Configuration Reference

Complete reference of all configuration options across a2a-rust crates.

Server Configuration

RequestHandlerBuilder

Option	Type	Default	Description
`with_agent_card`	`AgentCard`	None	Discovery card for `/.well-known/agent.json`
`with_task_store`	`impl TaskStore`	`InMemoryTaskStore`	Custom task storage backend
`with_task_store_config`	`TaskStoreConfig`	No limits	TTL and capacity for default store
`with_push_config_store`	`impl PushConfigStore`	`InMemoryPushConfigStore`	Custom push config storage
`with_push_sender`	`impl PushSender`	None	Webhook delivery implementation
`with_interceptor`	`impl ServerInterceptor`	Empty chain	Server middleware
`with_executor_timeout`	`Duration`	None	Max time for executor completion
`with_event_queue_capacity`	`usize`	64	Bounded channel size per stream
`with_max_event_size`	`usize`	16 MiB	Max serialized SSE event size
`with_max_concurrent_streams`	`usize`	Unbounded	Limit concurrent SSE connections
`with_event_queue_write_timeout`	`Duration`	5s	Write timeout for event queue sends
`with_metrics`	`impl Metrics`	`NoopMetrics`	Metrics observer for handler activity
`with_handler_limits`	`HandlerLimits`	See below	Configurable validation limits

HandlerLimits

Field	Type	Default	Description
`max_id_length`	`usize`	1,024	Maximum task/context ID length
`max_metadata_size`	`usize`	1 MiB	Maximum serialized metadata size
`max_cancellation_tokens`	`usize`	10,000	Cleanup sweep threshold
`max_token_age`	`Duration`	1 hour	Stale token eviction age
`push_delivery_timeout`	`Duration`	5s	Per-webhook delivery timeout

TaskStoreConfig

Field	Type	Default	Description
`max_capacity`	`Option<usize>`	10,000	Maximum stored tasks; oldest terminal tasks evicted on overflow
`task_ttl`	`Option<Duration>`	1 hour	TTL for completed/failed tasks
`eviction_interval`	`u64`	64	Writes between automatic eviction sweeps
`max_page_size`	`u32`	1,000	Maximum tasks per page in list queries

InMemoryPushConfigStore

Constructor	Default	Description
`::new()`	100	Default max push configs per task
`::with_max_configs_per_task(N)`	—	Custom per-task push config limit

DispatchConfig

Shared configuration for both JSON-RPC and REST dispatchers. Pass to JsonRpcDispatcher::with_config() or RestDispatcher::with_config().

Field	Type	Default	Description
`max_request_body_size`	`usize`	4 MiB	Larger bodies return 413
`body_read_timeout`	`Duration`	30s	Slow loris protection
`max_query_string_length`	`usize`	4,096	REST only; longer queries return 414
`sse_keep_alive_interval`	`Duration`	30s	Periodic keep-alive comment interval for SSE streams
`sse_channel_capacity`	`usize`	64	SSE response body channel buffer size

GrpcConfig

Configuration for the gRPC dispatcher (requires grpc feature).

Field	Type	Default	Description
`max_message_size`	`usize`	4 MiB	Maximum inbound/outbound message size
`concurrency_limit`	`usize`	256	Max concurrent gRPC requests per connection
`stream_channel_capacity`	`usize`	64	Bounded channel for streaming responses

PushRetryPolicy

Configurable retry policy for HttpPushSender. Pass via HttpPushSender::with_retry_policy().

Field	Type	Default	Description
`max_attempts`	`usize`	3	Maximum delivery attempts
`backoff`	`Vec<Duration>`	`[1s, 2s]`	Backoff durations between retries

RateLimitConfig

Field	Type	Default	Description
`requests_per_window`	`u64`	100	Max requests per caller per window
`window_secs`	`u64`	60	Window duration in seconds

Internal Limits

Limit	Value	Description
Event queue type	`broadcast`	Fan-out to multiple subscribers; slow readers skip missed events
Rate limiter cleanup interval	256 checks	Stale buckets (from departed callers) evicted every 256 `check()` calls
Rate limiter window CAS	Lock-free	Window transitions use `compare_exchange` to avoid TOCTOU races
Credential store poisoning	Fail-fast	`InMemoryCredentialsStore` panics on poisoned locks rather than returning `None`

Client Configuration

ClientBuilder

Option	Type	Default	Description
`with_protocol_binding`	`&str`	Auto-detect	Transport: `"JSONRPC"`, `"REST"`, or `"GRPC"`
`with_timeout`	`Duration`	30s	Per-request timeout
`with_connection_timeout`	`Duration`	10s	TCP connection timeout
`with_stream_connect_timeout`	`Duration`	30s	SSE connect timeout
`with_retry_policy`	`RetryPolicy`	None	Retry on transient errors
`with_accepted_output_modes`	`Vec<String>`	`["text/plain", "application/json"]`	MIME types accepted
`with_history_length`	`u32`	None	Messages in responses
`with_return_immediately`	`bool`	false	Don't wait for completion
`with_interceptor`	`impl CallInterceptor`	Empty chain	Client middleware

GrpcTransportConfig

Configuration for the gRPC client transport (requires grpc feature).

Field	Type	Default	Description
`timeout`	`Duration`	30s	Per-request timeout
`connect_timeout`	`Duration`	10s	Connection timeout
`max_message_size`	`usize`	4 MiB	Maximum message size
`stream_channel_capacity`	`usize`	64	Streaming response buffer

RetryPolicy

Field	Type	Default	Description
`max_retries`	`u32`	3	Maximum retry attempts
`initial_backoff`	`Duration`	500ms	Backoff before first retry
`max_backoff`	`Duration`	30s	Caps exponential growth
`backoff_multiplier`	`f64`	2.0	Multiplier per retry

SSE Parser Limits

Limit	Value	Description
Buffer cap	16 MiB	Max buffered SSE data (aligned with server)
Connect timeout	30s (default)	Initial connection timeout

HTTP Caching (Agent Card)

Header	Default	Description
`Cache-Control`	`public, max-age=60`	Configurable max-age
`ETag`	Auto-computed	Content hash
`Last-Modified`	Auto-set	Timestamp of last change

Feature Flags

`a2a-protocol-server`

Feature	Default	Description
`signing`	Off	Agent card signing
`tracing`	Off	Structured logging via `tracing` crate
`sqlite`	Off	SQLite-backed task and push config stores via `sqlx`
`websocket`	Off	WebSocket transport via `tokio-tungstenite`
`grpc`	Off	gRPC transport via `tonic`
`otel`	Off	OpenTelemetry metrics via `opentelemetry-otlp`

`a2a-protocol-client`

Feature	Default	Description
`signing`	Off	Agent card signing verification
`tracing`	Off	Structured logging via `tracing` crate
`tls-rustls`	Off	HTTPS via rustls (no OpenSSL dependency)
`websocket`	Off	WebSocket transport via `tokio-tungstenite`
`grpc`	Off	gRPC transport via `tonic`

`a2a-protocol-types`

Feature	Default	Description
`signing`	Off	JWS/ES256 agent card signing (RFC 8785 canonicalization)

`a2a-protocol-sdk` (umbrella)

Feature	Default	Description
`signing`	Off	Enables `signing` in all sub-crates
`tracing`	Off	Enables `tracing` in client and server
`tls-rustls`	Off	Enables `tls-rustls` in client
`grpc`	Off	Enables `grpc` in client and server
`otel`	Off	Enables `otel` in the server

Environment Variables

Variable	Description
`RUST_LOG`	Log level filter (when `tracing` feature is enabled)

Examples:

RUST_LOG=info              # Info and above
RUST_LOG=debug             # Debug and above
RUST_LOG=a2a_protocol_server=debug  # Debug for server crate only
RUST_LOG=a2a_protocol_server=trace,a2a_protocol_client=debug  # Per-crate levels

Next Steps

API Quick Reference — All public types at a glance
Pitfalls & Lessons Learned — Known issues and workarounds