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[debbugs-tracker] bug#18116: closed (24.3.92; url-http calls CALLBACK re


From: GNU bug Tracking System
Subject: [debbugs-tracker] bug#18116: closed (24.3.92; url-http calls CALLBACK recursively with malformed CBARGS if the former calls `delete-process')
Date: Fri, 19 Sep 2014 02:01:02 +0000

Your message dated Fri, 19 Sep 2014 06:00:07 +0400
with message-id <address@hidden>
and subject line Re: bug#18116: 24.3.92; url-http calls CALLBACK recursively 
with malformed CBARGS if the former calls `delete-process'
has caused the debbugs.gnu.org bug report #18116,
regarding 24.3.92; url-http calls CALLBACK recursively with malformed CBARGS if 
the former calls `delete-process'
to be marked as done.

(If you believe you have received this mail in error, please contact
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-- 
18116: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=18116
GNU Bug Tracking System
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--- Begin Message --- Subject: 24.3.92; url-http calls CALLBACK recursively with malformed CBARGS if the former calls `delete-process' Date: Sun, 27 Jul 2014 06:12:57 +0300
Note: this could be considered a regression from Emacs 24.3

With this test case:

```
(require 'url-http)

(defvar uht-counter 0)

(defun uht-callback (status)
  (declare (special url-http-process))
  (message "%s %s" uht-counter status)
  (delete-process url-http-process))

(defun uht-test ()
  (setq uht-counter (1+ uht-counter))
  ;; The port must not be open.
  (url-http (url-generic-parse-url "http://localhost:3333";) #'uht-callback 
(list 'foo)))
```

Evaluate `(uht-test)' and see two messages in the message log with the
same counter value. The second message outputs a different STATUS value,
caused by modification of `url-callback-arguments' in
`url-http-async-sentinel', like this:

4 (:error (error connection-failed failed with code 111
 :host localhost :service 3333) . foo)
4 (:error (error connection-failed deleted
 :host localhost :service 3333) :error (error connection-failed failed with 
code 111
 :host localhost :service 3333) . foo)

If the callback expects STATUS to contain some specific data structure,
that can cause breakage, see https://github.com/marijnh/tern/issues/350
for an example.

Now, I'm not entirely sure the problem is in `url-http'. It does not
manifest in Emacs 24.3, possibly because in the current pretest, when
the connection fails, the `url-http-process' is still alive when
`delete-process' is called in `uht-callback'. This is not the case in
the current stable Emacs (wherein, as a consequence, `uht-callback'
doesn't get called the second time), so this could be a regression in
the processes subsystem.


In GNU Emacs 24.3.92.3 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.8)
 of 2014-07-24 on axl
Repository revision: 117398 address@hidden
Windowing system distributor `The X.Org Foundation', version 11.0.11501000
System Description:     Ubuntu 14.04.1 LTS



--- End Message ---
--- Begin Message --- Subject: Re: bug#18116: 24.3.92; url-http calls CALLBACK recursively with malformed CBARGS if the former calls `delete-process' Date: Fri, 19 Sep 2014 06:00:07 +0400 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.1
Version: 24.3.93.4

On 09/12/2014 09:22 PM, Stefan Monnier wrote:

I think there is indeed a change of behavior in that the sentinel used
to be nil'd while running it.
[ This was changed because it prevented the sentinel from modifying itself.  ]

Okay, I guess.

To me, "When retrieval is completed, execute the function CALLBACK, using
the arguments listed in CBARGS." means that it will be called exactly with
the value of CBARGS passed to `url-http', whereas instead the list gets
prepended with stuff before it's passed to CALLBACK.

Can you improve those docstrings, to avoid such confusion in the future?

Done, I think (r117511). Although maybe we should remove the middle paragraph in `url-http' docstring and replace it with a reference to `url-retrieve-internal': its second sentence has very much the same contents, only using different words.


--- End Message ---

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