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bug#12051: 24.1; rcirc-send-message doesn't take multibyte into account.

From: Li Ian-Xue
Subject: bug#12051: 24.1; rcirc-send-message doesn't take multibyte into account.
Date: Thu, 26 Jul 2012 00:18:29 +0800

Hello developers,

I discovered recently that the irc client `rcirc', although has an
max-message-length set, but it simply uses (length str) for detecting
the output length, which is not desirable for multibyte users because
usually our characters encode to more than one byte, and this causes an
error that the client actually sends out more bytes than the standard
has required (512 bytes to my understanding).

This limit is easily reached since chinese characters are usually
encoded with 3 bytes for one character.

By this error, if the server truncates the result string simply by
bytes, then it's known to cause the string to become entirely scrambles
for xchat.

I'm attaching a patch to perform an binary search for multibyte strings,
and this patch should not have any penalties for original ascii users
since it begins with a (multibyte-string-p) to decide which style to use.

--- rcirc.el    2012-07-25 23:52:41.813226461 +0800
+++ rcirc-1.el  2012-07-25 23:55:20.813220626 +0800
@@ -792,21 +792,40 @@
 (defvar rcirc-max-message-length 420
   "Messages longer than this value will be split.")
+(defun rcirc-multibyte-position-at-byte (str bytes)
+  (if (multibyte-string-p str)
+      (rcirc-multibyte-position-at-byte-1 str bytes 0 0)
+      bytes))
+(defun rcirc-multibyte-position-at-byte-1 (str bytes now-chars now-bytes)
+  (let ((len (length str)))
+    (if (<= len 1)
+        now-chars
+      (let* ((half-len (/ len 2))
+             (lstr (substring str 0 half-len))
+             (rstr (substring str half-len len))
+             (now-bytes-1 (+ now-bytes (string-bytes lstr))))
+        (if (> now-bytes-1 bytes)
+            (rcirc-multibyte-position-at-byte-1 lstr bytes now-chars now-bytes)
+          (rcirc-multibyte-position-at-byte-1 rstr bytes (+ half-len 
now-chars) now-bytes-1))))))
 (defun rcirc-send-message (process target message &optional noticep silent)
   "Send TARGET associated with PROCESS a privmsg with text MESSAGE.
 If NOTICEP is non-nil, send a notice instead of privmsg.
 If SILENT is non-nil, do not print the message in any irc buffer."
   ;; max message length is 512 including CRLF
   (let* ((response (if noticep "NOTICE" "PRIVMSG"))
-         (oversize (> (length message) rcirc-max-message-length))
+         (oversize (> (string-bytes message) rcirc-max-message-length))
+         (adjusted-pos (if oversize
+                            (rcirc-multibyte-position-at-byte message 
          (text (if oversize
-                   (substring message 0 rcirc-max-message-length)
+                   (substring message 0 adjusted-pos)
          (text (if (string= text "")
                    " "
          (more (if oversize
-                   (substring message rcirc-max-message-length))))
+                   (substring message adjusted-pos))))
     (rcirc-get-buffer-create process target)
     (rcirc-send-string process (concat response " " target " :" text))
     (unless silent

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