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SSE client

Provide basic functionality to work with Casper events that streamed by SSE server. It connects to the server and collect events, from other side consumers obtain this stream and delegate the process to specific handlers.

Usage

import { SseClient, EventName } from 'casper-js-sdk';

const sseClient = new SseClient('http://<Node Address>:9999/events');

sseClient.subscribe(EventName.BlockAddedEventType, rawEvent => {
  try {
    const parsedEvent = rawEvent.parseAsBlockAddedEvent();
    console.log(`Block hash: ${parsedEvent.BlockAdded.blockHash}`);
  } catch (error) {
    console.error('Error processing event:', error);
  }
});

// Start the client with the last known event ID ( Optional )
const lastEventID = 1234;

sseClient.start(lastEventID);

Events List

Key Components

SseClient

SseClient serves as the primary interface for handling an SSE data stream. It encapsulates multiple responsibilities:

  • Connection Management:
    Establishes and manages an EventSource connection to the SSE endpoint. The client handles connection setup, monitors the stream for incoming messages, and cleans up resources when stopping.

  • Subscription Management:
    Provides methods to subscribe to and unsubscribe from specific event types. Each subscription links an event name with a handler function that will process matching events.

  • Event Dispatching:
    Listens for incoming messages, leverages the EventParser to check and parse messages, and dispatches parsed events to the corresponding subscription handler.

  • Error Handling:
    Monitors for errors during the SSE connection and raises exceptions when necessary.

Key Methods

  • subscribe

    subscribe(eventName: EventName, eventHandlerFn: EventHandlerFn): Result<boolean, string>

    Registers a handler for a specific event type. Returns a result indicating success or failure (e.g., if already subscribed).

  • unsubscribe

    unsubscribe(eventName: EventName): Result<boolean, string>

    Removes the subscription for the specified event type.

  • start

    start(eventId?: number): void

    Opens the connection to the SSE endpoint, optionally starting from a given event ID, and begins processing incoming events.

  • stop

    stop(): void

    Closes the SSE connection, stopping further event processing.

EventParser

EventParser is responsible for processing the raw data received from the SSE stream. Its core functions include:

  • Event Filtering:

    shouldHandleEvent(data: string, eventName: string): boolean

    Determines whether the raw event data contains the property corresponding to the expected event type. It parses the incoming JSON and checks for the presence of the event identifier.

  • Event Parsing:

    parseEvent(data: string, type: string, lastEventId: string): RawEvent

    Converts the raw string data into a structured RawEvent object, which contains metadata such as the event type, raw payload, and event ID.