smartproxy/ts/classes.snihandler.ts

import { Buffer } from 'buffer';

/**
 * SNI (Server Name Indication) handler for TLS connections.
 * Provides robust extraction of SNI values from TLS ClientHello messages
 * with support for fragmented packets, TLS 1.3 resumption, Chrome-specific
 * connection behaviors, and tab hibernation/reactivation scenarios.
 */
export class SniHandler {
  // TLS record types and constants
  private static readonly TLS_HANDSHAKE_RECORD_TYPE = 22;
  private static readonly TLS_APPLICATION_DATA_TYPE = 23;  // TLS Application Data record type
  private static readonly TLS_CLIENT_HELLO_HANDSHAKE_TYPE = 1;
  private static readonly TLS_SNI_EXTENSION_TYPE = 0x0000;
  private static readonly TLS_SESSION_TICKET_EXTENSION_TYPE = 0x0023;
  private static readonly TLS_SNI_HOST_NAME_TYPE = 0;
  private static readonly TLS_PSK_EXTENSION_TYPE = 0x0029; // Pre-Shared Key extension type for TLS 1.3
  private static readonly TLS_PSK_KE_MODES_EXTENSION_TYPE = 0x002D; // PSK Key Exchange Modes
  private static readonly TLS_EARLY_DATA_EXTENSION_TYPE = 0x002A; // Early Data (0-RTT) extension
  
  // Buffer for handling fragmented ClientHello messages
  private static fragmentedBuffers: Map<string, Buffer> = new Map();
  private static fragmentTimeout: number = 1000; // ms to wait for fragments before cleanup

  // Session tracking for tab reactivation scenarios
  private static sessionCache: Map<string, {
    sni: string;
    timestamp: number;
    clientRandom?: Buffer;
  }> = new Map();
  
  // Longer timeout for session cache (24 hours by default)
  private static sessionCacheTimeout: number = 24 * 60 * 60 * 1000; // 24 hours in milliseconds
  
  // Cleanup interval for session cache (run every hour)
  private static sessionCleanupInterval: NodeJS.Timeout | null = null;

  /**
   * Initialize the session cache cleanup mechanism.
   * This should be called during application startup.
   */
  public static initSessionCacheCleanup(): void {
    if (this.sessionCleanupInterval === null) {
      this.sessionCleanupInterval = setInterval(() => {
        this.cleanupSessionCache();
      }, 60 * 60 * 1000); // Run every hour
    }
  }

  /**
   * Clean up expired entries from the session cache
   */
  private static cleanupSessionCache(): void {
    const now = Date.now();
    const expiredKeys: string[] = [];
    
    this.sessionCache.forEach((session, key) => {
      if (now - session.timestamp > this.sessionCacheTimeout) {
        expiredKeys.push(key);
      }
    });
    
    expiredKeys.forEach(key => {
      this.sessionCache.delete(key);
    });
  }

  /**
   * Create a client identity key for session tracking
   * Uses source IP and optional client random for uniqueness
   * 
   * @param sourceIp - Client IP address
   * @param clientRandom - Optional TLS client random value
   * @returns A string key for the session cache
   */
  private static createClientKey(sourceIp: string, clientRandom?: Buffer): string {
    if (clientRandom) {
      // If we have the client random, use it for more precise tracking
      return `${sourceIp}:${clientRandom.toString('hex')}`;
    }
    // Fall back to just IP-based tracking
    return sourceIp;
  }

  /**
   * Store SNI information in the session cache
   * 
   * @param sourceIp - Client IP address
   * @param sni - The extracted SNI value
   * @param clientRandom - Optional TLS client random value
   */
  private static cacheSession(sourceIp: string, sni: string, clientRandom?: Buffer): void {
    const key = this.createClientKey(sourceIp, clientRandom);
    this.sessionCache.set(key, {
      sni,
      timestamp: Date.now(),
      clientRandom
    });
  }

  /**
   * Retrieve SNI information from the session cache
   * 
   * @param sourceIp - Client IP address
   * @param clientRandom - Optional TLS client random value
   * @returns The cached SNI or undefined if not found
   */
  private static getCachedSession(sourceIp: string, clientRandom?: Buffer): string | undefined {
    // Try with client random first for precision
    if (clientRandom) {
      const preciseKey = this.createClientKey(sourceIp, clientRandom);
      const preciseSession = this.sessionCache.get(preciseKey);
      if (preciseSession) {
        return preciseSession.sni;
      }
    }
    
    // Fall back to IP-only lookup
    const ipKey = this.createClientKey(sourceIp);
    const session = this.sessionCache.get(ipKey);
    if (session) {
      // Update the timestamp to keep the session alive
      session.timestamp = Date.now();
      return session.sni;
    }
    
    return undefined;
  }

  /**
   * Extract the client random value from a ClientHello message
   * 
   * @param buffer - The buffer containing the ClientHello
   * @returns The 32-byte client random or undefined if extraction fails
   */
  private static extractClientRandom(buffer: Buffer): Buffer | undefined {
    try {
      if (!this.isClientHello(buffer) || buffer.length < 46) {
        return undefined;
      }
      
      // In a ClientHello message, the client random starts at position 11
      // after record header (5 bytes), handshake type (1 byte), 
      // handshake length (3 bytes), and client version (2 bytes)
      return buffer.slice(11, 11 + 32);
    } catch (error) {
      return undefined;
    }
  }

  /**
   * Checks if a buffer contains a TLS handshake message (record type 22)
   * @param buffer - The buffer to check
   * @returns true if the buffer starts with a TLS handshake record type
   */
  public static isTlsHandshake(buffer: Buffer): boolean {
    return buffer.length > 0 && buffer[0] === this.TLS_HANDSHAKE_RECORD_TYPE;
  }
  
  /**
   * Checks if a buffer contains TLS application data (record type 23)
   * @param buffer - The buffer to check
   * @returns true if the buffer starts with a TLS application data record type
   */
  public static isTlsApplicationData(buffer: Buffer): boolean {
    return buffer.length > 0 && buffer[0] === this.TLS_APPLICATION_DATA_TYPE;
  }
  
  /**
   * Creates a connection ID based on source/destination information
   * Used to track fragmented ClientHello messages across multiple packets
   * 
   * @param connectionInfo - Object containing connection identifiers (IP/port)
   * @returns A string ID for the connection
   */
  public static createConnectionId(connectionInfo: { 
    sourceIp?: string; 
    sourcePort?: number; 
    destIp?: string; 
    destPort?: number; 
  }): string {
    const { sourceIp, sourcePort, destIp, destPort } = connectionInfo;
    return `${sourceIp}:${sourcePort}-${destIp}:${destPort}`;
  }
  
  /**
   * Handles potential fragmented ClientHello messages by buffering and reassembling
   * TLS record fragments that might span multiple TCP packets.
   * 
   * @param buffer - The current buffer fragment
   * @param connectionId - Unique identifier for the connection
   * @param enableLogging - Whether to enable logging
   * @returns A complete buffer if reassembly is successful, or undefined if more fragments are needed
   */
  public static handleFragmentedClientHello(
    buffer: Buffer,
    connectionId: string,
    enableLogging: boolean = false
  ): Buffer | undefined {
    const log = (message: string) => {
      if (enableLogging) {
        console.log(`[SNI Fragment] ${message}`);
      }
    };
    
    // Check if we've seen this connection before
    if (!this.fragmentedBuffers.has(connectionId)) {
      // New connection, start with this buffer
      this.fragmentedBuffers.set(connectionId, buffer);
      
      // Set timeout to clean up if we don't get a complete ClientHello
      setTimeout(() => {
        if (this.fragmentedBuffers.has(connectionId)) {
          this.fragmentedBuffers.delete(connectionId);
          log(`Connection ${connectionId} timed out waiting for complete ClientHello`);
        }
      }, this.fragmentTimeout);
      
      // Evaluate if this buffer already contains a complete ClientHello
      try {
        if (buffer.length >= 5) {
          const recordLength = (buffer[3] << 8) + buffer[4];
          if (buffer.length >= recordLength + 5) {
            log(`Initial buffer contains complete ClientHello, length: ${buffer.length}`);
            return buffer;
          }
        }
      } catch (e) {
        log(`Error checking initial buffer completeness: ${e}`);
      }
      
      log(`Started buffering connection ${connectionId}, initial size: ${buffer.length}`);
      return undefined; // Need more fragments
    } else {
      // Existing connection, append this buffer
      const existingBuffer = this.fragmentedBuffers.get(connectionId)!;
      const newBuffer = Buffer.concat([existingBuffer, buffer]);
      this.fragmentedBuffers.set(connectionId, newBuffer);
      
      log(`Appended to buffer for ${connectionId}, new size: ${newBuffer.length}`);
      
      // Check if we now have a complete ClientHello
      try {
        if (newBuffer.length >= 5) {
          const recordLength = (newBuffer[3] << 8) + newBuffer[4];
          if (newBuffer.length >= recordLength + 5) {
            log(`Assembled complete ClientHello, length: ${newBuffer.length}`);
            // Complete message received, remove from tracking
            this.fragmentedBuffers.delete(connectionId);
            return newBuffer;
          }
        }
      } catch (e) {
        log(`Error checking reassembled buffer completeness: ${e}`);
      }
      
      return undefined; // Still need more fragments
    }
  }

  /**
   * Checks if a buffer contains a TLS ClientHello message
   * @param buffer - The buffer to check
   * @returns true if the buffer appears to be a ClientHello message
   */
  public static isClientHello(buffer: Buffer): boolean {
    // Minimum ClientHello size (TLS record header + handshake header)
    if (buffer.length < 9) {
      return false;
    }

    // Check record type (must be TLS_HANDSHAKE_RECORD_TYPE)
    if (buffer[0] !== this.TLS_HANDSHAKE_RECORD_TYPE) {
      return false;
    }

    // Skip version and length in TLS record header (5 bytes total)
    // Check handshake type at byte 5 (must be CLIENT_HELLO)
    return buffer[5] === this.TLS_CLIENT_HELLO_HANDSHAKE_TYPE;
  }

  /**
   * Checks if a ClientHello message contains session resumption indicators
   * such as session tickets or PSK (Pre-Shared Key) extensions.
   * 
   * @param buffer - The buffer containing a ClientHello message
   * @param enableLogging - Whether to enable logging
   * @returns true if the ClientHello contains session resumption mechanisms
   */
  public static hasSessionResumption(
    buffer: Buffer,
    enableLogging: boolean = false
  ): boolean {
    const log = (message: string) => {
      if (enableLogging) {
        console.log(`[Session Resumption] ${message}`);
      }
    };
    
    if (!this.isClientHello(buffer)) {
      return false;
    }
    
    try {
      // Check for session ID presence first
      let pos = 5 + 1 + 3 + 2; // Position after handshake type, length and client version
      pos += 32; // Skip client random
      
      if (pos + 1 > buffer.length) return false;
      
      const sessionIdLength = buffer[pos];
      let hasNonEmptySessionId = sessionIdLength > 0;
      
      if (hasNonEmptySessionId) {
        log(`Detected non-empty session ID (length: ${sessionIdLength})`);
      }
      
      // Continue to check for extensions
      pos += 1 + sessionIdLength;
      
      // Skip cipher suites
      if (pos + 2 > buffer.length) return false;
      const cipherSuitesLength = (buffer[pos] << 8) + buffer[pos + 1];
      pos += 2 + cipherSuitesLength;
      
      // Skip compression methods
      if (pos + 1 > buffer.length) return false;
      const compressionMethodsLength = buffer[pos];
      pos += 1 + compressionMethodsLength;
      
      // Check for extensions
      if (pos + 2 > buffer.length) return false;
      
      // Look for session resumption extensions
      const extensionsLength = (buffer[pos] << 8) + buffer[pos + 1];
      pos += 2;
      
      // Extensions end position
      const extensionsEnd = pos + extensionsLength;
      if (extensionsEnd > buffer.length) return false;
      
      // Track resumption indicators
      let hasSessionTicket = false;
      let hasPSK = false;
      let hasEarlyData = false;
      
      // Iterate through extensions
      while (pos + 4 <= extensionsEnd) {
        const extensionType = (buffer[pos] << 8) + buffer[pos + 1];
        pos += 2;
        
        const extensionLength = (buffer[pos] << 8) + buffer[pos + 1];
        pos += 2;
        
        if (extensionType === this.TLS_SESSION_TICKET_EXTENSION_TYPE) {
          log('Found session ticket extension');
          hasSessionTicket = true;
          
          // Check if session ticket has non-zero length (active ticket)
          if (extensionLength > 0) {
            log(`Session ticket has length ${extensionLength} - active ticket present`);
          }
        } else if (extensionType === this.TLS_PSK_EXTENSION_TYPE) {
          log('Found PSK extension (TLS 1.3 resumption mechanism)');
          hasPSK = true;
        } else if (extensionType === this.TLS_EARLY_DATA_EXTENSION_TYPE) {
          log('Found Early Data extension (TLS 1.3 0-RTT)');
          hasEarlyData = true;
        }
        
        // Skip extension data
        pos += extensionLength;
      }
      
      // Consider it a resumption if any resumption mechanism is present
      const isResumption = hasSessionTicket || hasPSK || hasEarlyData || 
                         (hasNonEmptySessionId && !hasPSK); // Legacy resumption
      
      if (isResumption) {
        log('Session resumption detected: ' + 
            (hasSessionTicket ? 'session ticket, ' : '') +
            (hasPSK ? 'PSK, ' : '') +
            (hasEarlyData ? 'early data, ' : '') +
            (hasNonEmptySessionId ? 'session ID' : ''));
      }
      
      return isResumption;
    } catch (error) {
      log(`Error checking for session resumption: ${error}`);
      return false;
    }
  }
  
  /**
   * Detects characteristics of a tab reactivation TLS handshake
   * These often have specific patterns in Chrome and other browsers
   * 
   * @param buffer - The buffer containing a ClientHello message
   * @param enableLogging - Whether to enable logging
   * @returns true if this appears to be a tab reactivation handshake
   */
  public static isTabReactivationHandshake(
    buffer: Buffer, 
    enableLogging: boolean = false
  ): boolean {
    const log = (message: string) => {
      if (enableLogging) {
        console.log(`[Tab Reactivation] ${message}`);
      }
    };
    
    if (!this.isClientHello(buffer)) {
      return false;
    }
    
    try {
      // Check for session ID presence (tab reactivation often has a session ID)
      let pos = 5 + 1 + 3 + 2; // Position after handshake type, length and client version
      pos += 32; // Skip client random
      
      if (pos + 1 > buffer.length) return false;
      
      const sessionIdLength = buffer[pos];
      
      // Non-empty session ID is a good indicator
      if (sessionIdLength > 0) {
        log(`Detected non-empty session ID (length: ${sessionIdLength})`);
        
        // Skip to extensions
        pos += 1 + sessionIdLength;
        
        // Skip cipher suites
        if (pos + 2 > buffer.length) return false;
        const cipherSuitesLength = (buffer[pos] << 8) + buffer[pos + 1];
        pos += 2 + cipherSuitesLength;
        
        // Skip compression methods
        if (pos + 1 > buffer.length) return false;
        const compressionMethodsLength = buffer[pos];
        pos += 1 + compressionMethodsLength;
        
        // Check for extensions
        if (pos + 2 > buffer.length) return false;
        
        // Look for specific extensions that indicate tab reactivation
        const extensionsLength = (buffer[pos] << 8) + buffer[pos + 1];
        pos += 2;
        
        // Extensions end position
        const extensionsEnd = pos + extensionsLength;
        if (extensionsEnd > buffer.length) return false;
        
        // Tab reactivation often has session tickets but no SNI
        let hasSessionTicket = false;
        let hasSNI = false;
        let hasPSK = false;
        
        // Iterate through extensions
        while (pos + 4 <= extensionsEnd) {
          const extensionType = (buffer[pos] << 8) + buffer[pos + 1];
          pos += 2;
          
          const extensionLength = (buffer[pos] << 8) + buffer[pos + 1];
          pos += 2;
          
          if (extensionType === this.TLS_SESSION_TICKET_EXTENSION_TYPE) {
            hasSessionTicket = true;
          } else if (extensionType === this.TLS_SNI_EXTENSION_TYPE) {
            hasSNI = true;
          } else if (extensionType === this.TLS_PSK_EXTENSION_TYPE) {
            hasPSK = true;
          }
          
          // Skip extension data
          pos += extensionLength;
        }
        
        // Pattern for tab reactivation: session identifier + (ticket or PSK) but no SNI
        if ((hasSessionTicket || hasPSK) && !hasSNI) {
          log('Detected tab reactivation pattern: session resumption without SNI');
          return true;
        }
      }
    } catch (error) {
      log(`Error checking for tab reactivation: ${error}`);
    }
    
    return false;
  }

  /**
   * Extracts the SNI (Server Name Indication) from a TLS ClientHello message.
   * Implements robust parsing with support for session resumption edge cases.
   * 
   * @param buffer - The buffer containing the TLS ClientHello message
   * @param enableLogging - Whether to enable detailed debug logging
   * @returns The extracted server name or undefined if not found
   */
  public static extractSNI(buffer: Buffer, enableLogging: boolean = false): string | undefined {
    // Logging helper
    const log = (message: string) => {
      if (enableLogging) {
        console.log(`[SNI Extraction] ${message}`);
      }
    };

    try {
      // Buffer must be at least 5 bytes (TLS record header)
      if (buffer.length < 5) {
        log('Buffer too small for TLS record header');
        return undefined;
      }

      // Check record type (must be TLS_HANDSHAKE_RECORD_TYPE = 22)
      if (buffer[0] !== this.TLS_HANDSHAKE_RECORD_TYPE) {
        log(`Not a TLS handshake record: ${buffer[0]}`);
        return undefined;
      }

      // Check TLS version
      const majorVersion = buffer[1];
      const minorVersion = buffer[2];
      log(`TLS version: ${majorVersion}.${minorVersion}`);

      // Parse record length (bytes 3-4, big-endian)
      const recordLength = (buffer[3] << 8) + buffer[4];
      log(`Record length: ${recordLength}`);

      // Validate record length against buffer size
      if (buffer.length < recordLength + 5) {
        log('Buffer smaller than expected record length');
        return undefined;
      }

      // Start of handshake message in the buffer
      let pos = 5;

      // Check handshake type (must be CLIENT_HELLO = 1)
      if (buffer[pos] !== this.TLS_CLIENT_HELLO_HANDSHAKE_TYPE) {
        log(`Not a ClientHello message: ${buffer[pos]}`);
        return undefined;
      }

      // Skip handshake type (1 byte)
      pos += 1;

      // Parse handshake length (3 bytes, big-endian)
      const handshakeLength = (buffer[pos] << 16) + (buffer[pos + 1] << 8) + buffer[pos + 2];
      log(`Handshake length: ${handshakeLength}`);

      // Skip handshake length (3 bytes)
      pos += 3;

      // Check client version (2 bytes)
      const clientMajorVersion = buffer[pos];
      const clientMinorVersion = buffer[pos + 1];
      log(`Client version: ${clientMajorVersion}.${clientMinorVersion}`);

      // Skip client version (2 bytes)
      pos += 2;

      // Skip client random (32 bytes)
      pos += 32;

      // Parse session ID
      if (pos + 1 > buffer.length) {
        log('Buffer too small for session ID length');
        return undefined;
      }

      const sessionIdLength = buffer[pos];
      log(`Session ID length: ${sessionIdLength}`);

      // Skip session ID length (1 byte) and session ID
      pos += 1 + sessionIdLength;

      // Check if we have enough bytes left
      if (pos + 2 > buffer.length) {
        log('Buffer too small for cipher suites length');
        return undefined;
      }

      // Parse cipher suites length (2 bytes, big-endian)
      const cipherSuitesLength = (buffer[pos] << 8) + buffer[pos + 1];
      log(`Cipher suites length: ${cipherSuitesLength}`);

      // Skip cipher suites length (2 bytes) and cipher suites
      pos += 2 + cipherSuitesLength;

      // Check if we have enough bytes left
      if (pos + 1 > buffer.length) {
        log('Buffer too small for compression methods length');
        return undefined;
      }

      // Parse compression methods length (1 byte)
      const compressionMethodsLength = buffer[pos];
      log(`Compression methods length: ${compressionMethodsLength}`);

      // Skip compression methods length (1 byte) and compression methods
      pos += 1 + compressionMethodsLength;

      // Check if we have enough bytes for extensions length
      if (pos + 2 > buffer.length) {
        log('No extensions present or buffer too small');
        return undefined;
      }

      // Parse extensions length (2 bytes, big-endian)
      const extensionsLength = (buffer[pos] << 8) + buffer[pos + 1];
      log(`Extensions length: ${extensionsLength}`);

      // Skip extensions length (2 bytes)
      pos += 2;

      // Extensions end position
      const extensionsEnd = pos + extensionsLength;

      // Check if extensions length is valid
      if (extensionsEnd > buffer.length) {
        log('Extensions length exceeds buffer size');
        return undefined;
      }

      // Track if we found session tickets (for improved resumption handling)
      let hasSessionTicket = false;
      let hasPskExtension = false;

      // Iterate through extensions
      while (pos + 4 <= extensionsEnd) {
        // Parse extension type (2 bytes, big-endian)
        const extensionType = (buffer[pos] << 8) + buffer[pos + 1];
        log(`Extension type: 0x${extensionType.toString(16).padStart(4, '0')}`);

        // Skip extension type (2 bytes)
        pos += 2;

        // Parse extension length (2 bytes, big-endian)
        const extensionLength = (buffer[pos] << 8) + buffer[pos + 1];
        log(`Extension length: ${extensionLength}`);

        // Skip extension length (2 bytes)
        pos += 2;

        // Check if this is the SNI extension
        if (extensionType === this.TLS_SNI_EXTENSION_TYPE) {
          log('Found SNI extension');

          // Ensure we have enough bytes for the server name list
          if (pos + 2 > extensionsEnd) {
            log('Extension too small for server name list length');
            pos += extensionLength; // Skip this extension
            continue;
          }

          // Parse server name list length (2 bytes, big-endian)
          const serverNameListLength = (buffer[pos] << 8) + buffer[pos + 1];
          log(`Server name list length: ${serverNameListLength}`);

          // Skip server name list length (2 bytes)
          pos += 2;

          // Ensure server name list length is valid
          if (pos + serverNameListLength > extensionsEnd) {
            log('Server name list length exceeds extension size');
            break; // Exit the loop, extension parsing is broken
          }

          // End position of server name list
          const serverNameListEnd = pos + serverNameListLength;

          // Iterate through server names
          while (pos + 3 <= serverNameListEnd) {
            // Check name type (must be HOST_NAME_TYPE = 0 for hostname)
            const nameType = buffer[pos];
            log(`Name type: ${nameType}`);

            if (nameType !== this.TLS_SNI_HOST_NAME_TYPE) {
              log(`Unsupported name type: ${nameType}`);
              pos += 1; // Skip name type (1 byte)

              // Skip name length (2 bytes) and name data
              if (pos + 2 <= serverNameListEnd) {
                const nameLength = (buffer[pos] << 8) + buffer[pos + 1];
                pos += 2 + nameLength;
              } else {
                log('Invalid server name entry');
                break;
              }
              continue;
            }

            // Skip name type (1 byte)
            pos += 1;

            // Ensure we have enough bytes for name length
            if (pos + 2 > serverNameListEnd) {
              log('Server name entry too small for name length');
              break;
            }

            // Parse name length (2 bytes, big-endian)
            const nameLength = (buffer[pos] << 8) + buffer[pos + 1];
            log(`Name length: ${nameLength}`);

            // Skip name length (2 bytes)
            pos += 2;

            // Ensure we have enough bytes for the name
            if (pos + nameLength > serverNameListEnd) {
              log('Name length exceeds server name list size');
              break;
            }

            // Extract server name (hostname)
            const serverName = buffer.slice(pos, pos + nameLength).toString('utf8');
            log(`Extracted server name: ${serverName}`);
            return serverName;
          }
        } else if (extensionType === this.TLS_SESSION_TICKET_EXTENSION_TYPE) {
          // If we encounter a session ticket extension, mark it for later
          log('Found session ticket extension');
          hasSessionTicket = true;
          pos += extensionLength; // Skip this extension
        } else if (extensionType === this.TLS_PSK_EXTENSION_TYPE) {
          // TLS 1.3 PSK extension - mark for resumption support
          log('Found PSK extension (TLS 1.3 resumption indicator)');
          hasPskExtension = true;
          // We'll skip the extension here and process it separately if needed
          pos += extensionLength;
        } else {
          // Skip this extension
          pos += extensionLength;
        }
      }

      // Log if we found session resumption indicators but no SNI
      if (hasSessionTicket || hasPskExtension) {
        log('Session resumption indicators present but no SNI found');
      }

      log('No SNI extension found in ClientHello');
      return undefined;
    } catch (error) {
      log(`Error parsing SNI: ${error instanceof Error ? error.message : String(error)}`);
      return undefined;
    }
  }

  /**
   * Attempts to extract SNI from the PSK extension in a TLS 1.3 ClientHello.
   * 
   * In TLS 1.3, when a client attempts to resume a session, it may include 
   * the server name in the PSK identity hint rather than in the SNI extension.
   * 
   * @param buffer - The buffer containing the TLS ClientHello message
   * @param enableLogging - Whether to enable detailed debug logging
   * @returns The extracted server name or undefined if not found
   */
  public static extractSNIFromPSKExtension(
    buffer: Buffer,
    enableLogging: boolean = false
  ): string | undefined {
    const log = (message: string) => {
      if (enableLogging) {
        console.log(`[PSK-SNI Extraction] ${message}`);
      }
    };

    try {
      // Ensure this is a ClientHello
      if (!this.isClientHello(buffer)) {
        log('Not a ClientHello message');
        return undefined;
      }

      // Find the start position of extensions
      let pos = 5; // Start after record header
      
      // Skip handshake type (1 byte)
      pos += 1;
      
      // Skip handshake length (3 bytes)
      pos += 3;
      
      // Skip client version (2 bytes)
      pos += 2;
      
      // Skip client random (32 bytes)
      pos += 32;
      
      // Skip session ID
      if (pos + 1 > buffer.length) return undefined;
      const sessionIdLength = buffer[pos];
      pos += 1 + sessionIdLength;
      
      // Skip cipher suites
      if (pos + 2 > buffer.length) return undefined;
      const cipherSuitesLength = (buffer[pos] << 8) + buffer[pos + 1];
      pos += 2 + cipherSuitesLength;
      
      // Skip compression methods
      if (pos + 1 > buffer.length) return undefined;
      const compressionMethodsLength = buffer[pos];
      pos += 1 + compressionMethodsLength;
      
      // Check if we have extensions
      if (pos + 2 > buffer.length) {
        log('No extensions present');
        return undefined;
      }
      
      // Get extensions length
      const extensionsLength = (buffer[pos] << 8) + buffer[pos + 1];
      pos += 2;
      
      // Extensions end position
      const extensionsEnd = pos + extensionsLength;
      if (extensionsEnd > buffer.length) return undefined;

      // Look for PSK extension
      while (pos + 4 <= extensionsEnd) {
        const extensionType = (buffer[pos] << 8) + buffer[pos + 1];
        pos += 2;
        
        const extensionLength = (buffer[pos] << 8) + buffer[pos + 1];
        pos += 2;
        
        if (extensionType === this.TLS_PSK_EXTENSION_TYPE) {
          log('Found PSK extension');
          
          // PSK extension structure:
          // 2 bytes: identities list length
          if (pos + 2 > extensionsEnd) break;
          const identitiesLength = (buffer[pos] << 8) + buffer[pos + 1];
          pos += 2;
          
          // End of identities list
          const identitiesEnd = pos + identitiesLength;
          if (identitiesEnd > extensionsEnd) break;
          
          // Process each PSK identity
          while (pos + 2 <= identitiesEnd) {
            // Identity length (2 bytes)
            if (pos + 2 > identitiesEnd) break;
            const identityLength = (buffer[pos] << 8) + buffer[pos + 1];
            pos += 2;
            
            if (pos + identityLength > identitiesEnd) break;
            
            // Try to extract hostname from identity
            // Chrome often embeds the hostname in the PSK identity
            // This is a heuristic as there's no standard format
            if (identityLength > 0) {
              const identity = buffer.slice(pos, pos + identityLength);
              
              // Skip identity bytes
              pos += identityLength;
              
              // Skip obfuscated ticket age (4 bytes)
              if (pos + 4 <= identitiesEnd) {
                pos += 4;
              } else {
                break;
              }
              
              // Try to parse the identity as UTF-8
              try {
                const identityStr = identity.toString('utf8');
                log(`PSK identity: ${identityStr}`);
                
                // Check if the identity contains hostname hints
                // Chrome often embeds the hostname in a known format
                // Try to extract using common patterns
                
                // Pattern 1: Look for domain name pattern
                const domainPattern = /([a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?/i;
                const domainMatch = identityStr.match(domainPattern);
                if (domainMatch && domainMatch[0]) {
                  log(`Found domain in PSK identity: ${domainMatch[0]}`);
                  return domainMatch[0];
                }
                
                // Pattern 2: Chrome sometimes uses a specific format with delimiters
                // This is a heuristic approach since the format isn't standardized
                const parts = identityStr.split('|');
                if (parts.length > 1) {
                  for (const part of parts) {
                    if (part.includes('.') && !part.includes('/')) {
                      const possibleDomain = part.trim();
                      if (/^[a-z0-9.-]+$/i.test(possibleDomain)) {
                        log(`Found possible domain in PSK delimiter format: ${possibleDomain}`);
                        return possibleDomain;
                      }
                    }
                  }
                }
              } catch (e) {
                log('Failed to parse PSK identity as UTF-8');
              }
            }
          }
        } else {
          // Skip this extension
          pos += extensionLength;
        }
      }
      
      log('No hostname found in PSK extension');
      return undefined;
    } catch (error) {
      log(`Error parsing PSK: ${error instanceof Error ? error.message : String(error)}`);
      return undefined;
    }
  }

  /**
   * Checks if the buffer contains TLS 1.3 early data (0-RTT)
   * @param buffer - The buffer to check
   * @param enableLogging - Whether to enable logging
   * @returns true if early data is detected
   */
  public static hasEarlyData(
    buffer: Buffer,
    enableLogging: boolean = false
  ): boolean {
    const log = (message: string) => {
      if (enableLogging) {
        console.log(`[Early Data] ${message}`);
      }
    };
    
    try {
      // Check if this is a valid ClientHello first
      if (!this.isClientHello(buffer)) {
        return false;
      }
      
      // Find the extensions section
      let pos = 5; // Start after record header
      
      // Skip handshake type (1 byte)
      pos += 1;
      
      // Skip handshake length (3 bytes)
      pos += 3;
      
      // Skip client version (2 bytes)
      pos += 2;
      
      // Skip client random (32 bytes)
      pos += 32;
      
      // Skip session ID
      if (pos + 1 > buffer.length) return false;
      const sessionIdLength = buffer[pos];
      pos += 1 + sessionIdLength;
      
      // Skip cipher suites
      if (pos + 2 > buffer.length) return false;
      const cipherSuitesLength = (buffer[pos] << 8) + buffer[pos + 1];
      pos += 2 + cipherSuitesLength;
      
      // Skip compression methods
      if (pos + 1 > buffer.length) return false;
      const compressionMethodsLength = buffer[pos];
      pos += 1 + compressionMethodsLength;
      
      // Check if we have extensions
      if (pos + 2 > buffer.length) return false;
      
      // Get extensions length
      const extensionsLength = (buffer[pos] << 8) + buffer[pos + 1];
      pos += 2;
      
      // Extensions end position
      const extensionsEnd = pos + extensionsLength;
      if (extensionsEnd > buffer.length) return false;
      
      // Look for early data extension
      while (pos + 4 <= extensionsEnd) {
        const extensionType = (buffer[pos] << 8) + buffer[pos + 1];
        pos += 2;
        
        const extensionLength = (buffer[pos] << 8) + buffer[pos + 1];
        pos += 2;
        
        if (extensionType === this.TLS_EARLY_DATA_EXTENSION_TYPE) {
          log('Early Data (0-RTT) extension detected');
          return true;
        }
        
        // Skip to next extension
        pos += extensionLength;
      }
      
      return false;
    } catch (error) {
      log(`Error checking for early data: ${error}`);
      return false;
    }
  }
  
  /**
   * Attempts to extract SNI from an initial ClientHello packet and handles
   * session resumption edge cases more robustly than the standard extraction.
   * 
   * This method handles:
   * 1. Standard SNI extraction
   * 2. TLS 1.3 PSK-based resumption (Chrome, Firefox, etc.)
   * 3. Session ticket-based resumption
   * 4. Fragmented ClientHello messages
   * 5. TLS 1.3 Early Data (0-RTT)
   * 6. Chrome's connection racing behaviors
   * 7. Tab reactivation patterns with session cache
   * 
   * @param buffer - The buffer containing the TLS ClientHello message
   * @param connectionInfo - Optional connection information for fragment handling
   * @param enableLogging - Whether to enable detailed debug logging
   * @returns The extracted server name or undefined if not found
   */
  public static extractSNIWithResumptionSupport(
    buffer: Buffer,
    connectionInfo?: { 
      sourceIp?: string; 
      sourcePort?: number; 
      destIp?: string; 
      destPort?: number; 
    },
    enableLogging: boolean = false
  ): string | undefined {
    const log = (message: string) => {
      if (enableLogging) {
        console.log(`[SNI Extraction] ${message}`);
      }
    };
    
    // Check if we need to handle fragmented packets
    let processBuffer = buffer;
    if (connectionInfo) {
      const connectionId = this.createConnectionId(connectionInfo);
      const reassembledBuffer = this.handleFragmentedClientHello(
        buffer, 
        connectionId, 
        enableLogging
      );
      
      if (!reassembledBuffer) {
        log(`Waiting for more fragments on connection ${connectionId}`);
        return undefined; // Need more fragments to complete ClientHello
      }
      
      processBuffer = reassembledBuffer;
      log(`Using reassembled buffer of length ${processBuffer.length}`);
    }
    
    // First try the standard SNI extraction
    const standardSni = this.extractSNI(processBuffer, enableLogging);
    if (standardSni) {
      log(`Found standard SNI: ${standardSni}`);
      
      // If we extracted a standard SNI, cache it for future use
      if (connectionInfo?.sourceIp) {
        const clientRandom = this.extractClientRandom(processBuffer);
        this.cacheSession(connectionInfo.sourceIp, standardSni, clientRandom);
        log(`Cached SNI for future reference: ${standardSni}`);
      }
      
      return standardSni;
    }
    
    // Check for tab reactivation pattern
    const isTabReactivation = this.isTabReactivationHandshake(processBuffer, enableLogging);
    if (isTabReactivation && connectionInfo?.sourceIp) {
      // Try to get the SNI from our session cache for tab reactivation
      const cachedSni = this.getCachedSession(connectionInfo.sourceIp);
      if (cachedSni) {
        log(`Retrieved cached SNI for tab reactivation: ${cachedSni}`);
        return cachedSni;
      }
      log('Tab reactivation detected but no cached SNI found');
    }
    
    // Check for TLS 1.3 early data (0-RTT)
    const hasEarly = this.hasEarlyData(processBuffer, enableLogging);
    if (hasEarly) {
      log('TLS 1.3 Early Data detected, trying session cache');
      // For 0-RTT, check the session cache
      if (connectionInfo?.sourceIp) {
        const cachedSni = this.getCachedSession(connectionInfo.sourceIp);
        if (cachedSni) {
          log(`Retrieved cached SNI for 0-RTT: ${cachedSni}`);
          return cachedSni;
        }
      }
    }
    
    // If standard extraction failed and we have a valid ClientHello,
    // this might be a session resumption with non-standard format
    if (this.isClientHello(processBuffer)) {
      log('Detected ClientHello without standard SNI, possible session resumption');
      
      // Try to extract from PSK extension (TLS 1.3 resumption)
      const pskSni = this.extractSNIFromPSKExtension(processBuffer, enableLogging);
      if (pskSni) {
        log(`Extracted SNI from PSK extension: ${pskSni}`);
        
        // Cache this SNI for future reference
        if (connectionInfo?.sourceIp) {
          const clientRandom = this.extractClientRandom(processBuffer);
          this.cacheSession(connectionInfo.sourceIp, pskSni, clientRandom);
          log(`Cached PSK-derived SNI: ${pskSni}`);
        }
        
        return pskSni;
      }
      
      // If we have a session ticket but no SNI or PSK identity,
      // check our session cache as a last resort
      if (connectionInfo?.sourceIp) {
        const cachedSni = this.getCachedSession(connectionInfo.sourceIp);
        if (cachedSni) {
          log(`Using cached SNI as last resort: ${cachedSni}`);
          return cachedSni;
        }
      }
      
      log('Failed to extract SNI from resumption mechanisms');
    }
    
    return undefined;
  }
  
  /**
   * Main entry point for SNI extraction that handles all edge cases.
   * This should be called for each TLS packet received from a client.
   * 
   * The method uses connection tracking to handle fragmented ClientHello
   * messages and various TLS 1.3 behaviors, including Chrome's connection
   * racing patterns and tab reactivation behaviors.
   * 
   * @param buffer - The buffer containing TLS data
   * @param connectionInfo - Connection metadata (IPs and ports)
   * @param enableLogging - Whether to enable detailed debug logging
   * @param cachedSni - Optional cached SNI from previous connections (for racing detection)
   * @returns The extracted server name or undefined if not found or more data needed
   */
  public static processTlsPacket(
    buffer: Buffer,
    connectionInfo: {
      sourceIp: string;
      sourcePort: number;
      destIp: string;
      destPort: number;
      timestamp?: number;
    },
    enableLogging: boolean = false,
    cachedSni?: string
  ): string | undefined {
    const log = (message: string) => {
      if (enableLogging) {
        console.log(`[TLS Packet] ${message}`);
      }
    };
    
    // Add timestamp if not provided
    if (!connectionInfo.timestamp) {
      connectionInfo.timestamp = Date.now();
    }
    
    // Check if this is a TLS handshake or application data
    if (!this.isTlsHandshake(buffer) && !this.isTlsApplicationData(buffer)) {
      log('Not a TLS handshake or application data packet');
      return undefined;
    }
    
    // Create connection ID for tracking
    const connectionId = this.createConnectionId(connectionInfo);
    log(`Processing TLS packet for connection ${connectionId}, buffer length: ${buffer.length}`);
    
    // Handle application data with cached SNI (for connection racing)
    if (this.isTlsApplicationData(buffer)) {
      // First check if explicit cachedSni was provided
      if (cachedSni) {
        log(`Using provided cached SNI for application data: ${cachedSni}`);
        return cachedSni;
      }
      
      // Otherwise check our session cache
      const sessionCachedSni = this.getCachedSession(connectionInfo.sourceIp);
      if (sessionCachedSni) {
        log(`Using session-cached SNI for application data: ${sessionCachedSni}`);
        return sessionCachedSni;
      }
      
      log('Application data packet without cached SNI, cannot determine hostname');
      return undefined;
    }
    
    // For handshake messages, try the full extraction process
    const sni = this.extractSNIWithResumptionSupport(
      buffer,
      connectionInfo,
      enableLogging
    );
    
    if (sni) {
      log(`Successfully extracted SNI: ${sni}`);
      return sni;
    }
    
    // If we couldn't extract an SNI, check if this is a valid ClientHello
    // If it is, but we couldn't get an SNI, it might be a fragment or
    // a connection race situation
    if (this.isClientHello(buffer)) {
      // Check if we have a cached session for this IP
      const sessionCachedSni = this.getCachedSession(connectionInfo.sourceIp);
      if (sessionCachedSni) {
        log(`Using session cache for ClientHello without SNI: ${sessionCachedSni}`);
        return sessionCachedSni;
      }
      
      log('Valid ClientHello detected, but no SNI extracted - might need more data');
    }
    
    return undefined;
  }
}