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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.

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Classes

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EventEntry

Stored event entry.

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StreamEventList

List of event IDs for a stream.

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EventStore

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:

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store_event 

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

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replay_events_after 

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