Struct CallerScope 

pub struct CallerScope<'a> { /* private fields */ }

Available on crate features a2a-v1 and server only.

A RequestHandler acting on behalf of one caller.

Created by RequestHandler::for_caller. Every operation is scoped to the caller: tasks it creates are owned by the caller’s user_id, and a task owned by anyone else is reported as A2aError::TaskNotFound — the same answer as for a task that does not exist, so task IDs cannot be probed.

Implementations

impl CallerScope<'_>

pub fn owner(&self) -> Option<&str>

The authenticated user this scope acts for, or None without authentication.

pub async fn message_send(&self, msg: Message) -> Result<Task, A2aError>

Sends a message, creating a task and processing it through the executor.

When a runner config is present, invokes the agent through the ADK Runner for real LLM generation. The LLM response is recorded as an artifact on the task. Without a runner, performs state transitions only.

A message whose contextId matches one of this caller’s INPUT_REQUIRED tasks resumes that task; another caller’s task with the same contextId is never resumed.

Errors

Returns an error if task creation, state transitions, or store operations fail.

pub async fn message_stream( &self, msg: Message, ) -> Result<Pin<Box<dyn Stream<Item = Result<StreamResponse, A2aError>> + Send>>, A2aError>

Sends a streaming message, returning a stream of SSE events.

Drives the agent and translates its events as they arrive:

Agent event	A2A event
first, before any output	Task, then TaskStatusUpdateEvent — Working
content with partial = true	TaskArtifactUpdateEvent — append, not last chunk
content with partial = false	TaskArtifactUpdateEvent — final chunk
stream ends	TaskStatusUpdateEvent — Completed
stream errors	TaskStatusUpdateEvent — Failed

Chunks of one response share an artifact ID so a client can reassemble them, which is the same contract adk-python and adk-go implement over their A2A SDKs.

With no runner configured the task is created and completed without agent output, which keeps discovery-only deployments working.

Errors

Returns an error if task creation fails. Failures once streaming has begun are reported as a Failed status event, since the response has already started.

pub async fn tasks_get( &self, task_id: &str, history_len: Option<u32>, ) -> Result<Task, A2aError>

Retrieves one of this caller’s tasks by ID.

Optionally limits the number of history messages returned.

Errors

Returns A2aError::TaskNotFound if the task does not exist or belongs to another caller.

pub async fn tasks_cancel(&self, task_id: &str) -> Result<Task, A2aError>

Cancels one of this caller’s tasks by transitioning it to CANCELED state.

Validates that the task is not already in a terminal state before canceling.

Errors

Returns A2aError::TaskNotFound if the task does not exist or belongs to another caller, or A2aError::TaskNotCancelable if the task is in a terminal state.

pub async fn tasks_list( &self, params: ListTasksParams, ) -> Result<Vec<Task>, A2aError>

Lists this caller’s tasks matching the given parameters.

Supports filtering by context_id, state, and pagination via page_size. page_size applies after the owner filter.

Errors

Returns an error if the task store fails.

pub async fn tasks_subscribe( &self, task_id: &str, ) -> Result<Pin<Box<dyn Stream<Item = Result<StreamResponse, A2aError>> + Send>>, A2aError>

Returns the current state of one of this caller’s tasks as a short stream, then closes.

Important: this is a point-in-time snapshot, not a live subscription. It emits the task and its current status and then ends; it does not deliver subsequent updates. A client that needs live updates should use message/stream, which streams the agent’s events as they are produced.

A real re-attach would require a per-task event queue that outlives the request, which the A2A SDKs in adk-python and adk-go provide and this hand-rolled server does not yet.

Errors

Returns A2aError::TaskNotFound if the task does not exist or belongs to another caller, or A2aError::TaskNotCancelable if the task already reached a terminal state.

pub async fn push_config_create( &self, task_id: &str, config: TaskPushNotificationConfig, ) -> Result<TaskPushNotificationConfig, A2aError>

Creates a push notification configuration for one of this caller’s tasks.

Assigns a server-generated config ID and stores the config on the task.

Errors

Returns A2aError::TaskNotFound if the task does not exist or belongs to another caller.

pub async fn push_config_get( &self, task_id: &str, config_id: &str, ) -> Result<TaskPushNotificationConfig, A2aError>

Retrieves a push notification configuration by task ID and config ID.

Errors

Returns A2aError::TaskNotFound if the task or config does not exist, or the task belongs to another caller.

pub async fn push_config_list( &self, task_id: &str, ) -> Result<Vec<TaskPushNotificationConfig>, A2aError>

Lists all push notification configurations for one of this caller’s tasks.

Errors

Returns A2aError::TaskNotFound if the task does not exist or belongs to another caller.

pub async fn push_config_delete( &self, task_id: &str, config_id: &str, ) -> Result<(), A2aError>

Deletes a push notification configuration.

Errors

Returns A2aError::TaskNotFound if the task or config does not exist, or the task belongs to another caller.