bug#40748: 28.0.50; Switching wifi networks hangs dns lookups

bug#40748: 28.0.50; Switching wifi networks hangs dns lookups

[Eric Abrahamsen]

I'm on Emacs master, but this behavior has been evident for quite some
time, a year or two I think.

I often have trouble reconnecting Gnus' nntp servers after sleeping the
laptop in one location, and waking it up in another, connecting to a new
wifi network (I'm using Arch linux, if it matters).

I edebugged `nntp-open-connection', and realized that the error (which
is getting handled by `nnheader-report', that's why I didn't notice it)
is actually a dns error:

(error "news.gmane.io/nntp Temporary failure in name resol...")

Other Emacs network connections behave as normal. But this error for
this particular server persists until I restart Emacs.

Are DNS lookups cached? Cached per connection? Is there anything we can
do to flush whatever's "stuck"?

Here's the code that opens the connection; in my case it's
nntp-open-network-stream/network.

Happy to help with further debugging!

(let ((coding-system-for-read 'binary)
      (coding-system-for-write 'binary)
      (map '((nntp-open-network-stream network)
	     (network-only plain)	; compat
	     (nntp-open-plain-stream plain)
	     (nntp-open-ssl-stream tls)
	     (nntp-open-tls-stream tls))))
  (if (assoc nntp-open-connection-function map)
      (open-network-stream
       "nntpd" pbuffer nntp-address nntp-port-number
       :type (cadr (assoc nntp-open-connection-function map))
       :end-of-command "^\\([2345]\\|[.]\\).*\n"
       :capability-command "HELP\r\n"
       :success "^3"
       :starttls-function
       (lambda (capabilities)
	 (if (not (string-match "STARTTLS" capabilities))
	     nil
	   "STARTTLS\r\n")))
    (funcall nntp-open-connection-function pbuffer)))

bug#40748: 28.0.50; Switching wifi networks hangs dns lookups

[Dmitry Alexandrov]

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> I often have trouble reconnecting Gnus' nntp servers after sleeping the laptop in one location, and waking it up in another, connecting to a new wifi network

> I edebugged `nntp-open-connection', and realized that the error ‹…› is actually a dns error:

Looks familiar!

> Here's the code that opens the connection; in my case it's nntp-open-network-stream/network.

Could not it actually be an even deeper issue I outlined in bug#41234: 27.0.91; Synchronous network requests are failing with “Name or service not known” [1]?

[1] <mid:1rnogg6b.dag@gnui.org>
    <https://bugs.gnu.org/41234>

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bug#40748: 28.0.50; Switching wifi networks hangs dns lookups

[Lars Ingebrigtsen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> So I'm not sure how this can be an Emacs bug -- as far as I know,
> there's no way for libc clients to say "update all the DNS stuff now";
> it's supposed to happen automatically when you call getaddrinfo.  (If
> I'm wrong, somebody please correct me.)

This was almost a year ago -- does anybody have any further input here?
If not, I'm not sure there's anything we can do from the Emacs side
here...

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#40748: 28.0.50; Switching wifi networks hangs dns lookups

[Eric Abrahamsen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Lars Ingebrigtsen <larsi@gnus.org> writes:
>
>> So I'm not sure how this can be an Emacs bug -- as far as I know,
>> there's no way for libc clients to say "update all the DNS stuff now";
>> it's supposed to happen automatically when you call getaddrinfo.  (If
>> I'm wrong, somebody please correct me.)
>
> This was almost a year ago -- does anybody have any further input here?
> If not, I'm not sure there's anything we can do from the Emacs side
> here...

I do not, and it doesn't seem to be happening any more! My bug can be
closed, but I'm not sure about 41234, which it's been merged with.