Add fallback "updater", which prompts the user to update

osu.Desktop/OsuGameDesktop.cs

@@ -53,6 +53,8 @@ namespace osu.Desktop
 
 #if NET_FRAMEWORK
                 Add(new SquirrelUpdateManager());
+#else
+                Add(new SimpleUpdateManager());
 #endif
             }
         }

osu.Desktop/Updater/SimpleUpdateManager.cs

@@ -0,0 +1,103 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Newtonsoft.Json;
+using osu.Framework;
+using osu.Framework.Allocation;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.IO.Network;
+using osu.Framework.Platform;
+using osu.Game;
+using osu.Game.Graphics;
+using osu.Game.Overlays;
+using osu.Game.Overlays.Notifications;
+
+namespace osu.Desktop.Updater
+{
+    /// <summary>
+    /// An update manager that shows notifications if a newer release is detected.
+    /// Installation is left up to the user.
+    /// </summary>
+    internal class SimpleUpdateManager : CompositeDrawable
+    {
+        private NotificationOverlay notificationOverlay;
+        private string version;
+        private GameHost host;
+
+        [BackgroundDependencyLoader]
+        private void load(NotificationOverlay notification, OsuGameBase game, GameHost host)
+        {
+            notificationOverlay = notification;
+
+            this.host = host;
+            version = game.Version;
+
+            if (game.IsDeployedBuild)
+                Schedule(() => Task.Run(() => checkForUpdateAsync()));
+        }
+
+        private async void checkForUpdateAsync()
+        {
+            var releases = new JsonWebRequest<GitHubRelease>("https://api.github.com/repos/ppy/osu/releases/latest");
+            await releases.PerformAsync();
+
+            var latest = releases.ResponseObject;
+
+            if (latest.TagName != version)
+            {
+                notificationOverlay.Post(new SimpleNotification
+                {
+                    Text = $"A newer release of osu! has been found ({version} → {latest.TagName}).\n\n"
+                           + "Click here to download the new version, which can be installed over the top of your existing installation",
+                    Icon = FontAwesome.fa_upload,
+                    Activated = () =>
+                    {
+                        host.OpenUrlExternally(getBestUrl(latest));
+                        return true;
+                    }
+                });
+            }
+        }
+
+        private string getBestUrl(GitHubRelease release)
+        {
+            GitHubAsset bestAsset = null;
+
+            switch (RuntimeInfo.OS)
+            {
+                case RuntimeInfo.Platform.Windows:
+                    bestAsset = release.Assets?.FirstOrDefault(f => f.Name.EndsWith(".exe"));
+                    break;
+                case RuntimeInfo.Platform.MacOsx:
+                    bestAsset = release.Assets?.FirstOrDefault(f => f.Name.EndsWith(".dmg"));
+                    break;
+            }
+
+            return bestAsset?.BrowserDownloadUrl ?? release.HtmlUrl;
+        }
+
+        public class GitHubRelease
+        {
+            [JsonProperty("html_url")]
+            public string HtmlUrl { get; set; }
+
+            [JsonProperty("tag_name")]
+            public string TagName { get; set; }
+
+            [JsonProperty("assets")]
+            public List<GitHubAsset> Assets { get; set; }
+        }
+
+        public class GitHubAsset
+        {
+            [JsonProperty("name")]
+            public string Name { get; set; }
+
+            [JsonProperty("browser_download_url")]
+            public string BrowserDownloadUrl { get; set; }
+        }
+    }
+}