string-helper: add str_space_only()

include/common/string-helpers.h

@@ -9,6 +9,12 @@
  */
 bool string_null_or_empty(const char *s);
 
+/**
+ * str_space_only - Check if the string only contains white-space characters
+ * @s: string to check
+ */
+bool str_space_only(const char *s);
+
 /**
  * trim_last_field() - Trim last field of string splitting on provided delim
  * @buf: string to trim

src/common/string-helpers.c

@@ -204,3 +204,14 @@ str_equal(const char *a, const char *b)
 {
 	return a == b || (a && b && !strcmp(a, b));
 }
+
+bool
+str_space_only(const char *s)
+{
+	for (; *s; s++) {
+		if (!isspace(*s)) {
+			return false;
+		}
+	}
+	return true;
+}