SurrogateSelector.cs source code in C# .NET

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/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / Runtime / Serialization / SurrogateSelector.cs / 1 / SurrogateSelector.cs

                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
/*============================================================
** 
** Class: SurrogateSelector 
**
** 
** Purpose: A user-supplied class for doing the type to surrogate
**          mapping.
**
** 
===========================================================*/
namespace System.Runtime.Serialization { 
 
 	using System.Runtime.Remoting;
	using System; 
	using System.Collections;
	using System.Security.Permissions;
[System.Runtime.InteropServices.ComVisible(true)]
    public class SurrogateSelector : ISurrogateSelector { 

        internal SurrogateHashtable m_surrogates; 
        internal ISurrogateSelector m_nextSelector; 

        public SurrogateSelector() { 
            m_surrogates = new SurrogateHashtable(32);
        }

        // Adds a surrogate to the list of surrogates checked. 
        public virtual void AddSurrogate(Type type, StreamingContext context, ISerializationSurrogate surrogate) {
            if (type==null) { 
                throw new ArgumentNullException("type"); 
            }
            if (surrogate==null) { 
                throw new ArgumentNullException("surrogate");
            }

            SurrogateKey key = new SurrogateKey(type, context); 
            m_surrogates.Add(key, surrogate);  // Hashtable does duplicate checking.
        } 
 
        private static bool HasCycle(ISurrogateSelector selector) {
            ISurrogateSelector head; 
            ISurrogateSelector tail;

            BCLDebug.Assert(selector!=null, "[HasCycle]selector!=null");
 

            head = selector; 
            tail = selector; 

            while (head!=null) { 
                head = head.GetNextSelector();
                if (head==null) {
                    return true;
                } 
                if (head==tail) {
                    return false; 
                } 
                head = head.GetNextSelector();
                tail = tail.GetNextSelector(); 

                if (head==tail) {
                    return false;
                } 
            }
 
            return true; 

        } 

        // Adds another selector to check if we don't have  match within this selector.
        // The logic is:"Add this onto the list as the first thing that you check after yourself."
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.SerializationFormatter)] 		 
        public virtual void ChainSelector(ISurrogateSelector selector) {
            ISurrogateSelector temp; 
            ISurrogateSelector tempCurr; 
            ISurrogateSelector tempPrev;
            ISurrogateSelector tempEnd; 

            if (selector==null) {
                throw new ArgumentNullException("selector");
            } 

            // 
            // Verify that we don't try and add ourself twice. 
            //
            if (selector==this) { 
                throw new SerializationException(Environment.GetResourceString("Serialization_DuplicateSelector"));
            }

            // 
            // Verify that the argument doesn't contain a cycle.
            // 
            if (!HasCycle(selector)) { 
                throw new ArgumentException(Environment.GetResourceString("Serialization_SurrogateCycleInArgument"), "selector");
            } 

            //
            // Check for a cycle that would lead back to this.  We find the end of the list that we're being asked to
            // insert for use later. 
            //
            tempCurr = selector.GetNextSelector(); 
            tempEnd = selector; 
            while (tempCurr!=null && tempCurr!=this) {
                tempEnd = tempCurr; 
                tempCurr = tempCurr.GetNextSelector();
            }
            if (tempCurr==this) {
                throw new ArgumentException(Environment.GetResourceString("Serialization_SurrogateCycle"), "selector"); 
            }
 
            // 
            // Check for a cycle later in the list which would be introduced by this insertion.
            // 
            tempCurr = selector;
            tempPrev = selector;
            while(tempCurr!=null) {
                if (tempCurr==tempEnd) { 
                    tempCurr = this.GetNextSelector();
                } else { 
                    tempCurr = tempCurr.GetNextSelector(); 
                }
                if (tempCurr==null) { 
                    break;
                }
                if (tempCurr==tempPrev) {
                    throw new ArgumentException(Environment.GetResourceString("Serialization_SurrogateCycle"), "selector"); 
                }
 
                if (tempCurr==tempEnd) { 
                    tempCurr = this.GetNextSelector();
                } else { 
                    tempCurr = tempCurr.GetNextSelector();
                }

 
                if (tempPrev==tempEnd) {
                    tempPrev = this.GetNextSelector(); 
                } else { 
                    tempPrev = tempPrev.GetNextSelector();
                } 
                if (tempCurr==tempPrev) {
                    throw new ArgumentException(Environment.GetResourceString("Serialization_SurrogateCycle"), "selector");
                }
            } 

            // 
            // Add the new selector and it's entire chain of selectors as the next thing that 
            // we check.
            // 
            temp = m_nextSelector;
            m_nextSelector = selector;
            if (temp!=null) {
                tempEnd.ChainSelector(temp); 
            }
        } 
 
        // Get the next selector on the chain of selectors.
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.SerializationFormatter)] 		 
        public virtual ISurrogateSelector GetNextSelector() {
            return m_nextSelector;
        }
 
        // Gets the surrogate for a particular type.  If this selector can't
        // provide a surrogate, it checks with all of it's children before returning null. 
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.SerializationFormatter)] 		 
        public virtual ISerializationSurrogate GetSurrogate(Type type, StreamingContext context, out ISurrogateSelector selector) {
            if (type==null) { 
                throw new ArgumentNullException("type");
            }

            selector = this; 

            SurrogateKey key = new SurrogateKey(type, context); 
            ISerializationSurrogate temp = (ISerializationSurrogate)m_surrogates[key]; 
            if (temp!=null) {
                return temp; 
            }
            if (m_nextSelector!=null) {
                return m_nextSelector.GetSurrogate(type, context, out selector);
            } 
            return null;
        } 
 
        // Removes the surrogate associated with a given type.  Does not
        // check chained surrogates. 
        public virtual void RemoveSurrogate(Type type, StreamingContext context) {
            if (type==null) {
                throw new ArgumentNullException("type");
            } 

 
            SurrogateKey key = new SurrogateKey(type, context); 
            m_surrogates.Remove(key);
        } 
    }

    //<
 
 	[Serializable()]
    internal class SurrogateKey { 
        internal Type m_type; 
        internal StreamingContext m_context;
 
        internal SurrogateKey(Type type, StreamingContext context) {
            m_type = type;
            m_context = context;
        } 

        public override int GetHashCode() { 
            return m_type.GetHashCode(); 
        }
    } 

    // Subclass to override KeyEquals.
    class SurrogateHashtable : Hashtable {
        internal SurrogateHashtable(int size):base(size){ 
            ;
        } 
        // Must return true if the context to serialize for (givenContext) 
        // is a subset of the context for which the serialization selector is provided (presentContext)
        // Note: This is done by overriding KeyEquals rather than overriding Equals() in the SurrogateKey 
        // class because Equals() method must be commutative.
    	protected override bool KeyEquals(Object key, Object item){
            SurrogateKey givenValue = (SurrogateKey)item;
            SurrogateKey presentValue = (SurrogateKey)key; 
            return presentValue.m_type == givenValue.m_type &&
                   (presentValue.m_context.m_state & givenValue.m_context.m_state) == givenValue.m_context.m_state && 
                   presentValue.m_context.Context == givenValue.m_context.Context; 
        }
    } 

}
                        

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