From 0eff425bc7e3d6137ea3c59ad7436eafe5ef55d2 Mon Sep 17 00:00:00 2001
From: Silas Davis <silas@monax.io>
Date: Mon, 23 Oct 2017 18:51:49 +0100
Subject: [PATCH] fix zeroed buffer getting flushed to the empty event

---
 events/event_cache.go      | 12 ++++--------
 events/event_cache_test.go | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 8 deletions(-)
 create mode 100644 events/event_cache_test.go

diff --git a/events/event_cache.go b/events/event_cache.go
index 905f1096a..f508e873d 100644
--- a/events/event_cache.go
+++ b/events/event_cache.go
@@ -1,9 +1,5 @@
 package events
 
-const (
-	eventsBufferSize = 1000
-)
-
 // An EventCache buffers events for a Fireable
 // All events are cached. Filtering happens on Flush
 type EventCache struct {
@@ -14,8 +10,7 @@ type EventCache struct {
 // Create a new EventCache with an EventSwitch as backend
 func NewEventCache(evsw Fireable) *EventCache {
 	return &EventCache{
-		evsw:   evsw,
-		events: make([]eventInfo, eventsBufferSize),
+		evsw: evsw,
 	}
 }
 
@@ -27,7 +22,7 @@ type eventInfo struct {
 
 // Cache an event to be fired upon finality.
 func (evc *EventCache) FireEvent(event string, data EventData) {
-	// append to list
+	// append to list (go will grow our backing array exponentially)
 	evc.events = append(evc.events, eventInfo{event, data})
 }
 
@@ -37,5 +32,6 @@ func (evc *EventCache) Flush() {
 	for _, ei := range evc.events {
 		evc.evsw.FireEvent(ei.event, ei.data)
 	}
-	evc.events = make([]eventInfo, eventsBufferSize)
+	// Clear the buffer, since we only add to it with append it's safe to just set it to nil and maybe safe an allocation
+	evc.events = nil
 }
diff --git a/events/event_cache_test.go b/events/event_cache_test.go
new file mode 100644
index 000000000..ab321da3a
--- /dev/null
+++ b/events/event_cache_test.go
@@ -0,0 +1,35 @@
+package events
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEventCache_Flush(t *testing.T) {
+	evsw := NewEventSwitch()
+	evsw.Start()
+	evsw.AddListenerForEvent("nothingness", "", func(data EventData) {
+		// Check we are not initialising an empty buffer full of zeroed eventInfos in the EventCache
+		require.FailNow(t, "We should never receive a message on this switch since none are fired")
+	})
+	evc := NewEventCache(evsw)
+	evc.Flush()
+	// Check after reset
+	evc.Flush()
+	fail := true
+	pass := false
+	evsw.AddListenerForEvent("somethingness", "something", func(data EventData) {
+		if fail {
+			require.FailNow(t, "Shouldn't see a message until flushed")
+		}
+		pass = true
+	})
+	evc.FireEvent("something", struct{ int }{1})
+	evc.FireEvent("something", struct{ int }{2})
+	evc.FireEvent("something", struct{ int }{3})
+	fail = false
+	evc.Flush()
+	assert.True(t, pass)
+}