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

From: Kazuhiro Ito <[email-masked]>
Date: Fri, 03 Apr 2020 23:08:10 +0900

> Thanks for that. This should fix all those cases:

Thank you for the patch.  It works well on Cygwin environment.  But I
noticed different problems in dns-query when TCP is used.

1. dns-write function needs to be called with TCP-P option.
2. First 2 bytes of received data (length field) should be truncated
for dns-read function.  Or dns-read function should accept TCP-P
option like dns-wrote function.

> diff --git a/lisp/net/dns.el b/lisp/net/dns.el
> index 78d4827162..177df4e332 100644
> --- a/lisp/net/dns.el
> +++ b/lisp/net/dns.el
> @@ -315,8 +315,8 @@ dns-servers-up-to-date-p
>  (defun dns-set-servers ()
>    "Set `dns-servers' to a list of DNS servers or nil if none are found.
>  Parses \"/etc/resolv.conf\" or calls \"nslookup\"."
> +  (setq dns-servers nil)
>    (or (when (file-exists-p "/etc/resolv.conf")
> -	(setq dns-servers nil)
>  	(with-temp-buffer
>  	  (insert-file-contents "/etc/resolv.conf")
>  	  (goto-char (point-min))
> @@ -327,9 +327,9 @@ dns-set-servers
>  	(with-temp-buffer
>  	  (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)
> -	  (setq dns-servers (list (match-string 1))))))
> +          (when (re-search-forward
> +	   "^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))))
>  
> @@ -357,7 +357,9 @@ dns-make-network-process
>    `(let ((server ,server)
>  	 (coding-system-for-read 'binary)
>  	 (coding-system-for-write 'binary))
> -     (if (fboundp 'make-network-process)
> +     (if (and
> +          (fboundp 'make-network-process)
> +          (featurep 'make-network-process '(:type datagram)))
>  	 (make-network-process
>  	  :name "dns"
>  	  :coding 'binary
> @@ -365,9 +367,9 @@ dns-make-network-process
>  	  :host server
>  	  :service "domain"
>  	  :type 'datagram)
> -       ;; Older versions of Emacs doesn't have
> -       ;; `make-network-process', so we fall back on opening a TCP
> -       ;; connection to the DNS server.
> +       ;; Older versions of Emacs do not have `make-network-process',
> +       ;; and on MS-Windows datagram sockets are not supported, so we
> +       ;; fall back on opening a TCP connection to the DNS server.
>         (open-network-stream "dns" (current-buffer) server "domain"))))
>  
>  (defvar dns-cache (make-vector 4096 0))
> @@ -400,7 +402,9 @@ dns-query
>  	  type 'PTR))
>  
>    (if (not dns-servers)
> -      (message "No DNS server configuration found")
> +      (progn
> +        (message "No DNS server configuration found")
> +        nil)
>      (with-temp-buffer
>        (set-buffer-multibyte nil)
>        (let ((process (condition-case ()

-- 
Kazuhiro Ito