Adding Lancache support to the CDN Client.

SteamKit2/SteamKit2/Steam/CDN/Client.cs

@@ -16,7 +16,7 @@ namespace SteamKit2.CDN
     /// <summary>
     /// The <see cref="Client"/> class is used for downloading game content from the Steam servers.
     /// </summary>
-    public sealed class Client : IDisposable
+    public sealed partial class Client : IDisposable
     {
         HttpClient httpClient;
 
@@ -29,7 +29,6 @@ public sealed class Client : IDisposable
         /// </summary>
         public static TimeSpan ResponseBodyTimeout { get; set; } = TimeSpan.FromSeconds( 60 );
 
-
         /// <summary>
         /// Initializes a new instance of the <see cref="Client"/> class.
         /// </summary>
@@ -230,7 +229,16 @@ public async Task<int> DownloadDepotChunkAsync( uint depotId, DepotManifest.Chun
             var chunkID = Utils.EncodeHexString( chunk.ChunkID );
             var url = $"depot/{depotId}/chunk/{chunkID}";
 
-            using var request = new HttpRequestMessage( HttpMethod.Get, BuildCommand( server, url, cdnAuthToken, proxyServer ) );
+            HttpRequestMessage request;
+            if ( UseLancacheServer )
+            {
+                request = BuildLancacheRequest( server, url, cdnAuthToken );
+            }
+            else
+            {
+                var builtUrl = BuildCommand( server, url, cdnAuthToken, proxyServer );
+                request = new HttpRequestMessage( HttpMethod.Get, builtUrl );
+            }
 
             using var cts = new CancellationTokenSource();
             cts.CancelAfter( RequestTimeout );
@@ -313,6 +321,10 @@ public async Task<int> DownloadDepotChunkAsync( uint depotId, DepotManifest.Chun
                 DebugLog.WriteLine( nameof( CDN ), $"Failed to download a depot chunk {request.RequestUri}: {ex.Message}" );
                 throw;
             }
+            finally
+            {
+                request.Dispose();
+            }
         }
 
         static Uri BuildCommand( Server server, string command, string? query, Server? proxyServer )

SteamKit2/SteamKit2/Steam/CDN/ClientLancache.cs

@@ -0,0 +1,105 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'license.txt', which is part of this source code package.
+ */
+
+using System;
+using System.Linq;
+using System.Net;
+using System.Net.Http;
+using System.Net.Sockets;
+using System.Threading.Tasks;
+
+namespace SteamKit2.CDN
+{
+    public partial class Client
+    {
+        /// <summary>
+        /// When set to true, will attempt to download from a Lancache instance on the LAN rather than going out to Steam's CDNs.
+        /// </summary>
+        public static bool UseLancacheServer { get; private set; }
+
+        private static string TriggerDomain = "lancache.steamcontent.com";
+
+        /// <summary>
+        /// Attempts to automatically resolve a Lancache on the local network.  If detected, SteamKit will route all downloads through the cache
+        /// rather than through Steam's CDN.  Will try to detect the Lancache through the poisoned DNS entry for lancache.steamcontent.com
+        ///
+        /// This is a modified version from the original source : https://github.com/tpill90/lancache-prefill-common/blob/main/dotnet/LancacheIpResolver.cs
+        /// </summary>
+        public static async Task DetectLancacheServerAsync()
+        {
+            var ipAddresses = ( await Dns.GetHostAddressesAsync( TriggerDomain ) )
+                .Where( e => e.AddressFamily == AddressFamily.InterNetwork || e.AddressFamily == AddressFamily.InterNetworkV6 )
+                .ToArray();
+
+            if ( ipAddresses.Any( e => IsPrivateAddress(e) ) )
+            {
+                UseLancacheServer = true;
+                return;
+            }
+
+            //If there are no private IPs, then there can't be a Lancache instance. Lancache's IP must resolve to a private RFC 1918 address.
+            UseLancacheServer = false;
+        }
+
+        /// <summary>
+        /// Determines if an IP address is a private address, as specified in RFC1918
+        /// </summary>
+        /// <param name="toTest">The IP address that will be tested</param>
+        /// <returns>Returns true if the IP is a private address, false if it isn't private</returns>
+        internal static bool IsPrivateAddress( IPAddress toTest )
+        {
+            if ( IPAddress.IsLoopback( toTest ) )
+            {
+                return true;
+            }
+
+            byte[] bytes = toTest.GetAddressBytes();
+
+            // IPv4
+            if ( toTest.AddressFamily == AddressFamily.InterNetwork )
+            {
+                switch ( bytes[ 0 ] )
+                {
+                    case 10:
+                        return true;
+                    case 172:
+                        return bytes[ 1 ] >= 16 && bytes[ 1 ] < 32;
+                    case 192:
+                        return bytes[ 1 ] == 168;
+                    default:
+                        return false;
+                }
+            }
+
+            // IPv6
+            if ( toTest.AddressFamily == AddressFamily.InterNetworkV6 )
+            {
+                // Check for Unique Local Address (fc00::/7) and loopback (::1)
+                return ( bytes[ 0 ] & 0xFE ) == 0xFC || toTest.IsIPv6LinkLocal;
+            }
+
+            return false;
+        }
+
+        static HttpRequestMessage BuildLancacheRequest( Server server, string command, string? query)
+        {
+            var builder = new UriBuilder
+            {
+                Scheme = "http",
+                Host = "lancache.steamcontent.com",
+                Port = 80,
+                Path = command,
+                Query = query ?? string.Empty
+            };
+
+            var request = new HttpRequestMessage( HttpMethod.Get, builder.Uri );
+            request.Headers.Host = server.Host;
+            // User agent must match the Steam client in order for Lancache to correctly identify and cache Valve's CDN content
+            request.Headers.Add( "User-Agent", "Valve/Steam HTTP Client 1.0" );
+
+            return request;
+        }
+    }
+}

SteamKit2/Tests/CDNClientFacts.cs

@@ -119,6 +119,33 @@ public async Task ThrowsWhenDestinationBufferSmallerWithDepotKey()
             Assert.Equal( "destination", ex.ParamName );
         }
 
+        [Theory]
+        [InlineData( "10.0.0.1", true )]       // Private IPv4 (10.0.0.0/8)
+        [InlineData( "172.16.0.1", true )]     // Private IPv4 (172.16.0.0/12)
+        [InlineData( "192.168.0.1", true )]    // Private IPv4 (192.168.0.0/16)
+        [InlineData( "8.8.8.8", false )]       // Public IPv4
+        [InlineData( "127.0.0.1", true )]      // Loopback IPv4
+        public void IsPrivateAddress_IPv4Tests( string ipAddress, bool expected )
+        {
+            IPAddress address = IPAddress.Parse( ipAddress );
+            bool result = Client.IsPrivateAddress( address );
+
+            Assert.Equal( expected, result );
+        }
+
+        [Theory]
+        [InlineData( "fc00::1", true )]         // Private IPv6 (Unique Local Address)
+        [InlineData( "fe80::1", true )]         // Link-local IPv6
+        [InlineData( "2001:db8::1", false )]    // Public IPv6
+        [InlineData( "::1", true )]             // Loopback IPv6
+        public void IsPrivateAddress_IPv6Tests( string ipAddress, bool expected )
+        {
+            IPAddress address = IPAddress.Parse( ipAddress );
+            bool result = Client.IsPrivateAddress( address );
+
+            Assert.Equal( expected, result );
+        }
+
         sealed class TeapotHttpMessageHandler : HttpMessageHandler
         {
             protected override Task<HttpResponseMessage> SendAsync( HttpRequestMessage request, CancellationToken cancellationToken )