micro-utils/libmu/parse_mode.c

#include <stdlib.h>
#include <string.h>
#include "parse_mode.h"

#define U (S_ISUID | S_IRWXU)
#define G (S_ISGID | S_IRWXG)
#define O (S_IRWXO)
#define A (U | G | O)

#define WR_PERM (S_IWUSR | S_IWGRP | S_IWOTH)
#define EX_PERM (S_IXUSR | S_IXGRP | S_IXOTH)
#define RD_PERM (S_IRUSR | S_IRGRP | S_IROTH)
#define SU_PERM (S_ISUID | S_ISGID | S_ISVTX)
#define FULL_PERM (WR_PERM | EX_PERM | RD_PERM)

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;

	/* Default + */
	char append = 1;
	mode_t mask = 0;

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

			case 'w':
				mode |= WR_PERM;
				break;

			case 'x':
				mode |= EX_PERM;
				break;

			case 's':
				mode |= SU_PERM;
				break;

			case '+':
				append = 1;
				break;

			case '-':
				append = 0;
				break;

			case '=':
				append = 2;
				break;

			case 'g':
				mask |= G;
				break;

			case 'u':
				mask |= U;
				break;

			case 'o':
				mask |= O;
				break;

			case 'a':
				mask |= A;
				break;

			default:
				return 0;
		}
	}

	if (mask == 0)
		mask = U;

	mask &= mode;
	if (append == 0)
		mode = ~mode;

	if (append == 2)
		return mode & mask;

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