Main: Enforce UUID of reload state

common/connection.go

@@ -62,14 +62,30 @@ func Ready() error {
 }
 
 // Shutdown will notify the frontend that the backend is shutting down
-func Shutdown() error {
+func Shutdown() (string, error) {
 	if rpcFrontend == nil {
 		ConnectFrontend()
 	}
 
-	err := rpcFrontend.Call("RPCFrontendPacket.ShutdownBackend", struct{}{}, nil)
+	var stateUuid string
+	err := rpcFrontend.Call("RPCFrontendPacket.ShutdownBackend", struct{}{}, &stateUuid)
 	if err != nil {
 		logging.Error("COMMON", "Failed to notify frontend that backend is shutting down:", err)
 	}
-	return err
+
+	return stateUuid, err
+}
+
+// VerifyState will verify the state UUID with the frontend
+func VerifyState(stateUuid string) (bool, error) {
+	if rpcFrontend == nil {
+		ConnectFrontend()
+	}
+
+	valid := false
+	err := rpcFrontend.Call("RPCFrontendPacket.VerifyState", stateUuid, &valid)
+	if err != nil {
+		logging.Error("COMMON", "Failed to verify state UUID with frontend:", err)
+	}
+	return valid, err
 }

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"errors"
+	"io"
 	"net"
 	"net/rpc"
 	"os"
@@ -40,7 +41,7 @@ func main() {
 
 	// Start the backend instead of the frontend if the first argument is "backend"
 	if len(args) > 0 && args[0] == "backend" {
-		backendMain(len(args) > 1 && args[1] == "reload")
+		backendMain(len(args) > 1 && args[1] == "noreload")
 	} else {
 		frontendMain(len(args) > 0 && args[0] == "frontend")
 	}
@@ -54,7 +55,7 @@ type RPCPacket struct {
 }
 
 // backendMain starts all the servers and creates an RPC server to communicate with the frontend
-func backendMain(reload bool) {
+func backendMain(noreload bool) {
 	sigExit := make(chan os.Signal, 1)
 	signal.Notify(sigExit, syscall.SIGINT, syscall.SIGTERM)
 
@@ -73,6 +74,16 @@ func backendMain(reload bool) {
 
 	common.ConnectFrontend()
 
+	uuid := ""
+	if !noreload {
+		uuid = loadUuidFile()
+	}
+
+	reload, err := common.VerifyState(uuid)
+	if err != nil {
+		panic(err)
+	}
+
 	wg := &sync.WaitGroup{}
 	actions := []func(bool){nas.StartServer, gpcm.StartServer, qr2.StartServer, gpsp.StartServer, serverbrowser.StartServer, sake.StartServer, natneg.StartServer, api.StartServer, gamestats.StartServer}
 	wg.Add(len(actions))
@@ -105,12 +116,30 @@ func backendMain(reload bool) {
 	// Wait for a signal to shutdown
 	<-sigExit
 
-	err = common.Shutdown()
+	stateUuid, err := common.Shutdown()
 	if err != nil {
 		panic(err)
 	}
 
-	(&RPCPacket{}).Shutdown(struct{}{}, &struct{}{})
+	(&RPCPacket{}).Shutdown(stateUuid, &struct{}{})
+}
+
+func loadUuidFile() string {
+	stateFile, err := os.Open("state/uuid.txt")
+	if err != nil {
+		logging.Error("BACKEND", "Failed to open state file:", err)
+		return ""
+	}
+
+	defer stateFile.Close()
+
+	uuid, err := io.ReadAll(stateFile)
+	if err != nil {
+		logging.Error("BACKEND", "Failed to read state file:", err)
+		return ""
+	}
+
+	return string(uuid)
 }
 
 // RPCPacket.NewConnection is called by the frontend to notify the backend of a new connection
@@ -162,7 +191,7 @@ func (r *RPCPacket) CloseConnection(args RPCPacket, _ *struct{}) error {
 }
 
 // RPCPacket.Shutdown is called by the frontend to shutdown the backend
-func (r *RPCPacket) Shutdown(_ struct{}, _ *struct{}) error {
+func (r *RPCPacket) Shutdown(stateUuid string, _ *struct{}) error {
 	wg := &sync.WaitGroup{}
 	actions := []func(){nas.Shutdown, gpcm.Shutdown, qr2.Shutdown, gpsp.Shutdown, serverbrowser.Shutdown, sake.Shutdown, natneg.Shutdown, api.Shutdown, gamestats.Shutdown}
 	wg.Add(len(actions))
@@ -175,6 +204,21 @@ func (r *RPCPacket) Shutdown(_ struct{}, _ *struct{}) error {
 
 	wg.Wait()
 
+	stateFile, err := os.OpenFile("state/uuid.txt", os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
+	if err != nil {
+		panic(err)
+	}
+
+	_, err = stateFile.WriteString(stateUuid)
+	if err != nil {
+		panic(err)
+	}
+
+	err = stateFile.Close()
+	if err != nil {
+		panic(err)
+	}
+
 	os.Exit(0)
 	return nil
 }
@@ -197,8 +241,9 @@ var (
 	rpcMutex     sync.Mutex
 	rpcBusyCount sync.WaitGroup
 	backendReady = make(chan struct{})
+	frontendUuid string
 
-	connections = map[string]map[uint64]net.Conn{}
+	connections = map[string]map[uint64]*net.Conn{}
 )
 
 // frontendMain starts the backend process and communicates with it using RPC
@@ -231,7 +276,7 @@ func frontendMain(noBackend bool) {
 	}
 
 	for _, server := range servers {
-		connections[server.rpcName] = map[uint64]net.Conn{}
+		connections[server.rpcName] = map[uint64]*net.Conn{}
 		go frontendListen(server)
 	}
 
@@ -309,6 +354,7 @@ func waitForBackend() {
 			rpcMutex.Unlock()
 
 			logging.Notice("FRONTEND", "Connected to backend")
+
 			return
 		}
 	}
@@ -354,7 +400,8 @@ func handleConnection(server serverInfo, conn net.Conn, index uint64) {
 
 	rpcMutex.Lock()
 	rpcBusyCount.Add(1)
-	connections[server.rpcName][index] = conn
+	pConn := &conn
+	connections[server.rpcName][index] = pConn
 	rpcMutex.Unlock()
 
 	err := rpcClient.Call("RPCPacket.NewConnection", RPCPacket{Server: server.rpcName, Index: index, Address: conn.RemoteAddr().String(), Data: []byte{}}, nil)
@@ -400,6 +447,11 @@ func handleConnection(server serverInfo, conn net.Conn, index uint64) {
 	}
 
 	rpcMutex.Lock()
+	if connections[server.rpcName][index] != pConn {
+		rpcMutex.Unlock()
+		return
+	}
+
 	rpcBusyCount.Add(1)
 	delete(connections[server.rpcName], index)
 	rpcMutex.Unlock()
@@ -416,19 +468,23 @@ func handleConnection(server serverInfo, conn net.Conn, index uint64) {
 	}
 }
 
-var ErrBadIndex = errors.New("incorrect connection index")
+var (
+	ErrBadIndex = errors.New("incorrect connection index")
+	ErrorBusy   = errors.New("backend is busy")
+)
 
 // RPCFrontendPacket.SendPacket is called by the backend to send a packet to a connection
 func (r *RPCFrontendPacket) SendPacket(args RPCFrontendPacket, _ *struct{}) error {
 	rpcMutex.Lock()
 	defer rpcMutex.Unlock()
 
-	conn, ok := connections[args.Server][args.Index]
-	if !ok {
+	conn := connections[args.Server][args.Index]
+	if conn == nil {
 		return ErrBadIndex
 	}
 
-	_, err := conn.Write(args.Data)
+	_, err := (*conn).Write(args.Data)
+
 	return err
 }
 
@@ -437,20 +493,22 @@ func (r *RPCFrontendPacket) CloseConnection(args RPCFrontendPacket, _ *struct{})
 	rpcMutex.Lock()
 	defer rpcMutex.Unlock()
 
-	conn, ok := connections[args.Server][args.Index]
-	if !ok {
+	conn := connections[args.Server][args.Index]
+	if conn == nil {
 		return ErrBadIndex
 	}
 
 	delete(connections[args.Server], args.Index)
-	return conn.Close()
+
+	return (*conn).Close()
 }
 
 // RPCFrontendPacket.ReloadBackend is called by an external program to reload the backend
 func (r *RPCFrontendPacket) ReloadBackend(_ struct{}, _ *struct{}) error {
-	r.ShutdownBackend(struct{}{}, &struct{}{})
+	var stateUid string
+	r.ShutdownBackend(struct{}{}, &stateUid)
 
-	err := rpcClient.Call("RPCPacket.Shutdown", struct{}{}, nil)
+	err := rpcClient.Call("RPCPacket.Shutdown", stateUid, nil)
 	if err != nil && !strings.Contains(err.Error(), "An existing connection was forcibly closed by the remote host.") {
 		logging.Error("FRONTEND", "Failed to reload backend:", err)
 	}
@@ -467,7 +525,7 @@ func (r *RPCFrontendPacket) ReloadBackend(_ struct{}, _ *struct{}) error {
 }
 
 // RPCFrontendPacket.ShutdownBackend is called by an external program to shutdown the backend
-func (r *RPCFrontendPacket) ShutdownBackend(_ struct{}, _ *struct{}) error {
+func (r *RPCFrontendPacket) ShutdownBackend(_ struct{}, uuid *string) error {
 	logging.Notice("FRONTEND", "Shutting down backend")
 
 	// Lock indefinitely
@@ -477,11 +535,43 @@ func (r *RPCFrontendPacket) ShutdownBackend(_ struct{}, _ *struct{}) error {
 
 	go waitForBackend()
 
+	frontendUuid = common.RandomString(32)
+	*uuid = frontendUuid
+
+	return nil
+}
+
+// RPCFrontendPacket.VerifyState is called by the backend to verify the state UUID
+func (r *RPCFrontendPacket) VerifyState(uuid string, reload *bool) error {
+	if rpcMutex.TryLock() {
+		rpcMutex.Unlock()
+		logging.Error("FRONTEND", "Failed to verify UUID, backend is active")
+		*reload = false
+		return ErrorBusy
+	}
+
+	if uuid != frontendUuid {
+		logging.Notice("FRONTEND", "VerifyState: Resetting all connections")
+
+		// Close all connections
+		for _, server := range connections {
+			for index, conn := range server {
+				(*conn).Close()
+				delete(server, index)
+			}
+		}
+
+		*reload = false
+		return nil
+	}
+
+	*reload = true
 	return nil
 }
 
 // RPCFrontendPacket.Ready is called by the backend to indicate it is ready to accept connections
 func (r *RPCFrontendPacket) Ready(_ struct{}, _ *struct{}) error {
 	close(backendReady)
+
 	return nil
 }