feat!: Add pagination support to ListTaskPushNotificationConfig with Result wrapper (#552)

# Description
Implements pagination support for push notification config listing by
introducing
ListTaskPushNotificationConfigResult record, following the same pattern
as
ListTasksResult. This allows the API to return both the list of configs
and a
    nextPageToken for pagination.
    
Changes:
- Created ListTaskPushNotificationConfigResult record with configs list
and nextPageToken
    - Updated ListTaskPushNotificationConfigResponse to use Result type
    - Updated all server handlers to return Result wrapper
    - Updated ProtoUtils mappers for Result conversion
- Updated all transport implementations (REST, gRPC, JSONRPC) on both
client and server
    - Updated client interface and implementations
    - Fixed test to use Result type

Updated all PushNotificationConfigStore implementations and tests to use
the new

ListTaskPushNotificationConfigParams/ListTaskPushNotificationConfigResult
API
    instead of the old String-based getInfo method.
    
Changes to implementations:
- InMemoryPushNotificationConfigStore: Fixed bug where pageSize - 1 was
used
instead of pageSize, causing one less item to be returned than requested
- JpaDatabasePushNotificationConfigStore: Implemented pagination logic
matching
      the in-memory implementation
- Added helper methods for pagination: findFirstIndex,
convertPushNotificationConfig
- Updated all test files with getInfoAsList helper method to maintain
compatibility

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- [X] Ensure the tests pass
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Fixes #535 🦕

---------

Signed-off-by: Emmanuel Hugonnet <ehugonne@redhat.com>
Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>
Co-authored-by: Kabir Khan <kkhan@redhat.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: 4 people

client/base/src/main/java/io/a2a/client/AbstractClient.java

@@ -13,6 +13,7 @@
 import io.a2a.spec.DeleteTaskPushNotificationConfigParams;
 import io.a2a.spec.GetTaskPushNotificationConfigParams;
 import io.a2a.spec.ListTaskPushNotificationConfigParams;
+import io.a2a.spec.ListTaskPushNotificationConfigResult;
 import io.a2a.spec.ListTasksParams;
 import io.a2a.spec.ListTasksResult;
 import io.a2a.spec.Message;
@@ -271,26 +272,26 @@ public abstract TaskPushNotificationConfig getTaskPushNotificationConfiguration(
             @Nullable ClientCallContext context) throws A2AClientException;
 
     /**
-     * Retrieve the list of push notification configurations for a specific task.
+     * Retrieve the list of push notification configurations for a specific task with pagination support.
      *
      * @param request the parameters specifying which task's notification configs to retrieve
-     * @return the list of task push notification configs
+     * @return the result containing the list of task push notification configs and pagination information
      * @throws A2AClientException if getting the task push notification configs fails for any reason
      */
-    public List<TaskPushNotificationConfig> listTaskPushNotificationConfigurations(
+    public ListTaskPushNotificationConfigResult listTaskPushNotificationConfigurations(
             ListTaskPushNotificationConfigParams request) throws A2AClientException {
         return listTaskPushNotificationConfigurations(request, null);
     }
 
     /**
-     * Retrieve the list of push notification configurations for a specific task.
+     * Retrieve the list of push notification configurations for a specific task with pagination support.
      *
      * @param request the parameters specifying which task's notification configs to retrieve
      * @param context optional client call context for the request (may be {@code null})
-     * @return the list of task push notification configs
+     * @return the result containing the list of task push notification configs and pagination information
      * @throws A2AClientException if getting the task push notification configs fails for any reason
      */
-    public abstract List<TaskPushNotificationConfig> listTaskPushNotificationConfigurations(
+    public abstract ListTaskPushNotificationConfigResult listTaskPushNotificationConfigurations(
             ListTaskPushNotificationConfigParams request,
             @Nullable ClientCallContext context) throws A2AClientException;
 

client/base/src/main/java/io/a2a/client/Client.java

@@ -16,6 +16,7 @@
 import io.a2a.spec.EventKind;
 import io.a2a.spec.GetTaskPushNotificationConfigParams;
 import io.a2a.spec.ListTaskPushNotificationConfigParams;
+import io.a2a.spec.ListTaskPushNotificationConfigResult;
 import io.a2a.spec.ListTasksParams;
 import io.a2a.spec.ListTasksResult;
 import io.a2a.spec.Message;
@@ -108,7 +109,7 @@ public TaskPushNotificationConfig getTaskPushNotificationConfiguration(
     }
 
     @Override
-    public List<TaskPushNotificationConfig> listTaskPushNotificationConfigurations(
+    public ListTaskPushNotificationConfigResult listTaskPushNotificationConfigurations(
             ListTaskPushNotificationConfigParams request, @Nullable ClientCallContext context) throws A2AClientException {
         return clientTransport.listTaskPushNotificationConfigurations(request, context);
     }

client/transport/grpc/src/main/java/io/a2a/client/transport/grpc/GrpcTransport.java

@@ -29,6 +29,7 @@
 import io.a2a.spec.GetTaskRequest;
 import io.a2a.spec.ListTaskPushNotificationConfigParams;
 import io.a2a.spec.ListTaskPushNotificationConfigRequest;
+import io.a2a.spec.ListTaskPushNotificationConfigResult;
 import io.a2a.spec.ListTasksParams;
 import io.a2a.spec.ListTasksRequest;
 import io.a2a.spec.ListTasksResult;
@@ -265,23 +266,24 @@ public TaskPushNotificationConfig getTaskPushNotificationConfiguration(
     }
 
     @Override
-    public List<TaskPushNotificationConfig> listTaskPushNotificationConfigurations(
+    public ListTaskPushNotificationConfigResult listTaskPushNotificationConfigurations(
             ListTaskPushNotificationConfigParams request,
             @Nullable ClientCallContext context) throws A2AClientException {
         checkNotNullParam("request", request);
 
         io.a2a.grpc.ListTaskPushNotificationConfigRequest grpcRequest = io.a2a.grpc.ListTaskPushNotificationConfigRequest.newBuilder()
                 .setParent("tasks/" + request.id())
                 .setTenant(resolveTenant(request.tenant()))
+                .setPageSize(request.pageSize())
+                .setPageToken(request.pageToken())
                 .build();
         PayloadAndHeaders payloadAndHeaders = applyInterceptors(ListTaskPushNotificationConfigRequest.METHOD,
                 grpcRequest, agentCard, context);
 
         try {
             A2AServiceBlockingV2Stub stubWithMetadata = createBlockingStubWithMetadata(context, payloadAndHeaders);
-            return stubWithMetadata.listTaskPushNotificationConfig(grpcRequest).getConfigsList().stream()
-                    .map(FromProto::taskPushNotificationConfig)
-                    .collect(Collectors.toList());
+            io.a2a.grpc.ListTaskPushNotificationConfigResponse grpcResponse = stubWithMetadata.listTaskPushNotificationConfig(grpcRequest);
+            return FromProto.listTaskPushNotificationConfigResult(grpcResponse);
         } catch (StatusRuntimeException | StatusException e) {
             throw GrpcErrorMapper.mapGrpcError(e, "Failed to list task push notification config: ");
         }

client/transport/jsonrpc/src/main/java/io/a2a/client/transport/jsonrpc/JSONRPCTransport.java

@@ -45,6 +45,7 @@
 import io.a2a.spec.ListTaskPushNotificationConfigParams;
 import io.a2a.spec.ListTaskPushNotificationConfigRequest;
 import io.a2a.spec.ListTaskPushNotificationConfigResponse;
+import io.a2a.spec.ListTaskPushNotificationConfigResult;
 import io.a2a.spec.ListTasksParams;
 import io.a2a.spec.ListTasksRequest;
 import io.a2a.spec.ListTasksResponse;
@@ -222,7 +223,7 @@ public TaskPushNotificationConfig getTaskPushNotificationConfiguration(GetTaskPu
     }
 
     @Override
-    public List<TaskPushNotificationConfig> listTaskPushNotificationConfigurations(
+    public ListTaskPushNotificationConfigResult listTaskPushNotificationConfigurations(
             ListTaskPushNotificationConfigParams request,
             @Nullable ClientCallContext context) throws A2AClientException {
         checkNotNullParam("request", request);

client/transport/rest/src/main/java/io/a2a/client/transport/rest/RestTransport.java

@@ -41,6 +41,7 @@
 import io.a2a.spec.GetTaskRequest;
 import io.a2a.spec.ListTaskPushNotificationConfigParams;
 import io.a2a.spec.ListTaskPushNotificationConfigRequest;
+import io.a2a.spec.ListTaskPushNotificationConfigResult;
 import io.a2a.spec.ListTasksParams;
 import io.a2a.spec.ListTasksRequest;
 import io.a2a.spec.ListTasksResult;
@@ -334,7 +335,7 @@ public TaskPushNotificationConfig getTaskPushNotificationConfiguration(GetTaskPu
     }
 
     @Override
-    public List<TaskPushNotificationConfig> listTaskPushNotificationConfigurations(ListTaskPushNotificationConfigParams request, @Nullable ClientCallContext context) throws A2AClientException {
+    public ListTaskPushNotificationConfigResult listTaskPushNotificationConfigurations(ListTaskPushNotificationConfigParams request, @Nullable ClientCallContext context) throws A2AClientException {
         checkNotNullParam("request", request);
         io.a2a.grpc.ListTaskPushNotificationConfigRequest.Builder builder
                 = io.a2a.grpc.ListTaskPushNotificationConfigRequest.newBuilder();
@@ -356,7 +357,7 @@ public List<TaskPushNotificationConfig> listTaskPushNotificationConfigurations(L
             String httpResponseBody = response.body();
             io.a2a.grpc.ListTaskPushNotificationConfigResponse.Builder responseBuilder = io.a2a.grpc.ListTaskPushNotificationConfigResponse.newBuilder();
             JsonFormat.parser().merge(httpResponseBody, responseBuilder);
-            return ProtoUtils.FromProto.listTaskPushNotificationConfigParams(responseBuilder);
+            return ProtoUtils.FromProto.listTaskPushNotificationConfigResult(responseBuilder);
         } catch (A2AClientException e) {
             throw e;
         } catch (IOException | InterruptedException e) {

client/transport/rest/src/test/java/io/a2a/client/transport/rest/RestTransportTest.java

@@ -44,6 +44,7 @@
 import io.a2a.spec.FileWithUri;
 import io.a2a.spec.GetTaskPushNotificationConfigParams;
 import io.a2a.spec.ListTaskPushNotificationConfigParams;
+import io.a2a.spec.ListTaskPushNotificationConfigResult;
 import io.a2a.spec.Message;
 import io.a2a.spec.MessageSendConfiguration;
 import io.a2a.spec.MessageSendParams;
@@ -361,18 +362,18 @@ public void testListTaskPushNotificationConfigurations() throws Exception {
                 );
 
         RestTransport client = new RestTransport(CARD);
-        List<TaskPushNotificationConfig> taskPushNotificationConfigs = client.listTaskPushNotificationConfigurations(
+        ListTaskPushNotificationConfigResult result = client.listTaskPushNotificationConfigurations(
                 new ListTaskPushNotificationConfigParams("de38c76d-d54c-436c-8b9f-4c2703648d64"), null);
-        assertEquals(2, taskPushNotificationConfigs.size());
-        PushNotificationConfig pushNotificationConfig = taskPushNotificationConfigs.get(0).pushNotificationConfig();
+        assertEquals(2, result.configs().size());
+        PushNotificationConfig pushNotificationConfig = result.configs().get(0).pushNotificationConfig();
         assertNotNull(pushNotificationConfig);
         assertEquals("https://example.com/callback", pushNotificationConfig.url());
         assertEquals("10", pushNotificationConfig.id());
         AuthenticationInfo authenticationInfo = pushNotificationConfig.authentication();
         assertTrue(authenticationInfo.schemes().size() == 1);
         assertEquals("jwt", authenticationInfo.schemes().get(0));
         assertEquals("", authenticationInfo.credentials());
-        pushNotificationConfig = taskPushNotificationConfigs.get(1).pushNotificationConfig();
+        pushNotificationConfig = result.configs().get(1).pushNotificationConfig();
         assertNotNull(pushNotificationConfig);
         assertEquals("https://test.com/callback", pushNotificationConfig.url());
         assertEquals("5", pushNotificationConfig.id());

client/transport/spi/src/main/java/io/a2a/client/transport/spi/ClientTransport.java

@@ -10,6 +10,7 @@
 import io.a2a.spec.EventKind;
 import io.a2a.spec.GetTaskPushNotificationConfigParams;
 import io.a2a.spec.ListTaskPushNotificationConfigParams;
+import io.a2a.spec.ListTaskPushNotificationConfigResult;
 import io.a2a.spec.ListTasksParams;
 import io.a2a.spec.ListTasksResult;
 import io.a2a.spec.MessageSendParams;
@@ -102,14 +103,14 @@ TaskPushNotificationConfig getTaskPushNotificationConfiguration(
             @Nullable ClientCallContext context) throws A2AClientException;
 
     /**
-     * Retrieve the list of push notification configurations for a specific task.
+     * Retrieve the list of push notification configurations for a specific task with pagination support.
      *
      * @param request the parameters specifying which task's notification configs to retrieve
      * @param context optional client call context for the request (may be {@code null})
-     * @return the list of task push notification configs
+     * @return the result containing the list of task push notification configs and pagination information
      * @throws A2AClientException if getting the task push notification configs fails for any reason
      */
-    List<TaskPushNotificationConfig> listTaskPushNotificationConfigurations(
+    ListTaskPushNotificationConfigResult listTaskPushNotificationConfigurations(
             ListTaskPushNotificationConfigParams request,
             @Nullable ClientCallContext context) throws A2AClientException;
 

extras/push-notification-config-store-database-jpa/src/main/java/io/a2a/extras/pushnotificationconfigstore/database/jpa/JpaDatabasePushNotificationConfigStore.java

@@ -1,5 +1,7 @@
 package io.a2a.extras.pushnotificationconfigstore.database.jpa;
 
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 import jakarta.annotation.Priority;
@@ -11,7 +13,10 @@
 
 import io.a2a.json.JsonProcessingException;
 import io.a2a.server.tasks.PushNotificationConfigStore;
+import io.a2a.spec.ListTaskPushNotificationConfigParams;
+import io.a2a.spec.ListTaskPushNotificationConfigResult;
 import io.a2a.spec.PushNotificationConfig;
+import io.a2a.spec.TaskPushNotificationConfig;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -65,7 +70,8 @@ public PushNotificationConfig setInfo(String taskId, PushNotificationConfig noti
 
     @Transactional
     @Override
-    public List<PushNotificationConfig> getInfo(String taskId) {
+    public ListTaskPushNotificationConfigResult getInfo(ListTaskPushNotificationConfigParams params) {
+        String taskId = params.id();
         LOGGER.debug("Retrieving PushNotificationConfigs for Task '{}'", taskId);
         try {
             List<JpaPushNotificationConfig> jpaConfigs = em.createQuery(
@@ -88,13 +94,58 @@ public List<PushNotificationConfig> getInfo(String taskId) {
                     .toList();
 
             LOGGER.debug("Successfully retrieved {} PushNotificationConfigs for Task '{}'", configs.size(), taskId);
-            return configs;
+
+            // Handle pagination
+            if (configs.isEmpty()) {
+                return new ListTaskPushNotificationConfigResult(Collections.emptyList());
+            }
+
+            if (params.pageSize() <= 0) {
+                return new ListTaskPushNotificationConfigResult(convertPushNotificationConfig(configs, params), null);
+            }
+
+            // Apply pageToken filtering if provided
+            List<PushNotificationConfig> paginatedConfigs = configs;
+            if (params.pageToken() != null && !params.pageToken().isBlank()) {
+                int index = findFirstIndex(configs, params.pageToken());
+                if (index < configs.size()) {
+                    paginatedConfigs = configs.subList(index, configs.size());
+                }
+            }
+
+            // Apply page size limit
+            if (paginatedConfigs.size() <= params.pageSize()) {
+                return new ListTaskPushNotificationConfigResult(convertPushNotificationConfig(paginatedConfigs, params), null);
+            }
+
+            String nextToken = paginatedConfigs.get(params.pageSize()).token();
+            return new ListTaskPushNotificationConfigResult(
+                    convertPushNotificationConfig(paginatedConfigs.subList(0, params.pageSize()), params),
+                    nextToken);
         } catch (Exception e) {
             LOGGER.error("Failed to retrieve PushNotificationConfigs for Task '{}'", taskId, e);
             throw e;
         }
     }
 
+    private int findFirstIndex(List<PushNotificationConfig> configs, String token) {
+        for (int i = 0; i < configs.size(); i++) {
+            if (token.equals(configs.get(i).token())) {
+                return i;
+            }
+        }
+        return configs.size();
+    }
+
+    private List<TaskPushNotificationConfig> convertPushNotificationConfig(List<PushNotificationConfig> pushNotificationConfigList, ListTaskPushNotificationConfigParams params) {
+        List<TaskPushNotificationConfig> taskPushNotificationConfigList = new ArrayList<>(pushNotificationConfigList.size());
+        for (PushNotificationConfig pushNotificationConfig : pushNotificationConfigList) {
+            TaskPushNotificationConfig taskPushNotificationConfig = new TaskPushNotificationConfig(params.id(), pushNotificationConfig, params.tenant());
+            taskPushNotificationConfigList.add(taskPushNotificationConfig);
+        }
+        return taskPushNotificationConfigList;
+    }
+
     @Transactional
     @Override
     public void deleteInfo(String taskId, String configId) {