real_path_internal(): add comment explaining use of cwd

[thirdparty/git.git] / abspath.c

#include "cache.h"

/*
 * Do not use this for inspecting *tracked* content.  When path is a
 * symlink to a directory, we do not want to say it is a directory when
 * dealing with tracked content in the working tree.
 */
int is_directory(const char *path)
{
	struct stat st;
	return (!stat(path, &st) && S_ISDIR(st.st_mode));
}

/* We allow "recursive" symbolic links. Only within reason, though. */
#define MAXDEPTH 5

/*
 * Return the real path (i.e., absolute path, with symlinks resolved
 * and extra slashes removed) equivalent to the specified path.  (If
 * you want an absolute path but don't mind links, use
 * absolute_path().)  The return value is a pointer to a static
 * buffer.
 *
 * The input and all intermediate paths must be shorter than MAX_PATH.
 * The directory part of path (i.e., everything up to the last
 * dir_sep) must denote a valid, existing directory, but the last
 * component need not exist.  If die_on_error is set, then die with an
 * informative error message if there is a problem.  Otherwise, return
 * NULL on errors (without generating any output).
 *
 * If path is our buffer, then return path, as it's already what the
 * user wants.
 */
static const char *real_path_internal(const char *path, int die_on_error)
{
	static char bufs[2][PATH_MAX + 1], *buf = bufs[0], *next_buf = bufs[1];
	char *retval = NULL;

	/*
	 * If we have to temporarily chdir(), store the original CWD
	 * here so that we can chdir() back to it at the end of the
	 * function:
	 */
	char cwd[1024] = "";

	int buf_index = 1;

	int depth = MAXDEPTH;
	char *last_elem = NULL;
	struct stat st;

	/* We've already done it */
	if (path == buf || path == next_buf)
		return path;

	if (!*path) {
		if (die_on_error)
			die("The empty string is not a valid path");
		else
			goto error_out;
	}

	if (strlcpy(buf, path, PATH_MAX) >= PATH_MAX) {
		if (die_on_error)
			die("Too long path: %.*s", 60, path);
		else
			goto error_out;
	}

	while (depth--) {
		if (!is_directory(buf)) {
			char *last_slash = find_last_dir_sep(buf);
			if (last_slash) {
				last_elem = xstrdup(last_slash + 1);
				last_slash[1] = '\0';
			} else {
				last_elem = xstrdup(buf);
				*buf = '\0';
			}
		}

		if (*buf) {
			if (!*cwd && !getcwd(cwd, sizeof(cwd))) {
				if (die_on_error)
					die_errno("Could not get current working directory");
				else
					goto error_out;
			}

			if (chdir(buf)) {
				if (die_on_error)
					die_errno("Could not switch to '%s'", buf);
				else
					goto error_out;
			}
		}
		if (!getcwd(buf, PATH_MAX)) {
			if (die_on_error)
				die_errno("Could not get current working directory");
			else
				goto error_out;
		}

		if (last_elem) {
			size_t len = strlen(buf);
			if (len + strlen(last_elem) + 2 > PATH_MAX) {
				if (die_on_error)
					die("Too long path name: '%s/%s'",
					    buf, last_elem);
				else
					goto error_out;
			}
			if (len && !is_dir_sep(buf[len-1]))
				buf[len++] = '/';
			strcpy(buf + len, last_elem);
			free(last_elem);
			last_elem = NULL;
		}

		if (!lstat(buf, &st) && S_ISLNK(st.st_mode)) {
			ssize_t len = readlink(buf, next_buf, PATH_MAX);
			if (len < 0) {
				if (die_on_error)
					die_errno("Invalid symlink '%s'", buf);
				else
					goto error_out;
			}
			if (PATH_MAX <= len) {
				if (die_on_error)
					die("symbolic link too long: %s", buf);
				else
					goto error_out;
			}
			next_buf[len] = '\0';
			buf = next_buf;
			buf_index = 1 - buf_index;
			next_buf = bufs[buf_index];
		} else
			break;
	}

	retval = buf;
error_out:
	free(last_elem);
	if (*cwd && chdir(cwd))
		die_errno ("Could not change back to '%s'", cwd);

	return retval;
}

const char *real_path(const char *path)
{
	return real_path_internal(path, 1);
}

static const char *get_pwd_cwd(void)
{
	static char cwd[PATH_MAX + 1];
	char *pwd;
	struct stat cwd_stat, pwd_stat;
	if (getcwd(cwd, PATH_MAX) == NULL)
		return NULL;
	pwd = getenv("PWD");
	if (pwd && strcmp(pwd, cwd)) {
		stat(cwd, &cwd_stat);
		if ((cwd_stat.st_dev || cwd_stat.st_ino) &&
		    !stat(pwd, &pwd_stat) &&
		    pwd_stat.st_dev == cwd_stat.st_dev &&
		    pwd_stat.st_ino == cwd_stat.st_ino) {
			strlcpy(cwd, pwd, PATH_MAX);
		}
	}
	return cwd;
}

/*
 * Use this to get an absolute path from a relative one. If you want
 * to resolve links, you should use real_path.
 *
 * If the path is already absolute, then return path. As the user is
 * never meant to free the return value, we're safe.
 */
const char *absolute_path(const char *path)
{
	static char buf[PATH_MAX + 1];

	if (!*path) {
		die("The empty string is not a valid path");
	} else if (is_absolute_path(path)) {
		if (strlcpy(buf, path, PATH_MAX) >= PATH_MAX)
			die("Too long path: %.*s", 60, path);
	} else {
		size_t len;
		const char *fmt;
		const char *cwd = get_pwd_cwd();
		if (!cwd)
			die_errno("Cannot determine the current working directory");
		len = strlen(cwd);
		fmt = (len > 0 && is_dir_sep(cwd[len-1])) ? "%s%s" : "%s/%s";
		if (snprintf(buf, PATH_MAX, fmt, cwd, path) >= PATH_MAX)
			die("Too long path: %.*s", 60, path);
	}
	return buf;
}

/*
 * Unlike prefix_path, this should be used if the named file does
 * not have to interact with index entry; i.e. name of a random file
 * on the filesystem.
 */
const char *prefix_filename(const char *pfx, int pfx_len, const char *arg)
{
	static char path[PATH_MAX];
#ifndef WIN32
	if (!pfx_len || is_absolute_path(arg))
		return arg;
	memcpy(path, pfx, pfx_len);
	strcpy(path + pfx_len, arg);
#else
	char *p;
	/* don't add prefix to absolute paths, but still replace '\' by '/' */
	if (is_absolute_path(arg))
		pfx_len = 0;
	else if (pfx_len)
		memcpy(path, pfx, pfx_len);
	strcpy(path + pfx_len, arg);
	for (p = path + pfx_len; *p; p++)
		if (*p == '\\')
			*p = '/';
#endif
	return path;
}