Почему библиотека WPF Presentation обертывает строки в StringBuilder.ToString()?

Ответ 1

Единственное, о чем я могу думать, это то, что если первый параметр, передаваемый в stringBuilder, равен NULL, тогда stringbuilder вернет string.empty, а не null (см. http://msdn.microsoft.com/en-us/library/zb91weab(v=vs.100).aspx)

Строка может быть нулевой, хотя... так зачем беспокоиться?!

Просто проверка и возврат пустой строки будут намного эффективнее, чем создание экземпляра stringBuilder.

Второй параметр - это только рекомендуемый размер, который должен быть инициализирован stringbuilder...

Комментарии к вопросу OP правильные, кажется, что это слишком много.

Ответ 2

/// <SecurityNote> 
/// Critical: Calls the native InternetGetCookieEx(). There is potential for information disclosure. 
/// Safe: A WebPermission demand is made for the given URI.
/// </SecurityNote> 
[SecurityCritical, SecurityTreatAsSafe]
[FriendAccessAllowed] // called by PF.Application.GetCookie()
[SuppressMessage("Microsoft.Interoperability", "CA1404:CallGetLastErrorImmediatelyAfterPInvoke",
    Justification="It okay now. Be careful on change.")] 
internal static string GetCookie(Uri uri, bool throwIfNoCookie)
{ 
    // Always demand in order to prevent any cross-domain information leak. 
    SecurityHelper.DemandWebPermission(uri);

    UInt32 size = 0;
    string uriString = BindUriHelper.UriToString(uri);
    if (UnsafeNativeMethods.InternetGetCookieEx(uriString, null, null, ref size, 0, IntPtr.Zero))
    { 
        Debug.Assert(size > 0);
        size++; 
        System.Text.StringBuilder sb = new System.Text.StringBuilder((int)size); 
        // PresentationHost intercepts InternetGetCookieEx(). It will set the INTERNET_COOKIE_THIRD_PARTY
        // flag if necessary. 
        if (UnsafeNativeMethods.InternetGetCookieEx(uriString, null, sb, ref size, 0, IntPtr.Zero))
        {
            return sb.ToString();
        } 
    }
    if (!throwIfNoCookie && Marshal.GetLastWin32Error() == NativeMethods.ERROR_NO_MORE_ITEMS) 
        return null; 
    throw new Win32Exception(/*uses last error code*/);
}

/// <SecurityNote> 
/// Critical: Sets cookies via the native InternetSetCookieEx(); doesn't demand WebPermission for the given 
///     URI. This creates danger of overwriting someone else cookies.
///     The P3P header has to be from an authentic web response in order to be trusted at all. 
/// </SecurityNote>
[SecurityCritical]
private static bool SetCookieUnsafe(Uri uri, string cookieData, string p3pHeader)
{ 
    string uriString = BindUriHelper.UriToString(uri);
    // PresentationHost intercepts InternetSetCookieEx(). It will set the INTERNET_COOKIE_THIRD_PARTY 
    // flag if necessary. (This doesn't look very elegant but is much simpler than having to make the 
    // 3rd party decision here as well or calling into the native code (from PresentationCore).)
    uint res = UnsafeNativeMethods.InternetSetCookieEx( 
        uriString, null, cookieData, UnsafeNativeMethods.INTERNET_COOKIE_EVALUATE_P3P, p3pHeader);
    if(res == 0)
        throw new Win32Exception(/*uses last error code*/);
    return res != UnsafeNativeMethods.COOKIE_STATE_REJECT; 
}

    private const int MAX_PATH_LENGTH = 2048 ; 
    private const int MAX_SCHEME_LENGTH = 32;
    public const int MAX_URL_LENGTH = MAX_PATH_LENGTH + MAX_SCHEME_LENGTH + 3; /*=sizeof("://")*/ 

    //
    // Uri-toString does 3 things over the standard .toString()
    // 
    //  1) We don't unescape special control characters. The default Uri.ToString()
    //     will unescape a character like ctrl-g, or ctrl-h so the actual char is emitted. 
    //     However it considered safer to emit the escaped version. 
    //
    //  2) We truncate urls so that they are always <= MAX_URL_LENGTH 
    //
    // This method should be called whenever you are taking a Uri
    // and performing a p-invoke on it.
    // 
    internal static string UriToString(Uri uri)
    { 
        if (uri == null) 
        {
            throw new ArgumentNullException("uri"); 
        }

        return new StringBuilder(
            uri.GetComponents( 
                uri.IsAbsoluteUri ? UriComponents.AbsoluteUri : UriComponents.SerializationInfoString,
                UriFormat.SafeUnescaped), 
            MAX_URL_LENGTH).ToString(); 
    }