micro-utils/libmu/parse_mode.h

#ifndef _PARSE_MODE_H
#define _PARSE_MODE_H

#include <sys/stat.h>

#define U(x) (x << 6)
#define G(x) (x << 3)
#define O(x) (x)
#define A(x) (U(x) | G(x) | O(x))

#define WR_PERM (2)
#define EX_PERM (1)
#define RD_PERM (4)
#define FULL_PERM (7)

mode_t mu_parse_mode(const char *s, mode_t cur_mode) {
	char *p = NULL;

	mode_t mode = (mode_t)strtol(s, &p, 8);
	if (!*p && mode < 07777U)
		return mode;

	else if (mode > 07777U)
		return 0;

	mode = 0;
	int append = 1;
	mode_t mask = 0;

	for (size_t i = 0; i < strlen(s); i++) {
		switch (s[i]) {
			case 'r':
				mode |= A(RD_PERM);
				break;

			case 'w':
				mode |= A(WR_PERM);
				break;

			case 'x':
				mode |= A(EX_PERM);
				break;

			case '+':
				append = 1;
				break;

			case '-':
				append = 0;
				break;

			case 'g':
				mask |= G(FULL_PERM);
				break;

			case 'u':
				mask |= U(FULL_PERM);
				break;

			case 'o':
				mask |= O(FULL_PERM);
				break;

			case 'a':
				mask |= A(FULL_PERM);
				break;

			default:
				return 0;
		}
	}

	if (mask == 0)
		mask = U(FULL_PERM);

	mask = mask & mode;
	if (!append)
		mode = ~mode;

	return (cur_mode & ~mask) | (mode & mask);
}

#endif