Implement proper signal handler

README.md

@@ -135,6 +135,15 @@ This includes:
 - Protocol errors
 - TLS-specific connection issues
 
+### Graceful Shutdown
+
+When backer receives a termination signal (SIGTERM or SIGINT), it will:
+1. Log a warning message: "Shutdown signal received, shutting down immediately..."
+2. Stop accepting new connections and abort any in-progress downloads immediately
+3. Clean up resources and exit
+
+This ensures no partial/corrupted backups are left. Clients will need to restart their backup. For a forced immediate stop, use `SIGKILL`.
+
 ## Special Thanks
 
 This project was developed with the assistance of **opencode** (AI co-programmer powered by MIMO). The AI helped with:

cmd/backer/main.go

@@ -41,6 +41,10 @@ func main() {
 		log.Fatalf("Failed to create server: %v", err)
 	}
 
+	// Setup signal handling for immediate shutdown.
+	log.Infof("Installing signal handler")
+	setupSignalHandler(server)
+
 	log.Infof("Starting backer version %s at %s", version, server.Addr)
 
 	if backer.C.NoHTTPS {
@@ -60,6 +64,8 @@ func main() {
 			log.Fatalf("Failed to start server: %v", err)
 		}
 	}
+
+	log.Infof("Server stopped")
 }
 
 // defaultConfigPath returns the default config file path based on the OS.

cmd/backer/sigHandler.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	"os"
+	"os/signal"
+	"syscall"
+
+	"backer/internal/backer"
+	"backer/internal/log"
+)
+
+// setupSignalHandler sets up signal handling for immediate shutdown.
+// SIGTERM is commonly sent by systemd, k8s, and other container orchestrators.
+// SIGINT is sent on Ctrl+C.
+func setupSignalHandler(server *backer.ServerWrapper) {
+	signalCh := make(chan os.Signal, 1)
+	signal.Notify(signalCh, os.Interrupt, syscall.SIGTERM)
+
+	go func() {
+		<-signalCh
+		log.Warnf("Shutdown signal received, shutting down immediately...")
+		// Close the embedded http.Server directly.
+		if closeErr := server.Close(); closeErr != nil {
+			log.Errorf("Error during server shutdown: %v", closeErr)
+		}
+	}()
+}
+
+/* vim: setlocal ft=go noet ai ts=4 sw=4 sts=4: */

internal/backer/newServer.go

@@ -54,8 +54,8 @@ func withServerHeader(next http.Handler) http.Handler {
 }
 
 // NewServer starts new server instance with given config file.
-// It returns a serverWrapper that intercepts and classifies server errors.
+// It returns a ServerWrapper that intercepts and classifies server errors.
-func NewServer(configPath string) (*serverWrapper, error) { //nolint: revive
+func NewServer(configPath string) (*ServerWrapper, error) {
 	_ = log.Init("info", "") // Initialize logger with defaults for early logging.
 
 	if err := LoadConfig(configPath); err != nil {
@@ -175,7 +175,7 @@ func NewServer(configPath string) (*serverWrapper, error) { //nolint: revive
 	// HTTP mode if nohttps is enabled in config.
 	// HTTPS mode if nohttps is disabled in config.
 	if C.NoHTTPS {
-		return &serverWrapper{
+		return &ServerWrapper{
 			Server: &http.Server{
 				Addr:              fmt.Sprintf("%s:%d", C.Address, C.Port),
 				Handler:           withServerHeader(mux),
@@ -186,7 +186,7 @@ func NewServer(configPath string) (*serverWrapper, error) { //nolint: revive
 		}, nil
 	}
 
-	return &serverWrapper{
+	return &ServerWrapper{
 		Server: &http.Server{
 			Addr:              fmt.Sprintf("%s:%d", C.Address, C.Port),
 			Handler:           withServerHeader(mux),
@@ -284,15 +284,15 @@ func getCompressionAlgorithm(requestedExt string) string {
 }
 
 type (
-	// serverWrapper wraps [http.Server] to intercept and classify errors.
+	// ServerWrapper wraps [http.Server] to intercept and classify errors.
-	serverWrapper struct {
+	ServerWrapper struct {
 		*http.Server
 	}
 )
 
 // Serve starts the server and classifies any errors returned.
 // TLS-related errors are logged at debug level, other errors at warn level.
-func (sw *serverWrapper) Serve() error {
+func (sw *ServerWrapper) Serve() error {
 	err := sw.ListenAndServe()
 
 	if err != nil {
@@ -307,7 +307,7 @@ func (sw *serverWrapper) Serve() error {
 }
 
 // ServeTLS starts the TLS server and classifies any errors returned.
-func (sw *serverWrapper) ServeTLS(certFile, keyFile string) error {
+func (sw *ServerWrapper) ServeTLS(certFile, keyFile string) error {
 	err := sw.ListenAndServeTLS(certFile, keyFile)
 
 	if err != nil {