Refactor pkg packages

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

pkg/cri/util/strings.go

@@ -0,0 +1,59 @@
+/*
+   Copyright The containerd 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 util
+
+import "strings"
+
+// InStringSlice checks whether a string is inside a string slice.
+// Comparison is case insensitive.
+func InStringSlice(ss []string, str string) bool {
+	for _, s := range ss {
+		if strings.EqualFold(s, str) {
+			return true
+		}
+	}
+	return false
+}
+
+// SubtractStringSlice subtracts string from string slice.
+// Comparison is case insensitive.
+func SubtractStringSlice(ss []string, str string) []string {
+	var res []string
+	for _, s := range ss {
+		if strings.EqualFold(s, str) {
+			continue
+		}
+		res = append(res, s)
+	}
+	return res
+}
+
+// MergeStringSlices merges 2 string slices into one and remove duplicated elements.
+func MergeStringSlices(a []string, b []string) []string {
+	set := map[string]struct{}{}
+	for _, s := range a {
+		set[s] = struct{}{}
+	}
+	for _, s := range b {
+		set[s] = struct{}{}
+	}
+	var ss []string
+	for s := range set {
+		ss = append(ss, s)
+	}
+	return ss
+}