@lodestar/api/lib/beacon/server/events.js

A Typescript REST client for the Ethereum Consensus API

import { ApiError, createFastifyRoutes } from "../../utils/server/index.js";
import { eventTypes, getDefinitions, getEventSerdes } from "../routes/events.js";
export function getRoutes(config, methods) {
    const eventSerdes = getEventSerdes(config);
    const serverRoutes = createFastifyRoutes(getDefinitions(config), methods);
    return {
        // Non-JSON route. Server Sent Events (SSE)
        eventstream: {
            ...serverRoutes.eventstream,
            handler: async (req, res) => {
                const validTopics = new Set(Object.values(eventTypes));
                for (const topic of req.query.topics) {
                    if (!validTopics.has(topic)) {
                        throw new ApiError(400, `Invalid topic: ${topic}`);
                    }
                }
                const controller = new AbortController();
                try {
                    // Add injected headers from other plugins. This is required for fastify-cors for example
                    // From: https://github.com/NodeFactoryIo/fastify-sse-v2/blob/b1686a979fbf655fb9936c0560294a0c094734d4/src/plugin.ts
                    for (const [key, value] of Object.entries(res.getHeaders())) {
                        if (value !== undefined)
                            res.raw.setHeader(key, value);
                    }
                    res.raw.setHeader("Content-Type", "text/event-stream");
                    res.raw.setHeader("Cache-Control", "no-cache,no-transform");
                    res.raw.setHeader("Connection", "keep-alive");
                    // It was reported that chrome and firefox do not play well with compressed event-streams https://github.com/lolo32/fastify-sse/issues/2
                    res.raw.setHeader("x-no-compression", 1);
                    // In case this beacon node is behind a NGINX, instruct it to disable buffering which can disrupt SSE by
                    // infinitely buffering it. http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_buffering
                    // Source: https://stackoverflow.com/questions/13672743/eventsource-server-sent-events-through-nginx
                    res.raw.setHeader("X-Accel-Buffering", "no");
                    await new Promise((resolve, reject) => {
                        void methods.eventstream({
                            topics: req.query.topics,
                            signal: controller.signal,
                            onEvent: (event) => {
                                try {
                                    const data = eventSerdes.toJson(event);
                                    res.raw.write(serializeSSEEvent({ event: event.type, data }));
                                }
                                catch (e) {
                                    reject(e);
                                }
                            },
                        });
                        // The stream will never end by the server unless the node is stopped.
                        // In that case the BeaconNode class will call server.close() and end this connection.
                        // The client may disconnect and we need to clean the subscriptions.
                        req.socket.once("close", () => resolve());
                        req.socket.once("end", () => resolve());
                    });
                    // api.eventstream will never stop, so no need to ever call `res.raw.end();`
                }
                finally {
                    controller.abort();
                }
            },
        },
    };
}
export function serializeSSEEvent(chunk) {
    return [`event: ${chunk.event}`, `data: ${JSON.stringify(chunk.data)}`, "\n"].join("\n");
}
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