CriticalFileToken.cs source code in C# .NET

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Code:

/ DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / TrustUi / MS / Internal / documents / Application / CriticalFileToken.cs / 1 / CriticalFileToken.cs

                            //------------------------------------------------------------------------------ 
// 
//    Copyright (C) Microsoft Corporation.  All rights reserved. 
//
//  
//  The CriticalFileToken class ensures file represented is the one the
//  user has authorized us to manipulate. 
//  
//
// History: 
//  08/28/2005: [....]: Initial implementation.
//-----------------------------------------------------------------------------

using System; 
using System.Security;
using System.Security.Permissions; 
 
using MS.Internal.PresentationUI;
 
namespace MS.Internal.Documents.Application
{
/// 
/// The CriticalFileToken class ensures file represented is the one the 
/// user has authorized us to manipulate.
///  
///  
/// Responsibility:
/// Allow XpsViewer to safely pass around information on which file the user 
/// has authorized us to manipulate on thier behalf.  Ensure that the creator
/// of the object has the privledge to manipulate the file represented.
///
/// Design Comments: 
/// Many classes need to perform privledged operations files on behalf of the
/// user.  However only DocObjHost and FilePresentation can assert it is user 
/// sourced data. 
///
/// As such we need them to create this 'token' which will will use as the only 
/// source of authoritative information for which files we are manipulating.
///
/// As any SecurityCritical code can create SecurityCriticalData, we add the
/// demand for FileIOPermission that represents the rights that will be asserted 
/// for in conjuction with this data.
///  
[FriendAccessAllowed] 
internal sealed class CriticalFileToken
{ 
    #region Constructors
    //-------------------------------------------------------------------------
    // Constructors
    //------------------------------------------------------------------------- 

    ///  
    /// Critical: 
    ///  - as this sets the _location which is Critical.
    /// TreatAsSafe: 
    ///  - the caller already has the value
    ///  - the caller must satisfy the demand which this token grants
    /// 
    [SecurityCritical, SecurityTreatAsSafe] 
    internal CriticalFileToken(Uri location)
    { 
        string path = location.LocalPath; 
        new FileIOPermission(
            FileIOPermissionAccess.Read | FileIOPermissionAccess.Write, 
            path)
        .Demand();

        _location = location; 
    }
    #endregion Constructors 
 
    #region Object Members
    //-------------------------------------------------------------------------- 
    // Object Members
    //-------------------------------------------------------------------------

    ///  
    /// Compares the values.
    ///  
    /// True if they are equal. 
    /// 
    /// Critical: 
    ///  - accesses _location
    /// TreatAsSafe:
    ///  - does not leak information, simple compares to values the caller
    ///     already had 
    /// 
    [SecurityCritical, SecurityTreatAsSafe] 
    public static bool operator ==(CriticalFileToken a, CriticalFileToken b) 
    {
        bool result = false; 

        if (((object)a) == null)
        {
            if (((object)b) == null) 
            {
                result = true; 
            } 
        }
        else 
        {
            if (((object)b) != null)
            {
                result = a._location.ToString().Equals( 
                b._location.ToString(),
                StringComparison.OrdinalIgnoreCase); 
            } 
        }
        return result; 
    }

    /// 
    /// Compares the values. 
    /// 
    public static bool operator !=(CriticalFileToken a, CriticalFileToken b) 
    { 

        return !(a==b); 
    }

    /// 
    /// Compares the values. 
    /// 
    public override bool Equals(object obj) 
    { 
        return (this == (obj as CriticalFileToken));
    } 

    /// 
    /// See Object.GetHashCode();
    ///  
    public override int GetHashCode()
    { 
        return base.GetHashCode(); 
    }
    #endregion Object Members 

    #region Internal Properties
    //--------------------------------------------------------------------------
    // Internal Properties 
    //--------------------------------------------------------------------------
 
    ///  
    /// The location for which the creator satisfied ReadWrite access.
    ///  
    /// 
    /// Critical:
    ///  - the location is sensitive data; it could leak information
    ///    about the system; file structure, OS and user. 
    /// 
    internal Uri Location 
    { 
        [SecurityCritical]
        get 
        {
            return _location;
        }
    } 
    #endregion Internal Properties
 
    #region Private Fields 
    //-------------------------------------------------------------------------
    // Private Fields 
    //--------------------------------------------------------------------------

    /// 
    /// Critical - by definition as this is a wrapper for Critical data. 
    /// 
    [SecurityCritical] 
    private Uri _location; 
    #endregion Private Fields
} 
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
                        

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