Support http service graceful restart (#416)

* support http service graceful restart

* fix dependencies

vendor/github.com/facebookgo/grace/gracehttp/http.go

@@ -0,0 +1,186 @@
+// Package gracehttp provides easy to use graceful restart
+// functionality for HTTP server.
+package gracehttp
+
+import (
+	"bytes"
+	"crypto/tls"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
+
+	"github.com/facebookgo/grace/gracenet"
+	"github.com/facebookgo/httpdown"
+)
+
+var (
+	verbose    = flag.Bool("gracehttp.log", true, "Enable logging.")
+	didInherit = os.Getenv("LISTEN_FDS") != ""
+	ppid       = os.Getppid()
+)
+
+// An app contains one or more servers and associated configuration.
+type app struct {
+	servers   []*http.Server
+	http      *httpdown.HTTP
+	net       *gracenet.Net
+	listeners []net.Listener
+	sds       []httpdown.Server
+	errors    chan error
+}
+
+func newApp(servers []*http.Server) *app {
+	return &app{
+		servers:   servers,
+		http:      &httpdown.HTTP{},
+		net:       &gracenet.Net{},
+		listeners: make([]net.Listener, 0, len(servers)),
+		sds:       make([]httpdown.Server, 0, len(servers)),
+
+		// 2x num servers for possible Close or Stop errors + 1 for possible
+		// StartProcess error.
+		errors: make(chan error, 1+(len(servers)*2)),
+	}
+}
+
+func (a *app) listen() error {
+	for _, s := range a.servers {
+		// TODO: default addresses
+		l, err := a.net.Listen("tcp", s.Addr)
+		if err != nil {
+			return err
+		}
+		if s.TLSConfig != nil {
+			l = tls.NewListener(l, s.TLSConfig)
+		}
+		a.listeners = append(a.listeners, l)
+	}
+	return nil
+}
+
+func (a *app) serve() {
+	for i, s := range a.servers {
+		a.sds = append(a.sds, a.http.Serve(s, a.listeners[i]))
+	}
+}
+
+func (a *app) wait() {
+	var wg sync.WaitGroup
+	wg.Add(len(a.sds) * 2) // Wait & Stop
+	go a.signalHandler(&wg)
+	for _, s := range a.sds {
+		go func(s httpdown.Server) {
+			defer wg.Done()
+			if err := s.Wait(); err != nil {
+				a.errors <- err
+			}
+		}(s)
+	}
+	wg.Wait()
+}
+
+func (a *app) term(wg *sync.WaitGroup) {
+	for _, s := range a.sds {
+		go func(s httpdown.Server) {
+			defer wg.Done()
+			if err := s.Stop(); err != nil {
+				a.errors <- err
+			}
+		}(s)
+	}
+}
+
+func (a *app) signalHandler(wg *sync.WaitGroup) {
+	ch := make(chan os.Signal, 10)
+	signal.Notify(ch, syscall.SIGINT, syscall.SIGTERM, syscall.SIGUSR2)
+	for {
+		sig := <-ch
+		switch sig {
+		case syscall.SIGINT, syscall.SIGTERM:
+			// this ensures a subsequent INT/TERM will trigger standard go behaviour of
+			// terminating.
+			signal.Stop(ch)
+			a.term(wg)
+			return
+		case syscall.SIGUSR2:
+			// we only return here if there's an error, otherwise the new process
+			// will send us a TERM when it's ready to trigger the actual shutdown.
+			if _, err := a.net.StartProcess(); err != nil {
+				a.errors <- err
+			}
+		}
+	}
+}
+
+// Serve will serve the given http.Servers and will monitor for signals
+// allowing for graceful termination (SIGTERM) or restart (SIGUSR2).
+func Serve(servers ...*http.Server) error {
+	a := newApp(servers)
+
+	// Acquire Listeners
+	if err := a.listen(); err != nil {
+		return err
+	}
+
+	// Some useful logging.
+	if *verbose {
+		if didInherit {
+			if ppid == 1 {
+				log.Printf("Listening on init activated %s", pprintAddr(a.listeners))
+			} else {
+				const msg = "Graceful handoff of %s with new pid %d and old pid %d"
+				log.Printf(msg, pprintAddr(a.listeners), os.Getpid(), ppid)
+			}
+		} else {
+			const msg = "Serving %s with pid %d"
+			log.Printf(msg, pprintAddr(a.listeners), os.Getpid())
+		}
+	}
+
+	// Start serving.
+	a.serve()
+
+	// Close the parent if we inherited and it wasn't init that started us.
+	if didInherit && ppid != 1 {
+		if err := syscall.Kill(ppid, syscall.SIGTERM); err != nil {
+			return fmt.Errorf("failed to close parent: %s", err)
+		}
+	}
+
+	waitdone := make(chan struct{})
+	go func() {
+		defer close(waitdone)
+		a.wait()
+	}()
+
+	select {
+	case err := <-a.errors:
+		if err == nil {
+			panic("unexpected nil error")
+		}
+		return err
+	case <-waitdone:
+		if *verbose {
+			log.Printf("Exiting pid %d.", os.Getpid())
+		}
+		return nil
+	}
+}
+
+// Used for pretty printing addresses.
+func pprintAddr(listeners []net.Listener) []byte {
+	var out bytes.Buffer
+	for i, l := range listeners {
+		if i != 0 {
+			fmt.Fprint(&out, ", ")
+		}
+		fmt.Fprint(&out, l.Addr())
+	}
+	return out.Bytes()
+}