express-smart-logger-pro/README.md

Professional Express logging middleware with advanced features and zero configuration

# Express Smart Logger Pro

**Professional Express logging middleware that goes beyond basic logging.**

## What This Package Does

This isn't just a logger - it's a **developer productivity tool** that automatically:
- Logs every request with unique trace IDs
- Links related requests together with correlation IDs
- Tracks performance trends over time
- Captures full error context automatically
- Hides sensitive data with smart masking
- Provides performance insights and monitoring
- Adapts to development vs production environments

## Why This Package is Different

**Other logging packages:**
- Only do basic request/response logging
- Require manual setup and configuration
- Don't provide performance insights
- Don't link related requests together
- Don't capture error context automatically

**This package:**
- **Zero configuration** - Just plug it in
- **Request correlation** - Automatically links related requests
- **Performance insights** - Tracks trends, not just individual requests
- **Error context** - Full debugging information automatically
- **Production ready** - Enterprise-grade monitoring capabilities
- **Developer workflow** - Perfect for debugging complex systems

## Quick Start

### Install
```bash
npm install express-smart-logger-pro
```

### Use
```javascript
const express = require('express');
const logger = require('express-smart-logger-pro');

const app = express();
app.use(logger()); // That's it!

app.get('/user', (req, res) => {
  res.json({ 
    name: 'John',
    password: 'secret123' // Will be hidden automatically
  });
});
```

## All Features (Built-In, No Extra Setup)

### 🔍 **Core Logging (Always Active)**
- **Trace ID** - Every request gets unique ID like `[TRACE-abc123]`
- **Request Details** - Method, URL, status, duration
- **Response Data** - What your API returns (with sensitive data hidden)
- **Performance** - Request timing and slow request detection
- **Environment** - Colored logs in dev, JSON in production

### 🚀 **Advanced Features (Always Active)**
- **Request Correlation** - Automatically links related requests together
- **Performance Insights** - Tracks performance trends over time
- **Error Context** - Captures full request context when errors occur
- **Smart Masking** - Hides passwords, tokens, secrets automatically

### 📊 **Performance Monitoring (Always Active)**
- **Trend Tracking** - Average, Min, Max response times per endpoint
- **Error Rates** - Track error counts per endpoint
- **Performance Degradation** - Detect when endpoints slow down
- **Historical Data** - Performance data over time

### 🛡️ **Security Features (Always Active)**
- **Auto-Masking** - Hides sensitive fields automatically
- **Smart Masking** - Uses asterisks (`********`) instead of generic text
- **Default Protection** - Covers: password, token, secret, key, auth, authorization
- **Custom Fields** - Add your own sensitive fields to hide

## Extra Features (Turn On When Needed)

```javascript
// Basic usage - all advanced features work automatically
app.use(logger());

// Enhanced usage - enable additional logging
app.use(logger({
  logBody: true,                    // Log incoming request data
  logHeaders: true,                 // Log user-agent and IP address  
  logSize: true,                    // Log request/response sizes
  mask: ['creditCard', 'ssn'],      // Hide additional sensitive fields
  slowThreshold: 2000,              // Alert for requests slower than 2 seconds
  enableCorrelation: true,          // Link related requests together
  enablePerformanceInsights: true,  // Track performance trends over time
  enableErrorContext: true          // Capture full error context
}));
```

## What You'll See

### Development (Colored logs )
```
[TRACE-abc123] GET /user 200 (15ms)
Correlation ID: def456
Request Size: 45 bytes
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) Chrome/120.0.0.0
IP: 192.168.1.100
Request Body: {
  "email": "john@example.com",
  "password": "********"
}
Performance: Avg: 12ms, Min: 8ms, Max: 25ms
Response Size: 89 bytes
Response: {
  "name": "John",
  "password": "********"
}
```

### Production (JSON logs )
```json
{
  "traceId": "abc123",
  "correlationId": "def456",
  "timestamp": "2024-01-15T10:30:00.000Z",
  "method": "GET",
  "url": "/user",
  "status": 200,
  "duration": 15,
  "requestSize": 45,
  "responseSize": 89,
  "userAgent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Chrome/120.0.0.0",
  "ip": "192.168.1.100",
  "requestBody": {
    "email": "john@example.com",
    "password": "********"
  },
  "performance": {
    "avgTime": 12,
    "minTime": 8,
    "maxTime": 25,
    "count": 150,
    "errorCount": 2
  },
  "response": {
    "name": "John",
    "password": "********"
  }
}
```

## Advanced Developer Features

### Request Correlation
Automatically links related requests together:
```javascript
// All requests in a user session get the same correlation ID
// Perfect for debugging complex workflows and user journeys
// Track entire user sessions from login to logout
```

### Performance Insights
Tracks performance trends over time:
```javascript
// Shows: Average, Min, Max response times per endpoint
// Error rates and performance degradation alerts
// Historical performance data for optimization
// Identify which endpoints are slowing down over time
```

### Enhanced Error Context
When errors occur, automatically captures:
```javascript
// Full request context (headers, body, trace ID)
// Performance data at time of error
// Correlation with other requests in the session
// Perfect for debugging production issues
```

### Performance Monitoring API
Access performance data programmatically:
```javascript
const logger = require('express-smart-logger');

// Get performance stats for all endpoints
const stats = logger.getPerformanceStats();
console.log(stats);

// Clear performance data
logger.clearPerformanceStats();

// Get request correlation data
const correlations = logger.getRequestCorrelation();
```

## What Gets Hidden Automatically

These fields are automatically hidden with asterisks:
- `password` → `********`
- `token` → `****`
- `secret` → `******`
- `key` → `***`
- `auth` → `****`
- `authorization` → `************`

## Usage Examples

### Basic Usage
```javascript
app.use(logger());
```

### With Request Body Logging
```javascript
app.use(logger({
  logBody: true,
  logHeaders: true
}));
```

### With Custom Masking
```javascript
app.use(logger({
  mask: ['creditCard', 'ssn', 'apiKey']
}));
```

### Full Enterprise Setup
```javascript
app.use(logger({
  logBody: true,
  logHeaders: true,
  logSize: true,
  mask: ['creditCard', 'ssn', 'apiKey'],
  slowThreshold: 2000,
  enableCorrelation: true,
  enablePerformanceInsights: true,
  enableErrorContext: true
}));
```

## Environment Detection

- **Development**: Colored console output with trace IDs and correlation IDs
- **Production**: Structured JSON logs for log aggregation and monitoring

Set `NODE_ENV=production` to enable production mode.

## Use Cases

- **API Development** - Quick debugging with request correlation
- **Production APIs** - Enterprise-grade monitoring and insights
- **Microservices** - Track requests across service boundaries
- **Complex Workflows** - Debug user journeys with correlation IDs
- **Performance Optimization** - Identify slow endpoints and trends
- **Error Investigation** - Full context for production debugging

## This Package Solves Real Problems

- **"Why is my API slow?"** → Performance insights show trends over time
- **"Which requests are related?"** → Correlation IDs link them automatically
- **"What happened when this error occurred?"** → Full error context captured
- **"How is my API performing?"** → Historical performance data available
- **"Debug this user session"** → Correlation IDs track entire workflows

## License

MIT