added UTC-compatible time zone coercion to null

Author: Crypt32

Asn1Parser/Utils/DateTimeUtils.cs

@@ -19,6 +19,7 @@ public static Byte[] Encode(DateTime time, TimeZoneInfo? zone, Boolean UTC, Bool
             // it was requested. See ITU-T X.690, section 11.7
             suffix += (time.Millisecond / 1000d).ToString(CultureInfo.InvariantCulture).Substring(1);
         }
+        zone = coerceTimeZone(zone);
         if (zone == null) {
             preValue = time.ToUniversalTime().ToString(format) + suffix + "Z";
         } else {
@@ -46,7 +47,15 @@ public static DateTime Decode(Asn1Reader asn, out TimeZoneInfo? zone) {
 
         return extractDateTime(SB.ToString(), out zone);
     }
-
+    
+    static TimeZoneInfo? coerceTimeZone(TimeZoneInfo? zone) {
+        // if zone is explicitly specified, but its offset against UTC is zero, we do not encode zone.
+        if ((zone?.BaseUtcOffset.TotalMinutes ?? 0) == 0) {
+            return null;
+        }
+        
+        return zone;
+    }
     static DateTime extractDateTime(String strValue, out TimeZoneInfo? zone) {
         zone = null;
         Boolean hasZone = extractZoneShift(strValue, out Int32 hours, out Int32 minutes, out Int32 zoneDelimiter);

tests/Asn1Parser.Tests/Asn1DateTimeTests.cs

@@ -13,6 +13,7 @@ public class Asn1DateTimeTests {
     public void TestZuluSimple() {
         var dt = DateTime.ParseExact("2024-08-07 16:12:37", "yyyy-MM-dd HH:mm:ss", null);
         var gt = new Asn1GeneralizedTime(dt);
+        Assert.AreEqual(DateTimeKind.Local, gt.Value.Kind);
         assertDateTimeEncode(Asn1Type.GeneralizedTime, gt, dt, "yyyyMMddHHmmssZ");
     }
     [TestMethod, Description("Test date/time with fractions and fraction is zero")]