🛠️ Express API Middleware Logger

A lightweight and developer-friendly middleware that provides structured and contextual logging for Express APIs.

This middleware helps developers easily trace API calls, debug issues, and monitor request/response cycles by capturing detailed logs. It supports time-based log batching and works seamlessly in both development and production environments with minimal setup.

📦 Installation

Install the core logging package:

npm install logs-ks

⚙️ Quick Setup

index.ts – Initialize Logger

import express from 'express';
import { Logger } from 'logs-ks';

const app = express();

// Initialize logger with custom configuration
// Note: Logger.init() must be called before using the middleware
Logger.init({
  writeLogTime: 5, // Write logs to file every 5 minutes
  logWithEnd: true, // Default false logging response at the end of API calls
  logWithSummary: true, // Default false logging api summary like > 2025-06-13 10:11:12 | GET  200 /api/v2/user 20 ms
});

router.ts – Apply Middleware per Route

import express, { Request, Response } from 'express';
import { loggerMiddleware, LoggerContext, logEmitter } from 'logs-ks';

const router = express.Router();

// request api localhost:3000/api/foo?page=1&limit=10
router.get('/api/:id', loggerMiddleware(), async (req: Request, res: Response) => {
  try {
    const { id } = req.params;
    const data = await getController(id);
    res.json(data);
  } catch (error: unknown) {
    res.status(500).send(error);
  }
});

// Use loggerMiddleware(false) to disable logging the response payload
// Useful for lightweight GET endpoints
router.get('/api/user/all', loggerMiddleware(false), (req, res) => res.json({ code: 200, payload: '...too much data' }));

async function getController(id) {
  const logger = LoggerContext.get();

  logger.addService({ type: 'DB' }, { name: 'findUser', argument: { id } });
  const findUser = await findUserDB({ id });
  logger.endService(findUser);

  return { code: 200, payload: { foo: 'bar' } };
}

// Listen for when a log file is finalized (previous file that finished writing)
// `filePath` refers to the last log file that was completed and closed
logEmitter.on('file-end', (filePath) => {
  console.log(`New log file created: ${filePath}`);
  // You can trigger backup, upload to S3, or notify devs here
});

export default router;

🧪 Example Log Output (JSON)

{
  "api": "api/foo?page=1&limit=10",
  "method": "GET",
  "authorization": null,
  "status": 200,
  "message": "OK",
  "inputTimestamp": "2025-06-13T10:11:12.000Z",
  "outputTimestamp": "2025-06-13T10:11:12.020Z",
  "processingTime": "20 ms",
  "request": {
    "headers": {},
    "params": { id: "foo"},
    "query": { page: "1", limit: "10" },
    "body": {},
    "detail": {}
  },
  "services": [{
    "id": 1,
    "type": "DB",
    "request": { "name": "findUser", "argument": { "id": "foo" } },
    "response": { "id": "foo", "name": "foobar" },
    "processingTime": "5 ms",
    "startTime": "2025-06-11T10:11:12.010Z",
    "endTime": "2025-06-11T10:11:12.015Z"
  }],
  "response": {
    "code": 200,
    "payload": { "foo": "bar" }
  },
  "summary": "2025-06-13 10:11:12 | GET  200 /api/user 20 ms"
}

type {
  api: string;
  method: string;
  authorization: string | JwtPayload | null;
  status: number;
  message: string;
  inputTimestamp: string;
  outputTimestamp: string;
  processingTime: string;
  request: {
    headers: Record<string, string>; // soon
    params: Record<string, string>;
    query: Record<string, string>;
    body: Record<string, any>;
    detail: Record<string, any>; // soon
  };
  services: Array<{
    id: number;
    type: 'DB' | 'API' | 'REDIS' | 'S3' | 'FILE' | 'FUNC';
    request: {
      name: string;
      argument: Record<string, any>;
    };
    response: Record<string, any> | Array<Record<string, any>>;
    processingTime: string;
    startTime: string;
    endTime: string;
  }>;
  response: Record<string, any>;
  summary: string;
}

🧩 Features

• ✅ Plug-and-play Express middleware
• 📄 Structured logs for easy debugging
• ⏱️ Time-based file writes for performance
• 🔍 Contextual request/response trace logging
• 💻 Console + file output support

📁 Output

Log files will be saved automatically in the working directory (or custom location if configured via logs-ks).

• 📂 Default path: ./logs/app-logs-${yy}-${mm}-${dd}-${hh}${mi}.jsonl
• (e.g. logs/app-log-25-06-13-1300.jsonl)