DnsCache.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / WCF / WCF / 3.5.30729.1 / untmp / Orcas / SP / ndp / cdf / src / WCF / ServiceModel / System / ServiceModel / Channels / DnsCache.cs / 1 / DnsCache.cs
                        

                        
                            //---------------------------------------------------------------------------- 
// Copyright (c) Microsoft Corporation.  All rights reserved.
//---------------------------------------------------------------------------
namespace System.ServiceModel.Channels
{ 
    using System.Collections.Generic;
    using System.Diagnostics; 
    using System.Net; 
    using System.Net.NetworkInformation;
    using System.Net.Sockets; 
    using System.Security.Permissions;
    using System.ServiceModel;
    using System.ServiceModel.Dispatcher;
    using System.Text; 

    static class DnsCache 
    { 
        const int mruWatermark = 64;
        static MruCache resolveCache = new MruCache(mruWatermark); 
        static readonly TimeSpan cacheTimeout = TimeSpan.FromSeconds(2);
        static string machineName;

        static object ThisLock 
        {
            get 
            { 
                return resolveCache;
            } 
        }

        public static string MachineName
        { 
            get
            { 
                if (machineName == null) 
                {
                    lock (ThisLock) 
                    {
                        if (machineName == null)
                        {
                            try 
                            {
                                machineName = Dns.GetHostEntry(String.Empty).HostName; 
                            } 
                            catch (SocketException exception)
                            { 
                                if (DiagnosticUtility.ShouldTraceInformation)
                                {
                                    DiagnosticUtility.ExceptionUtility.TraceHandledException(exception,
                                        TraceEventType.Information); 
                                }
                                // we fall back to the NetBios machine if Dns fails 
                                machineName = UnsafeNativeMethods.GetComputerName(ComputerNameFormat.PhysicalNetBIOS); 
                            }
                        } 
                    }
                }

                return machineName; 
            }
        } 
 
        public static IPHostEntry Resolve(string hostName)
        { 
            IPHostEntry hostEntry = null;
            DateTime now = DateTime.UtcNow;

            lock (ThisLock) 
            {
                DnsCacheEntry cacheEntry; 
                if (resolveCache.TryGetValue(hostName, out cacheEntry)) 
                {
                    if (now.Subtract(cacheEntry.TimeStamp) > cacheTimeout) 
                    {
                        resolveCache.Remove(hostName);
                    }
                    else 
                    {
                        if (cacheEntry.HostEntry == null) 
                        { 
                            throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(
                                new EndpointNotFoundException(SR.GetString(SR.DnsResolveFailed, hostName))); 
                        }
                        hostEntry = cacheEntry.HostEntry;
                    }
                } 
            }
 
            if (hostEntry == null) 
            {
                SocketException dnsException = null; 
                try
                {
                    hostEntry = Dns.GetHostEntry(hostName);
                } 
                catch (SocketException e)
                { 
                    dnsException = e; 
                }
 
                lock (ThisLock)
                {
                    // MruCache doesn't have a this[] operator, so we first remove (just in case it exists already)
                    resolveCache.Remove(hostName); 
                    resolveCache.Add(hostName, new DnsCacheEntry(hostEntry, now));
                } 
 
                if (dnsException != null)
                { 
                    throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(
                        new EndpointNotFoundException(SR.GetString(SR.DnsResolveFailed, hostName), dnsException));
                }
            } 

            return hostEntry; 
        } 

        class DnsCacheEntry 
        {
            IPHostEntry hostEntry;
            DateTime timeStamp;
 
            public DnsCacheEntry(IPHostEntry hostEntry, DateTime timeStamp)
            { 
                this.hostEntry = hostEntry; 
                this.timeStamp = timeStamp;
            } 

            public IPHostEntry HostEntry
            {
                get 
                {
                    return hostEntry; 
                } 
            }
 
            public DateTime TimeStamp
            {
                get
                { 
                    return timeStamp;
                } 
            } 
        }
    } 
}

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

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