04-error-handling-logging

04-Error-Handling-Logging

Logging System Architecture

The project uses a centralized logging system implemented in logger.ts with configurable log levels.

Logger Integration

All classes receive a Logger instance via dependency injection and must use it for all logging operations.

CRITICAL LOGGING RULES - MUST FOLLOW

✅ ALWAYS DO:

1. Use Logger instance: Never use console.log - always use the injected Logger
2. Appropriate log levels: Use error/warn/info/debug according to severity
3. Structured logging: Include relevant context (clientId, operation, etc.)
4. Log before errors: Log context before throwing exceptions
5. Event emission: Emit events for error conditions to enable monitoring

❌ NEVER DO:

1. Direct console output: Never use console.log, console.error, etc.
2. Silent failures: Never catch errors without logging them
3. Expose sensitive data: Don't log passwords, tokens, or sensitive information
4. Generic error messages: Avoid vague messages like "Error occurred"
5. Log flooding: Don't log inside tight loops without throttling

Error Handling Patterns

✅ PROPER Error Handling:

// Class with proper logging setup
export class SessionManager extends EventEmitter {
  constructor(private logger: Logger) {
    super();
  }

  public registerClient(client: AgentClient): void {
    try {
      this.logger.info(`Registering client: ${client.id} (${client.type})`);
      this.clients.set(client.id, client);
      this.emit('clientConnected', client);
      this.logger.info(`Client registered successfully: ${client.id}`);
    } catch (error: unknown) {
      this.logger.error(`Failed to register client ${client.id}:`, error);
      this.emit('error', { operation: 'registerClient', clientId: client.id, error });
      throw error;
    }
  }
}

❌ INCORRECT Patterns:

// Bad - no logging
public registerClient(client: AgentClient): void {
  this.clients.set(client.id, client); // Silent operation
}

// Bad - console usage
public registerClient(client: AgentClient): void {
  console.log('Registering client:', client.id); // Wrong logging method
}

// Bad - swallowing errors
public registerClient(client: AgentClient): void {
  try {
    this.clients.set(client.id, client);
  } catch (error) {
    // Silent failure - very bad!
  }
}