schema: improve errors, disallow dangling spaces.

schema/helpers.go

@@ -0,0 +1,25 @@
+package schema
+
+import (
+	"unicode"
+	"unicode/utf8"
+)
+
+// isTrimmed checks if strings.TrimSpace(v) == v, i.e. that the value doesn't have dangling spaces
+func isTrimmed(s string) bool {
+	if len(s) == 0 {
+		return true
+	}
+
+	first, _ := utf8.DecodeRuneInString(s)
+	if unicode.IsSpace(first) {
+		return false
+	}
+
+	last, _ := utf8.DecodeLastRuneInString(s)
+	if unicode.IsSpace(last) {
+		return false
+	}
+
+	return true
+}