url: convert the zone id from a IPv6 URL to correct scope id

  if(hostname[0] == '[') {

    /* This looks like an IPv6 address literal. See if there is an address

       scope. */

    char *percent = strchr(++hostname, '%');

    char *zoneid;

    size_t hlen;

    uc = curl_url_get(uh, CURLUPART_ZONEID, &zoneid, 0);

    conn->bits.ipv6_ip = TRUE;

    if(percent) {

      unsigned int identifier_offset = 3;

    /* cut off the brackets! */

    hostname++;

    hlen = strlen(hostname);

    hostname[hlen - 1] = 0;

    if(!uc && zoneid) {

      char *endp;

      unsigned long scope;

      if(strncmp("%25", percent, 3) != 0) {

        infof(data,

              "Please URL encode %% as %%25, see RFC 6874.\n");

        identifier_offset = 1;

      }

      scope = strtoul(percent + identifier_offset, &endp, 10);

      if(*endp == ']') {

        /* The address scope was well formed.  Knock it out of the

           hostname. */

        memmove(percent, endp, strlen(endp) + 1);

      scope = strtoul(zoneid, &endp, 10);

      if(!*endp && (scope < UINT_MAX)) {

        /* A plain number, use it direcly as a scope id. */

        conn->scope_id = (unsigned int)scope;

      }

#ifdef HAVE_IF_NAMETOINDEX

      else {

        /* Zone identifier is not numeric */

#if defined(HAVE_NET_IF_H) && defined(IFNAMSIZ) && defined(HAVE_IF_NAMETOINDEX)

        char ifname[IFNAMSIZ + 2];

        char *square_bracket;

        unsigned int scopeidx = 0;

        strncpy(ifname, percent + identifier_offset, IFNAMSIZ + 2);

        /* Ensure nullbyte termination */

        ifname[IFNAMSIZ + 1] = '\0';

        square_bracket = strchr(ifname, ']');

        if(square_bracket) {

          /* Remove ']' */

          *square_bracket = '\0';

          scopeidx = if_nametoindex(ifname);

          if(scopeidx == 0) {

            infof(data, "Invalid network interface: %s; %s\n", ifname,

        scopeidx = if_nametoindex(zoneid);

        if(!scopeidx)

          infof(data, "Invalid zoneid id: %s; %s\n", zoneid,

                strerror(errno));

          }

        }

        if(scopeidx > 0) {

          char *p = percent + identifier_offset + strlen(ifname);

          /* Remove zone identifier from hostname */

          memmove(percent, p, strlen(p) + 1);

          conn->scope_id = scopeidx;

        }

        else

#endif /* HAVE_NET_IF_H && IFNAMSIZ */

          infof(data, "Invalid IPv6 address format\n");

          conn->scope_id = scopeidx;

      }

#endif /* HAVE_IF_NAMETOINDEX */

      free(zoneid);

    }

    percent = strchr(hostname, ']');

    if(percent)

      /* terminate IPv6 numerical at end bracket */

      *percent = 0;

  }

  /* make sure the connect struct gets its own copy of the host name */