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

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

vendor/github.com/openebs/lib-csi/pkg/common/env/env.go

@@ -0,0 +1,113 @@
+/*
+Copyright 2019 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 env
+
+import (
+	"os"
+	"strconv"
+	"strings"
+)
+
+const (
+	// KubeConfig is the ENV variable to fetch kubernetes kubeconfig
+	KubeConfig = "OPENEBS_IO_KUBE_CONFIG"
+
+	// KubeMaster is the ENV variable to fetch kubernetes master's address
+	KubeMaster = "OPENEBS_IO_K8S_MASTER"
+)
+
+// EnvironmentSetter abstracts setting of environment variable
+type EnvironmentSetter func(envKey string, value string) (err error)
+
+// EnvironmentGetter abstracts fetching value from an environment variable
+type EnvironmentGetter func(envKey string) (value string)
+
+// EnvironmentLookup abstracts looking up an environment variable
+type EnvironmentLookup func(envKey string) (value string, present bool)
+
+// Set sets the provided environment variable
+//
+// NOTE:
+//  This is an implementation of EnvironmentSetter
+func Set(envKey string, value string) (err error) {
+	return os.Setenv(string(envKey), value)
+}
+
+// Get fetches value from the provided environment variable
+//
+// NOTE:
+//  This is an implementation of EnvironmentGetter
+func Get(envKey string) (value string) {
+	return getEnv(string(envKey))
+}
+
+// GetOrDefault fetches value from the provided environment variable
+// which on empty returns the defaultValue
+// NOTE: os.Getenv is used here instead of os.LookupEnv because it is
+// not required to know if the environment variable is defined on the system
+func GetOrDefault(e string, defaultValue string) (value string) {
+	envValue := Get(e)
+	if len(envValue) == 0 {
+		// ENV not defined or set to ""
+		return defaultValue
+	}
+	return envValue
+}
+
+// Lookup looks up an environment variable
+//
+// NOTE:
+//  This is an implementation of EnvironmentLookup
+func Lookup(envKey string) (value string, present bool) {
+	return lookupEnv(string(envKey))
+}
+
+// Truthy returns boolean based on the environment variable's value
+//
+// The lookup value can be truthy (i.e. 1, t, TRUE, true) or falsy (0, false,
+// etc) based on strconv.ParseBool logic
+func Truthy(envKey string) (truth bool) {
+	v, found := Lookup(envKey)
+	if !found {
+		return
+	}
+	truth, _ = strconv.ParseBool(v)
+	return
+}
+
+// LookupOrFalse looks up an environment variable and returns a string "false"
+// if environment variable is not present. It returns appropriate values for
+// other cases.
+func LookupOrFalse(envKey string) string {
+	val, present := Lookup(envKey)
+	if !present {
+		return "false"
+	}
+	return strings.TrimSpace(val)
+}
+
+// getEnv fetches the provided environment variable's value
+func getEnv(envKey string) (value string) {
+	return strings.TrimSpace(os.Getenv(envKey))
+}
+
+// lookupEnv looks up the provided environment variable
+func lookupEnv(envKey string) (value string, present bool) {
+	value, present = os.LookupEnv(envKey)
+	value = strings.TrimSpace(value)
+	return
+}