Start api directory, which will become a module.

api/hasher/hasher.go

@@ -0,0 +1,52 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package hasher
+
+import (
+	"crypto/sha256"
+	"encoding/json"
+	"fmt"
+	"sort"
+)
+
+// SortArrayAndComputeHash sorts a string array and
+// returns a hash for it
+func SortArrayAndComputeHash(s []string) (string, error) {
+	sort.Strings(s)
+	data, err := json.Marshal(s)
+	if err != nil {
+		return "", err
+	}
+	return Encode(Hash(string(data)))
+}
+
+// Copied from https://github.com/kubernetes/kubernetes
+// /blob/master/pkg/kubectl/util/hash/hash.go
+func Encode(hex string) (string, error) {
+	if len(hex) < 10 {
+		return "", fmt.Errorf(
+			"input length must be at least 10")
+	}
+	enc := []rune(hex[:10])
+	for i := range enc {
+		switch enc[i] {
+		case '0':
+			enc[i] = 'g'
+		case '1':
+			enc[i] = 'h'
+		case '3':
+			enc[i] = 'k'
+		case 'a':
+			enc[i] = 'm'
+		case 'e':
+			enc[i] = 't'
+		}
+	}
+	return string(enc), nil
+}
+
+// Hash returns the hex form of the sha256 of the argument.
+func Hash(data string) string {
+	return fmt.Sprintf("%x", sha256.Sum256([]byte(data)))
+}

api/hasher/hasher_test.go

@@ -0,0 +1,41 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package hasher_test
+
+import (
+	"testing"
+
+	. "sigs.k8s.io/kustomize/v3/api/hasher"
+)
+
+func TestSortArrayAndComputeHash(t *testing.T) {
+	array1 := []string{"a", "b", "c", "d"}
+	array2 := []string{"c", "b", "d", "a"}
+	h1, err := SortArrayAndComputeHash(array1)
+	if err != nil {
+		t.Errorf("unexpected error %v", err)
+	}
+	if h1 == "" {
+		t.Errorf("failed to hash %v", array1)
+	}
+	h2, err := SortArrayAndComputeHash(array2)
+	if err != nil {
+		t.Errorf("unexpected error %v", err)
+	}
+	if h2 == "" {
+		t.Errorf("failed to hash %v", array2)
+	}
+	if h1 != h2 {
+		t.Errorf("hash is not consistent with reordered list: %s %s", h1, h2)
+	}
+}
+
+func TestHash(t *testing.T) {
+	// hash the empty string to be sure that sha256 is being used
+	expect := "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+	sum := Hash("")
+	if expect != sum {
+		t.Errorf("expected hash %q but got %q", expect, sum)
+	}
+}