string-util: add common implementation of function that converts sized character buffers to NUL terminated C strings

src/basic/string-util.h

@@ -239,6 +239,16 @@ bool streq_skip_trailing_chars(const char *s1, const char *s2, const char *ok);
 
 char *string_replace_char(char *str, char old_char, char new_char);
 
+typedef enum MakeCStringMode {
+        MAKE_CSTRING_REFUSE_TRAILING_NUL,
+        MAKE_CSTRING_ALLOW_TRAILING_NUL,
+        MAKE_CSTRING_REQUIRE_TRAILING_NUL,
+        _MAKE_CSTRING_MODE_MAX,
+        _MAKE_CSTRING_MODE_INVALID = -1,
+} MakeCStringMode;
+
+int make_cstring(const char *s, size_t n, MakeCStringMode mode, char **ret);
+
 size_t strspn_from_end(const char *str, const char *accept);
 
 char *strdupspn(const char *a, const char *accept);