Redirect an empty RDAP path to the /help response

The behavior when someone hits the plain RDAP base URL isn't specified
by the spec. Currently we just return a plain 404 which isn't
particularly nice or helpful -- so it would probably be nicer to just
redirect to the /help response instead.

tested on alpha,
https://pubapi-dot-domain-registry-alpha.appspot.com/rdap redirects to https://pubapi-dot-domain-registry-alpha.appspot.com/rdap/help

Author: gbrodman

core/src/main/java/google/registry/env/common/pubapi/WEB-INF/web.xml

@@ -25,6 +25,10 @@
   </servlet-mapping>
 
   <!-- RDAP (new WHOIS). -->
+  <servlet-mapping>
+    <servlet-name>pubapi-servlet</servlet-name>
+    <url-pattern>/rdap</url-pattern>
+  </servlet-mapping>
   <servlet-mapping>
     <servlet-name>pubapi-servlet</servlet-name>
     <url-pattern>/rdap/*</url-pattern>

core/src/main/java/google/registry/module/RequestComponent.java

@@ -62,6 +62,7 @@
 import google.registry.rdap.RdapAutnumAction;
 import google.registry.rdap.RdapDomainAction;
 import google.registry.rdap.RdapDomainSearchAction;
+import google.registry.rdap.RdapEmptyAction;
 import google.registry.rdap.RdapEntityAction;
 import google.registry.rdap.RdapEntitySearchAction;
 import google.registry.rdap.RdapHelpAction;
@@ -261,6 +262,8 @@ interface RequestComponent {
 
   RdapDomainSearchAction rdapDomainSearchAction();
 
+  RdapEmptyAction rdapEmptyAction();
+
   RdapEntityAction rdapEntityAction();
 
   RdapEntitySearchAction rdapEntitySearchAction();

core/src/main/java/google/registry/module/pubapi/PubApiRequestComponent.java

@@ -24,6 +24,7 @@
 import google.registry.rdap.RdapAutnumAction;
 import google.registry.rdap.RdapDomainAction;
 import google.registry.rdap.RdapDomainSearchAction;
+import google.registry.rdap.RdapEmptyAction;
 import google.registry.rdap.RdapEntityAction;
 import google.registry.rdap.RdapEntitySearchAction;
 import google.registry.rdap.RdapHelpAction;
@@ -55,6 +56,9 @@ public interface PubApiRequestComponent {
   RdapAutnumAction rdapAutnumAction();
   RdapDomainAction rdapDomainAction();
   RdapDomainSearchAction rdapDomainSearchAction();
+
+  RdapEmptyAction rdapEmptyAction();
+
   RdapEntityAction rdapEntityAction();
   RdapEntitySearchAction rdapEntitySearchAction();
   RdapHelpAction rdapHelpAction();

core/src/main/java/google/registry/rdap/RdapEmptyAction.java

@@ -0,0 +1,54 @@
+// Copyright 2025 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.rdap;
+
+import static google.registry.request.Action.Method.GET;
+import static google.registry.request.Action.Method.HEAD;
+
+import google.registry.request.Action;
+import google.registry.request.Response;
+import google.registry.request.auth.Auth;
+import jakarta.inject.Inject;
+import java.io.IOException;
+
+/**
+ * RDAP action that serves the empty string, redirecting to the help page.
+ *
+ * <p>This isn't technically required, but if someone requests the base url it seems nice to give
+ * them the help response.
+ */
+@Action(
+    service = Action.GaeService.PUBAPI,
+    path = "/rdap",
+    method = {GET, HEAD},
+    auth = Auth.AUTH_PUBLIC)
+public class RdapEmptyAction implements Runnable {
+
+  private final Response response;
+
+  @Inject
+  public RdapEmptyAction(Response response) {
+    this.response = response;
+  }
+
+  @Override
+  public void run() {
+    try {
+      response.sendRedirect(RdapHelpAction.PATH);
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+  }
+}

core/src/main/java/google/registry/rdap/RdapHelpAction.java

@@ -31,12 +31,14 @@
 /** RDAP (new WHOIS) action for help requests. */
 @Action(
     service = GaeService.PUBAPI,
-    path = "/rdap/help",
+    path = RdapHelpAction.PATH,
     method = {GET, HEAD},
     isPrefix = true,
     auth = Auth.AUTH_PUBLIC)
 public class RdapHelpAction extends RdapActionBase {
 
+  public static final String PATH = "/rdap/help";
+
   /** The help path for the RDAP terms of service. */
   public static final String TOS_PATH = "/tos";
 

core/src/test/java/google/registry/rdap/RdapEmptyActionTest.java

@@ -0,0 +1,42 @@
+// Copyright 2025 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.rdap;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import google.registry.testing.FakeResponse;
+import jakarta.servlet.http.HttpServletResponse;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+/** Tests for {@link RdapEmptyAction}. */
+public class RdapEmptyActionTest {
+
+  private FakeResponse fakeResponse;
+  private RdapEmptyAction action;
+
+  @BeforeEach
+  void beforeEach() {
+    fakeResponse = new FakeResponse();
+    action = new RdapEmptyAction(fakeResponse);
+  }
+
+  @Test
+  void testRedirect() {
+    action.run();
+    assertThat(fakeResponse.getStatus()).isEqualTo(HttpServletResponse.SC_FOUND);
+    assertThat(fakeResponse.getPayload()).isEqualTo("Redirected to /rdap/help");
+  }
+}

core/src/test/resources/google/registry/module/pubapi/pubapi_routing.txt

@@ -1,6 +1,7 @@
 SERVICE PATH                 CLASS                      METHODS  OK MIN  USER_POLICY
 PUBAPI  /_dr/whois           WhoisAction                POST     n  APP  ADMIN
 PUBAPI  /check               CheckApiAction             GET      n  NONE PUBLIC
+PUBAPI  /rdap                RdapEmptyAction            GET,HEAD n  NONE PUBLIC
 PUBAPI  /rdap/autnum/(*)     RdapAutnumAction           GET,HEAD n  NONE PUBLIC
 PUBAPI  /rdap/domain/(*)     RdapDomainAction           GET,HEAD n  NONE PUBLIC
 PUBAPI  /rdap/domains        RdapDomainSearchAction     GET,HEAD n  NONE PUBLIC

core/src/test/resources/google/registry/module/routing.txt

@@ -56,6 +56,7 @@ BACKEND  /_dr/task/uploadBsaUnavailableNames                UploadBsaUnavailable
 BACKEND  /_dr/task/wipeOutContactHistoryPii                 WipeOutContactHistoryPiiAction                 GET                 n  APP  ADMIN
 PUBAPI   /_dr/whois                                         WhoisAction                                    POST                n  APP  ADMIN
 PUBAPI   /check                                             CheckApiAction                                 GET                 n  NONE PUBLIC
+PUBAPI   /rdap                                              RdapEmptyAction                                GET,HEAD            n  NONE PUBLIC
 PUBAPI   /rdap/autnum/(*)                                   RdapAutnumAction                               GET,HEAD            n  NONE PUBLIC
 PUBAPI   /rdap/domain/(*)                                   RdapDomainAction                               GET,HEAD            n  NONE PUBLIC
 PUBAPI   /rdap/domains                                      RdapDomainSearchAction                         GET,HEAD            n  NONE PUBLIC