bug#22173: 25.1.50; server-reply-print does not avoid escape boundaries properly

[Jason Feng]

When printing a large amount of data over the emacs client protocol, any
printed data with spaces or newlines or other quoted characters may get
parts of the escape sequence inserted into the decoded stream due to
splitting.

Given any current emacs server instance, the bug can be triggered by
using emacsclient -e to evaluate the following code:

  (concat (make-string (- server-msg-size (length "-print ") 3) ?a) " ")

A patched version of the function that I'm currently using in my setup
appears to solve the problem:

(defun server-reply-print (qtext proc)
    "Send a `-print QTEXT' command to client PROC.
QTEXT must be already quoted.
This handles splitting the command if it would be bigger than
`server-msg-size'."
    (let ((prefix "-print ")
          part)
      (while (> (+ (length qtext) (length prefix) 1) server-msg-size)
        ;; We have to split the string
        (setq part (substring qtext 0 (- server-msg-size (length prefix) 1)))
        ;; Don't split in the middle of a quote sequence
        (if (string-match (rx (group "&") (* (group "&&")) eol) part)
            ;; There is an uneven number of & at the end
          (setq part (substring part 0 -1)))
        (setq qtext (substring qtext (length part)))
        (server-send-string proc (concat prefix part "\n"))
        (setq prefix "-print-nonl "))
      (server-send-string proc (concat prefix qtext "\n"))))

In GNU Emacs 25.1.50.2 (x86_64-pc-linux-gnu, GTK+ Version 3.10.8)
 of 2015-12-10
Windowing system distributor 'The X.Org Foundation', version 11.0.11501000
System Description:          Ubuntu 14.04.3 LTS

Configured using:
 'configure --build=x86_64-linux-gnu --prefix=/usr
 '--includedir=${prefix}/include' '--mandir=${prefix}/share/man'
 '--infodir=${prefix}/share/info' --sysconfdir=/etc --localstatedir=/var
 '--libdir=${prefix}/lib/x86_64-linux-gnu'
 '--libexecdir=${prefix}/lib/x86_64-linux-gnu' --disable-maintainer-mode
 --disable-dependency-tracking --prefix=/usr --sharedstatedir=/var/lib
 --program-suffix=-snapshot --with-x=yes --with-x-toolkit=gtk3
 'CFLAGS=-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat
 -Werror=format-security' CPPFLAGS=-D_FORTIFY_SOURCE=2
 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
  shell-dirtrack-mode: t
  iswitchb-mode: t
  diff-auto-refine-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Indenting region...done
Mark set [3 times]
=> [{:left-arm [-1.8972638273399445 -1.8972638273399445], :right-arm 
[-1.2571756745781983 -1.2571756745781983], :left-leg [-1.8218243292336378 
-1.8036620006694457], :right-leg [-1.3379306529203474 -1.3197683243561553]} 
{:left-arm [-1.8972638273399445 -1.8972638273399445], :right-arm 
[-1.2571756745781983 -1.2571756745781983], :left-leg [-1.8129101936957523 
-1.3286824598940408], :right-leg [-2.133467249511094 -1.0081254040786989]} 
{:left-arm [-1.8972638273399445 -1.8972638273399445], :right-arm 
[-1.2571756745781983 -1.2571756745781983], :left-leg [-1.3379306529203474 
-1.3197683243561553], :right-leg [-1.8218243292336378 -1.8036620006694457]} 
{:left-arm [-1.8972638273399445 -1.8972638273399445], :right-arm 
[-1.2571756745781983 -1.2571756745781983], :left-leg [-2.133467249511094 
-1.0081254040786989], :right-leg [-1.8129101936957523 -1.3286824598940408]}]
Mark set
=> 7730
Mark set [2 times]
Type "q" in help window to delete it.
mouse-2, RET: find function's definition
uncompressing server.el.gz...done
Note: file is write protected
Quit

Load-path shadows:
/usr/share/emacs/site-lisp/dictionaries-common/ispell hides 
/usr/share/emacs/25.1.50/lisp/textmodes/ispell
/usr/share/emacs/site-lisp/dictionaries-common/flyspell hides 
/usr/share/emacs/25.1.50/lisp/textmodes/flyspell
/home/jason/elisp/ruby-mode hides 
/usr/share/emacs/25.1.50/lisp/progmodes/ruby-mode
/home/jason/elisp/dns hides /usr/share/emacs/25.1.50/lisp/net/dns

Features:
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hashtable-print-readable backquote dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 295641 26396)
 (symbols 48 36677 0)
 (miscs 40 1394 2304)
 (strings 32 69087 8909)
 (string-bytes 1 2161821)
 (vectors 16 30924)
 (vector-slots 8 689437 7213)
 (floats 8 352 591)
 (intervals 56 7101 45)
 (buffers 976 30)
 (heap 1024 57288 2916))