Do not download instance types if cache loadable

and environment INCUS_DOWNLOAD_INSTANCE_TYPES set to false, because most
enterprise environment can not access internet directly, so they can put
instance types in cache and set `INCUS_DOWNLOAD_INSTANCE_TYPES = false`.

Signed-off-by: JUN JIE NAN <[email protected]>

Author: nanjj

cmd/incusd/instance_instance_types.go

@@ -153,7 +153,18 @@ func instanceRefreshTypes(ctx context.Context, s *state.State) error {
 
 	// Set an initial value from the cache
 	if instanceTypes == nil {
-		_ = instanceLoadCache()
+		instanceTypes = map[string]map[string]*instanceType{}
+	}
+
+	if len(instanceTypes) == 0 {
+		err := instanceLoadCache()
+		if err != nil {
+			logger.Error("instance load cache error", logger.Ctx{"err": err})
+		}
+	}
+
+	if len(instanceTypes) != 0 && util.IsFalse(os.Getenv("INCUS_DOWNLOAD_INSTANCE_TYPES")) {
+		return nil
 	}
 
 	// Get the list of instance type sources