How to trap an error when connecting to a news server

How to trap an error when connecting to a news server

[gnus via info-gnus-english]

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I have this code:

(defun news-check ()
(message "The result is %d" (gnus-group-get-new-news))
)

(defun news-update ()
(interactive)
(setq quit-for t)
(while (eq quit-for t) ;; this stops if a key is pressed
(setq nnnn 0) ;; This counts seconds and displays them
(while (and (< nnnn 600) (eq t quit-for))
(setq quit-for (sit-for 1)) ;; wait for a second, or a key
(message "count %s" nnnn)
(setq nnnn (+ 1 nnnn))
)
(message "checking...")
(news-check) ;; this calls the above news check
)
)

If the server closes the connection, then this while loop stops. How can
I trap the error and continue the loop so that it tries again in 600
seconds?

I have tried using the condition-case mentioned in the manual but it
seemed to have no effect:

(defun news-check ()
(condition-case err
(message "The result is %s" (gnus-group-get-new-news))
(news-error
(message "I expect the server closed again %s",err)
)
)
)

Sorry if you see this more than once. I posted it to the newsgroup but now I
suspect the newsgroup is read-only.

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Re: How to trap an error when connecting to a news server

[Bob Newell]

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>
>
> (defun news-check ()
>  (condition-case err
>      (message "The result is %s" (gnus-group-get-new-news))
>    (news-error
>     (message "I expect the server closed again %s",err)
>     )
>    )
> )
>
> I could be mistaken in this, but in your code above, where did you get
> 'news-error' as the name of the error condition raised? I can't find this
> anywhere in the gnus source tree. Do you know for sure that
> gnus-group-get-new-news (or anything it calls) raises that condition?


-- 
Bob Newell
Honolulu, Hawai`i

Via Linux/Emacs/Gnus/BBDB.

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RE: How to trap an error when connecting to a news server

[gnus via info-gnus-english]

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On Sat, 4 Jan 2020 at 7:09 PM, Bob Newell < bobnewell@bobnewell.net > wrote:> > 
(defun news-check ()
(condition-case err
(message "The result is %s" (gnus-group-get-new-news))
(news-error
(message "I expect the server closed again %s",err)
)
)
)

I could be mistaken in this, but in your code above, where did you get
'news-error' as the name of the error condition raised? I can't find this
anywhere in the gnus source tree. Do you know for sure that
gnus-group-get-new-news (or anything it calls) raises that condition?


Thank you for your response. It is useful to me that you ask this. I could not
tell from the manual that "arith-error" in the example had a specific meaning,
so I arbitrarily changed it.
https://www.gnu.org/software/emacs/manual/html_node/elisp/Handling-Errors.html

How do I tell what the error condition will be? The code in nntp.el is this (I
think this is where the server closed condition occurs) :
(defun nntp-report (&rest args)
"Report an error from the nntp backend. The first string in ARGS
can be a format string. For some commands, the failed command may be
retried once before actually displaying the error report."
(if nntp--report-1
(progn
;; Throw out to nntp-with-open-group-error so that the connection may
;; be restored and the command retried."
(when nntp-record-commands
(nntp-record-command "*** CONNECTION LOST ***"))
(throw 'nntp-with-open-group-error t))

(when nntp-record-commands
(nntp-record-command "*** CALLED nntp-report ***"))

(nnheader-report 'nntp args)

(apply 'error args)
))



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RE: How to trap an error when connecting to a news server

[gnus via info-gnus-english]

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The backtrace shows this:
Debugger entered--Lisp error: (error "Server closed connection")
signal(error ("Server closed connection"))
error("Server closed connection")
apply(error "Server closed connection")
nntp-report("Server closed connection")
nntp-accept-process-output(#<process nntpd>)
nntp-accept-response()

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