Ensure server is not in a conflicting state before initiating a transfer (pterodactyl#4403)

Author: matthewpi

app/Http/Controllers/Admin/Servers/ServerTransferController.php

@@ -97,6 +97,8 @@ public function transfer(Request $request, Server $server)
             // Check if the selected daemon is online.
             $this->daemonConfigurationRepository->setNode($node)->getSystemInformation();
 
+            $server->validateTransferState();
+
             // Create a new ServerTransfer entry.
             $transfer = new ServerTransfer();
 

app/Models/Server.php

@@ -400,4 +400,21 @@ public function validateCurrentState()
             throw new ServerStateConflictException($this);
         }
     }
+
+    /**
+     * Checks if the server is currently in a transferable state. If not, an
+     * exception is raised. This should be called whenever something needs to make
+     * sure the server is able to be transferred and is not currently being transferred
+     * or installed.
+     */
+    public function validateTransferState()
+    {
+        if (
+            !$this->isInstalled() ||
+            $this->status === self::STATUS_RESTORING_BACKUP ||
+            !is_null($this->transfer)
+        ) {
+            throw new ServerStateConflictException($this);
+        }
+    }
 }