fix: Network discovery blocked on Android-based devices

Assets/Discovery/Android/AndroidManifestHelper.cs

@@ -0,0 +1,123 @@
+// 2022-02-20: Modified version of AndroidManifestHelper by Clancey (see Mirror PR #2887)
+// Modifications made by Coburn (SoftwareGuy).
+
+// This helper script should only used on Android build targets.
+#if UNITY_EDITOR && UNITY_ANDROID
+using System.Xml;
+using System.IO;
+
+using UnityEditor;
+using UnityEditor.Android;
+using UnityEditor.Build;
+using UnityEditor.Build.Reporting;
+using UnityEngine;
+
+[InitializeOnLoad]
+public class AndroidManifestHelper : IPreprocessBuildWithReport, IPostprocessBuildWithReport, IPostGenerateGradleAndroidProject
+{
+    public int callbackOrder { get { return 99999; } }
+
+    public void OnPostGenerateGradleAndroidProject(string path)
+    {
+        string manifestFolder = Path.Combine(path, "src/main");
+        string sourceFile = manifestFolder + "/AndroidManifest.xml";
+
+        // Load android manfiest file
+        var doc = new XmlDocument();
+        doc.Load(sourceFile);
+
+        string androidNamepsaceURI;
+        var element = (XmlElement)doc.SelectSingleNode("/manifest");
+        if (element == null)
+        {
+            Debug.LogError("Could not find the manifest tag in android manifest.");
+            return;
+        }
+
+        // Get android namespace URI from the manifest
+        androidNamepsaceURI = element.GetAttribute("xmlns:android");
+        if (string.IsNullOrEmpty(androidNamepsaceURI))
+        {
+            Debug.LogError("Could not find the Android Namespace in manifest.");
+            return;
+        }
+
+        // As the name suggests, add or remove the required things.
+        AddOrRemoveTag(doc,
+               androidNamepsaceURI,
+               "/manifest",
+               "uses-permission",
+               "android.permission.CHANGE_WIFI_MULTICAST_STATE",
+               true,
+               false);
+        AddOrRemoveTag(doc,
+               androidNamepsaceURI,
+               "/manifest",
+               "uses-permission",
+               "android.permission.INTERNET",
+               true,
+               false);
+
+        // Finally, save it.
+        doc.Save(sourceFile);
+    }
+
+    private static void AddOrRemoveTag(XmlDocument doc, string @namespace, string path, string elementName, string name, bool required, bool modifyIfFound, params string[] attrs) // name, value pairs	
+    {
+        XmlNodeList nodes = doc.SelectNodes(path + "/" + elementName);
+        XmlElement element = null;
+        foreach (XmlElement e in nodes)
+        {
+            if (name == null || name == e.GetAttribute("name", @namespace))
+            {
+                element = e;
+                break;
+            }
+        }
+
+        if (required)
+        {
+            if (element == null)
+            {
+                XmlNode parent = doc.SelectSingleNode(path);
+                element = doc.CreateElement(elementName);
+                element.SetAttribute("name", @namespace, name);
+                parent.AppendChild(element);
+            }
+
+            for (int i = 0; i < attrs.Length; i += 2)
+            {
+                if (modifyIfFound || string.IsNullOrEmpty(element.GetAttribute(attrs[i], @namespace)))
+                {
+                    if (attrs[i + 1] != null)
+                    {
+                        element.SetAttribute(attrs[i], @namespace, attrs[i + 1]);
+                    }
+                    else
+                    {
+                        element.RemoveAttribute(attrs[i], @namespace);
+                    }
+                }
+            }
+        }
+        else
+        {
+            if (element != null && modifyIfFound)
+            {
+                element.ParentNode.RemoveChild(element);
+            }
+        }
+    }
+
+    public void OnPostprocessBuild(BuildReport report)
+    {
+        // Unused.
+    }
+
+    public void OnPreprocessBuild(BuildReport report)
+    {
+        // Unused.
+    }
+
+}
+#endif

Assets/Discovery/NetworkDiscoveryBase.cs

@@ -12,6 +12,11 @@
 // forked from https://github.com/in0finite/MirrorNetworkDiscovery
 // Both are MIT Licensed
 
+// Updated 2022-02-20 by Coburn (SoftwareGuy)
+// This update has changes integrated from the Mirror PR #2887
+// PR author: Clancey; 22 Aug 2021
+// Source: https://github.com/vis2k/Mirror/pull/2887/
+
 namespace Mirage.Discovery
 {
     /// <summary>
@@ -81,6 +86,12 @@ void OnApplicationQuit()
 
         void Shutdown()
         {
+#if UNITY_ANDROID
+            // If we're on Android, then tell the Android OS that
+            // we're done with multicasting and it may save battery again.
+            EndMulticastLock();
+#endif
+
             if (serverUdpClient != null)
             {
                 try
@@ -89,7 +100,7 @@ void Shutdown()
                 }
                 catch (Exception)
                 {
-                    // it is just close, swallow the error
+                    // If it's already closed, then just swallow the error. There's no need to show it.
                 }
 
                 serverUdpClient = null;
@@ -103,7 +114,7 @@ void Shutdown()
                 }
                 catch (Exception)
                 {
-                    // it is just close, swallow the error
+                    // Again, if it's already closed, then just swallow the error.
                 }
 
                 clientUdpClient = null;
@@ -137,6 +148,11 @@ public void AdvertiseServer()
 
         public async UniTask ServerListenAsync()
         {
+#if UNITY_ANDROID
+            // Tell Android to allow us to use Multicasting.
+            BeginMulticastLock();
+
+#endif
             while (true)
             {
                 try
@@ -145,12 +161,12 @@ public async UniTask ServerListenAsync()
                 }
                 catch (ObjectDisposedException)
                 {
-                    // socket has been closed
+                    // This socket's been disposed, that's okay, we'll handle it
                     break;
                 }
                 catch (Exception)
                 {
-                    // if we get an invalid request,  just ignore it
+                    // Invalid request or something else. Just ignore it.
                 }
             }
         }
@@ -224,9 +240,47 @@ protected virtual void ProcessClientRequest(Request request, IPEndPoint endpoint
         /// <returns>The message to be sent back to the client or null</returns>
         protected abstract Response ProcessRequest(Request request, IPEndPoint endpoint);
 
-        #endregion
+#endregion
+
+#region Android specific functions for Multicasting support
+
+#if UNITY_ANDROID
+        AndroidJavaObject multicastLock;
+        bool hasMulticastLock;
+
+        void BeginMulticastLock() {
+            if (hasMulticastLock)
+                return;
+
+            if (Application.platform == RuntimePlatform.Android)
+            {
+                using (AndroidJavaObject activity = new AndroidJavaClass("com.unity3d.player.UnityPlayer").GetStatic<AndroidJavaObject>("currentActivity"))
+                {
+                    using (AndroidJavaObject wifiManager = activity.Call<AndroidJavaObject>("getSystemService", "wifi"))
+                    {
+                        multicastLock = wifiManager.Call<AndroidJavaObject>("createMulticastLock", "lock");
+                        multicastLock.Call("acquire");
+                        hasMulticastLock = true;
+                    }
+                }
+			}
+        }
+
+        void EndMulticastLock()
+        {
+            // Don't have a multicast lock? Short-circuit.
+            if (!hasMulticastLock)
+                return;
+
+            // Release the lock.
+            multicastLock?.Call("release");
+            hasMulticastLock = false;
+        }
+#endif
+
+#endregion
 
-        #region Client
+#region Client
 
         /// <summary>
         /// Start Active Discovery
@@ -359,6 +413,6 @@ async Task ReceiveGameBroadcastAsync(UdpClient udpClient)
         /// <param name="endpoint">Address of the server that replied</param>
         protected abstract void ProcessResponse(Response response, IPEndPoint endpoint);
 
-        #endregion
+#endregion
     }
 }