feat(engine): add Shutdown method for graceful shutdown support

- Add server and serverLock fields to Engine struct
- Add Shutdown() method that calls http.Server.Shutdown()
- Modify Run/RunTLS/RunUnix/RunListener to store server reference
- Add RunWithShutdown convenience method with signal handling
- Add comprehensive tests for graceful shutdown (8 test cases)
- Fix lint errors (errorlint, testifylint, errcheck)

Author: Narita-1095305

gin.go

@@ -5,6 +5,7 @@
 package gin
 
 import (
+	"context"
 	"fmt"
 	"html/template"
 	"net"
@@ -186,6 +187,11 @@ type Engine struct {
 	maxSections      uint16
 	trustedProxies   []string
 	trustedCIDRs     []*net.IPNet
+
+	// server holds a reference to the HTTP server for graceful shutdown.
+	// This is set when one of the Run* methods is called.
+	server     *http.Server
+	serverLock sync.Mutex
 }
 
 var _ IRouter = (*Engine)(nil)
@@ -534,6 +540,30 @@ func parseIP(ip string) net.IP {
 	return parsedIP
 }
 
+// Shutdown gracefully shuts down the server without interrupting any active connections.
+// Shutdown works by first closing all open listeners, then closing all idle connections,
+// and then waiting indefinitely for connections to return to idle and then shut down.
+// If the provided context expires before the shutdown is complete, Shutdown returns the
+// context's error, otherwise it returns any error returned from closing the Server's
+// underlying Listener(s).
+//
+// When Shutdown is called, Serve, ListenAndServe, and ListenAndServeTLS immediately
+// return ErrServerClosed. Make sure the program doesn't exit and waits instead for
+// Shutdown to return.
+//
+// This method returns nil if the server has not been started.
+func (engine *Engine) Shutdown(ctx context.Context) error {
+	engine.serverLock.Lock()
+	srv := engine.server
+	engine.serverLock.Unlock()
+
+	if srv == nil {
+		return nil
+	}
+
+	return srv.Shutdown(ctx)
+}
+
 // Run attaches the router to a http.Server and starts listening and serving HTTP requests.
 // It is a shortcut for http.ListenAndServe(addr, router)
 // Note: this method will block the calling goroutine indefinitely unless an error happens.
@@ -551,6 +581,11 @@ func (engine *Engine) Run(addr ...string) (err error) {
 		Addr:    address,
 		Handler: engine.Handler(),
 	}
+
+	engine.serverLock.Lock()
+	engine.server = server
+	engine.serverLock.Unlock()
+
 	err = server.ListenAndServe()
 	return
 }
@@ -571,6 +606,11 @@ func (engine *Engine) RunTLS(addr, certFile, keyFile string) (err error) {
 		Addr:    addr,
 		Handler: engine.Handler(),
 	}
+
+	engine.serverLock.Lock()
+	engine.server = server
+	engine.serverLock.Unlock()
+
 	err = server.ListenAndServeTLS(certFile, keyFile)
 	return
 }
@@ -597,6 +637,11 @@ func (engine *Engine) RunUnix(file string) (err error) {
 	server := &http.Server{ // #nosec G112
 		Handler: engine.Handler(),
 	}
+
+	engine.serverLock.Lock()
+	engine.server = server
+	engine.serverLock.Unlock()
+
 	err = server.Serve(listener)
 	return
 }
@@ -654,6 +699,11 @@ func (engine *Engine) RunListener(listener net.Listener) (err error) {
 	server := &http.Server{ // #nosec G112
 		Handler: engine.Handler(),
 	}
+
+	engine.serverLock.Lock()
+	engine.server = server
+	engine.serverLock.Unlock()
+
 	err = server.Serve(listener)
 	return
 }

graceful.go

@@ -0,0 +1,69 @@
+// Copyright 2014 Manu Martinez-Almeida. All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+package gin
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+)
+
+// ShutdownConfig holds configuration for graceful shutdown.
+type ShutdownConfig struct {
+	// Timeout is the maximum duration to wait for active connections to finish.
+	// Default: 10 seconds
+	Timeout time.Duration
+
+	// Signals are the OS signals that will trigger shutdown.
+	// Default: SIGINT, SIGTERM
+	Signals []os.Signal
+}
+
+// RunWithShutdown starts the HTTP server and handles graceful shutdown on SIGINT/SIGTERM.
+// It blocks until the server is shut down.
+// The timeout parameter specifies the maximum duration to wait for active connections to finish.
+func (engine *Engine) RunWithShutdown(addr string, timeout time.Duration) error {
+	return engine.RunWithShutdownConfig(addr, ShutdownConfig{
+		Timeout: timeout,
+		Signals: []os.Signal{syscall.SIGINT, syscall.SIGTERM},
+	})
+}
+
+// RunWithShutdownConfig starts the HTTP server with custom shutdown configuration.
+// It blocks until the server is shut down.
+func (engine *Engine) RunWithShutdownConfig(addr string, config ShutdownConfig) error {
+	if config.Timeout == 0 {
+		config.Timeout = 10 * time.Second
+	}
+	if len(config.Signals) == 0 {
+		config.Signals = []os.Signal{syscall.SIGINT, syscall.SIGTERM}
+	}
+
+	ctx, stop := signal.NotifyContext(context.Background(), config.Signals...)
+	defer stop()
+
+	errCh := make(chan error, 1)
+	go func() {
+		if err := engine.Run(addr); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			errCh <- err
+		}
+		close(errCh)
+	}()
+
+	select {
+	case err := <-errCh:
+		return err
+	case <-ctx.Done():
+	}
+
+	shutdownCtx, cancel := context.WithTimeout(context.Background(), config.Timeout)
+	defer cancel()
+
+	return engine.Shutdown(shutdownCtx)
+}