/*
 * Count how many bytes str would contain if it would be rss escapped
 */
static int
rss_escaped_len(const char *str)
{
  int i;
  int len = 0;

  for(i=0; i<strlen(str); i++) {
    switch (str[i]) {
    case '>':
    case '<':
      len += 4;
      break;

    case '&':
      len += 5;
      break;

    case '\"':
    case '\'':
      len += 6;
      break;

    default:
      len++;
      break;
    }
  }

  return len;
}


/*
 * RSS (xml) escape a string
 */
static const char*
rss_escape(const char *str)
{
  static char buf[1024];
  char esc[7];
  int esc_len;
  char *p;
  char *p_end;
  int len;
  int i;

  len = rss_escaped_len(str);
  len = MIN(len, sizeof(buf) - 1);

  p = buf;
  p_end = buf + len;

  memset(buf, 0, sizeof(buf));

  for(i=0; i<strlen(str); i++) {

    switch (str[i]) {
    case '<':
      strcpy(esc, "&lt;");
      break;

    case '>':
      strcpy(esc, "&gt;");
      break;

    case '&':
      strcpy(esc, "&amp;");
      break;

    case '\"':
      strcpy(esc, "&quot;");
      break;

    case '\'':
      strcpy(esc, "&apos;");
      break;

    default:
      esc[0] = str[i];
      esc[1] = 0;
      break;
    }

    esc_len = strlen(esc);

    if(p_end < p+esc_len)
      break;

    strcpy(p, esc);
    p += esc_len;
  }

  p[len] = '\0';

  return buf;
}