Add stayalive endpoint

This is used by Zui to prevent orhpaned Zed processes by exiting when a client
stops polling the stayalive endpoint.

Closes 4863

cmd/zed/serve/command.go

@@ -1,14 +1,12 @@
 package serve
 
 import (
-	"context"
 	"errors"
 	"flag"
 	"io"
 	"net"
 	"os"
 	"os/signal"
-	"runtime"
 	"syscall"
 
 	"github.com/brimdata/zed/cli"
@@ -31,7 +29,7 @@ The serve command listens for Zed lake API requests on the provided
 interface and port, executes the requests, and returns results.
 Requests may be issued to this service via the "zed api" command.
 `,
-	HiddenFlags: "brimfd,portfile",
+	HiddenFlags: "enablestayalive,portfile",
 	New:         New,
 }
 
@@ -40,9 +38,6 @@ type Command struct {
 	conf     service.Config
 	logflags logflags.Flags
 
-	// brimfd is a file descriptor passed through by Zui desktop. If set the
-	// command will exit if the fd is closed.
-	brimfd          int
 	listenAddr      string
 	portFile        string
 	rootContentFile string
@@ -53,12 +48,12 @@ func New(parent charm.Command, f *flag.FlagSet) (charm.Command, error) {
 	c.conf.Auth.SetFlags(f)
 	c.conf.Version = cli.Version()
 	c.logflags.SetFlags(f)
-	f.IntVar(&c.brimfd, "brimfd", -1, "pipe read fd passed by Zui to signal Zui closure")
 	f.Func("cors.origin", "CORS allowed origin (may be repeated)", func(s string) error {
 		c.conf.CORSAllowedOrigins = append(c.conf.CORSAllowedOrigins, s)
 		return nil
 	})
 	f.StringVar(&c.conf.DefaultResponseFormat, "defaultfmt", service.DefaultZedFormat, "default response format")
+	f.BoolVar(&c.conf.EnableStayAlive, "enablestayalive", false, "enable stayalive endpoint (used by Zui to prevent orphaned Zed processes)")
 	f.StringVar(&c.listenAddr, "l", ":9867", "[addr]:port to listen on")
 	f.StringVar(&c.portFile, "portfile", "", "write listen port to file")
 	f.StringVar(&c.rootContentFile, "rootcontentfile", "", "file to serve for GET /")
@@ -92,16 +87,12 @@ func (c *Command) Run(args []string) error {
 		return err
 	}
 	defer logger.Sync()
-	if c.brimfd != -1 {
-		if ctx, err = c.watchBrimFd(ctx, logger); err != nil {
-			return err
-		}
-	}
 	c.conf.Logger = logger
 	core, err := service.NewCore(ctx, c.conf)
 	if err != nil {
 		return err
 	}
+	ctx = core.StayAliveContext(ctx)
 	defer core.Shutdown()
 	sigch := make(chan os.Signal, 1)
 	signal.Notify(sigch, os.Interrupt)
@@ -122,21 +113,6 @@ func (c *Command) Run(args []string) error {
 	return srv.Wait()
 }
 
-func (c *Command) watchBrimFd(ctx context.Context, logger *zap.Logger) (context.Context, error) {
-	if runtime.GOOS == "windows" {
-		return nil, errors.New("flag -brimfd not applicable to windows")
-	}
-	f := os.NewFile(uintptr(c.brimfd), "brimfd")
-	logger.Info("Listening to Zui process pipe", zap.String("fd", f.Name()))
-	ctx, cancel := context.WithCancel(ctx)
-	go func() {
-		io.Copy(io.Discard, f)
-		logger.Info("Brim fd closed, shutting down")
-		cancel()
-	}()
-	return ctx, nil
-}
-
 func (c *Command) writePortFile(addr string) error {
 	_, port, err := net.SplitHostPort(addr)
 	if err != nil {

pkg/httpd/server.go

@@ -77,6 +77,9 @@ func (s *Server) serve(ctx context.Context, ln net.Listener) {
 		reason = "server error"
 	case <-ctx.Done():
 		reason = "context closed"
+		if err := context.Cause(ctx); !errors.Is(err, context.Canceled) {
+			reason = err.Error()
+		}
 	}
 
 	s.logger.Info("Shutting down", zap.String("reason", reason), zap.Error(srvErr))

service/core.go

@@ -49,6 +49,12 @@ type Config struct {
 	RootContent           io.ReadSeeker
 	Version               string
 	Logger                *zap.Logger
+	// EnableStayAlive when true enables the stayalive endpoint. If a client
+	// begins polling the stayalive endpoint then exits, the Zed process will
+	// also exit. This is used by the Zui application to ensure that the Zed
+	// process exits in the event that the Zui process is terminated with
+	// SIGKILL.
+	EnableStayAlive bool
 }
 
 type Core struct {
@@ -65,6 +71,7 @@ type Core struct {
 	runningQueriesMu sync.Mutex
 	subscriptions    map[chan event]struct{}
 	subscriptionsMu  sync.RWMutex
+	stayAliveCancel  context.CancelCauseFunc
 }
 
 func NewCore(ctx context.Context, conf Config) (*Core, error) {
@@ -142,17 +149,18 @@ func NewCore(ctx context.Context, conf Config) (*Core, error) {
 	routerAPI.Use(corsMiddleware(conf.CORSAllowedOrigins))
 
 	c := &Core{
-		auth:           authenticator,
-		compiler:       compiler.NewLakeCompiler(root),
-		conf:           conf,
-		engine:         engine,
-		logger:         conf.Logger.Named("core"),
-		root:           root,
-		registry:       registry,
-		routerAPI:      routerAPI,
-		routerAux:      routerAux,
-		runningQueries: make(map[string]*queryStatus),
-		subscriptions:  make(map[chan event]struct{}),
+		auth:            authenticator,
+		compiler:        compiler.NewLakeCompiler(root),
+		conf:            conf,
+		engine:          engine,
+		logger:          conf.Logger.Named("core"),
+		root:            root,
+		registry:        registry,
+		routerAPI:       routerAPI,
+		routerAux:       routerAux,
+		runningQueries:  make(map[string]*queryStatus),
+		subscriptions:   make(map[chan event]struct{}),
+		stayAliveCancel: func(error) {}, // noop
 	}
 
 	c.addAPIServerRoutes()
@@ -186,6 +194,9 @@ func (c *Core) addAPIServerRoutes() {
 	c.authhandle("/pool/{pool}/stats", handlePoolStats).Methods("GET")
 	c.authhandle("/query", handleQuery).Methods("OPTIONS", "POST")
 	c.authhandle("/query/status/{requestID}", handleQueryStatus).Methods("GET")
+	if c.conf.EnableStayAlive {
+		c.authhandle("/stayalive", handleStayAlive).Methods("GET")
+	}
 }
 
 func (c *Core) handler(f func(*Core, *ResponseWriter, *Request)) http.Handler {
@@ -244,6 +255,13 @@ func (c *Core) Shutdown() {
 	c.logger.Info("Shutdown")
 }
 
+func (c *Core) StayAliveContext(ctx context.Context) context.Context {
+	if c.conf.EnableStayAlive {
+		ctx, c.stayAliveCancel = context.WithCancelCause(ctx)
+	}
+	return ctx
+}
+
 func (c *Core) publishEvent(w *ResponseWriter, name string, data interface{}) {
 	marshaler := zson.NewZNGMarshaler()
 	marshaler.Decorate(zson.StyleSimple)

service/handlers.go

@@ -782,3 +782,10 @@ func handleEvents(c *Core, w *ResponseWriter, r *Request) {
 		}
 	}
 }
+
+func handleStayAlive(c *Core, w *ResponseWriter, r *Request) {
+	w.WriteHeader(http.StatusOK)
+	r.Logger.Info("Stay Alive entered")
+	<-r.Context().Done()
+	c.stayAliveCancel(errors.New("stay alive exited"))
+}

service/ztests/orphaned-by-zui.yaml

@@ -1,16 +1,12 @@
 script: |
-  source mockzui.sh
-  zed create test
-  echo ===
-  kill -9 $MOCKZUI_PID 2>/dev/null
-  awaitdeadservice
+  LAKE_EXTRA_FLAGS="-enablestayalive -log.level=info" source service.sh
+  ! curl -m 0.1 $ZED_LAKE/stayalive 2> /dev/null
+  zq -z 'msg == "Shutting down" | drop ts' lake.log
 
 inputs:
-  - name: mockzui.sh
-    source: mockzui.sh
+  - name: service.sh
 
 outputs:
   - name: stdout
-    regexp: |
-      pool created: test \w{27}
-      ===
+    data: |
+      {level:"info",logger:"httpd",msg:"Shutting down",reason:"stay alive exited"}

service/ztests/service.sh

@@ -26,7 +26,7 @@ zed serve -l=localhost:0 -lake=$lakeroot -portfile=$portdir/lake -log.level=warn
 lakepid=$!
 awaitfile $portdir/lake
 
-trap "rm -rf $portdir; kill $lakepid;" EXIT
+trap "rm -rf $portdir; kill $lakepid || true" EXIT
 
 export ZED_LAKE=http://localhost:$(cat $portdir/lake)
 export LAKE_PATH=$lakeroot