Fix request's received_time (#459)

* Use std::chrono for the request received_time.

* Update Development/nmos/api_utils.cpp

* Update Development/nmos/tai.h

* Update links

---------

Co-authored-by: jonathan-r-thorpe <64410119+jonathan-r-thorpe@users.noreply.github.com>

Author: lo-simon

Development/nmos/api_utils.cpp

@@ -701,7 +701,15 @@ namespace nmos
         add_api_finally_handler(api_, hsts, gate);
         auto api = [api_, &gate](web::http::http_request req) mutable
         {
+            // hmm, in Windows, the boost version of the time_point::now sometimes returns the same value after a small time increment.
+            // This issue does not seem to happen in the std::chrono implementation.
+#if defined(_WIN32) && defined (BST_THREAD_BOOST)
+            // calculate received_time using std::chrono
+            const auto now = tai_clock::time_point(tai_clock::duration(std::chrono::system_clock::now().time_since_epoch().count() + tai_clock::tai_offset().count()));
+            req.headers().add(details::received_time, nmos::make_version(tai_from_time_point(now)));
+#else
             req.headers().add(details::received_time, nmos::make_version());
+#endif
             slog::log<slog::severities::too_much_info>(gate, SLOG_FLF)
                 << stash_remote_address(req.remote_address())
                 << stash_http_method(req.method())

Development/nmos/tai.h

@@ -28,7 +28,7 @@ namespace nmos
         // tai_clock::time_point (or tai_clock::duration, since NMOS uses relative timestamps in a few places)
     };
 
-    // tai_clock is a std::chrono Clock for generating and manipulating tai timestamps
+    // tai_clock is a bst::chrono Clock for generating and manipulating tai timestamps
     struct tai_clock
     {
         // "It is suggested (although not mandated) that these timestamps are stored with nanosecond resolution."
@@ -46,6 +46,9 @@ namespace nmos
         // time points; nmos::strictly_increasing_update is used to prevent duplicate values in nmos::resources
         static const bool is_steady = bst::chrono::system_clock::is_steady;
 
+        // UTC is 37 seconds behind TAI; see comments below for details
+        static const duration tai_offset() { return bst::chrono::seconds(37); }
+
         static time_point now()
         {
             // "NMOS specifications shall use the PTP/SMPTE Epoch, i.e. 1 January 1970 00:00:00 TAI."
@@ -69,11 +72,9 @@ namespace nmos
             // and https://en.wikipedia.org/wiki/International_Atomic_Time
             // and https://github.com/HowardHinnant/date/issues/129
             // and https://cr.yp.to/proto/utctai.html
-            // and https://www.iers.org/SharedDocs/News/EN/BulletinC.html
-            // and https://www.ietf.org/timezones/data/leap-seconds.list
-            static const duration tai_offset = bst::chrono::seconds(37);
-
-            return time_point(tai_offset + bst::chrono::system_clock::now().time_since_epoch());
+            // and https://datacenter.iers.org/data/latestVersion/bulletinC.txt
+            // and https://data.iana.org/time-zones/data/leap-seconds.list
+            return time_point(tai_offset() + bst::chrono::system_clock::now().time_since_epoch());
         }
     };