[WIP] Populate home AZ cache if it's not filled

cns/restserver/homeazmonitor.go

@@ -10,7 +10,6 @@
 	"github.com/Azure/azure-container-networking/cns/logger"
 	"github.com/Azure/azure-container-networking/cns/types"
 	"github.com/Azure/azure-container-networking/nmagent"
-	"github.com/patrickmn/go-cache"
 	"github.com/pkg/errors"
 )
 
@@ -22,7 +21,7 @@
 
 type HomeAzMonitor struct {
 	nmagentClient
 	values *cache.Cache
 	// channel used as signal to end of the goroutine for populating home az cache
 	closing                  chan struct{}
 	cacheRefreshIntervalSecs time.Duration
@@ -33,7 +32,7 @@
 	return &HomeAzMonitor{
 		nmagentClient:            client,
 		cacheRefreshIntervalSecs: cacheRefreshIntervalSecs,
 		values:                   cache.New(cache.NoExpiration, cache.NoExpiration),
 		closing:                  make(chan struct{}),
 	}
 }
@@ -45,19 +44,30 @@
 
 // updateCacheValue updates home az cache value
 func (h *HomeAzMonitor) updateCacheValue(resp cns.GetHomeAzResponse) {
 	h.values.Set(homeAzCacheKey, resp, cache.NoExpiration)
 }
 
 // readCacheValue reads home az cache value
 func (h *HomeAzMonitor) readCacheValue() cns.GetHomeAzResponse {
-	cachedResp, found := h.values.Get(homeAzCacheKey)
-	if !found {
-		return cns.GetHomeAzResponse{Response: cns.Response{
+	if cachedResp, found := h.values.Get(homeAzCacheKey); found {
+		return cachedResp.(cns.GetHomeAzResponse)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), ContextTimeOut)
+	defer cancel()
+	h.Populate(ctx)
+
+	if cachedResp, found := h.values.Get(homeAzCacheKey); found {
+		return cachedResp.(cns.GetHomeAzResponse)
+	}
+
+	return cns.GetHomeAzResponse{
+		Response: cns.Response{
 			ReturnCode: types.NotFound,
 			Message:    "HomeAz Cache is unavailable",
-		}, HomeAzResponse: cns.HomeAzResponse{IsSupported: false}}
+		},
+		HomeAzResponse: cns.HomeAzResponse{IsSupported: false},
 	}
-	return cachedResp.(cns.GetHomeAzResponse)
 }
 
 // Start starts a new thread to refresh home az cache