fastmcp.server.event_store

EventStore implementation backed by AsyncKeyValue.

This module provides an EventStore implementation that enables SSE polling/resumability for Streamable HTTP transports. Events are stored using the key_value package's AsyncKeyValue protocol, allowing users to configure any compatible backend (in-memory, Redis, etc.) following the same pattern as ResponseCachingMiddleware.

Classes

EventEntry ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/event_store.py#L26" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

Stored event entry.

StreamEventList ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/event_store.py#L34" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

List of event IDs for a stream.

EventStore ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/event_store.py#L40" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

EventStore implementation backed by AsyncKeyValue.

Enables SSE polling/resumability by storing events that can be replayed when clients reconnect. Works with any AsyncKeyValue backend (memory, Redis, etc.) following the same pattern as ResponseCachingMiddleware and OAuthProxy.

Args:

• storage: AsyncKeyValue backend. Defaults to MemoryStore.
• max_events_per_stream: Maximum events to retain per stream. Default 100.
• ttl: Event TTL in seconds. Default 3600 (1 hour). Set to None for no expiration.

Methods:

store_event ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/event_store.py#L94" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

store_event(self, stream_id: StreamId, message: JSONRPCMessage | None) -> EventId

Store an event and return its ID.

Args:

• stream_id: ID of the stream the event belongs to
• message: The JSON-RPC message to store, or None for priming events

Returns:

• The generated event ID for the stored event

replay_events_after ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/event_store.py#L135" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

replay_events_after(self, last_event_id: EventId, send_callback: EventCallback) -> StreamId | None

Replay events that occurred after the specified event ID.

Args:

• last_event_id: The ID of the last event the client received
• send_callback: A callback function to send events to the client

Returns:

• The stream ID of the replayed events, or None if the event ID was not found