Minimal WebSocket Tail-F Server for Laravel Logs

app.js

import { WebSocketServer } from 'ws';
import fs from 'fs';
import path from 'path';
import readline from 'readline';

/*****************************************************************************************
 *  Minimal WebSocket‑based “tail‑f” server for Laravel log files
 *  ------------------------------------------------------------------
 *  • One WebSocket per browser tab.
 *  • Client sends  { event:'getLumenLog', data:{ date:'DD‑MM‑YYYY' } }.
 *  • Server:
 *      1. Streams the entire file for that date.
 *      2. Watches the file and pushes any new lines to the same socket.
 *      3. Cleans up watcher on socket close or when the client switches dates.
 *****************************************************************************************/

const logDir = path.join(process.cwd(), 'storage', 'logs');     // Laravel log folder
const wss = new WebSocketServer({ port: 3001 });                // WS server

/* Map<ws, { filePath, watcher, lastSize }> keeps per‑client watch state     */
const clientWatchers = new Map();

/** Convert DD‑MM‑YYYY → YYYY‑MM‑DD (local timezone safe) */
function parseDateFromDDMMYYYY(dateStr) {
    const [day, month, year] = dateStr.split('-').map(Number);
    const localDate = new Date(year, month - 1, day);

    // Format to YYYY-MM-DD in local time
    const yyyy = localDate.getFullYear();
    const mm = String(localDate.getMonth() + 1).padStart(2, '0');
    const dd = String(localDate.getDate()).padStart(2, '0');

    const formattedDate = `${yyyy}-${mm}-${dd}`;
  
    return formattedDate;
}

/** Build full log‑file path from DD‑MM‑YYYY */
function getLogFilePathFromDate(dateStr) {
    const date = parseDateFromDDMMYYYY(dateStr);
    
    return path.join(logDir, `laravel-${date}.log`);
}


/*───────────────────────────────────────────────────────────────────────────*
 *  CORE: start / stop watching a log file for ONE WS client                 *
 *───────────────────────────────────────────────────────────────────────────*/

/**
 * Begin streaming `filePath` to a specific WebSocket (`ws`).
 *  1. Send the whole file once.
 *  2. Watch for new bytes and push each appended line in real‑time.
 */

function startWatchingFile(ws, filePath) {

    let lastSize = 0;

    // 1. Read and send full file content initially
    fs.readFile(filePath, 'utf-8', (err, data) => {
        if (!err && data) {
            const lines = data.trimEnd().split("\n").reverse();
            for (const line of lines) {
                if (line.trim()) {
                    const payload = JSON.stringify({ event: 'log', data: line });
                    if (ws.readyState === ws.OPEN) ws.send(payload);
                }
            }
            lastSize = Buffer.byteLength(data);     // Set lastSize to current file size
        }

        // 2. Start watching for changes after initial send
        const watcher = fs.watch(filePath, (eventType) => {
            if (eventType !== 'change') return;

            fs.stat(filePath, (err, stats) => {
                
                if (err || stats.size <= lastSize) return;

                const start = lastSize;
                const end = stats.size - 1;
                lastSize = stats.size;

                const stream = fs.createReadStream(filePath, { start, end });
                
                /* Stream only the fresh bytes */
                const rl = readline.createInterface({ input: stream });
                
                rl.on('line', (line) => {
                    if (line.trim()) {
                        const payload = JSON.stringify({ event: 'log', data: line });
                        if (ws.readyState === ws.OPEN) ws.send(payload);
                    }
                });
            });
        });

        /* Save watcher so we can close it later */
        clientWatchers.set(ws, { filePath, watcher, lastSize });
    });
}

/** Stop and clean up the watcher associated with a WebSocket client */
function stopWatchingFile(ws) {
  const info = clientWatchers.get(ws);
  
  if (info?.watcher) {
    info.watcher.close();       // stop fs.watch
  }
  clientWatchers.delete(ws);    // remove from map
}

/*───────────────────────────────────────────────────────────────────────────*
 *  WEBSOCKET EVENT HANDLERS                                                 *
 *───────────────────────────────────────────────────────────────────────────*/
wss.on('connection', (ws) => {

  ws.on('close', () => {
    stopWatchingFile(ws);
  });

  ws.on('message', async (message) => {
    try {
        const data = JSON.parse(message.toString());

        if (data.event === 'getLumenLog') {
            const dateStr = data?.data?.date;
            const filePath = getLogFilePathFromDate(dateStr);
            
            if (!filePath) return;

             /* Ignore if client already watching this file */
            const existingWatcher = clientWatchers.get(ws);
            if (existingWatcher?.filePath === filePath) return;

            /* Switch file: clean old watcher, ensure new file exists, start watcher */
            stopWatchingFile(ws);
            
             try {
                await fs.promises.access(filePath, fs.constants.F_OK);
            } catch {
                // File does not exist — inform client and return
                if (ws.readyState === ws.OPEN) {
                    ws.send(JSON.stringify({
                        event: 'error',
                        message: `Log file not found for date ${dateStr}`
                    }));
                }
                return;
            }

            startWatchingFile(ws, filePath);
        }

    } catch (err) {

    }
  });
});

🧩 A lightweight Node.js WebSocket server that streams and live-tails Laravel log files (storage/logs/laravel-YYYY-MM-DD.log) to clients in real-time. Supports per-tab watchers, file switching, and automatic cleanup.

🔧 Usage: Client sends { event: "getLumenLog", data: { date: "DD-MM-YYYY" } }, server streams initial file + watches for new lines.

💡 Built for integration with Angular or any frontend via native WebSocket AP