support hot-update

@@ -81,15 +81,27 @@ func NewApp() *App {
 
 
 func (app *App) Run() {
 func (app *App) Run() {
 	addr := fmt.Sprintf("%s:%d", HttpAddr, HttpPort)
 	addr := fmt.Sprintf("%s:%d", HttpAddr, HttpPort)
-	var err error
+	var (
+		err error
+		l   net.Listener
+	)
 	if UseFcgi {
 	if UseFcgi {
-		l, e := net.Listen("tcp", addr)
-		if e != nil {
-			BeeLogger.Fatal("Listen: ", e)
+		l, err = net.Listen("tcp", addr)
+		if err != nil {
+			BeeLogger.Fatal("Listen: ", err)
 		}
 		}
 		err = fcgi.Serve(l, app.Handlers)
 		err = fcgi.Serve(l, app.Handlers)
 	} else {
 	} else {
-		err = http.ListenAndServe(addr, app.Handlers)
+		server := &http.Server{Handler: app.Handlers}
+		laddr, err := net.ResolveTCPAddr("tcp", addr)
+		if nil != err {
+			BeeLogger.Fatal("ResolveTCPAddr:", err)
+		}
+		l, err = GetInitListner(laddr)
+		theStoppable = newStoppable(l)
+		err = server.Serve(theStoppable)
+		theStoppable.wg.Wait()
+		CloseSelf()
 	}
 	}
 	if err != nil {
 	if err != nil {
 		BeeLogger.Fatal("ListenAndServe: ", err)
 		BeeLogger.Fatal("ListenAndServe: ", err)

+// Zero-downtime restarts in Go.
+package beego
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"os/exec"
+	"os/signal"
+	"reflect"
+	"strconv"
+	"sync"
+	"syscall"
+)
+
+const (
+	FDKey = "BEEGO_HOT_FD"
+)
+
+// Export an error equivalent to net.errClosing for use with Accept during
+// a graceful exit.
+var ErrClosing = errors.New("use of closed network connection")
+var ErrInitStart = errors.New("init from")
+
+// Allows for us to notice when the connection is closed.
+type conn struct {
+	net.Conn
+	wg *sync.WaitGroup
+}
+
+func (c conn) Close() error {
+	err := c.Conn.Close()
+	c.wg.Done()
+	return err
+}
+
+type stoppableListener struct {
+	net.Listener
+	count   int64
+	stopped bool
+	wg      sync.WaitGroup
+}
+
+var theStoppable *stoppableListener
+
+func newStoppable(l net.Listener) (sl *stoppableListener) {
+	sl = &stoppableListener{Listener: l}
+
+	// this goroutine monitors the channel. Can't do this in
+	// Accept (below) because once it enters sl.Listener.Accept()
+	// it blocks. We unblock it by closing the fd it is trying to
+	// accept(2) on.
+	go func() {
+		WaitSignal(l)
+		sl.stopped = true
+		sl.Listener.Close()
+	}()
+	return
+}
+
+func (sl *stoppableListener) Accept() (c net.Conn, err error) {
+	c, err = sl.Listener.Accept()
+	if err != nil {
+		return
+	}
+	sl.wg.Add(1)
+	// Wrap the returned connection, so that we can observe when
+	// it is closed.
+	c = conn{Conn: c, wg: &sl.wg}
+
+	return
+}
+
+func WaitSignal(l net.Listener) error {
+	ch := make(chan os.Signal, 1)
+	signal.Notify(ch, syscall.SIGTERM, syscall.SIGHUP)
+	for {
+		sig := <-ch
+		log.Println(sig.String())
+		switch sig {
+
+		case syscall.SIGTERM:
+			return nil
+		case syscall.SIGHUP:
+			err := Restart(l)
+			if nil != err {
+				return err
+			}
+			return nil
+		}
+	}
+	return nil // It'll never get here.
+}
+
+func CloseSelf() error {
+	ppid := os.Getpid()
+	if ppid == 1 { // init provided sockets, for example systemd
+		return nil
+	}
+	p, err := os.FindProcess(ppid)
+	if err != nil {
+		return err
+	}
+	return p.Kill()
+}
+
+// Re-exec this image without dropping the listener passed to this function.
+func Restart(l net.Listener) error {
+	argv0, err := exec.LookPath(os.Args[0])
+	if nil != err {
+		return err
+	}
+	wd, err := os.Getwd()
+	if nil != err {
+		return err
+	}
+	v := reflect.ValueOf(l).Elem().FieldByName("fd").Elem()
+	fd := uintptr(v.FieldByName("sysfd").Int())
+	allFiles := append([]*os.File{os.Stdin, os.Stdout, os.Stderr},
+		os.NewFile(fd, string(v.FieldByName("sysfile").String())))
+
+	p, err := os.StartProcess(argv0, os.Args, &os.ProcAttr{
+		Dir:   wd,
+		Env:   append(os.Environ(), fmt.Sprintf("%s=%d", FDKey, fd)),
+		Files: allFiles,
+	})
+	if nil != err {
+		return err
+	}
+	log.Printf("spawned child %d\n", p.Pid)
+	return nil
+}
+
+func GetInitListner(tcpaddr *net.TCPAddr) (l net.Listener, err error) {
+	countStr := os.Getenv(FDKey)
+	if countStr == "" {
+		return net.ListenTCP("tcp", tcpaddr)
+	} else {
+		count, err := strconv.Atoi(countStr)
+		if err != nil {
+			return nil, err
+		}
+		f := os.NewFile(uintptr(count), "listen socket")
+		l, err = net.FileListener(f)
+		if err != nil {
+			return nil, err
+		}
+		return l, nil
+	}
+}