Error Handling

Error Types

Connection Errors

Connection errors occur during the initial WebSocket handshake or due to network issues.

socket.on('connect_error', (error) => {
  console.error('Connection failed:', error.message);
  
  switch (error.type) {
    case 'TransportError':
      handleTransportError(error);
      break;
    case 'timeout':
      handleTimeoutError(error);
      break;
    case 'poll error':
      handlePollError(error);
      break;
    default:
      handleGenericError(error);
  }
});

Authentication Errors

Authentication errors occur during connection establishment.

For detailed authentication error codes and handling, see Authentication Error Codes.

socket.on('news:error', (error) => {
  console.error('Authentication failed:', error.code);
  // Handle specific authentication errors
  // See authentication documentation for detailed handling
});

Application-Level Errors

Application errors occur during WebSocket operations and data processing.

socket.on('error', (error) => {
  console.error('WebSocket error:', error);
  
  switch (error.type) {
    case 'ValidationError':
      console.log('Data validation failed');
      break;
    case 'ProcessingError':
      console.log('Server processing error');
      break;
    case 'TimeoutError':
      console.log('Operation timeout');
      break;
    default:
      console.log('Unknown application error');
  }
});

Error Handling Strategies

Exponential Backoff

Implement exponential backoff to avoid overwhelming the server during reconnection attempts.

class ExponentialBackoff {
  constructor(initialDelay = 1000, maxDelay = 30000, factor = 2) {
    this.initialDelay = initialDelay;
    this.maxDelay = maxDelay;
    this.factor = factor;
    this.attempts = 0;
  }
  
  getDelay() {
    const delay = Math.min(
      this.initialDelay * Math.pow(this.factor, this.attempts),
      this.maxDelay
    );
    this.attempts++;
    return delay;
  }
  
  reset() {
    this.attempts = 0;
  }
}

// Usage
const backoff = new ExponentialBackoff();

socket.on('disconnect', () => {
  const delay = backoff.getDelay();
  console.log(`Reconnecting in ${delay}ms...`);
  
  setTimeout(() => {
    socket.connect();
  }, delay);
});

socket.on('connect', () => {
  backoff.reset(); // Reset on successful connection
});

Circuit Breaker Pattern

Prevent cascading failures by implementing a circuit breaker pattern.

class CircuitBreaker {
  constructor(threshold = 5, timeout = 60000) {
    this.failureThreshold = threshold;
    this.timeout = timeout;
    this.failureCount = 0;
    this.lastFailureTime = null;
    this.state = 'CLOSED'; // CLOSED, OPEN, HALF_OPEN
  }
  
  canAttempt() {
    if (this.state === 'CLOSED') {
      return true;
    }
    
    if (this.state === 'OPEN') {
      if (Date.now() - this.lastFailureTime > this.timeout) {
        this.state = 'HALF_OPEN';
        return true;
      }
      return false;
    }
    
    if (this.state === 'HALF_OPEN') {
      return true;
    }
    
    return false;
  }
  
  recordSuccess() {
    this.failureCount = 0;
    this.state = 'CLOSED';
  }
  
  recordFailure() {
    this.failureCount++;
    this.lastFailureTime = Date.now();
    
    if (this.failureCount >= this.failureThreshold) {
      this.state = 'OPEN';
    }
  }
}

// Usage
const circuitBreaker = new CircuitBreaker();

function attemptConnection() {
  if (!circuitBreaker.canAttempt()) {
    console.log('Circuit breaker is OPEN, skipping connection attempt');
    return;
  }
  
  socket.connect();
}

socket.on('connect', () => {
  circuitBreaker.recordSuccess();
});

socket.on('connect_error', () => {
  circuitBreaker.recordFailure();
});

Retry Logic

Implement intelligent retry logic with different strategies for different error types.

class RetryManager {
  constructor() {
    this.maxRetries = {
      'INVALID_API_KEY': 0,      // Don't retry invalid API key
      'PLAN_EXPIRED': 0,         // Don't retry expired plan
      'CONNECTION_LIMIT': 3,     // Limited retries for connection limit
      'NETWORK_ERROR': 10,       // More retries for network issues
      'DEFAULT': 5
    };
    
    this.retryCount = {};
  }
  
  shouldRetry(errorCode) {
    const maxRetries = this.maxRetries[errorCode] || this.maxRetries.DEFAULT;
    const currentRetries = this.retryCount[errorCode] || 0;
    
    return currentRetries < maxRetries;
  }
  
  incrementRetry(errorCode) {
    this.retryCount[errorCode] = (this.retryCount[errorCode] || 0) + 1;
  }
  
  resetRetries(errorCode = null) {
    if (errorCode) {
      this.retryCount[errorCode] = 0;
    } else {
      this.retryCount = {};
    }
  }
}

// Usage
const retryManager = new RetryManager();

socket.on('news:error', (error) => {
  if (retryManager.shouldRetry(error.code)) {
    retryManager.incrementRetry(error.code);
    
    setTimeout(() => {
      console.log(`Retrying connection (attempt ${retryManager.retryCount[error.code]})`);
      socket.connect();
    }, 5000);
  } else {
    console.error('Max retries reached for error:', error.code);
    handleFinalError(error);
  }
});

socket.on('connect', () => {
  retryManager.resetRetries();
});

Error Recovery

Automatic Reconnection

Configure automatic reconnection with customizable parameters.

const socket = io('wss://api.byul.ai/news-v2', {
  auth: { apiKey: process.env.BYUL_API_KEY },
  
  // Reconnection configuration
  reconnection: true,
  reconnectionAttempts: 10,
  reconnectionDelay: 1000,
  reconnectionDelayMax: 5000,
  randomizationFactor: 0.5,
  
  // Timeout configuration
  timeout: 20000
});

// Handle reconnection events
socket.on('reconnect_attempt', (attemptNumber) => {
  console.log(`Reconnection attempt #${attemptNumber}`);
});

socket.on('reconnect', (attemptNumber) => {
  console.log(`Reconnected after ${attemptNumber} attempts`);
  restoreSubscriptions();
});

socket.on('reconnect_error', (error) => {
  console.error('Reconnection failed:', error);
});

socket.on('reconnect_failed', () => {
  console.error('All reconnection attempts failed');
  handleConnectionFailure();
});

State Recovery

Restore application state after reconnection.

class StateManager {
  constructor() {
    this.subscriptions = new Map();
    this.connectionState = 'disconnected';
  }
  
  saveSubscription(id, params) {
    this.subscriptions.set(id, params);
  }
  
  removeSubscription(id) {
    this.subscriptions.delete(id);
  }
  
  restoreSubscriptions(socket) {
    console.log(`Restoring ${this.subscriptions.size} subscriptions`);
    
    for (const [id, params] of this.subscriptions) {
      socket.emit('news:subscribe', params);
    }
  }
  
  clearSubscriptions() {
    this.subscriptions.clear();
  }
}

// Usage
const stateManager = new StateManager();

// Save subscription when created
socket.emit('news:subscribe', { symbol: 'AAPL', startDate: '2024-01-01T00:00:00.000Z' });
stateManager.saveSubscription('aapl-news', { symbol: 'AAPL' });

// Restore on reconnection
socket.on('reconnect', () => {
  stateManager.restoreSubscriptions(socket);
});

Graceful Degradation

Implement fallback mechanisms when WebSocket connection fails.

class FallbackManager {
  constructor() {
    this.fallbackActive = false;
    this.pollInterval = null;
  }
  
  activateFallback() {
    if (this.fallbackActive) return;
    
    console.log('Activating fallback to REST API polling');
    this.fallbackActive = true;
    
    // Start polling REST API
    this.pollInterval = setInterval(() => {
      this.pollRestAPI();
    }, 30000); // Poll every 30 seconds
  }
  
  deactivateFallback() {
    if (!this.fallbackActive) return;
    
    console.log('Deactivating fallback, WebSocket restored');
    this.fallbackActive = false;
    
    if (this.pollInterval) {
      clearInterval(this.pollInterval);
      this.pollInterval = null;
    }
  }
  
  async pollRestAPI() {
    try {
      const response = await fetch('https://api.byul.ai/api/v2/news', {
        headers: {
          'X-API-Key': process.env.BYUL_API_KEY
        }
      });
      
      const data = await response.json();
      // Process data same as WebSocket
      this.processNewsData(data.items);
      
    } catch (error) {
      console.error('Fallback REST API failed:', error);
    }
  }
  
  processNewsData(articles) {
    // Same processing logic as WebSocket data
    articles.forEach(article => {
      console.log(`News: ${article.title}`);
    });
  }
}

// Usage
const fallbackManager = new FallbackManager();

socket.on('disconnect', () => {
  fallbackManager.activateFallback();
});

socket.on('connect', () => {
  fallbackManager.deactivateFallback();
});

User Experience

Error Notifications

Provide clear error messages and recovery instructions to users.

class ErrorNotificationManager {
  constructor() {
    this.notifications = new Map();
  }
  
  showError(type, message, actions = []) {
    const notification = {
      id: Date.now(),
      type,
      message,
      actions,
      timestamp: new Date()
    };
    
    this.notifications.set(notification.id, notification);
    this.displayNotification(notification);
  }
  
  displayNotification(notification) {
    const errorDiv = document.createElement('div');
    errorDiv.className = `error-notification ${notification.type}`;
    errorDiv.innerHTML = `
      <div class="error-message">${notification.message}</div>
      <div class="error-actions">
        ${notification.actions.map(action => 
          `<button onclick="${action.handler}">${action.text}</button>`
        ).join('')}
      </div>
    `;
    
    document.getElementById('notifications').appendChild(errorDiv);
  }
  
  clearError(id) {
    this.notifications.delete(id);
    // Remove from DOM
    const element = document.getElementById(`notification-${id}`);
    if (element) {
      element.remove();
    }
  }
}

// Usage
const errorNotifications = new ErrorNotificationManager();

socket.on('news:error', (error) => {
  if (error.code === 'PLAN_EXPIRED') {
    errorNotifications.showError('warning', 
      'Your subscription has expired. Please renew to continue using WebSocket features.',
      [
        { text: 'Renew Subscription', handler: 'window.open("https://byul.ai/pricing")' },
        { text: 'Contact Support', handler: 'window.open("https://byul.ai/contact")' }
      ]
    );
  }
});

Connection Status Indicator

Display real-time connection status to users.

class ConnectionStatusIndicator {
  constructor() {
    this.statusElement = document.getElementById('connection-status');
    this.indicatorElement = document.getElementById('connection-indicator');
  }
  
  updateStatus(status, message = '') {
    const statusConfig = {
      'connected': {
        class: 'connected',
        text: 'Connected',
        color: '#10B981'
      },
      'connecting': {
        class: 'connecting',
        text: 'Connecting...',
        color: '#F59E0B'
      },
      'disconnected': {
        class: 'disconnected',
        text: 'Disconnected',
        color: '#EF4444'
      },
      'error': {
        class: 'error',
        text: 'Connection Error',
        color: '#EF4444'
      }
    };
    
    const config = statusConfig[status];
    
    if (this.statusElement) {
      this.statusElement.textContent = message || config.text;
      this.statusElement.className = `status ${config.class}`;
    }
    
    if (this.indicatorElement) {
      this.indicatorElement.style.backgroundColor = config.color;
    }
  }
}

// Usage
const statusIndicator = new ConnectionStatusIndicator();

socket.on('connect', () => {
  statusIndicator.updateStatus('connected');
});

socket.on('disconnect', () => {
  statusIndicator.updateStatus('disconnected');
});

socket.on('connect_error', () => {
  statusIndicator.updateStatus('error', 'Connection failed');
});

Monitoring and Logging

Error Metrics Collection

Collect error metrics for monitoring and debugging.

class ErrorMetrics {
  constructor() {
    this.metrics = {
      connectionErrors: 0,
      authenticationErrors: 0,
      subscriptionErrors: 0,
      reconnectionAttempts: 0,
      successfulReconnections: 0
    };
  }
  
  incrementMetric(metricName) {
    if (this.metrics.hasOwnProperty(metricName)) {
      this.metrics[metricName]++;
    }
  }
  
  getMetrics() {
    return { ...this.metrics };
  }
  
  resetMetrics() {
    Object.keys(this.metrics).forEach(key => {
      this.metrics[key] = 0;
    });
  }
  
  logMetrics() {
    console.log('WebSocket Error Metrics:', this.metrics);
  }
}

// Usage
const errorMetrics = new ErrorMetrics();

socket.on('connect_error', () => {
  errorMetrics.incrementMetric('connectionErrors');
});

socket.on('news:error', () => {
  errorMetrics.incrementMetric('authenticationErrors');
});

socket.on('reconnect_attempt', () => {
  errorMetrics.incrementMetric('reconnectionAttempts');
});

socket.on('reconnect', () => {
  errorMetrics.incrementMetric('successfulReconnections');
});

// Log metrics periodically
setInterval(() => {
  errorMetrics.logMetrics();
}, 300000); // Every 5 minutes

Best Practices

Error Classification

Categorize errors by type (transient vs permanent)
Implement different retry strategies for different error types
Log errors with sufficient context for debugging

Recovery Strategies

Use exponential backoff for reconnection attempts
Implement circuit breaker pattern for cascading failures
Provide fallback mechanisms when WebSocket fails

User Experience

Display clear error messages and recovery instructions
Show connection status indicators
Provide manual retry options for users

Monitoring

Collect error metrics and connection statistics
Set up alerts for high error rates
Monitor reconnection success rates

Getting Started

Connection

News

Error Handling

Examples

Error Handling

Error Types

Connection Errors

Authentication Errors

Application-Level Errors

Error Handling Strategies

Exponential Backoff

Circuit Breaker Pattern

Retry Logic

Error Recovery

Automatic Reconnection

State Recovery

Graceful Degradation

User Experience

Error Notifications

Connection Status Indicator

Monitoring and Logging

Error Metrics Collection

Best Practices

Getting Started

Connection

News

Error Handling

Examples

​Error Types

​Connection Errors

​Authentication Errors

​Application-Level Errors

​Error Handling Strategies

​Exponential Backoff

​Circuit Breaker Pattern

​Retry Logic

​Error Recovery

​Automatic Reconnection

​State Recovery

​Graceful Degradation

​User Experience

​Error Notifications

​Connection Status Indicator

​Monitoring and Logging

​Error Metrics Collection

​Best Practices

Error Types

Connection Errors

Authentication Errors

Application-Level Errors

Error Handling Strategies

Exponential Backoff

Circuit Breaker Pattern

Retry Logic

Error Recovery

Automatic Reconnection

State Recovery

Graceful Degradation

User Experience

Error Notifications

Connection Status Indicator

Monitoring and Logging

Error Metrics Collection

Best Practices