report a peer's port change locally without rewriting it

Keep IConfigurationManager source-compatible for plugin implementers.

Emby.Server.Implementations/ApplicationHost.cs

@@ -792,6 +792,43 @@ namespace Emby.Server.Implementations
             }
         }
 
+        /// <summary>
+        /// Works out what a configuration update means for the ports this process bound at startup.
+        /// </summary>
+        /// <param name="boundHttpPort">The HTTP port this process is bound to.</param>
+        /// <param name="boundHttpsPort">The HTTPS port this process is bound to.</param>
+        /// <param name="configuredHttpPort">The HTTP port the shared configuration now carries.</param>
+        /// <param name="configuredHttpsPort">The HTTPS port the shared configuration now carries.</param>
+        /// <param name="isPortAuthorized">Whether the shared configuration still marks the port as authorized.</param>
+        /// <param name="isApplyingRemoteInvalidation">Whether this update is another instance's write being applied.</param>
+        /// <returns>What the update requires of this instance.</returns>
+        internal static PortChangeOutcome EvaluatePortChange(
+            int boundHttpPort,
+            int boundHttpsPort,
+            int configuredHttpPort,
+            int configuredHttpsPort,
+            bool isPortAuthorized,
+            bool isApplyingRemoteInvalidation)
+        {
+            // Nothing is bound yet, so nothing has gone stale.
+            if (boundHttpPort == 0 || boundHttpsPort == 0)
+            {
+                return default;
+            }
+
+            if (configuredHttpPort == boundHttpPort && configuredHttpsPort == boundHttpsPort)
+            {
+                return default;
+            }
+
+            // Whoever wrote the change, this process is still listening on a port the configuration no
+            // longer names, so the pending restart is reported either way. The authorization flag belongs
+            // to the instance that made the change: it cleared the flag along with the port, and clearing
+            // it again here would write shared configuration on that instance's behalf and announce it a
+            // second time.
+            return new PortChangeOutcome(true, isPortAuthorized && !isApplyingRemoteInvalidation);
+        }
+
         /// <summary>
         /// Called when [configuration updated].
         /// </summary>
@@ -799,28 +836,24 @@ namespace Emby.Server.Implementations
         /// <param name="e">The <see cref="EventArgs"/> instance containing the event data.</param>
         private void OnConfigurationUpdated(object sender, EventArgs e)
         {
-            var requiresRestart = false;
             var networkConfiguration = ConfigurationManager.GetNetworkConfiguration();
 
-            // Don't do anything if these haven't been set yet, and don't clear the authorization flag on
-            // behalf of another instance: it already wrote that flag along with the port change, so
-            // repeating the save here only races it.
-            if (HttpPort != 0 && HttpsPort != 0 && !ConfigurationInvalidationContext.IsApplyingRemoteInvalidation)
-            {
-                // Need to restart if ports have changed
-                if (networkConfiguration.InternalHttpPort != HttpPort
-                    || networkConfiguration.InternalHttpsPort != HttpsPort)
-                {
-                    if (ConfigurationManager.Configuration.IsPortAuthorized)
-                    {
-                        ConfigurationManager.Configuration.IsPortAuthorized = false;
-                        ConfigurationManager.SaveConfiguration();
+            var portChange = EvaluatePortChange(
+                HttpPort,
+                HttpsPort,
+                networkConfiguration.InternalHttpPort,
+                networkConfiguration.InternalHttpsPort,
+                ConfigurationManager.Configuration.IsPortAuthorized,
+                ConfigurationInvalidationContext.IsApplyingRemoteInvalidation);
 
-                        requiresRestart = true;
-                    }
-                }
+            if (portChange.ClearsPortAuthorization)
+            {
+                ConfigurationManager.Configuration.IsPortAuthorized = false;
+                ConfigurationManager.SaveConfiguration();
             }
 
+            var requiresRestart = portChange.RequiresRestart;
+
             if (ValidateSslCertificate(networkConfiguration))
             {
                 requiresRestart = true;

Emby.Server.Implementations/PortChangeOutcome.cs

@@ -0,0 +1,14 @@
+namespace Emby.Server.Implementations
+{
+    /// <summary>
+    /// What a configuration update carrying different ports requires of the instance reading it.
+    /// </summary>
+    /// <param name="RequiresRestart">
+    /// Whether this process is still bound to a port the shared configuration no longer names, and so has
+    /// to report a pending restart.
+    /// </param>
+    /// <param name="ClearsPortAuthorization">
+    /// Whether this instance is the one that has to clear the port authorization flag and save it.
+    /// </param>
+    internal readonly record struct PortChangeOutcome(bool RequiresRestart, bool ClearsPortAuthorization);
+}