Merge pull request #1877 from jedevc/cache-dockerutil-features

dockerutil: cache feature collection

util/dockerutil/client.go

@@ -13,6 +13,9 @@ import (
 // Client represents an active docker object.
 type Client struct {
 	cli command.Cli
+
+	featuresOnce  sync.Once
+	featuresCache map[Feature]bool
 }
 
 // NewClient initializes a new docker client.
@@ -64,6 +67,13 @@ func (c *Client) LoadImage(ctx context.Context, name string, status progress.Wri
 }
 
 func (c *Client) Features(ctx context.Context, name string) map[Feature]bool {
+	c.featuresOnce.Do(func() {
+		c.featuresCache = c.features(ctx, name)
+	})
+	return c.featuresCache
+}
+
+func (c *Client) features(ctx context.Context, name string) map[Feature]bool {
 	features := make(map[Feature]bool)
 	if dapi, err := c.API(name); err == nil {
 		if info, err := dapi.Info(ctx); err == nil {