From 11e1a99e14bab661834d05ccbb2d8ac52d174089 Mon Sep 17 00:00:00 2001
From: Jakob Borg <jakob@nym.se>
Date: Tue, 29 Sep 2015 17:17:09 +0200
Subject: [PATCH] Subscribing to events should not bump event ID (fixes #2329)

---
 lib/events/events.go      | 20 ++++++++++++--------
 lib/events/events_test.go |  5 +++--
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/lib/events/events.go b/lib/events/events.go
index 21dbcc0ae..07c6ccbe6 100644
--- a/lib/events/events.go
+++ b/lib/events/events.go
@@ -105,7 +105,7 @@ func (t EventType) MarshalText() ([]byte, error) {
 const BufferSize = 64
 
 type Logger struct {
-	subs   map[int]*Subscription
+	subs   []*Subscription
 	nextID int
 	mutex  sync.Mutex
 }
@@ -119,7 +119,6 @@ type Event struct {
 
 type Subscription struct {
 	mask    EventType
-	id      int
 	events  chan Event
 	timeout *time.Timer
 }
@@ -133,7 +132,6 @@ var (
 
 func NewLogger() *Logger {
 	return &Logger{
-		subs:  make(map[int]*Subscription),
 		mutex: sync.NewMutex(),
 	}
 }
@@ -143,13 +141,13 @@ func (l *Logger) Log(t EventType, data interface{}) {
 	if debug {
 		dl.Debugln("log", l.nextID, t.String(), data)
 	}
+	l.nextID++
 	e := Event{
 		ID:   l.nextID,
 		Time: time.Now(),
 		Type: t,
 		Data: data,
 	}
-	l.nextID++
 	for _, s := range l.subs {
 		if s.mask&t != 0 {
 			select {
@@ -169,12 +167,10 @@ func (l *Logger) Subscribe(mask EventType) *Subscription {
 	}
 	s := &Subscription{
 		mask:    mask,
-		id:      l.nextID,
 		events:  make(chan Event, BufferSize),
 		timeout: time.NewTimer(0),
 	}
-	l.nextID++
-	l.subs[s.id] = s
+	l.subs = append(l.subs, s)
 	l.mutex.Unlock()
 	return s
 }
@@ -184,7 +180,15 @@ func (l *Logger) Unsubscribe(s *Subscription) {
 	if debug {
 		dl.Debugln("unsubscribe")
 	}
-	delete(l.subs, s.id)
+	for i, ss := range l.subs {
+		if s == ss {
+			last := len(l.subs) - 1
+			l.subs[i] = l.subs[last]
+			l.subs[last] = nil
+			l.subs = l.subs[:last]
+			break
+		}
+	}
 	close(s.events)
 	l.mutex.Unlock()
 }
diff --git a/lib/events/events_test.go b/lib/events/events_test.go
index 2f91dafea..8b194b746 100644
--- a/lib/events/events_test.go
+++ b/lib/events/events_test.go
@@ -134,6 +134,7 @@ func TestIDs(t *testing.T) {
 	s := l.Subscribe(events.AllEvents)
 	defer l.Unsubscribe(s)
 	l.Log(events.DeviceConnected, "foo")
+	_ = l.Subscribe(events.AllEvents)
 	l.Log(events.DeviceConnected, "bar")
 
 	ev, err := s.Poll(timeout)
@@ -152,8 +153,8 @@ func TestIDs(t *testing.T) {
 	if ev.Data.(string) != "bar" {
 		t.Fatal("Incorrect event:", ev)
 	}
-	if !(ev.ID > id) {
-		t.Fatalf("ID not incremented (%d !> %d)", ev.ID, id)
+	if ev.ID != id+1 {
+		t.Fatalf("ID not incremented (%d != %d)", ev.ID, id+1)
 	}
 }