pathcanon.c   [plain text]

#pragma prototyped
/*
 * Glenn Fowler
 * AT&T Labs Research
 *
 * in-place path name canonicalization -- preserves the logical view
 * pointer to trailing 0 in path returned
 *
 *	remove redundant .'s and /'s
 *	move ..'s to the front
 *	/.. preserved (for pdu and newcastle hacks)
 *	FS_3D handles ...
 *	if (flags&PATH_PHYSICAL) then symlinks resolved at each component
 *	if (flags&PATH_DOTDOT) then each .. checked for access
 *	if (flags&PATH_EXISTS) then path must exist at each component
 *	if (flags&PATH_VERIFIED(n)) then first n chars of path exist
 * 
 * longer pathname possible if (flags&PATH_PHYSICAL) or FS_3D ... involved
 * 0 returned on error and if (flags&(PATH_DOTDOT|PATH_EXISTS)) then path
 * will contain the components following the failure point
 */

#include <ast.h>
/* #include <ls.h> */
/* #include <fs3d.h> */
#include <errno.h>
#include <error.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>

char*
pathcanon(char* path, int flags)
{
	register char*	p;
	register char*	r;
	register char*	s;
	register char*	t;
	register int	dots;
	char*		phys;
	char*		v;
	int		loop;
	int		oerrno;
#if defined(FS_3D)
	long		visits = 0;
#endif

	oerrno = errno;
	dots = loop = 0;
	phys = path;
	v = path + ((flags >> 5) & 01777);
	if (*path == '/' && *(path + 1) == '/')
		do path++; while (*path == '/' && *(path + 1) == '/');
	p = r = s = t = path;
	for (;;) switch (*t++ = *s++)
	{
	case '.':
		dots++;
		break;
	case 0:
		s--;
		/*FALLTHROUGH*/
	case '/':
		while (*s == '/') s++;
		switch (dots)
		{
		case 1:
			t -= 2;
			break;
		case 2:
			if ((flags & (PATH_DOTDOT|PATH_EXISTS)) == PATH_DOTDOT && (t - 2) >= v)
			{
				struct stat	st;

				*(t - 2) = 0;
				if (stat(phys, &st))
				{
					strcpy(path, s);
					return 0;
				}
				*(t - 2) = '.';
			}
#if PRESERVE_TRAILING_SLASH
			if (t - 5 < r) r = t;
#else
			if (t - 5 < r)
			{
				if (t - 4 == r) t = r + 1;
				else r = t;
			}
#endif
			else for (t -= 5; t > r && *(t - 1) != '/'; t--);
			break;
		case 3:
#if defined(FS_3D)
			{
				char*		x;
				char*		o;
				int		c;

				o = t;
				if ((t -= 5) <= path) t = path + 1;
				c = *t;
				*t = 0;
				if (x = pathnext(phys, s - (*s != 0), &visits))
				{
					r = path;
					if (t == r + 1) x = r;
					v = s = t = x;
				}
				else
				{
					*t = c;
					t = o;
				}
			}
#else
			r = t;
#endif
			break;
		default:
			if ((flags & PATH_PHYSICAL) && loop < 32 && (t - 1) > path)
			{
				int	c;
				char	buf[PATH_MAX];

				c = *(t - 1);
				*(t - 1) = 0;
				dots = pathgetlink(phys, buf, sizeof(buf));
				*(t - 1) = c;
				if (dots > 0)
				{
					loop++;
					strcpy(buf + dots, s - (*s != 0));
					if (*buf == '/') p = r = path;
					v = s = t = p;
					strcpy(p, buf);
				}
				else if (dots < 0 && errno == ENOENT)
				{
					if (flags & PATH_EXISTS)
					{
						strcpy(path, s);
						return 0;
					}
					flags &= ~(PATH_PHYSICAL|PATH_DOTDOT);
				}
				dots = 4;
			}
			break;
		}
		if (dots >= 4 && (flags & PATH_EXISTS) && (t - 1) >= v && (t > path + 1 || (t > path && *(t - 1) && *(t - 1) != '/')))
		{
			struct stat	st;

			*(t - 1) = 0;
			if (stat(phys, &st))
			{
				strcpy(path, s);
				return 0;
			}
			v = t;
			if (*s) *(t - 1) = '/';
		}
		if (!*s)
		{
			if (t > path && !*(t - 1)) t--;
			if (t == path) *t++ = '.';
#if DONT_PRESERVE_TRAILING_SLASH
			else if (t > path + 1 && *(t - 1) == '/') t--;
#else
			else if ((s <= path || *(s - 1) != '/') && t > path + 1 && *(t - 1) == '/') t--;
#endif
			*t = 0;
			errno = oerrno;
			return t;
		}
		dots = 0;
		p = t;
		break;
	default:
		dots = 4;
		break;
	}
}