FilteredXmlReader.cs source code in C# .NET

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                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Framework / System / Windows / Markup / FilteredXmlReader.cs / 1305600 / FilteredXmlReader.cs
                        

                        
                            //---------------------------------------------------------------------------- 
//
// 
//    Copyright (C) Microsoft Corporation.  All rights reserved.
//  
//
// Description: An implementation of XmlReader that filters out certain bits 
//  of underlying XML that we don't want exposed to our caller. 
//
// Additional remarks: This class is originally created so the 
//  XamlSerializer implementers won't have to worry about things like the
//  x:Uid attribute that may have been applied everywhere.  We skip them
//  during the attribute access/traversal methods.  If somebody gets content
//  some other way, like with "GetInnerXml", "GetOuterXml", or "GetRemainder", 
//  we don't modify that data. The caller will get all the x:Uid attributes.
// 
//  The initial implementation disallows index-based attribute access because 
//  that involves a lot more logic - not only does the Uid attribute need to
//  be cloaked, we'll need to determine whether or not the 
//  "xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" attribute needs to be cloaked too.  (There
//  may be a perfectly valid "def" attribute alongside the Uid.)
//
// The challenge with doing a complete filter is the fact that we can't 
//  "seek ahead" and rewind.  XmlReader is a forward-only interface.  So it
//  there are situations where it is possible for a x:Uid to slip by.  The 
//  example is the following: 
//
//   
//
// When we get to this element, CheckForUidAttribute will return an erroneous
//  result because it is looking for the wrong prefix.  It can't look for the
//  correct prefix because it doesn't know what to look for... until *after* 
//  we've passed it and the definition prefix is updated.  XmlReader internally
//  knows this info ahead of time, but we can't get to it from a subclass. 
// 
// Rather than give inconsistent results, we'll throw an exception to tell the
//  user that they can't have content like this - defining the Definition 
//  prefix within this chunk of XML is not allowed.
//
// History:
//  07/31/2003 : RogerCh - Initial creation 
//
//--------------------------------------------------------------------------- 
 
using System;       // InvalidOperationException
using System.IO;    // TextReader 
using System.Xml;   // XmlTextReader

using MS.Utility;   // ExceptionStringTable
 
namespace System.Windows.Markup
{ 
internal class FilteredXmlReader : XmlTextReader 
{
    //----------------------------------------------------- 
    //
    //  Public Constructors
    //
    //----------------------------------------------------- 

    // None 
 
    //------------------------------------------------------
    // 
    //  Public Properties
    //
    //-----------------------------------------------------
 
    #region Public Properties
 
    public override int AttributeCount 
    {
        get 
        {
            int baseCount = base.AttributeCount;

            // If there's an UID, we're going to hide it from the user. 
            if( haveUid )
                return baseCount - 1; 
            else 
                return baseCount;
        } 
    }

    public override bool HasAttributes
    { 
        get
        { 
            // This should be a simple yes/no, but unfortunately we need the 
            //  total count and whether one of them is UID to tell.
            return (AttributeCount != 0); 
        }
    }

    public override string this[ int attributeIndex ] 
    {
        get 
        { 
            return GetAttribute( attributeIndex ); // Defined elsewhere in this file.
        } 
    }

    public override string this[ string attributeName ]
    { 
        get
        { 
            return GetAttribute( attributeName ); // Defined elsewhere in this file. 
        }
    } 

    public override string this[ string localName, string namespaceUri ]
    {
        get 
        {
            return GetAttribute( localName, namespaceUri ); // Defined elsewhere in this file. 
        } 
    }
 
    #endregion Public Properties

    //------------------------------------------------------
    // 
    //  Public Methods
    // 
    //------------------------------------------------------ 

    #region Public Methods 

    public override string GetAttribute( int attributeIndex )
    {
        // Index-based acccess are not allowed.  See remark at top of this file. 
        throw new InvalidOperationException(
            SR.Get(SRID.ParserFilterXmlReaderNoIndexAttributeAccess)); 
    } 

    public override string GetAttribute( string attributeName ) 
    {
        if( attributeName == uidQualifiedName )
        {
            return null;  // ...these aren't the attributes you're looking for... 
        }
        else 
        { 
            return base.GetAttribute( attributeName );
        } 
    }

    public override string GetAttribute( string localName, string namespaceUri )
    { 
        if( localName == uidLocalName &&
            namespaceUri == uidNamespace) 
        { 
            return null;  // ...these aren't the attributes you're looking for...
        } 
        else
        {
            return base.GetAttribute( localName, namespaceUri );
        } 
    }
 
    public override void MoveToAttribute( int attributeIndex ) 
    {
        // Index-based acccess are not allowed.  See remark at top of this file. 
        throw new InvalidOperationException(
            SR.Get(SRID.ParserFilterXmlReaderNoIndexAttributeAccess));
    }
 
    public override bool MoveToAttribute( string attributeName )
    { 
        if( attributeName == uidQualifiedName ) 
        {
            return false;  // ...these aren't the attributes you're looking for... 
        }
        else
        {
            return base.MoveToAttribute( attributeName ); 
        }
    } 
 
    public override bool MoveToAttribute( string localName, string namespaceUri )
    { 
        if( localName == uidLocalName &&
            namespaceUri == uidNamespace)
        {
            return false;  // ...these aren't the attributes you're looking for... 
        }
        else 
        { 
            return base.MoveToAttribute( localName, namespaceUri );
        } 
    }

    public override bool MoveToFirstAttribute()
    { 
        bool success = base.MoveToFirstAttribute();
 
        success = CheckForUidOrNamespaceRedef(success); 

        return success; 
    }

    public override bool MoveToNextAttribute()
    { 
        bool success = base.MoveToNextAttribute();
 
        success = CheckForUidOrNamespaceRedef(success); 

        return success; 
    }

    public override bool Read()
    { 
        bool success = base.Read();
 
        if( success ) 
        {
            CheckForUidAttribute(); 
        }

        return success;
    } 

    #endregion Public Methods 
 
    //-----------------------------------------------------
    // 
    //  Public Events
    //
    //------------------------------------------------------
 
    // None
 
    //----------------------------------------------------- 
    //
    //  Internal Constructors 
    //
    //-----------------------------------------------------

    #region Internal Constructors 

    internal FilteredXmlReader( string xmlFragment, XmlNodeType fragmentType, XmlParserContext context ) : 
        base( xmlFragment, fragmentType, context ) 
    {
        haveUid = false; 
        uidPrefix = defaultPrefix;
        uidQualifiedName = uidPrefix + ":" + uidLocalName;
    }
 
    #endregion Internal Constructors
 
    //----------------------------------------------------- 
    //
    //  Internal Properties 
    //
    //------------------------------------------------------

    // None 

    //----------------------------------------------------- 
    // 
    //  Internal Methods
    // 
    //------------------------------------------------------

    // None
 
    //------------------------------------------------------
    // 
    //  Internal Events 
    //
    //----------------------------------------------------- 

    // None

    //------------------------------------------------------ 
    //
    //  Private Methods 
    // 
    //-----------------------------------------------------
 
    #region Private Methods

    // Using our best known information on the fully qualified name for the Uid
    //  attribute, look for it on the current node. 
    private void CheckForUidAttribute()
    { 
        if( base.GetAttribute(uidQualifiedName) != null ) // Do NOT use base[uidQualifiedName], that just comes right back to us. 
            haveUid = true;
        else 
            haveUid = false;
    }

    // We've just moved the attribute "cursor" to the next node.  This may 
    //  be an Uid node - which we want to skip.  Or we may end up at a
    //  xmlns:???="http://schemas.microsoft.com/winfx/2006/xaml" where we need to pick up a new prefix. 
    private bool CheckForUidOrNamespaceRedef(bool previousSuccessValue) 
    {
        bool success = previousSuccessValue; 

        if( success &&
            base.LocalName == uidLocalName &&
            base.NamespaceURI == uidNamespace) 
        {
            // We've found an Uid tag, based on URI Namespace and "Uid" text 
            //  value.  However, the prefix before the "Uid" may or may not be 
            //  what we think it is.  Check and update as needed.
            CheckForPrefixUpdate(); 

            // Move again because we want to skip this.
            success = base.MoveToNextAttribute();
        } 

        // We may be handing a xmlns definition back to the user at this point. 
        //  this may be the "Definition" re-definition.  (It's nasty that we 
        //  might run into its *use* above, before we get the *definition* here.)
        CheckForNamespaceRedef(); 

        return success;
    }
 
    // This is called whenever we have a match based on LocalName and NamespaceURI.
    //  If the prefix has changed, we update our best known information on prefix 
    //  and the fully qualified name. 
    private void CheckForPrefixUpdate()
    { 
        if( base.Prefix != uidPrefix )
        {
            uidPrefix = base.Prefix;
            uidQualifiedName = uidPrefix + ":" + uidLocalName; 

            // Prefix updated - run a check again for Uid. 
            CheckForUidAttribute(); 
        }
    } 

    // This is called whenever a node is about to be returned to the user.  We
    //  check to see if it's a "xmlns" node that re-defines the "Definition"
    //  namespace. 
    private void CheckForNamespaceRedef()
    { 
        // xmlns node example: < [...] xmlns:someprefix="http://schemas.microsoft.com/winfx/2006/xaml" [...}/> 
        //  base.Name = "xmlns:someprefix"
        //  base.LocalName = "someprefix" 
        //  base.Prefix = "xmlns"
        //  base.Value ="http://schemas.microsoft.com/winfx/2006/xaml" = uidNamespace

        if( base.Prefix == "xmlns" &&         // Fixed via XML spec 
            base.LocalName != uidPrefix &&    // Hey, this prefix isn't the one we think it is.
            base.Value == uidNamespace) 
        { 
            throw new InvalidOperationException(
                SR.Get(SRID.ParserFilterXmlReaderNoDefinitionPrefixChangeAllowed)); 
        }
    }

    #endregion Private Methods 

    //----------------------------------------------------- 
    // 
    //  Private Fields
    // 
    //-----------------------------------------------------

    #region Private Fields
 
    // These are fixed, by definition of the Uid feature.
    const string uidLocalName = "Uid"; 
    const string uidNamespace = XamlReaderHelper.DefinitionNamespaceURI; 
    const string defaultPrefix = "def";
 
    // Best known information on the Definition prefix, updated as we know more.
          string uidPrefix;
    // Best known information on the fully qualified name, updated as we know more.
    //  (Updated at same time as uidPrefix.) 
          string uidQualifiedName;
 
    // Every time we move to another XML element, we try to see if there is 
    //  a "x:UID" on the node.
    bool  haveUid; 

    #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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