Relax stop validation conditions

src/main/java/de/rwth/idsg/steve/service/CentralSystemService16_ServiceValidator.java

@@ -48,7 +48,7 @@ public class CentralSystemService16_ServiceValidator {
     private static final DateTime MAX = new DateTime(Long.MAX_VALUE);
 
     private final Clock clock;
-    private final Duration operationalDeltaForNow;
+    private final Duration operationalDelta;
 
     @Autowired
     public CentralSystemService16_ServiceValidator(Clock clock) {
@@ -64,7 +64,7 @@ public SteveException validateStart(StartTransactionRequest params) {
             return new SteveException("StartTransaction.meterStart must not be negative");
         }
 
-        if (params.getTimestamp().getMillis() > clock.instant().plus(operationalDeltaForNow).toEpochMilli()) {
+        if (params.getTimestamp().getMillis() > clock.instant().plus(operationalDelta).toEpochMilli()) {
             return new SteveException("StartTransaction.timestamp is in the future");
         }
 
@@ -88,7 +88,7 @@ public SteveException validateStop(TransactionRecord thisTx, StopTransactionRequ
             return new SteveException("start.timestamp is after stop.timestamp");
         }
 
-        if (stopParams.getTimestamp().getMillis() > clock.instant().plus(operationalDeltaForNow).toEpochMilli()) {
+        if (stopParams.getTimestamp().getMillis() > clock.instant().plus(operationalDelta).toEpochMilli()) {
             return new SteveException("stop.timestamp is in the future");
         }
 
@@ -145,19 +145,22 @@ private SteveException validateMeterValuesInternal(List<MeterValue> meterValues,
             return new SteveException("MeterValue.timestamp is empty");
         }
 
-        if (latest.getMillis() > clock.instant().plus(operationalDeltaForNow).toEpochMilli()) {
+        // allow operational delta tolerance for the following timestamp checks, since charge points
+        // may have slight clock drift and meter values can be sampled a little bit later or before
+        // our reference point.
+        long deltaMillis = operationalDelta.toMillis();
+
+        if (latest.getMillis() > clock.instant().toEpochMilli() + deltaMillis) {
             return new SteveException("at least one MeterValue.timestamp is in the future");
         }
 
-        if (stopTimestamp != null && latest.isAfter(stopTimestamp)) {
-            return new SteveException("at least one MeterValue.timestamp is after stop.timestamp");
+        if (stopTimestamp != null) {
+            if (latest.getMillis() > stopTimestamp.getMillis() + deltaMillis) {
+                return new SteveException("at least one MeterValue.timestamp is after stop.timestamp");
+            }
         }
 
-        // allow the same operational delta tolerance for start timestamp check, since charge points
-        // may have slight clock drift and meter values can be sampled before the StartTransaction
-        // message is processed on the server side
         if (startTimestamp != null) {
-            long deltaMillis = operationalDeltaForNow.toMillis();
             if (earliest.getMillis() < startTimestamp.getMillis() - deltaMillis) {
                 return new SteveException("at least one MeterValue.timestamp is before start.timestamp");
             }

src/test/java/de/rwth/idsg/steve/service/CentralSystemService16ServiceValidatorTest.java

@@ -209,9 +209,10 @@ public void validateStop_transactionDataFutureTimestamp_returnsError() {
 
     @Test
     public void validateStop_transactionDataAfterStopTimestamp_returnsError() {
+        // more than 5 minutes (operational delta) after stop
         var tx = tx("100", DateTime.parse("2026-02-17T09:00:00Z"), null, null, null);
         var params = stopParams(DateTime.parse("2026-02-17T10:00:00Z"), "200")
-            .withTransactionData(List.of(meterValue("2026-02-17T10:00:01Z")));
+            .withTransactionData(List.of(meterValue("2026-02-17T10:10:00Z")));
         var result = validator.validateStop(tx, params);
 
         Assertions.assertNotNull(result);
@@ -251,6 +252,22 @@ public void validateStop_transactionDataAtStartTimestamp_isAllowed() {
         Assertions.assertNull(result);
     }
 
+    /**
+     * this behavior is coming from a real station in the field: the latest of meterValues is 1 second
+     * after stopTimestamp, because the station sampled stop timestamp first, and then later the timestamp
+     * for this meterValue entry.
+     */
+    @Test
+    public void validateStop_transactionDataOneSecondAfterStop_isAllowed() {
+        var tx = tx("100", DateTime.parse("2026-02-17T09:00:00Z"), null, null, null);
+
+        var params = stopParams(DateTime.parse("2026-02-17T10:00:00Z"), "200")
+            .withTransactionData(List.of(meterValue("2026-02-17T10:00:01Z")));
+        var result = validator.validateStop(tx, params);
+
+        Assertions.assertNull(result);
+    }
+
     @Test
     public void validateMeterValues_timestampsOutOfOrder_returnsError() {
         var result = validator.validateMeterValues(meterValuesParams(1, List.of(