c-go: Use http Etag cache

Add a new command-line cachedir flag to specify where to store the http
cache responses. This cache will only be used for OpenAPI Swagger spec
for now (as this is the only end-point that returns an ETag).

Kubernetes-commit: d7bba25d4a42f346f1963c86fc0dab43aa4f242e

rest/config.go

@@ -71,6 +71,10 @@ type Config struct {
 	// TODO: demonstrate an OAuth2 compatible client.
 	BearerToken string
 
+	// CacheDir is the directory where we'll store HTTP cached responses.
+	// If set to empty string, no caching mechanism will be used.
+	CacheDir string
+
 	// Impersonate is the configuration that RESTClient will use for impersonation.
 	Impersonate ImpersonationConfig
 

rest/config_test.go

@@ -249,6 +249,7 @@ func TestAnonymousConfig(t *testing.T) {
 		expected.BearerToken = ""
 		expected.Username = ""
 		expected.Password = ""
+		expected.CacheDir = ""
 		expected.AuthProvider = nil
 		expected.AuthConfigPersister = nil
 		expected.TLSClientConfig.CertData = nil

rest/transport.go

@@ -89,6 +89,7 @@ func (c *Config) TransportConfig() (*transport.Config, error) {
 		},
 		Username:    c.Username,
 		Password:    c.Password,
+		CacheDir:    c.CacheDir,
 		BearerToken: c.BearerToken,
 		Impersonate: transport.ImpersonationConfig{
 			UserName: c.Impersonate.UserName,