Allow for null paging inside Collection response envelopes (#1019)

---------

Co-authored-by: Karthik Ramgopal <kramgopa@linkedin.com>

CHANGELOG.md

@@ -14,6 +14,9 @@ and what APIs have changed, if applicable.
 
 ## [Unreleased]
 
+## [29.58.6] - 2024-09-08
+- Allow for null paging inside Collection response envelopes
+
 ## [29.58.5] - 2024-09-04
 - Respect glob collection subscriptions on reconnect
 
@@ -5725,7 +5728,8 @@ patch operations can re-use these classes for generating patch messages.
 
 ## [0.14.1]
 
-[Unreleased]: https://github.com/linkedin/rest.li/compare/v29.58.5...master
+[Unreleased]: https://github.com/linkedin/rest.li/compare/v29.58.6...master
+[29.58.6]: https://github.com/linkedin/rest.li/compare/v29.58.5...v29.58.6
 [29.58.5]: https://github.com/linkedin/rest.li/compare/v29.58.4...v29.58.5
 [29.58.4]: https://github.com/linkedin/rest.li/compare/v29.58.3...v29.58.4
 [29.58.3]: https://github.com/linkedin/rest.li/compare/v29.58.2...v29.58.3

gradle.properties

@@ -1,4 +1,4 @@
-version=29.58.5
+version=29.58.6
 group=com.linkedin.pegasus
 org.gradle.configureondemand=true
 org.gradle.parallel=true

restli-server/src/main/java/com/linkedin/restli/internal/server/response/CollectionResponseBuilder.java

@@ -51,7 +51,23 @@ public RestLiResponse buildResponse(RoutingResult routingResult, D responseData)
     CollectionResponseEnvelope response = responseData.getResponseEnvelope();
     RestLiResponse.Builder builder = new RestLiResponse.Builder();
     CollectionResponse<AnyRecord> collectionResponse = new CollectionResponse<>(AnyRecord.class);
-    collectionResponse.setPaging(response.getCollectionResponsePaging());
+
+    // Technically, there is no way to set paging to null in application code since CollectionResult doesn't allow
+    // it. However, it is possible to use a custom rest.li filter to strip out paging from the ResponseEnvelope in
+    // case use cases don't want index based paging. This null check detects and elegantly handles such cases.
+    //
+    // An alternative would be to support null indexed based paging natively inside CollectionResult and all its
+    // upstream objects. However, doing so needs several changes inside framework code, and is potentially fragile.
+    // Hence, we prefer a point fix here.
+    if (response.getCollectionResponsePaging() != null)
+    {
+      collectionResponse.setPaging(response.getCollectionResponsePaging());
+    }
+    else
+    {
+      collectionResponse.removePaging();
+    }
+
     DataList elementsMap = (DataList) collectionResponse.data().get(CollectionResponse.ELEMENTS);
     for (RecordTemplate entry : response.getCollectionResponse())
     {

restli-server/src/test/java/com/linkedin/restli/internal/server/response/TestCollectionResponseBuilder.java

@@ -29,6 +29,7 @@
 import com.linkedin.r2.message.rest.RestRequestBuilder;
 import com.linkedin.restli.common.CollectionMetadata;
 import com.linkedin.restli.common.CollectionResponse;
+import com.linkedin.restli.common.HttpStatus;
 import com.linkedin.restli.common.LinkArray;
 import com.linkedin.restli.common.ResourceMethod;
 import com.linkedin.restli.internal.server.RoutingResult;
@@ -226,6 +227,36 @@ public <D extends RestLiResponseData<? extends CollectionResponseEnvelope>> void
     EasyMock.verify(mockContext);
   }
 
+  @DataProvider(name = "testNullPaging")
+  public Object[][] testNullPaging()
+  {
+    return BUILDERS.values().stream().map(builder -> new Object[]{builder}).toArray(Object[][]::new);
+  }
+
+  @Test(dataProvider = "testNullPaging")
+  public <D extends RestLiResponseData<? extends CollectionResponseEnvelope>>
+    void testNullPaging(CollectionResponseBuilder<D> responseBuilder)
+  {
+    Map<String, String> headers = ResponseBuilderUtil.getHeaders();
+
+    ServerResourceContext mockContext = EasyMock.createMock(ServerResourceContext.class);
+    ResourceMethodDescriptor mockDescriptor = EasyMock.createMock(ResourceMethodDescriptor.class);
+    RoutingResult routingResult = new RoutingResult(mockContext, mockDescriptor);
+
+    Foo metadata = new Foo().setStringField("metadata").setIntField(7);
+    final List<Foo> generatedList = generateTestList();
+
+    RestLiResponse response = responseBuilder.buildResponse(routingResult,
+        responseBuilder.buildResponseData(HttpStatus.S_200_OK, generatedList, null, metadata, headers,
+            Collections.emptyList()));
+
+    Assert.assertTrue(response.getEntity() instanceof CollectionResponse);
+    CollectionResponse<?> collectionResponse = (CollectionResponse<?>) response.getEntity();
+    Assert.assertEquals(collectionResponse.getElements(), generatedList);
+    Assert.assertEquals(collectionResponse.getMetadataRaw(), metadata.data());
+    Assert.assertFalse(collectionResponse.hasPaging());
+  }
+
   @DataProvider(name = "exceptionTestData")
   public Object[][] exceptionDataProvider()
   {