baseline: OpenMU upstream b5a0961 (fresh source)

src/Network/IpAddressExtensions.cs

@@ -0,0 +1,39 @@
+// <copyright file="IpAddressExtensions.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.Network;
+
+using System.Diagnostics.CodeAnalysis;
+using System.Net;
+
+/// <summary>
+/// Extensions for <see cref="IPAddress"/>.
+/// </summary>
+public static class IpAddressExtensions
+{
+    private static HashSet<IPAddress>? _localIpAddresses;
+
+    /// <summary>
+    /// Determines whether the address in on same (this) host.
+    /// </summary>
+    /// <param name="address">The next server address.</param>
+    /// <returns>
+    ///   <c>true</c> if the specified address is on same host as this machine; otherwise, <c>false</c>.
+    /// </returns>
+    public static bool IsOnSameHost([NotNullWhen(true)] this IPAddress? address)
+    {
+        if (address is null)
+        {
+            return false;
+        }
+
+        if (IPAddress.IsLoopback(address))
+        {
+            return true;
+        }
+
+        _localIpAddresses ??= Dns.GetHostAddresses(Dns.GetHostName()).ToHashSet();
+        return _localIpAddresses.Contains(address);
+    }
+}