Xboard/docs/en/development/device-limit.md

Online Device Limit Design

Overview

This document describes the design and implementation of the online device limit feature in Xboard.

Design Goals

1. Accurate Control

   • Precise counting of online devices
   • Real-time monitoring of device status
   • Accurate device identification

2. Performance Optimization

   • Minimal impact on system performance
   • Efficient device tracking
   • Optimized resource usage

3. User Experience

   • Smooth connection experience
   • Clear error messages
   • Graceful handling of limit exceeded cases

Implementation Details

1. Device Identification

Device ID Generation

public function generateDeviceId($user, $request) {
    return md5(
        $user->id . 
        $request->header('User-Agent') . 
        $request->ip()
    );
}

Device Information Storage

[
    'device_id' => 'unique_device_hash',
    'user_id' => 123,
    'ip' => '192.168.1.1',
    'user_agent' => 'Mozilla/5.0...',
    'last_active' => '2024-03-21 10:00:00'
]

2. Connection Management

Connection Check

public function checkDeviceLimit($user, $deviceId) {
    $onlineDevices = $this->getOnlineDevices($user->id);
    
    if (count($onlineDevices) >= $user->device_limit) {
        if (!in_array($deviceId, $onlineDevices)) {
            throw new DeviceLimitExceededException();
        }
    }
    
    return true;
}

Device Status Update

public function updateDeviceStatus($userId, $deviceId) {
    Redis::hset(
        "user:{$userId}:devices",
        $deviceId,
        json_encode([
            'last_active' => now(),
            'status' => 'online'
        ])
    );
}

3. Cleanup Mechanism

Inactive Device Cleanup

public function cleanupInactiveDevices() {
    $inactiveThreshold = now()->subMinutes(30);
    
    foreach ($this->getUsers() as $user) {
        $devices = $this->getOnlineDevices($user->id);
        
        foreach ($devices as $deviceId => $info) {
            if ($info['last_active'] < $inactiveThreshold) {
                $this->removeDevice($user->id, $deviceId);
            }
        }
    }
}

Error Handling

Error Types

1. Device Limit Exceeded

   class DeviceLimitExceededException extends Exception {
       protected $message = 'Device limit exceeded';
       protected $code = 4001;
   }
   

2. Invalid Device

   class InvalidDeviceException extends Exception {
       protected $message = 'Invalid device';
       protected $code = 4002;
   }
   

Error Messages

return [
    'device_limit_exceeded' => 'Maximum number of devices reached',
    'invalid_device' => 'Device not recognized',
    'device_expired' => 'Device session expired'
];

Performance Considerations

1. Cache Strategy

   • Use Redis for device tracking
   • Implement cache expiration
   • Optimize cache structure

2. Database Operations

   • Minimize database queries
   • Use batch operations
   • Implement query optimization

3. Memory Management

   • Efficient data structure
   • Regular cleanup of expired data
   • Memory usage monitoring

Security Measures

1. Device Verification

   • Validate device information
   • Check for suspicious patterns
   • Implement rate limiting

2. Data Protection

   • Encrypt sensitive information
   • Implement access control
   • Regular security audits

Future Improvements

1. Enhanced Features

   • Device management interface
   • Device activity history
   • Custom device names

2. Performance Optimization

   • Improved caching strategy
   • Better cleanup mechanism
   • Reduced memory usage

3. Security Enhancements

   • Advanced device fingerprinting
   • Fraud detection
   • Improved encryption

Conclusion

This design provides a robust and efficient solution for managing online device limits while maintaining good performance and user experience. Regular monitoring and updates will ensure the system remains effective and secure.