dcrouter/ts/mail/delivery/smtp/connection-manager.ts

/**
 * SMTP Connection Manager
 * Responsible for managing socket connections to the SMTP server
 */

import * as plugins from '../../../plugins.js';
import { IConnectionManager } from './interfaces.js';
import { ISessionManager } from './interfaces.js';
import { SmtpResponseCode, SMTP_DEFAULTS } from './constants.js';
import { SmtpLogger } from './utils/logging.js';
import { getSocketDetails, formatMultilineResponse } from './utils/helpers.js';

/**
 * Manager for SMTP connections
 * Handles connection setup, event listeners, and lifecycle management
 */
export class ConnectionManager implements IConnectionManager {
  /**
   * Set of active socket connections
   */
  private activeConnections: Set<plugins.net.Socket | plugins.tls.TLSSocket> = new Set();
  
  /**
   * Reference to the session manager
   */
  private sessionManager: ISessionManager;
  
  /**
   * SMTP server options
   */
  private options: {
    hostname: string;
    maxConnections: number;
    socketTimeout: number;
  };
  
  /**
   * Command handler function
   */
  private commandHandler: (socket: plugins.net.Socket | plugins.tls.TLSSocket, line: string) => void;
  
  /**
   * Creates a new connection manager
   * @param sessionManager - Session manager instance
   * @param commandHandler - Command handler function
   * @param options - Connection manager options
   */
  constructor(
    sessionManager: ISessionManager,
    commandHandler: (socket: plugins.net.Socket | plugins.tls.TLSSocket, line: string) => void,
    options: {
      hostname?: string;
      maxConnections?: number;
      socketTimeout?: number;
    } = {}
  ) {
    this.sessionManager = sessionManager;
    this.commandHandler = commandHandler;
    
    this.options = {
      hostname: options.hostname || SMTP_DEFAULTS.HOSTNAME,
      maxConnections: options.maxConnections || SMTP_DEFAULTS.MAX_CONNECTIONS,
      socketTimeout: options.socketTimeout || SMTP_DEFAULTS.SOCKET_TIMEOUT
    };
  }
  
  /**
   * Handle a new connection
   * @param socket - Client socket
   */
  public handleNewConnection(socket: plugins.net.Socket): void {
    // Check if maximum connections reached
    if (this.hasReachedMaxConnections()) {
      this.rejectConnection(socket, 'Too many connections');
      return;
    }
    
    // Add socket to active connections
    this.activeConnections.add(socket);
    
    // Set up socket options
    socket.setKeepAlive(true);
    socket.setTimeout(this.options.socketTimeout);
    
    // Set up event handlers
    this.setupSocketEventHandlers(socket);
    
    // Create a session for this connection
    this.sessionManager.createSession(socket, false);
    
    // Log the new connection
    const socketDetails = getSocketDetails(socket);
    SmtpLogger.logConnection(socket, 'connect');
    
    // Send greeting
    this.sendGreeting(socket);
  }
  
  /**
   * Handle a new secure TLS connection
   * @param socket - Client TLS socket
   */
  public handleNewSecureConnection(socket: plugins.tls.TLSSocket): void {
    // Check if maximum connections reached
    if (this.hasReachedMaxConnections()) {
      this.rejectConnection(socket, 'Too many connections');
      return;
    }
    
    // Add socket to active connections
    this.activeConnections.add(socket);
    
    // Set up socket options
    socket.setKeepAlive(true);
    socket.setTimeout(this.options.socketTimeout);
    
    // Set up event handlers
    this.setupSocketEventHandlers(socket);
    
    // Create a session for this connection
    this.sessionManager.createSession(socket, true);
    
    // Log the new secure connection
    SmtpLogger.logConnection(socket, 'connect');
    
    // Send greeting
    this.sendGreeting(socket);
  }
  
  /**
   * Set up event handlers for a socket
   * @param socket - Client socket
   */
  public setupSocketEventHandlers(socket: plugins.net.Socket | plugins.tls.TLSSocket): void {
    // Store existing socket event handlers before adding new ones
    const existingDataHandler = socket.listeners('data')[0];
    const existingCloseHandler = socket.listeners('close')[0];
    const existingErrorHandler = socket.listeners('error')[0];
    const existingTimeoutHandler = socket.listeners('timeout')[0];
    
    // Remove existing event handlers if they exist
    if (existingDataHandler) socket.removeListener('data', existingDataHandler);
    if (existingCloseHandler) socket.removeListener('close', existingCloseHandler);
    if (existingErrorHandler) socket.removeListener('error', existingErrorHandler);
    if (existingTimeoutHandler) socket.removeListener('timeout', existingTimeoutHandler);
    
    // Data event - process incoming data from the client
    let buffer = '';
    socket.on('data', (data) => {
      // Get current session and update activity timestamp
      const session = this.sessionManager.getSession(socket);
      if (session) {
        this.sessionManager.updateSessionActivity(session);
      }
      
      // Buffer incoming data
      buffer += data.toString();
      
      // Process complete lines
      let lineEndPos;
      while ((lineEndPos = buffer.indexOf(SMTP_DEFAULTS.CRLF)) !== -1) {
        // Extract a complete line
        const line = buffer.substring(0, lineEndPos);
        buffer = buffer.substring(lineEndPos + 2); // +2 to skip CRLF
        
        // Process non-empty lines
        if (line.length > 0) {
          // In DATA state, the command handler will process the data differently
          this.commandHandler(socket, line);
        }
      }
    });
    
    // Close event - clean up when connection is closed
    socket.on('close', (hadError) => {
      this.handleSocketClose(socket, hadError);
    });
    
    // Error event - handle socket errors
    socket.on('error', (err) => {
      this.handleSocketError(socket, err);
    });
    
    // Timeout event - handle socket timeouts
    socket.on('timeout', () => {
      this.handleSocketTimeout(socket);
    });
  }
  
  /**
   * Get the current connection count
   * @returns Number of active connections
   */
  public getConnectionCount(): number {
    return this.activeConnections.size;
  }
  
  /**
   * Check if the server has reached the maximum number of connections
   * @returns True if max connections reached
   */
  public hasReachedMaxConnections(): boolean {
    return this.activeConnections.size >= this.options.maxConnections;
  }
  
  /**
   * Close all active connections
   */
  public closeAllConnections(): void {
    const connectionCount = this.activeConnections.size;
    if (connectionCount === 0) {
      return;
    }
    
    SmtpLogger.info(`Closing all connections (count: ${connectionCount})`);
    
    for (const socket of this.activeConnections) {
      try {
        // Send service closing notification
        this.sendServiceClosing(socket);
        
        // End the socket
        socket.end();
      } catch (error) {
        SmtpLogger.error(`Error closing connection: ${error instanceof Error ? error.message : String(error)}`);
      }
    }
    
    // Clear active connections
    this.activeConnections.clear();
  }
  
  /**
   * Handle socket close event
   * @param socket - Client socket
   * @param hadError - Whether the socket was closed due to error
   */
  private handleSocketClose(socket: plugins.net.Socket | plugins.tls.TLSSocket, hadError: boolean): void {
    // Remove from active connections
    this.activeConnections.delete(socket);
    
    // Get the session before removing it
    const session = this.sessionManager.getSession(socket);
    
    // Remove from session manager
    this.sessionManager.removeSession(socket);
    
    // Log connection close
    SmtpLogger.logConnection(socket, 'close', session);
  }
  
  /**
   * Handle socket error event
   * @param socket - Client socket
   * @param error - Error object
   */
  private handleSocketError(socket: plugins.net.Socket | plugins.tls.TLSSocket, error: Error): void {
    // Get the session
    const session = this.sessionManager.getSession(socket);
    
    // Log the error
    SmtpLogger.logConnection(socket, 'error', session, error);
    
    // Close the socket if not already closed
    if (!socket.destroyed) {
      socket.destroy();
    }
  }
  
  /**
   * Handle socket timeout event
   * @param socket - Client socket
   */
  private handleSocketTimeout(socket: plugins.net.Socket | plugins.tls.TLSSocket): void {
    // Get the session
    const session = this.sessionManager.getSession(socket);
    
    if (session) {
      // Log the timeout
      SmtpLogger.warn(`Socket timeout from ${session.remoteAddress}`, {
        sessionId: session.id,
        remoteAddress: session.remoteAddress,
        state: session.state,
        timeout: this.options.socketTimeout
      });
      
      // Send timeout notification
      this.sendResponse(socket, `${SmtpResponseCode.SERVICE_NOT_AVAILABLE} Connection timeout - closing connection`);
    } else {
      // Log timeout without session context
      const socketDetails = getSocketDetails(socket);
      SmtpLogger.warn(`Socket timeout without session from ${socketDetails.remoteAddress}:${socketDetails.remotePort}`);
    }
    
    // Close the socket
    try {
      socket.end();
    } catch (error) {
      SmtpLogger.error(`Error ending timed out socket: ${error instanceof Error ? error.message : String(error)}`);
    }
  }
  
  /**
   * Reject a connection
   * @param socket - Client socket
   * @param reason - Reason for rejection
   */
  private rejectConnection(socket: plugins.net.Socket | plugins.tls.TLSSocket, reason: string): void {
    // Log the rejection
    const socketDetails = getSocketDetails(socket);
    SmtpLogger.warn(`Connection rejected from ${socketDetails.remoteAddress}:${socketDetails.remotePort}: ${reason}`);
    
    // Send rejection message
    this.sendResponse(socket, `${SmtpResponseCode.SERVICE_NOT_AVAILABLE} ${this.options.hostname} Service temporarily unavailable - ${reason}`);
    
    // Close the socket
    try {
      socket.end();
    } catch (error) {
      SmtpLogger.error(`Error ending rejected socket: ${error instanceof Error ? error.message : String(error)}`);
    }
  }
  
  /**
   * Send greeting message
   * @param socket - Client socket
   */
  private sendGreeting(socket: plugins.net.Socket | plugins.tls.TLSSocket): void {
    const greeting = `${SmtpResponseCode.SERVICE_READY} ${this.options.hostname} ESMTP service ready`;
    this.sendResponse(socket, greeting);
  }
  
  /**
   * Send service closing notification
   * @param socket - Client socket
   */
  private sendServiceClosing(socket: plugins.net.Socket | plugins.tls.TLSSocket): void {
    const message = `${SmtpResponseCode.SERVICE_CLOSING} ${this.options.hostname} Service closing transmission channel`;
    this.sendResponse(socket, message);
  }
  
  /**
   * Send response to client
   * @param socket - Client socket
   * @param response - Response to send
   */
  private sendResponse(socket: plugins.net.Socket | plugins.tls.TLSSocket, response: string): void {
    try {
      socket.write(`${response}${SMTP_DEFAULTS.CRLF}`);
      SmtpLogger.logResponse(response, socket);
    } catch (error) {
      // Log error and destroy socket
      SmtpLogger.error(`Error sending response: ${error instanceof Error ? error.message : String(error)}`, {
        response,
        remoteAddress: socket.remoteAddress,
        remotePort: socket.remotePort,
        error: error instanceof Error ? error : new Error(String(error))
      });
      
      socket.destroy();
    }
  }
}