refact(csi): use common lib-csi imports (#263)

Signed-off-by: shubham <shubham.bajpai@mayadata.io>

vendor/github.com/openebs/lib-csi/pkg/client/k8s/config.go

@@ -0,0 +1,100 @@
+/*
+Copyright 2020 The OpenEBS Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package k8s
+
+import (
+	"strings"
+
+	"github.com/openebs/lib-csi/pkg/common/env"
+	"github.com/pkg/errors"
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/clientcmd"
+)
+
+// ConfigGetter abstracts fetching of kubernetes client config
+type ConfigGetter interface {
+	Get() (*rest.Config, error)
+	Name() string
+}
+
+// configFromENV is an implementation of ConfigGetter
+type configFromENV struct{}
+
+// Name returns the name of this config getter instance
+func (c *configFromENV) Name() string {
+	return "k8s-config-from-env"
+}
+
+// Get returns kubernetes rest config based on kubernetes environment values
+func (c *configFromENV) Get() (*rest.Config, error) {
+	k8sMaster := env.Get(env.KubeMaster)
+	kubeConfig := env.Get(env.KubeConfig)
+
+	if len(strings.TrimSpace(k8sMaster)) == 0 && len(strings.TrimSpace(kubeConfig)) == 0 {
+		return nil, errors.New("missing kubernetes master as well as kubeconfig: failed to get kubernetes client config")
+	}
+
+	return clientcmd.BuildConfigFromFlags(k8sMaster, kubeConfig)
+}
+
+// configFromREST is an implementation of ConfigGetter
+type configFromREST struct{}
+
+// Name returns the name of this config getter instance
+func (c *configFromREST) Name() string {
+	return "k8s-config-from-rest"
+}
+
+// Get returns kubernetes rest config based on in-cluster config implementation
+func (c *configFromREST) Get() (*rest.Config, error) {
+	return rest.InClusterConfig()
+}
+
+// ConfigGetters holds a list of ConfigGetter instances
+//
+// NOTE:
+//  This is an implementation of ConfigGetter
+type ConfigGetters []ConfigGetter
+
+// Name returns the name of this config getter instance
+func (c ConfigGetters) Name() string {
+	return "list-of-k8s-config-getter"
+}
+
+// Get fetches the kubernetes client config that is used to make kubernetes API
+// calls. It makes use of its list of getter instances to fetch kubernetes
+// config.
+func (c ConfigGetters) Get() (config *rest.Config, err error) {
+	var errs []error
+	for _, g := range c {
+		config, err = g.Get()
+		if err == nil {
+			return
+		}
+		errs = append(errs, errors.Wrapf(err, "failed to get kubernetes client config via %s", g.Name()))
+	}
+	// at this point; all getters have failed
+	err = errors.Errorf("%+v", errs)
+	err = errors.Wrap(err, "failed to get kubernetes client config")
+	return
+}
+
+// Config provides appropriate config getter instances that help in fetching
+// kubernetes client config to invoke kubernetes API calls
+func Config() ConfigGetter {
+	return ConfigGetters{&configFromENV{}, &configFromREST{}}
+}