Shut down on server "RESTART" control message

Fixes #131

TunnelKit/Sources/Protocols/OpenVPN/AppExtension/OpenVPNTunnelProvider+Interaction.swift

@@ -142,6 +142,9 @@ extension OpenVPNTunnelProvider {
         /// Default gateway could not be attained.
         case gatewayUnattainable
         
+        /// Remove server has shut down.
+        case serverShutdown
+        
         /// The server replied in an unexpected way.
         case unexpectedReply
     }

TunnelKit/Sources/Protocols/OpenVPN/AppExtension/OpenVPNTunnelProvider.swift

@@ -876,6 +876,9 @@ extension OpenVPNTunnelProvider {
                 
             case .noRouting:
                 return .routing
+                
+            case .serverShutdown:
+                return .serverShutdown
 
             default:
                 return .unexpectedReply

TunnelKit/Sources/Protocols/OpenVPN/OpenVPNError.swift

@@ -77,4 +77,7 @@ public enum OpenVPNError: String, Error {
 
     /// Missing routing information.
     case noRouting
+
+    /// Remote server shut down (--explicit-exit-notify).
+    case serverShutdown
 }

TunnelKit/Sources/Protocols/OpenVPN/OpenVPNSession.swift

@@ -907,6 +907,11 @@ public class OpenVPNSession: Session {
 
     // Ruby: handle_ctrl_msg
     private func handleControlMessage(_ message: String) {
+        if CoreConfiguration.logsSensitiveData {
+            log.debug("Received control message: \"\(message)\"")
+        }
+
+        // disconnect on authentication failure
         guard !message.hasPrefix("AUTH_FAILED") else {
 
             // XXX: retry without client options
@@ -921,14 +926,18 @@ public class OpenVPNSession: Session {
             return
         }
         
-        guard (negotiationKey.controlState == .preIfConfig) else {
+        // disconnect on remote server restart (--explicit-exit-notify)
+        guard !message.hasPrefix("RESTART") else {
+            log.debug("Disconnecting due to server shutdown")
+            deferStop(.shutdown, OpenVPNError.serverShutdown)
+            return
+        }
+        
+        // handle authentication from now on
+        guard negotiationKey.controlState == .preIfConfig else {
             return
         }
 
-        if CoreConfiguration.logsSensitiveData {
-            log.debug("Received control message: \"\(message)\"")
-        }
-        
         let completeMessage: String
         if let continuated = continuatedPushReplyMessage {
             completeMessage = "\(continuated),\(message)"