bug#33145: 27.0.50; rcirc race receives duplicate messages

bug#33145: 27.0.50; rcirc race receives duplicate messages

[Basil L. Contovounesios]

Currently, rcirc-filter clears the accumulator variable
rcirc-process-output only after each of its constituent lines has been
fed to rcirc-process-server-response, which in turn runs the abnormal
hook rcirc-receive-message-functions.

If this hook contains a function which allows process filters to be run,
e.g. by way of accept-process-output, and if process output arrives soon
enough, then rcirc-filter might be called more than once before its
previous invocation has managed to clear rcirc-process-output.

In other words, subsequent invocations may see process output that is
already being handled by previous invocations, thus potentially printing
duplicate messages in the process buffer.

Patch addressing this to follow.

Thanks,

-- 
Basil

In GNU Emacs 27.0.50 (build 31, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2018-10-24 built on thunk
Repository revision: 00027ff9d0f646662458bdb47cc7e2214f439698
Windowing system distributor 'The X.Org Foundation', version 11.0.12001000
System Description: Debian GNU/Linux buster/sid

Configured using:
 'configure --config-cache --prefix=/home/blc/.local --with-mailutils
 --with-x-toolkit=lucid --with-modules --with-file-notification=yes
 --with-x 'CC=ccache gcc' 'CFLAGS=-O2 -march=native -pipe''

Configured features:
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bug#33145: 27.0.50; rcirc race receives duplicate messages

[Basil L. Contovounesios]

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From b5af2a63844fcdceab4520dae9c298c240a07df2 Mon Sep 17 00:00:00 2001
From: "Basil L. Contovounesios" <contovob@tcd.ie>
Date: Thu, 25 Oct 2018 03:35:57 +0100
Subject: [PATCH] Avoid race in rcirc process filter (bug#33145)

* lisp/net/rcirc.el (rcirc-filter): Clear rcirc-process-output
before processing its constituent lines.  Otherwise, if rcirc-filter
runs again before the last rcirc-process-server-response is
finished, the contents of rcirc-process-output could be duplicated.
---
 lisp/net/rcirc.el | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/lisp/net/rcirc.el b/lisp/net/rcirc.el
index fe9c71a21c..893ff5829b 100644
--- a/lisp/net/rcirc.el
+++ b/lisp/net/rcirc.el
@@ -751,12 +751,12 @@ rcirc-filter
   (with-rcirc-process-buffer process
     (setq rcirc-last-server-message-time (current-time))
     (setq rcirc-process-output (concat rcirc-process-output output))
-    (when (= (aref rcirc-process-output
-                   (1- (length rcirc-process-output))) ?\n)
-      (mapc (lambda (line)
-              (rcirc-process-server-response process line))
-            (split-string rcirc-process-output "[\n\r]" t))
-      (setq rcirc-process-output nil))))
+    (when (= ?\n (aref rcirc-process-output
+                       (1- (length rcirc-process-output))))
+      (let ((lines (split-string rcirc-process-output "[\n\r]" t)))
+        (setq rcirc-process-output nil)
+        (dolist (line lines)
+          (rcirc-process-server-response process line))))))
 
 (defun rcirc-reschedule-timeout (process)
   (with-rcirc-process-buffer process
-- 
2.19.1


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"Basil L. Contovounesios" <contovob@tcd.ie> writes:

> Patch addressing this to follow.

I attach said patch.

Thanks,

-- 
Basil

bug#33145: 27.0.50; rcirc race receives duplicate messages

[Eli Zaretskii]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Date: Thu, 25 Oct 2018 04:07:33 +0100
> 
> > Patch addressing this to follow.
> 
> I attach said patch.

Thanks, pushed to the emacs-26 branch.