assumed to be an error, unless
+    // certain platforms prove to consistently deviate, at which point we'll cope
+    // with it by adding offsets.
+
+    // Create a new clock from time_t(0) and make sure that it represents 0
+    // seconds from the system_clock's time_since_epoch. Then convert that back
+    // to a time_t and verify that it's the same as before.
+    const time_t time_t_epoch{};
+    auto clock = std::chrono::system_clock::from_time_t(time_t_epoch);
+    if (std::chrono::duration_cast<std::chrono::seconds>(clock.time_since_epoch()).count() != 0) {
+        return false;
+    }
+
+    time_t time_val = std::chrono::system_clock::to_time_t(clock);
+    if (time_val != time_t_epoch) {
+        return false;
+    }
+
+    // Check that the above zero time is actually equal to the known unix timestamp.
+    struct tm epoch;
+#ifdef HAVE_GMTIME_R
+    if (gmtime_r(&time_val, &epoch) == nullptr) {
+#else
+    if (gmtime_s(&epoch, &time_val) != 0) {
+#endif
+        return false;
+    }
+
+    if ((epoch.tm_sec != 0)  ||
+       (epoch.tm_min  != 0)  ||
+       (epoch.tm_hour != 0)  ||
+       (epoch.tm_mday != 1)  ||
+       (epoch.tm_mon  != 0)  ||
+       (epoch.tm_year != 70)) {
+        return false;
+    }
+    return true;
+}
+
 template <typename T>
 T GetTime()
 {
@@ -47,6 +90,14 @@ template std::chrono::seconds GetTime();
 template std::chrono::milliseconds GetTime();
 template std::chrono::microseconds GetTime();
 
+template <typename T>
+static T GetSystemTime()
+{
+    const auto now = std::chrono::duration_cast<T>(std::chrono::system_clock::now().time_since_epoch());
+    assert(now.count() > 0);
+    return now;
+}
+
 void SetMockTime(int64_t nMockTimeIn)
 {
     Assert(nMockTimeIn >= 0);
@@ -65,23 +116,17 @@ std::chrono::seconds GetMockTime()
 
 int64_t GetTimeMillis()
 {
-    int64_t now = (boost::posix_time::microsec_clock::universal_time() -
-                   boost::posix_time::ptime(boost::gregorian::date(1970,1,1))).total_milliseconds();
-    assert(now > 0);
-    return now;
+    return int64_t{GetSystemTime<std::chrono::milliseconds>().count()};
 }
 
 int64_t GetTimeMicros()
 {
-    int64_t now = (boost::posix_time::microsec_clock::universal_time() -
-                   boost::posix_time::ptime(boost::gregorian::date(1970,1,1))).total_microseconds();
-    assert(now > 0);
-    return now;
+    return int64_t{GetSystemTime<std::chrono::microseconds>().count()};
 }
 
 int64_t GetSystemTimeInSeconds()
 {
-    return GetTimeMicros()/1000000;
+    return int64_t{GetSystemTime<std::chrono::seconds>().count()};
 }
 
 std::string FormatISO8601DateTime(int64_t nTime) {

src/util/time.h

@@ -79,4 +79,7 @@ struct timeval MillisToTimeval(int64_t nTimeout);
  */
 struct timeval MillisToTimeval(std::chrono::milliseconds ms);
 
+/** Sanity check epoch match normal Unix epoch */
+bool ChronoSanityCheck();
+
 #endif // BITCOIN_UTIL_TIME_H