1 files changed, 43 insertions, 0 deletions
diff --git a/pkg/name/check.go b/pkg/name/check.go
new file mode 100644
index 0000000..e9a240a
--- /dev/null
+++ b/pkg/name/check.go
@@ -0,0 +1,43 @@
+// Copyright 2018 Google LLC All Rights Reserved.
+//
+// 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 name
+
+import (
+	"strings"
+	"unicode/utf8"
+)
+
+// stripRunesFn returns a function which returns -1 (i.e. a value which
+// signals deletion in strings.Map) for runes in 'runes', and the rune otherwise.
+func stripRunesFn(runes string) func(rune) rune {
+	return func(r rune) rune {
+		if strings.ContainsRune(runes, r) {
+			return -1
+		}
+		return r
+	}
+}
+
+// checkElement checks a given named element matches character and length restrictions.
+// Returns true if the given element adheres to the given restrictions, false otherwise.
+func checkElement(name, element, allowedRunes string, minRunes, maxRunes int) error {
+	numRunes := utf8.RuneCountInString(element)
+	if (numRunes < minRunes) || (maxRunes < numRunes) {
+		return newErrBadName("%s must be between %d and %d characters in length: %s", name, minRunes, maxRunes, element)
+	} else if len(strings.Map(stripRunesFn(allowedRunes), element)) != 0 {
+		return newErrBadName("%s can only contain the characters `%s`: %s", name, allowedRunes, element)
+	}
+	return nil
+}