cmd/syncthing, lib/events, lib/sync: Add timeout to REST event API, remove Ping (fixes #3933)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3941

lib/events/events.go

@@ -10,7 +10,6 @@ package events
 import (
 	"errors"
 	"runtime"
-	stdsync "sync"
 	"time"
 
 	"github.com/syncthing/syncthing/lib/sync"
@@ -19,8 +18,7 @@ import (
 type EventType int
 
 const (
-	Ping EventType = 1 << iota
-	Starting
+	Starting EventType = 1 << iota
 	StartupComplete
 	DeviceDiscovered
 	DeviceConnected
@@ -55,8 +53,6 @@ var runningTests = false
 
 func (t EventType) String() string {
 	switch t {
-	case Ping:
-		return "Ping"
 	case Starting:
 		return "Starting"
 	case StartupComplete:
@@ -279,11 +275,11 @@ type bufferedSubscription struct {
 	next int
 	cur  int // Current SubscriptionID
 	mut  sync.Mutex
-	cond *stdsync.Cond
+	cond *sync.TimeoutCond
 }
 
 type BufferedSubscription interface {
-	Since(id int, into []Event) []Event
+	Since(id int, into []Event, timeout time.Duration) []Event
 }
 
 func NewBufferedSubscription(s *Subscription, size int) BufferedSubscription {
@@ -292,7 +288,7 @@ func NewBufferedSubscription(s *Subscription, size int) BufferedSubscription {
 		buf: make([]Event, size),
 		mut: sync.NewMutex(),
 	}
-	bs.cond = stdsync.NewCond(bs.mut)
+	bs.cond = sync.NewTimeoutCond(bs.mut)
 	go bs.pollingLoop()
 	return bs
 }
@@ -319,12 +315,21 @@ func (s *bufferedSubscription) pollingLoop() {
 	}
 }
 
-func (s *bufferedSubscription) Since(id int, into []Event) []Event {
+func (s *bufferedSubscription) Since(id int, into []Event, timeout time.Duration) []Event {
 	s.mut.Lock()
 	defer s.mut.Unlock()
 
-	for id >= s.cur {
-		s.cond.Wait()
+	// Check once first before generating the TimeoutCondWaiter
+	if id >= s.cur {
+		waiter := s.cond.SetupWait(timeout)
+		defer waiter.Stop()
+
+		for id >= s.cur {
+			if eventsAvailable := waiter.Wait(); !eventsAvailable {
+				// Timed out
+				return into
+			}
+		}
 	}
 
 	for i := s.next; i < len(s.buf); i++ {