Struct HandlerLimits 

pub struct HandlerLimits {
    pub max_id_length: usize,
    pub max_metadata_size: usize,
    pub max_cancellation_tokens: usize,
    pub max_token_age: Duration,
    pub push_delivery_timeout: Duration,
    pub max_artifacts_per_task: usize,
    pub max_context_locks: usize,
    pub max_push_configs_per_task: usize,
    pub max_parts_per_artifact: usize,
    pub max_total_push_configs: usize,
    pub subscribe_reattach_interval: Duration,
    pub subscribe_max_idle: Duration,
}

Configurable limits for the request handler.

All fields have sensible defaults. Create with HandlerLimits::default() and override individual values as needed.

Example

use a2a_protocol_server::handler::HandlerLimits;

let limits = HandlerLimits::default()
    .with_max_id_length(2048)
    .with_max_metadata_size(2 * 1024 * 1024);

Fields

max_id_length: usize

Maximum allowed length for task/context IDs. Default: 1024.

max_metadata_size: usize

Maximum allowed serialized size for metadata fields in bytes. Default: 1 MiB.

max_cancellation_tokens: usize

Maximum cancellation token map entries before cleanup sweep. Default: 10,000.

A sweep threshold, not a hard bound: the sweep only evicts cancelled or aged-out entries whose executor is gone — a token belonging to a live task is never removed, so with more than this many tasks genuinely in flight the map tracks the in-flight count instead.

max_token_age: Duration

Maximum age for cancellation tokens. Default: 1 hour.

push_delivery_timeout: Duration

Timeout for individual push webhook deliveries. Default: 5 seconds.

Bounds how long the handler waits for a single push notification delivery to complete, preventing one slow webhook from blocking all subsequent deliveries.

max_artifacts_per_task: usize

Maximum number of artifacts per task. Default: 1000.

Prevents unbounded memory growth and O(n²) serialization cost when executors emit many artifacts. Once the limit is reached, new artifact updates are rejected.

max_context_locks: usize

Maximum number of per-context locks before cleanup. Default: 10,000.

Context locks serialize concurrent SendMessage requests for the same context_id. Stale entries (where no other reference is held) are pruned when this limit is reached. Like max_cancellation_tokens this is a prune threshold, not a hard bound — entries currently held by in-flight requests are never pruned.

max_push_configs_per_task: usize

Maximum number of push notification configs per task. Default: 100.

Enforced by the handler on CreateTaskPushNotificationConfig so the cap applies uniformly across all store backends. Without it, the SQL stores (which do not self-enforce) let a client mint unbounded configs for a single task — a disk-exhaustion vector, and a delivery-amplification vector since every stream event fans out to all of a task’s configs. Updating an existing config (same id) does not count against the cap.

max_parts_per_artifact: usize

Maximum number of parts a single artifact may accumulate. Default: 10,000.

max_artifacts_per_task bounds the artifact count, but a stream of TaskArtifactUpdateEvents with append: true grows one artifact’s parts without bound. Since executors routinely stream model output derived from attacker-influenced prompts, this bounds the cumulative per-artifact (and thus per-task) size. Appends that would exceed the cap are dropped.

max_total_push_configs: usize

Global ceiling on the total number of push configs a store may hold (per-tenant for tenant-scoped stores). Default: 100,000.

Complements max_push_configs_per_task: the per-task cap alone lets a client mint configs for unboundedly many distinct task ids (100 each), growing a SQL-backed table without limit. Enforced whenever the store reports a count (see PushConfigStore::count); stores that do not report one are unaffected.

subscribe_reattach_interval: Duration

How often a SubscribeToTask stream re-checks whether its task has finished, once the current turn’s event queue has closed. Default: 250ms.

A task’s queue lives only as long as one executor invocation, so an agent that parks a task in input_required closes the queue at every turn boundary. Spec §3.1.6 requires the stream to run until a terminal state, so it waits here for the next turn rather than ending. Only an idle stream pays this cost — a live queue delivers events immediately.

subscribe_max_idle: Duration

How long a SubscribeToTask stream waits for a parked task to make progress before ending. Default: 5 minutes.

Without a bound, a task left in input_required forever would pin a connection forever. Ending the stream is safe: §3.5.2 makes reconnection an expected flow, and the client gets a fresh snapshot when it resubscribes.

Implementations

impl HandlerLimits

pub const fn with_subscribe_reattach_interval( self, interval: Duration, ) -> HandlerLimits

Sets how often an idle SubscribeToTask stream re-checks its task.

pub const fn with_subscribe_max_idle(self, max_idle: Duration) -> HandlerLimits

Sets how long a SubscribeToTask stream waits on a parked task.

pub const fn with_max_id_length(self, length: usize) -> HandlerLimits

Sets the maximum allowed length for task/context IDs.

pub const fn with_max_metadata_size(self, size: usize) -> HandlerLimits

Sets the maximum serialized size for metadata fields in bytes.

pub const fn with_max_cancellation_tokens(self, max: usize) -> HandlerLimits

Sets the maximum cancellation token map entries before cleanup.

pub const fn with_max_token_age(self, age: Duration) -> HandlerLimits

Sets the maximum age for cancellation tokens.

pub const fn with_push_delivery_timeout( self, timeout: Duration, ) -> HandlerLimits

Sets the timeout for individual push webhook deliveries.

pub const fn with_max_artifacts_per_task(self, max: usize) -> HandlerLimits

Sets the maximum number of artifacts per task.

pub const fn with_max_push_configs_per_task(self, max: usize) -> HandlerLimits

Sets the maximum number of push notification configs per task.

pub const fn with_max_total_push_configs(self, max: usize) -> HandlerLimits

Sets the global (per-tenant for tenant stores) ceiling on total push notification configs. Enforced only when the store reports a count.

pub const fn with_max_parts_per_artifact(self, max: usize) -> HandlerLimits

Sets the maximum number of parts a single artifact may accumulate.

pub const fn with_max_context_locks(self, max: usize) -> HandlerLimits

Sets the maximum number of per-context locks before cleanup.

Trait Implementations

impl Clone for HandlerLimits

fn clone(&self) -> HandlerLimits

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for HandlerLimits

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Default for HandlerLimits

fn default() -> HandlerLimits

Returns the “default value” for a type.