Controller info endpoint and API integration examples (#75)

* Controller API: introduce controller's information endpoint

* Prevent generation of empty events after channel closure

* Allow events to be buffered in the events channel

* Controller API: introduce controller's information endpoint[1]

* IntegrationGuide.md: a couple of Python and Golang examples

* Rephrase a sentence

Co-authored-by: Fedor Korotkov <fedor.korotkov@gmail.com>

---------

Co-authored-by: Fedor Korotkov <fedor.korotkov@gmail.com>

pkg/client/client.go

@@ -266,3 +266,9 @@ func (client *Client) ServiceAccounts() *ServiceAccountsService {
 		client: client,
 	}
 }
+
+func (client *Client) Controller() *ControllerService {
+	return &ControllerService{
+		client: client,
+	}
+}

pkg/client/controller.go

@@ -0,0 +1,23 @@
+package client
+
+import (
+	"context"
+	v1 "github.com/cirruslabs/orchard/pkg/resource/v1"
+	"net/http"
+)
+
+type ControllerService struct {
+	client *Client
+}
+
+func (service *ControllerService) Info(ctx context.Context) (v1.ControllerInfo, error) {
+	var controllerInfo v1.ControllerInfo
+
+	err := service.client.request(ctx, http.MethodGet, "controller/info", nil, &controllerInfo,
+		nil)
+	if err != nil {
+		return controllerInfo, err
+	}
+
+	return controllerInfo, nil
+}

pkg/client/events.go

@@ -20,7 +20,7 @@ func NewEventStreamer(client *Client, endpoint string) *EventStreamer {
 	streamer := &EventStreamer{
 		client:        client,
 		endpoint:      endpoint,
-		eventsChannel: make(chan v1.Event),
+		eventsChannel: make(chan v1.Event, 64),
 	}
 	go streamer.stream()
 	return streamer
@@ -46,16 +46,23 @@ func (streamer *EventStreamer) stream() {
 }
 
 func (streamer *EventStreamer) readAvailableEvents() ([]v1.Event, bool) {
-	// blocking wait for at least one event
-	result := []v1.Event{<-streamer.eventsChannel}
+	var result []v1.Event
 
+	// blocking wait for at least one event
+	nextEvent, ok := <-streamer.eventsChannel
+	if !ok {
+		return result, true
+	}
+	result = append(result, nextEvent)
+
+	// non-blocking wait for more events, if any
 	for {
 		select {
-		case nextEvent, more := <-streamer.eventsChannel:
-			result = append(result, nextEvent)
-			if !more {
+		case nextEvent, ok := <-streamer.eventsChannel:
+			if !ok {
 				return result, true
 			}
+			result = append(result, nextEvent)
 		default:
 			return result, false
 		}

pkg/resource/v1/v1.go

@@ -90,3 +90,8 @@ const (
 	// (either via API or from within a VM via `sudo shutdown -now`).
 	VMStatusStopped VMStatus = "stopped"
 )
+
+type ControllerInfo struct {
+	Version string `json:"version"`
+	Commit  string `json:"commit"`
+}