tardis-machine/dist/http/replay.js

Locally runnable server with built-in data caching, providing both tick-level historical and consolidated real-time cryptocurrency market data via HTTP and WebSocket APIs

import { once } from 'node:events';
import { replay } from 'tardis-dev';
import { debug } from "../debug.js";
export const replayHttp = async (req, res) => {
    try {
        const startTimestamp = new Date().getTime();
        const requestUrl = new URL(req.url, 'http://localhost');
        const optionsString = requestUrl.searchParams.get('options') ?? undefined;
        const replayOptions = JSON.parse(optionsString);
        debug('GET /replay request started, options: %o', replayOptions);
        const streamedMessagesCount = await writeMessagesToResponse(res, replayOptions);
        const endTimestamp = new Date().getTime();
        debug('GET /replay request finished, options: %o, time: %d seconds, total messages count:%d', replayOptions, (endTimestamp - startTimestamp) / 1000, streamedMessagesCount);
    }
    catch (e) {
        const errorInfo = {
            responseText: e.responseText,
            message: e.message,
            url: e.url
        };
        debug('GET /replay request error: %o', e);
        console.error('GET /replay request error:', e);
        if (!res.finished) {
            res.statusCode = e.status || 500;
            res.end(JSON.stringify(errorInfo));
        }
    }
};
async function writeMessagesToResponse(res, replayOptions) {
    const responsePrefixBuffer = Buffer.from('{"localTimestamp":"');
    const responseMiddleBuffer = Buffer.from('","message":');
    const responseSuffixBuffer = Buffer.from('}\n');
    const newLineBuffer = Buffer.from('\n');
    const BATCH_SIZE = 32;
    // not 100% sure that's necessary since we're returning ndjson in fact, not json
    res.setHeader('Content-Type', 'application/x-json-stream');
    let buffers = [];
    let totalMessagesCount = 0;
    const messages = replay({ ...replayOptions, skipDecoding: true });
    for await (let messageWithTimestamp of messages) {
        totalMessagesCount++;
        if (messageWithTimestamp === undefined) {
            // if received message is undefined  (disconnect)
            // return it as new line
            buffers.push(newLineBuffer);
        }
        else {
            // instead of writing each message directly to response,
            // let's batch them and send in BATCH_SIZE  batches (each message is 5 buffers: prefix etc)
            // also instead of converting messages to string or parsing them let's manually stich together desired json response using buffers which is faster
            buffers.push(responsePrefixBuffer, messageWithTimestamp.localTimestamp, responseMiddleBuffer, messageWithTimestamp.message, responseSuffixBuffer);
            if (buffers.length >= BATCH_SIZE * 5) {
                const ok = res.write(Buffer.concat(buffers));
                buffers = [];
                if (!ok) {
                    await once(res, 'drain');
                }
            }
        }
    }
    if (buffers.length > 0) {
        res.write(Buffer.concat(buffers));
        buffers = [];
    }
    res.end('');
    return totalMessagesCount;
}
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