Win32 Security in Managed C++

Listing 6 WinSTL's token_information helper template

/* /////////////////////////////////////////////////////////////
 * ...
 *
 * Extract from winstl_token_information.h
 *
 * Copyright (C) 2003, Synesis Software Pty Ltd.
 * (Licensed under the Synesis Software Standard Source License:
 *  http://www.synesis.com.au/licenses/ssssl.html)
 *
 * ...
 * ////////////////////////////////////////////////////////// */

namespace winstl
{
  template <TOKEN_INFORMATION_CLASS C>
  struct token_information_traits;


  template <>
  struct token_information_traits<TokenUser>
  {
    typedef TOKEN_USER  data_type;
  };

  ... // More specialisations of token_information_traits

  template< TOKEN_INFORMATION_CLASS C
          , ws_typename_param_k     X = stlsoft::null_exception
          , ws_typename_param_k     D = token_information_traits<C>::data_type
          , ws_typename_param_k     A = processheap_allocator<ss_byte_t>
          >
  class token_information
  {
  public:
    typedef token_information<C, X, D, A> class_type;
    typedef token_information_traits<C>   traits_type;
    typedef X                             exception_thrower_type;
    typedef D                             data_type;
    typedef A                             allocator_type;

  // Construction
  public:
    /// Constructs an instance from the given access token
    ws_explicit_k token_information(HANDLE hToken)
      : m_data(0)
    {
      DWORD cbRequired;
      DWORD dwError;

      ::GetTokenInformation(hToken, C, NULL, 0, &cbRequired);
      dwError = ::GetLastError();
      if(ERROR_INSUFFICIENT_BUFFER != dwError)
      {
        // Report error
        exception_thrower_type()(dwError);
      }
      else
      {
        data_type *data = (data_type*)allocator_type().allocate(cbRequired);

        if(NULL == data)
        {
          // Report error
          exception_thrower_type()(ERROR_NOT_ENOUGH_MEMORY);

          // Set the last error, in case the client code is not           // using exception reporting
          ::SetLastError(ERROR_NOT_ENOUGH_MEMORY);
        }
        else
        {
          if(!::GetTokenInformation(hToken, C, data, cbRequired, &cbRequired))
          {
            // Scope the last error, in case the client code is not             // using exception reporting
            dwError = ::GetLastError();

            allocator_type().deallocate((ss_byte_t*)data);

            // Report error
            ::SetLastError(dwError);
            exception_thrower_type()(dwError);
          }
          else
          {
            // Success
            m_data = data;

            ::SetLastError(ERROR_SUCCESS);
          }
        }
      }
    }
    ~token_information()
    {
      allocator_type().deallocate((ss_byte_t*)m_data);
    }

  // Conversion
  public:
    operator data_type *();
    operator data_type const *() const;

    data_type *operator ->();
    data_type const *operator ->() const;

    ws_bool_t operator !() const;

  /// Members
  private:
    data_type *m_data;

  /// Not to be implemented
  private:
    token_information(token_information const &);
    token_information &operator =(token_information const &);
  };

} // namespace winstl