Throw an EPP exception when using discount on premium domains (#351)

We should communicate to the users why this command failed, that they
are not allowed to use discounted allocation tokens on premium domains.
Currently it still fails, but we don't yet tell them why.

core/src/main/java/google/registry/flows/domain/DomainCreateFlow.java

@@ -187,6 +187,7 @@ import org.joda.time.Duration;
  * @error {@link DomainFlowUtils.UnexpectedClaimsNoticeException}
  * @error {@link DomainFlowUtils.UnsupportedFeeAttributeException}
  * @error {@link DomainFlowUtils.UnsupportedMarkTypeException}
+ * @error {@link DomainPricingLogic.AllocationTokenInvalidForPremiumNameException}
  */
 @ReportingSpec(ActivityReportField.DOMAIN_CREATE)
 public class DomainCreateFlow implements TransactionalFlow {

core/src/main/java/google/registry/flows/domain/DomainPricingLogic.java

@@ -14,12 +14,12 @@
 
 package google.registry.flows.domain;
 
-import static com.google.common.base.Preconditions.checkArgument;
 import static google.registry.pricing.PricingEngineProxy.getDomainFeeClass;
 import static google.registry.pricing.PricingEngineProxy.getDomainRenewCost;
 
 import com.google.common.net.InternetDomainName;
 import google.registry.flows.EppException;
+import google.registry.flows.EppException.CommandUseErrorException;
 import google.registry.flows.FlowScope;
 import google.registry.flows.custom.DomainPricingCustomLogic;
 import google.registry.flows.custom.DomainPricingCustomLogic.CreatePriceParameters;
@@ -182,13 +182,14 @@ public final class DomainPricingLogic {
   }
 
   private Money getDomainCreateCostWithDiscount(
-      String domainName, DateTime date, int years, Optional<AllocationToken> allocationToken) {
+      String domainName, DateTime date, int years, Optional<AllocationToken> allocationToken)
+      throws EppException {
     DomainPrices domainPrices = PricingEngineProxy.getPricesForDomainName(domainName, date);
-    checkArgument(
-        !allocationToken.isPresent()
-            || allocationToken.get().getDiscountFraction() == 0.0
-            || !domainPrices.isPremium(),
-        "A nonzero discount code cannot be applied to premium domains");
+    if (allocationToken.isPresent()
+        && allocationToken.get().getDiscountFraction() != 0.0
+        && domainPrices.isPremium()) {
+      throw new AllocationTokenInvalidForPremiumNameException();
+    }
     Money oneYearCreateCost = domainPrices.getCreateCost();
     Money totalDomainCreateCost = oneYearCreateCost.multipliedBy(years);
     // If a discount is applicable, apply it only to the first year
@@ -200,4 +201,12 @@ public final class DomainPricingLogic {
     }
     return totalDomainCreateCost;
   }
+
+  /** An allocation token was provided that is invalid for premium domains. */
+  public static class AllocationTokenInvalidForPremiumNameException
+      extends CommandUseErrorException {
+    public AllocationTokenInvalidForPremiumNameException() {
+      super("A nonzero discount code cannot be applied to premium domains");
+    }
+  }
 }

core/src/test/java/google/registry/flows/domain/DomainCreateFlowTest.java

@@ -129,6 +129,7 @@ import google.registry.flows.domain.DomainFlowUtils.TrailingDashException;
 import google.registry.flows.domain.DomainFlowUtils.UnexpectedClaimsNoticeException;
 import google.registry.flows.domain.DomainFlowUtils.UnsupportedFeeAttributeException;
 import google.registry.flows.domain.DomainFlowUtils.UnsupportedMarkTypeException;
+import google.registry.flows.domain.DomainPricingLogic.AllocationTokenInvalidForPremiumNameException;
 import google.registry.flows.domain.token.AllocationTokenFlowUtils.AllocationTokenNotInPromotionException;
 import google.registry.flows.domain.token.AllocationTokenFlowUtils.AllocationTokenNotValidForRegistrarException;
 import google.registry.flows.domain.token.AllocationTokenFlowUtils.AllocationTokenNotValidForTldException;
@@ -1227,9 +1228,9 @@ public class DomainCreateFlowTest extends ResourceFlowTestCase<DomainCreateFlow,
             .build());
     clock.advanceOneMilli();
     setEppInput("domain_create_premium_allocationtoken.xml");
-    assertThat(assertThrows(IllegalArgumentException.class, this::runFlow))
-        .hasMessageThat()
-        .isEqualTo("A nonzero discount code cannot be applied to premium domains");
+    assertAboutEppExceptions()
+        .that(assertThrows(AllocationTokenInvalidForPremiumNameException.class, this::runFlow))
+        .marshalsToXml();
   }
 
   @Test

docs/flows.md

@@ -302,6 +302,7 @@ An EPP flow that creates a new domain resource.
     *   The current registry phase allows registrations only with signed marks.
     *   The current registry phase does not allow for general registrations.
     *   Signed marks are only allowed during sunrise.
+    *   An allocation token was provided that is invalid for premium domains.
 *   2003
     *   The provided mark does not match the desired domain label.
     *   Fees must be explicitly acknowledged when creating domains during the