WebSocketHeartbeatConfig

interface WebSocketHeartbeatConfig<
  TIncoming = unknown,
  TOutgoing = unknown,
> {
  intervalMs: number;
  isAck?: (message: TIncoming) => boolean;
  message?: () => TOutgoing;
  timeoutMs?: number;
}

• intervalMs is the delay between heartbeat messages.

• message() builds the payload. It is sent through the outgoing struct. Nothing is sent when it is omitted or returns undefined.

• After struct encoding, non-JSON values fail with TypeError through the same serializer as session.send; that heartbeat failure ends the logical session without reconnecting.

• isAck(message) receives each decoded incoming message. When it returns true, the message is treated as the acknowledgement and is not delivered to receive.

• timeoutMs is how long to wait for an acknowledgement after a heartbeat. Missing it fails the session.

• intervalMs and timeoutMs must be positive, finite, and at most 2_147_483_647.

Set it with withWebSocketHeartbeat or the heartbeat request option.