DefaultRequestHandlerV2._setup_active_task registers empty push subscriptions due to proto3 truthiness check

[AXEG0]

Bug

DefaultRequestHandlerV2._setup_active_task registers a push-notification subscription on every SendMessage request that carries a SendMessageConfiguration, even when the caller did not set task_push_notification_config. Result: empty-URL rows accumulate in the push_notification_configs table and (depending on the configured PushNotificationSender) can throw at send time with httpx.UnsupportedProtocol.

Root cause

a2a/server/request_handlers/default_request_handler_v2.py (1.0.2) lines 215–219:

if (
    self._push_config_store
    and params.configuration
    and params.configuration.task_push_notification_config
):
    await self._push_config_store.set_info(
        task_id,
        params.configuration.task_push_notification_config,
        call_context,
    )

Both params.configuration and params.configuration.task_push_notification_config are proto3 message fields, and in proto3 Python every message — including a default-constructed empty one — has bool() == True. The condition therefore fires on every SendMessage whose request carries any SendMessageConfiguration, regardless of whether the caller actually requested push notifications.

Reproducer:

from a2a.types.a2a_pb2 import SendMessageConfiguration, TaskPushNotificationConfig

cfg = SendMessageConfiguration()
print(bool(cfg))                                            # True
print(bool(cfg.task_push_notification_config))              # True
print(cfg.HasField("task_push_notification_config"))        # False
print(bool(TaskPushNotificationConfig()))                   # True (also unconditionally)

Real-world trigger

Callers commonly send SendMessageConfiguration(return_immediately=True) to dispatch a long-running task and pick up the result later via tasks/get or push notifications they registered separately. With the current code, every such call registers an empty-URL subscription as a side effect, which then either:

• delivers nothing silently (if the sender no-ops on empty URL), or
• throws httpx.UnsupportedProtocol: Request URL is missing an 'http://' or 'https://' protocol on the first state transition (default BasePushNotificationSender).

We hit (b) in production — a tg-gateway-style consumer using SendMessageConfiguration(return_immediately=True) accumulated 3 empty-URL rows in the SQLite store before we noticed.

Suggested fix

Replace the truthiness checks with HasField, the documented proto3 way to test optional message-typed presence:

if (
    self._push_config_store
    and params.HasField('configuration')
    and params.configuration.HasField('task_push_notification_config')
):
    await self._push_config_store.set_info(...)

HasField works for message-typed fields and optional-marked scalars, and the same pattern is already used elsewhere in this file (line 141: if params.HasField('page_size'):).

A defensive store implementation should additionally reject (or skip) empty-url configs at set_info, but the root cause sits in the handler.

Environment

• a2a-sdk==1.0.2
• Python 3.12
• DefaultRequestHandlerV2, DatabasePushNotificationConfigStore

Workaround we shipped

gideon (downstream consumer) skip-and-warns on empty url in our set_info override and added a boot-time sweeper that GCs the table on agent restart: https://github.com/42-com/gideon/issues/39 — happy to remove both layers once this is fixed upstream.

[bartek-w]

Thank you for reporting the issue. It should be fixed in next release.