C function to strip leading and trailing whitespace from a line of text

configfile.c

/*
 * written by kyle isom <[email protected]>
 * license: isc / public domain dual license
 * one of the functions i wrote for the lurker project
 *     (https://github.com/kisom/lurker) 
 *
 * C function to strip leading and trailing whitespace 
 * from a string
 * added as a gist because I am not near a compiler or editor and want to commit
 * my notes to memory
 */

/*
 * Internal function to strip the leading and trailing whitespace off a line 
 * of text.
 *     arguments:
 *         - buffer: a line of text. in lurker, this is already guaranteed 
 *           to be an allocated buffer with a line of text in it, and it is
 *           guaranteed not to have any newlines or carriage returns. if it 
 *           is used elsewhere, the checks may need to be tweaked.
 *     returns:
 *         - NULL on function failure (i.e. malloc error, NULL string passed 
 *           in, empty string passed in)
 *         - char * pointer to a string containing the stripped string
 *           IMPORTANT: this will need to be freed by the caller.
 */
char
*strip(char *buf)
{
        size_t start, end;
        char *l_start, *l_end, *stripped;
        size_t buf_sz, strip_sz;
        short int found_start, found_end;

        buf_sz = 0;
        strip_sz = 0;
        found_start = 0;        /* set to 1 to stop searching */
        found_end   = 0;
        start = 0;

        /* 
         * Ensure we aren't dealing with a single char or unallocated
         * buffer.
         */
        if ((NULL == buf) || ('\0' == buf[0]))
            return NULL;

        /* Figure out the size of the buffer. */
        while ('\0' != buf[++buf_sz]) { }

        end = strlen(buf);

        /* 
         * Stop conditions: the pointers meet and haven't found the
         * first and last non-whitespace characters.
         */
        while ((start < end) && !(found_start && found_end)) {
            if (!found_start)
                switch (buf[start]) {
                case ' ':
                case '\t':
                    start++;
                    break;
                default:
                    found_start = 1;
                    break;
                }

            if (!found_end)
                switch (buf[end]) {
                case ' ':
                case '\t':
                case '\0':
                    end--;
                    break;
                default:
                    end++;
                    found_end = 1;
                    break;
                }
        }

        strip_sz = end - start; 
        if (0 == strip_sz)
            return NULL;

        stripped = calloc(strip_sz + 1, sizeof(char));
        if (NULL == stripped)
            return NULL;

        snprintf(stripped, strip_sz + 1, "%s", buf + start);

        return stripped;
}