Add IPv4 fallback from IPv6 failure.

Co-authored-by: BaronGreenback <jimcartlidge@yahoo.co.uk>

2 files changed, 131 insertions, 3 deletions

diff --git a/Jellyfin.Networking/HappyEyeballs/HttpClientExtension.cs b/Jellyfin.Networking/HappyEyeballs/HttpClientExtension.cs
new file mode 100644
index 0000000000..12b42cc6e1
--- /dev/null
+++ b/Jellyfin.Networking/HappyEyeballs/HttpClientExtension.cs
@@ -0,0 +1,117 @@
+using System.Diagnostics.Metrics;
+using System.IO;
+using System.Net.Http;
+using System.Net.Sockets;
+using System.Threading;
+using System.Threading.Tasks;
+
+/*
+    Copyright (c) 2021 ppy Pty Ltd <contact@ppy.sh>.
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+*/
+
+namespace Jellyfin.Networking.HappyEyeballs
+{
+    /// <summary>
+    /// Defines the <see cref="HttpClientExtension"/> class.
+    ///
+    /// Implementation taken from https://github.com/ppy/osu-framework/pull/4191 .
+    /// </summary>
+    public static class HttpClientExtension
+    {
+        private const int ConnectionEstablishTimeout = 2000;
+
+        /// <summary>
+        /// Gets a value indicating whether the initial IPv6 check has been performed (to determine whether v6 is available or not).
+        /// </summary>
+        private static bool _hasResolvedIPv6Availability;
+
+        /// <summary>
+        /// Gets or sets a value indicating whether IPv6 should be preferred. Value may change based on runtime failures.
+        /// </summary>
+        public static bool? UseIPv6 { get; set; } = null;
+
+        /// <summary>
+        /// Implements the httpclient callback method.
+        /// </summary>
+        /// <param name="context">The <see cref="SocketsHttpConnectionContext"/> instance.</param>
+        /// <param name="cancellationToken">The <see cref="CancellationToken"/> instance.</param>
+        /// <returns>The http steam.</returns>
+        public static async ValueTask<Stream> OnConnect(SocketsHttpConnectionContext context, CancellationToken cancellationToken)
+        {
+            // Until .NET supports an implementation of Happy Eyeballs (https://tools.ietf.org/html/rfc8305#section-2),
+            // let's make IPv4 fallback work in a simple way. This issue is being tracked at https://github.com/dotnet/runtime/issues/26177
+            // and expected to be fixed in .NET 6.
+            if (UseIPv6 == true)
+            {
+                try
+                {
+                    var localToken = cancellationToken;
+
+                    if (!_hasResolvedIPv6Availability)
+                    {
+                        // to make things move fast, use a very low timeout for the initial ipv6 attempt.
+                        using var quickFailCts = new CancellationTokenSource(ConnectionEstablishTimeout);
+                        using var linkedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, quickFailCts.Token);
+
+                        localToken = linkedTokenSource.Token;
+                    }
+
+                    return await AttemptConnection(AddressFamily.InterNetworkV6, context, localToken).ConfigureAwait(false);
+                }
+#pragma warning disable CA1031 // Do not catch general exception types
+                catch
+#pragma warning restore CA1031 // Do not catch general exception types
+                {
+                    // very naively fallback to ipv4 permanently for this execution based on the response of the first connection attempt.
+                    // Network manager will reset this value in the case of physical network changes / interruptions.
+                    UseIPv6 = false;
+                }
+                finally
+                {
+                    _hasResolvedIPv6Availability = true;
+                }
+            }
+
+            // fallback to IPv4.
+            return await AttemptConnection(AddressFamily.InterNetwork, context, cancellationToken).ConfigureAwait(false);
+        }
+
+        private static async ValueTask<Stream> AttemptConnection(AddressFamily addressFamily, SocketsHttpConnectionContext context, CancellationToken cancellationToken)
+        {
+            // The following socket constructor will create a dual-mode socket on systems where IPV6 is available.
+            var socket = new Socket(addressFamily, SocketType.Stream, ProtocolType.Tcp)
+            {
+                // Turn off Nagle's algorithm since it degrades performance in most HttpClient scenarios.
+                NoDelay = true
+            };
+
+            try
+            {
+                await socket.ConnectAsync(context.DnsEndPoint, cancellationToken).ConfigureAwait(false);
+                // The stream should take the ownership of the underlying socket,
+                // closing it when it's disposed.
+                return new NetworkStream(socket, ownsSocket: true);
+            }
+            catch
+            {
+                socket.Dispose();
+                throw;
+            }
+        }
+    }
+}
diff --git a/Jellyfin.Networking/Manager/NetworkManager.cs b/Jellyfin.Networking/Manager/NetworkManager.cs
index 9e06cdfe71..631e9cdb8d 100644
--- a/Jellyfin.Networking/Manager/NetworkManager.cs
+++ b/Jellyfin.Networking/Manager/NetworkManager.cs
@@ -594,6 +594,7 @@ namespace Jellyfin.Networking.Manager
 
             IsIP4Enabled = Socket.OSSupportsIPv4 && config.EnableIPV4;
             IsIP6Enabled = Socket.OSSupportsIPv6 && config.EnableIPV6;
+            HappyEyeballs.HttpClientExtension.UseIPv6 = IsIP6Enabled;
 
             if (!IsIP6Enabled && !IsIP4Enabled)
             {
@@ -838,9 +839,19 @@ namespace Jellyfin.Networking.Manager
             try
             {
                 await Task.Delay(2000).ConfigureAwait(false);
-                InitialiseInterfaces();
-                // Recalculate LAN caches.
-                InitialiseLAN(_configurationManager.GetNetworkConfiguration());
+
+                var config = _configurationManager.GetNetworkConfiguration();
+                // Have we lost IPv6 capability?
+                if (IsIP6Enabled && !Socket.OSSupportsIPv6)
+                {
+                    UpdateSettings(config);
+                }
+                else
+                {
+                    InitialiseInterfaces();
+                    // Recalculate LAN caches.
+                    InitialiseLAN(config);
+                }
 
                 NetworkChanged?.Invoke(this, EventArgs.Empty);
             }