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//------------------------------------------------------------
// Copyright (c) Microsoft Corporation. All rights reserved.
//------------------------------------------------------------
namespace System.ServiceModel.Channels
{
using System;
using System.Runtime;
using System.Security.Cryptography;
sealed class DuplicateMessageDetector : IDisposable
{
HashAlgorithm hashAlgorithm;
[Fx.Tag.Cache(typeof(string), Fx.Tag.CacheAttrition.PartialPurgeOnEachAccess, SizeLimit = "maxListLength parameter to constructor")]
DuplicateDetector<string> duplicateDetector;
[Fx.Tag.SynchronizationObject()]
object thisLock;
bool disposed;
public DuplicateMessageDetector(int maxListLength)
{
Fx.Assert(maxListLength > 0, "maxListLength must be > 0");
this.disposed = false;
this.hashAlgorithm = HashAlgorithm.Create();
this.thisLock = new object();
this.duplicateDetector = new DuplicateDetector<string>(maxListLength);
}
public bool IsDuplicate(ArraySegment<byte> msgBytes, out string hashString)
{
Fx.Assert(msgBytes != null, "messageBytes can't be null");
Fx.Assert(msgBytes.Count > 0, "messageBytes.Count must be > 0");
byte[] hash;
bool notDuplicate = true;
lock (this.thisLock)
{
if (disposed)
{
throw FxTrace.Exception.AsError(new ObjectDisposedException(this.GetType().ToString()));
}
hash = this.hashAlgorithm.ComputeHash(msgBytes.Array, msgBytes.Offset, msgBytes.Count);
}
hashString = Convert.ToBase64String(hash);
Fx.Assert(string.IsNullOrEmpty(hashString) == false, "computed hashstring is null or empty");
lock (this.thisLock)
{
//the act of retreiving an existing item pushes it to the front of the MRU list, ensuring
//that the oldest hashes are trimmed first when we hit the max length.
notDuplicate = this.duplicateDetector.AddIfNotDuplicate(hashString);
}
return !notDuplicate;
}
public void RemoveEntry(string msgHash)
{
Fx.Assert(!string.IsNullOrEmpty(msgHash), "Message hash should never be null or empty");
lock (this.thisLock)
{
if (this.disposed)
{
throw FxTrace.Exception.AsError(new ObjectDisposedException(this.GetType().ToString()));
}
this.duplicateDetector.Remove(msgHash);
}
}
public void Dispose()
{
if (this.disposed)
{
return;
}
lock (this.thisLock)
{
if (!this.disposed)
{
this.disposed = true;
if (this.duplicateDetector != null)
{
this.duplicateDetector.Clear();
}
this.hashAlgorithm.Clear();
this.hashAlgorithm = null;
}
}
}
}
}
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