kubectl: Move utility functions to util package

`parseFileSource()` and `parseLiteralSource()` are utility functions.
We have a package already for utility functions, `kubectl/util/`.

Move utility functions to `kubectl/util`, capitalize function names to
export from package.

pkg/kubectl/util/util.go

@@ -18,7 +18,10 @@ package util
 
 import (
 	"crypto/md5"
+	"errors"
 	"fmt"
+	"path"
+	"strings"
 	"time"
 
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -44,3 +47,45 @@ func HashObject(obj runtime.Object, codec runtime.Codec) (string, error) {
 	}
 	return fmt.Sprintf("%x", md5.Sum(data)), nil
 }
+
+// ParseFileSource parses the source given.
+//
+//  Acceptable formats include:
+//   1.  source-path: the basename will become the key name
+//   2.  source-name=source-path: the source-name will become the key name and
+//       source-path is the path to the key file.
+//
+// Key names cannot include '='.
+func ParseFileSource(source string) (keyName, filePath string, err error) {
+	numSeparators := strings.Count(source, "=")
+	switch {
+	case numSeparators == 0:
+		return path.Base(source), source, nil
+	case numSeparators == 1 && strings.HasPrefix(source, "="):
+		return "", "", fmt.Errorf("key name for file path %v missing.", strings.TrimPrefix(source, "="))
+	case numSeparators == 1 && strings.HasSuffix(source, "="):
+		return "", "", fmt.Errorf("file path for key name %v missing.", strings.TrimSuffix(source, "="))
+	case numSeparators > 1:
+		return "", "", errors.New("Key names or file paths cannot contain '='.")
+	default:
+		components := strings.Split(source, "=")
+		return components[0], components[1], nil
+	}
+}
+
+// ParseLiteralSource parses the source key=val pair into its component pieces.
+// This functionality is distinguished from strings.SplitN(source, "=", 2) since
+// it returns an error in the case of empty keys, values, or a missing equals sign.
+func ParseLiteralSource(source string) (keyName, value string, err error) {
+	// leading equal is invalid
+	if strings.Index(source, "=") == 0 {
+		return "", "", fmt.Errorf("invalid literal source %v, expected key=value", source)
+	}
+	// split after the first equal (so values can have the = character)
+	items := strings.SplitN(source, "=", 2)
+	if len(items) != 2 {
+		return "", "", fmt.Errorf("invalid literal source %v, expected key=value", source)
+	}
+
+	return items[0], items[1], nil
+}