[patch] Re: getfsent(3) and spaces in fstab

mitrohin a.s. swp at uni-altai.ru
Mon Aug 4 19:07:24 PDT 2003


On Mon, Aug 04, 2003 at 02:33:31AM +0200, Simon Barner wrote:
> Hi Terry,
> 
> > You need to add '\\' to the list of characters that can be escaped,
> > or you've just traded the inability to specify '\t' or ' ' for an
> > inability to speciy '\\'.
> 
> Oh yes, I have overlook this special case. I revised my patch in order
> to get this right.
> 
> Simon

helo.

imho - expensive algorithm... i want to see anything more simple... 
like "gtok()" instead "es_strsep() + remove_escapes()"?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *gtok(char **s, char const *delim)
{
	int quoted, escaped;
	static char const esc_set[] = {  't',  'r',  'n',  'a', 0 };
	static char const esc_rep[] = { '\t', '\r', '\n', '\a', 0 };
	char *tok, *r, *w, *p;

	if (!s || !*s || !*(tok = *s + strspn(*s, delim)) || *tok == '#')
		return NULL;

	for (quoted = escaped = 0, r = w = tok; *r; r++) {
		if (!escaped) {
			if (*r == '\\') {
				escaped = 1;
				continue;
			}
			if (*r == '\"') {
				quoted ^= -1;
				continue;
			}
			if (!quoted && strchr(delim, *r)) {
				r++;
				break;
			}
		} else {
			escaped = 0;
			if ((p = strchr(esc_set, *r)) != NULL) {
				*w++ = esc_rep[p - esc_set];
				continue;
			}
		}
		*w++ = *r;
	}
	*w = 0;
	*s = r;

	return tok;
}

#if 0
main()
{
	char *s, *t, buf[0x1000];

	while (fgets(buf, sizeof buf, stdin))
		for (s = buf; t = gtok(&s, " \t\r\n"); )
			printf("\"%s\"\n", t);

	return 0;
}
#endif

/swp

> --- fstab.c.orig	Fri Aug  1 17:18:00 2003
> +++ fstab.c	Mon Aug  4 01:46:55 2003
> @@ -49,6 +49,7 @@
>  #include <errno.h>
>  #include <fstab.h>
>  #include <paths.h>
> +#include <stdbool.h>
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <string.h>
> @@ -84,6 +85,140 @@
>  	_fs_fstab.fs_spec = buf;
>  }
>  
> +/*
> + * Get next token from string *stringp, where tokens are possibly-empty
> + * strings separated by characters from delim.
> + *
> + * Writes NULs into the string at *stringp to end tokens.
> + * delim need not remain constant from call to call.
> + * On return, *stringp points past the last NUL written (if there might
> + * be further tokens), or is NULL (if there are definitely no more tokens).
> + *
> + * If *stringp is NULL, es_strsep returns NULL.
> + *
> + * In contrast to strsep(3), es_strsep will allow escaped delimiters
> + * within a token. These escaped characters as well as the special case
> + * '\\' will be converted appropriately ('\<delim>' -> '<delim>, '\\' -> '\'
> + *
> + */
> +char *
> +es_strsep(char **stringp, const char *delim)
> +{
> +	bool	escaped=false;
> +	char	*s, *t, *u;
> +	int	i;
> +
> +
> +	if (*stringp == '\0')	/* empty string */
> +		return NULL;
> +	s = *stringp;
> +	s += strspn (s, delim);	/* skip delimiters */
> +
> +	if (*s == '\0')		/* string consists only of delimiters */
> +		return NULL;
> +	
> +	/*
> +	 * skip a string consisting of non-delimiters,
> +	 * escapted delimiters or '\\'
> +	*/
> +	for (t = s; *t != '\0'; ++t) {
> +		if (*t == '\\') {
> +		    if (escaped) {	/* convert \\ to \ */
> +			--t;
> +		        u = t;
> +		        escaped = false;
> +		        while (u[0] != '\0') {
> +		            u[0] = u[1];
> +		            ++u;
> +		        }
> +		    } else		/* start \-Sequence */
> +			escaped = true;
> +		    continue;
> +		}
> +		
> +		/* search for delimiter */
> +		for (i=0; delim[i] != '\0'; ++i) {
> +		    if (*t == delim[i])
> +		        break;
> +		}
> +		
> +		/* un-escaped delimiter found => end of token */
> +		if (!escaped && delim[i] != '\0')
> +		    break;
> +		    
> +		/* escaped delimiter found => remove / */
> +		if (escaped) {
> +    		    --t;
> +	            u = t;
> +                    escaped = false;
> +		    while (u[0] != '\0') {
> +		        u[0] = u[1];
> +		        ++u;
> +		    }
> +		}
> +	}
> +
> +	if (*t != '\0') {
> +		*t = '\0';		/* end current token */
> +		*stringp = t+1;		/* *t != '\0' => *(t+1) is valid */
> +	} else
> +		*stringp = 0;		/* end of string reached */	
> +	
> +	return s;			/* return current token */
> +}
> +
> +/*
> + * This function converts escaped characters:
> + * '\<delim>' -> '<delim>', '\\' -> '\'
> + * 
> + * If there are unescaped delimiters, 'false' will be return to indicate
> + * an error, otherwise remove_escape returns 'true'.
> + */
> +bool remove_escapes (char **s, const char* delim) {
> +	bool	escaped=false;
> +	char	*t, *u;
> +	int	i;
> +	
> +	for (t = *s; *t != '\0'; ++t) {
> +		if (*t == '\\') {
> +		    if (escaped) {	/* convert \\ to \ */
> +			--t;
> +		        u = t;
> +		        escaped = false;
> +		        while (u[0] != '\0') {
> +		            u[0] = u[1];
> +		            ++u;
> +		        }
> +		    } else		/* start \-Sequence */
> +			escaped = true;
> +		    continue;
> +		}
> +		
> +		/* search for delimiter */
> +		for (i=0; delim[i] != '\0'; ++i) {
> +		    if (*t == delim[i])
> +		        break;
> +		}
> +		
> +		/* un-escaped delimiter found => error */
> +		if (!escaped && delim[i] != '\0')
> +			return false;
> +
> +		/* escaped delimiter found => remove / */
> +		if (escaped) {
> +    		    --t;
> +	            u = t;
> +                    escaped = false;
> +		    while (u[0] != '\0') {
> +		        u[0] = u[1];
> +		        ++u;
> +		    }
> +		}
> +	}
> +	
> +	return true;
> +}
> +
>  static int
>  fstabscan()
>  {
> @@ -101,9 +236,19 @@
>  		++LineNo;
>  		if (*line == '#' || *line == '\n')
>  			continue;
> -		if (!strpbrk(p, " \t")) {
> +
> +		/* escapted white-spaces only are allowed in old-style format */
> +		cp = p;
> +		while ((cp = strpbrk(cp, " \t")) != 0 &&
> +			cp != p && cp[-1] == '\\')
> +			++cp;
> +		if (cp == 0) {
>  			_fs_fstab.fs_spec = strsep(&p, ":\n");
> +			if (!remove_escapes (&_fs_fstab.fs_spec, " \t"))
> +			    goto bad;
>  			_fs_fstab.fs_file = strsep(&p, ":\n");
> +			if (!remove_escapes (&_fs_fstab.fs_file, " \t"))
> +			    goto bad;
>  			fixfsfile();
>  			_fs_fstab.fs_type = strsep(&p, ":\n");
>  			if (_fs_fstab.fs_type) {
> @@ -124,13 +269,15 @@
>  			goto bad;
>  		}
>  /* OLD_STYLE_FSTAB */
> -		while ((cp = strsep(&p, " \t\n")) != NULL && *cp == '\0')
> +		while ((cp = es_strsep(&p, " \t\n")) != NULL && *cp == '\0')
>  			;
>  		_fs_fstab.fs_spec = cp;
>  		if (!_fs_fstab.fs_spec || *_fs_fstab.fs_spec == '#')
>  			continue;
> -		while ((cp = strsep(&p, " \t\n")) != NULL && *cp == '\0')
> +		while ((cp = es_strsep(&p, " \t\n")) != NULL && *cp == '\0')
>  			;
> +		if (cp == 0)
> +			goto bad;
>  		_fs_fstab.fs_file = cp;
>  		fixfsfile();
>  		while ((cp = strsep(&p, " \t\n")) != NULL && *cp == '\0')





More information about the freebsd-hackers mailing list