Code:
/ 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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