events: Add pubsub global interface for OSM events

This commit introduces a glogal interface to pass messages and events,
from multiple writers to multiple readers, based on topic.

Single channel mechanisms suffers from some coupling still, where
the object holding the channel or channel itself has to be passed around.

Additionally, we are seeing situations where individual modules could be
interested in being notified for certain events so they could run
their own isolated logic (mind the isolation), current single channel model
poses several quite some issues on that front (need a middleman multiplexer, etc.)

This commit doesn't yet introduce a consumer of this API, though in subsequent
we will introduce/rework some channel uses that will immediately greatly benefit
from this feature (proxy's global boadcasting, configurator, etc.)

Addresses openservicemesh#1914

cmd/osm-controller/osm-controller.go

@@ -138,6 +138,7 @@ func main() {
 	}
 
 	featureflags.Initialize(optionalFeatures)
+	events.GetPubSubInstance() // Just to generate the interface, single routine context
 
 	// Initialize kube config and client
 	kubeConfig, err := clientcmd.BuildConfigFromFlags("", kubeConfigFile)

pkg/kubernetes/event_handlers.go

@@ -8,6 +8,7 @@ import (
 
 	a "github.com/openservicemesh/osm/pkg/announcements"
 	"github.com/openservicemesh/osm/pkg/constants"
+	"github.com/openservicemesh/osm/pkg/kubernetes/events"
 )
 
 var emitLogs = os.Getenv(constants.EnvVarLogKubernetesEvents) == "true"
@@ -60,6 +61,11 @@ func GetKubernetesEventHandlers(informerName, providerName string, announce chan
 				logNotObservedNamespace(obj, eventTypes.Add)
 				return
 			}
+			events.GetPubSubInstance().Publish(events.PubSubMessage{
+				AnnouncementType: eventTypes.Add,
+				NewObj:           obj,
+				OldObj:           nil,
+			})
 			sendAnnouncement(eventTypes.Add, obj)
 		},
 
@@ -68,6 +74,11 @@ func GetKubernetesEventHandlers(informerName, providerName string, announce chan
 				logNotObservedNamespace(newObj, eventTypes.Update)
 				return
 			}
+			events.GetPubSubInstance().Publish(events.PubSubMessage{
+				AnnouncementType: eventTypes.Update,
+				NewObj:           oldObj,
+				OldObj:           newObj,
+			})
 			sendAnnouncement(eventTypes.Update, oldObj)
 		},
 
@@ -76,6 +87,11 @@ func GetKubernetesEventHandlers(informerName, providerName string, announce chan
 				logNotObservedNamespace(obj, eventTypes.Delete)
 				return
 			}
+			events.GetPubSubInstance().Publish(events.PubSubMessage{
+				AnnouncementType: eventTypes.Delete,
+				NewObj:           nil,
+				OldObj:           obj,
+			})
 			sendAnnouncement(eventTypes.Delete, obj)
 		},
 	}

pkg/kubernetes/events/event_pubsub.go

@@ -0,0 +1,49 @@
+package events
+
+import (
+	"github.com/cskr/pubsub"
+
+	"github.com/openservicemesh/osm/pkg/announcements"
+)
+
+const (
+	// Default number of events a subscriber channel will buffer
+	defaultAnnouncementChannelSize = 512
+)
+
+var (
+	// Globally accessible instance, through singleton pattern GetPubSubInstance
+	pubSubInstance *osmPubsub
+)
+
+// Object which implements the PubSub interface
+type osmPubsub struct {
+	pSub *pubsub.PubSub
+}
+
+// Subscribe is the Subscribe implementation for PubSub
+func (c *osmPubsub) Subscribe(aTypes ...announcements.AnnouncementType) chan interface{} {
+	subTypes := []string{}
+	for _, v := range aTypes {
+		subTypes = append(subTypes, string(v))
+	}
+
+	return c.pSub.Sub(subTypes...)
+}
+
+// Publish is the Publish implementation for PubSub
+func (c *osmPubsub) Publish(message PubSubMessage) {
+	c.pSub.Pub(message, message.AnnouncementType.String())
+}
+
+// GetPubSubInstance returns a unique, global scope PubSub interface instance
+// Note that spawning the instance is not thread-safe. First call should happen on
+// a single-routine context to avoid races.
+func GetPubSubInstance() PubSub {
+	if pubSubInstance == nil {
+		pubSubInstance = &osmPubsub{
+			pSub: pubsub.New(defaultAnnouncementChannelSize),
+		}
+	}
+	return pubSubInstance
+}

pkg/kubernetes/events/event_pubsub_test.go

@@ -0,0 +1,62 @@
+package events
+
+import (
+	"reflect"
+	"testing"
+	"time"
+
+	gomock "github.com/golang/mock/gomock"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/openservicemesh/osm/pkg/announcements"
+)
+
+func TestPubSubEvents(t *testing.T) {
+	assert := assert.New(t)
+	mockCtrl := gomock.NewController(t)
+	defer mockCtrl.Finish()
+
+	testCases := []struct {
+		register      announcements.AnnouncementType
+		publish       PubSubMessage
+		expectMessage bool
+	}{
+		{
+			register: announcements.BackpressureAdded,
+			publish: PubSubMessage{
+				AnnouncementType: announcements.ConfigMapAdded,
+				NewObj:           struct{}{},
+				OldObj:           nil,
+			},
+			expectMessage: false,
+		},
+		{
+			register: announcements.BackpressureAdded,
+			publish: PubSubMessage{
+				AnnouncementType: announcements.BackpressureAdded,
+				NewObj:           nil,
+				OldObj:           "randomString",
+			},
+			expectMessage: true,
+		},
+	}
+
+	for i := range testCases {
+		subscribedChanel := GetPubSubInstance().Subscribe(testCases[i].register)
+		GetPubSubInstance().Publish(testCases[i].publish)
+
+		select {
+		case psMesg := <-subscribedChanel:
+			assert.True(testCases[i].expectMessage)
+
+			psCast, ok := psMesg.(PubSubMessage)
+			assert.True(ok)
+
+			equal := reflect.DeepEqual(psCast, testCases[i].publish)
+			assert.True(equal)
+
+		case <-time.After(1 * time.Second):
+			assert.False(testCases[i].expectMessage)
+		}
+	}
+}

pkg/kubernetes/events/types.go

@@ -1,6 +1,7 @@
 package events
 
 import (
+	"github.com/openservicemesh/osm/pkg/announcements"
 	"github.com/openservicemesh/osm/pkg/logger"
 )
 
@@ -24,3 +25,19 @@ const (
 	// CertificateIssuanceFailure signifies that a request to issue a certificate failed
 	CertificateIssuanceFailure = "FatalCertificateIssuanceFailure"
 )
+
+// PubSubMessage represents a common messages abstraction to pass through the PubSub interface
+type PubSubMessage struct {
+	AnnouncementType announcements.AnnouncementType
+	OldObj           interface{}
+	NewObj           interface{}
+}
+
+// PubSub is a simple interface to call for pubsub functionality in front of a pubsub implementation
+type PubSub interface {
+	// Subscribe returns a channel subscribed to the specific type/s of announcement/s passed by parameter
+	Subscribe(aTypes ...announcements.AnnouncementType) chan interface{}
+
+	// Publish publishes the message to all subscribers that have subscribed to <message.AnnouncementType> topic
+	Publish(message PubSubMessage)
+}