bug#40343: 28.0.50; dns-set-servers fails on IPv6 available Windows

[Robert Pluim]

>>>>> On Tue, 31 Mar 2020 20:06:50 +0900, Kazuhiro Ito <kzhr@d1.dion.ne.jp> 
>>>>> said:

    Kazuhiro> dns-set-servers function fails to set dns-servers on Windows with 
IPv6
    Kazuhiro> available network.
    >> 
    Kazuhiro> (progn
    Kazuhiro> (require 'dns)
    Kazuhiro> (dns-set-servers)
    Kazuhiro> dns-servers)
    >> 
    -> (nil)
    >> 
    >> dns.el isnʼt going to work on Windows anyway, since Emacs doesnʼt
    >> support UDP network processes on Windows.

    Kazuhiro> Cygwin's Emacs, which seems to support UDP network processes, uses
    Kazuhiro> Windows's nslookup.exe, so has this problem too.  

Thatʼs not a Windows Emacs :-)

    Kazuhiro> # Actually I don't directly use dns.el.  It is gravatar.el which 
uses
    Kazuhiro> # dns.el.

True. We should teach emacs about res_query.

Does this work for you:

diff --git a/lisp/net/dns.el b/lisp/net/dns.el
index 78d4827162..fd2ea99ac6 100644
--- a/lisp/net/dns.el
+++ b/lisp/net/dns.el
@@ -328,7 +328,7 @@ dns-set-servers
          (call-process "nslookup" nil t nil "localhost")
          (goto-char (point-min))
          (re-search-forward
-          "^Address:[ \t]*\\([0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+\\)" nil t)
+          "^Address:[ 
\t]*\\([0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+\\)\\|\\([[:xdigit:]:]*\\)" nil t)
          (setq dns-servers (list (match-string 1))))))
   (when (fboundp 'network-interface-list)
     (setq dns-servers-valid-for-interfaces (network-interface-list))))