Ensure millis precision in timestamps of outgoing messages

ISO8601 does not specify that fractional seconds shall be omitted if
given. Enforce that an on full seconds, the millis resolution is
retained for outgoing messages and that incoming messages of any
precision can be parsed.

On incoming messages with...
* ...seconds precision, assume that millis are zero.
* ...millis precision, assume that micros are zero.
* ...micros precision, assume that nanos are zero.

This retains proper timestamp comparison.

Author: TomMarkuske

OCPP-J/src/main/java/eu/chargetime/ocpp/JSONCommunicator.java

@@ -9,6 +9,8 @@
 import java.lang.reflect.Type;
 import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeFormatterBuilder;
+import java.time.format.ResolverStyle;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -46,6 +48,16 @@ public class JSONCommunicator extends Communicator {
 
   private static final Logger logger = LoggerFactory.getLogger(JSONCommunicator.class);
 
+  /**
+   * a derivation of ISO_INSTANT that always serializes to three millisecond digits, even if zero
+   */
+  public static final DateTimeFormatter ISO_INSTANT_WITH_MILLIS_PRECISION =
+      new DateTimeFormatterBuilder()
+          .parseCaseInsensitive()
+          .appendInstant(3)
+          .toFormatter()
+          .withResolverStyle(ResolverStyle.STRICT);
+
   private static final int INDEX_MESSAGEID = 0;
   private static final int TYPENUMBER_CALL = 2;
   private static final int INDEX_CALL_ACTION = 2;
@@ -94,7 +106,7 @@ private static class ZonedDateTimeSerializer
     @Override
     public JsonElement serialize(
         ZonedDateTime zonedDateTime, Type type, JsonSerializationContext jsonSerializationContext) {
-      return new JsonPrimitive(zonedDateTime.format(DateTimeFormatter.ISO_INSTANT));
+      return new JsonPrimitive(zonedDateTime.format(ISO_INSTANT_WITH_MILLIS_PRECISION));
     }
 
     @Override

ocpp-v1_6/src/test/java/eu/chargetime/ocpp/test/JSONCommunicatorTest.java

@@ -102,6 +102,22 @@ public void unpackPayload_aCalendarPayload_returnsTestModelWithACalendar() throw
     assertThat(model.getCalendarTest().compareTo(someDate), is(0));
   }
 
+  @Test
+  public void unpackPayload_aCalendarPayload_parsesNoFractionalAsZeroFractional() throws Exception {
+    // Given
+    String aCalendar = "2016-04-28T07:16:11Z";
+    String payload = "{\"calendarTest\":\"%s\"}";
+
+    ZonedDateTime someDate = ZonedDateTime.parse("2016-04-28T07:16:11.000Z");
+
+    // When
+    TestModel model =
+        communicator.unpackPayload(String.format(payload, aCalendar), TestModel.class);
+
+    // Then
+    assertThat(model.getCalendarTest().compareTo(someDate), is(0));
+  }
+
   @Test
   public void unpackPayload_anIntegerPayload_returnsTestModelWithAnInteger() throws Exception {
     // Given
@@ -276,6 +292,24 @@ public void pack_bootNotificationRequest_returnsBootNotificationRequestPayload()
     assertThat(payload, equalTo(expected));
   }
 
+  @Test
+  public void pack_bootNotificationConfirmation_limitsTimeFractionalDigitsToThree()
+      throws Exception {
+    // Given
+    String expected =
+        "{\"currentTime\":\"2016-04-28T06:41:13.123Z\",\"interval\":300,\"status\":\"Accepted\"}";
+    BootNotificationConfirmation confirmation = new BootNotificationConfirmation();
+    confirmation.setCurrentTime(createDateTimeInNanos(1461825673123456789L)); // will be truncated
+    confirmation.setInterval(300);
+    confirmation.setStatus(RegistrationStatus.Accepted);
+
+    // When
+    Object payload = communicator.packPayload(confirmation);
+
+    // Then
+    assertThat(payload, equalTo(expected));
+  }
+
   @Test
   public void pack_bootNotificationConfirmation_returnsBootNotificationConfirmationPayload()
       throws Exception {
@@ -294,6 +328,24 @@ public void pack_bootNotificationConfirmation_returnsBootNotificationConfirmatio
     assertThat(payload, equalTo(expected));
   }
 
+  @Test
+  public void pack_bootNotificationConfirmation_alwaysFormatsTimeWithThreeFractionalDigits()
+      throws Exception {
+    // Given
+    String expected =
+        "{\"currentTime\":\"2016-04-28T06:41:13.000Z\",\"interval\":300,\"status\":\"Accepted\"}";
+    BootNotificationConfirmation confirmation = new BootNotificationConfirmation();
+    confirmation.setCurrentTime(createDateTimeInMillis(1461825673000L)); // will not be truncated
+    confirmation.setInterval(300);
+    confirmation.setStatus(RegistrationStatus.Accepted);
+
+    // When
+    Object payload = communicator.packPayload(confirmation);
+
+    // Then
+    assertThat(payload, equalTo(expected));
+  }
+
   @Test
   public void disconnect_disconnects() {
     // When
@@ -319,4 +371,9 @@ public void sendError_transmitsError() throws Exception {
   private ZonedDateTime createDateTimeInMillis(long dateInMillis) {
     return Instant.ofEpochMilli(dateInMillis).atOffset(ZoneOffset.UTC).toZonedDateTime();
   }
+
+  private ZonedDateTime createDateTimeInNanos(long dateInNanos) {
+    return Instant.ofEpochSecond(dateInNanos / 1000000000, dateInNanos % 1000000000)
+        .atOffset(ZoneOffset.UTC).toZonedDateTime();
+  }
 }