* @param[out] str Pointer to resuling string
* @return zero on success, non-zero on failure
*/
* @param[out] str Pointer to resuling string
* @return zero on success, non-zero on failure
*/
-static int read_string(void *ctx, char **pos, unsigned int *len, char **str)
+static int read_string(void *ctx, const char **pos, unsigned int *len,
+ char **str)