Allow http client reuse in dynamic client

By using ForConfigAndClient, we are more likely to reuse the http connection.

We expose an HTTPClient, but also we default to the manager HTTPClient.

pkg/patterns/declarative/watch.go

@@ -55,6 +55,9 @@ type WatchChildrenOptions struct {
 	// RESTConfig is the configuration for connecting to the cluster.
 	RESTConfig *rest.Config
 
+	// HTTPClient is the HTTP client to use for requests.
+	HTTPClient *http.Client
+
 	// LabelMaker is used to build the labels we should watch on.
 	LabelMaker LabelMaker
 
@@ -88,6 +91,21 @@ func WatchChildren(options WatchChildrenOptions) error {
 		return fmt.Errorf("labelMaker is required to scope watches")
 	}
 
+	var httpClient *http.Client
+	if options.HTTPClient != nil {
+		httpClient = options.HTTPClient
+	} else {
+		if options.RESTConfig != nil {
+			hc, err := rest.HTTPClientFor(options.RESTConfig)
+			if err != nil {
+				return err
+			}
+			httpClient = hc
+		} else if options.Manager != nil {
+			httpClient = options.Manager.GetHTTPClient()
+		}
+	}
+
 	if options.RESTConfig == nil {
 		if options.Manager != nil {
 			options.RESTConfig = options.Manager.GetConfig()
@@ -100,23 +118,19 @@ func WatchChildren(options WatchChildrenOptions) error {
 	if options.Manager != nil {
 		restMapper = options.Manager.GetRESTMapper()
 	} else {
-		client, err := rest.HTTPClientFor(options.RESTConfig)
-		if err != nil {
-			return err
-		}
-		rm, err := commonclient.NewDiscoveryRESTMapper(options.RESTConfig, client)
+		rm, err := commonclient.NewDiscoveryRESTMapper(options.RESTConfig, httpClient)
 		if err != nil {
 			return err
 		}
 		restMapper = rm
 	}
 
-	client, err := dynamic.NewForConfig(options.RESTConfig)
+	dynamicClient, err := dynamic.NewForConfigAndClient(options.RESTConfig, httpClient)
 	if err != nil {
 		return err
 	}
 
-	dw, events, err := watch.NewDynamicWatch(restMapper, client)
+	dw, events, err := watch.NewDynamicWatch(restMapper, dynamicClient)
 	if err != nil {
 		return fmt.Errorf("creating dynamic watch: %v", err)
 	}