patch 9.1.1651: Cannot use clientserver over socket

Problem:  Cannot use clientserver over Unix domain socket
Solution: Implement socketserver functionality (Foxe Chen).

fixes: #3509
closes: #17839

Signed-off-by: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/builtin.txt

@@ -13046,6 +13046,7 @@ scrollbind		Compiled with 'scrollbind' support. (always true)
 showcmd			Compiled with 'showcmd' support.
 signs			Compiled with |:sign| support.
 smartindent		Compiled with 'smartindent' support. (always true)
+socketserver		Compiled with socket server functionality. (Unix only)
 sodium			Compiled with libsodium for better crypt support
 sound			Compiled with sound support, e.g. `sound_playevent()`
 spell			Compiled with spell checking support |spell|.

runtime/doc/remote.txt

@@ -1,4 +1,4 @@
-*remote.txt*    For Vim version 9.1.  Last change: 2022 Feb 17
+*remote.txt*    For Vim version 9.1.  Last change: 2025 Aug 18
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -61,7 +61,10 @@ The following command line arguments are available:
    --servername {name}		Become the server {name}.  When used together
 				with one of the --remote commands: connect to
 				server {name} instead of the default (see
-				below).  The name used will be uppercase.
+				below).  The name used will be uppercase.  If
+				using the socketserver, you can specify a
+				path, see |socketserver-name| for more
+				details.
 								*--remote-send*
    --remote-send {keys}		Send {keys} to server and exit.  The {keys}
 				are not mapped.  Special key names are
@@ -72,6 +75,12 @@ The following command line arguments are available:
 				on stdout.
 								*--serverlist*
    --serverlist			Output a list of server names.
+								*--clientserver*
+   --clientserver {method}	Use the specified method {method} as the
+				backend for clientserver functionality. Can
+				either be "socket" or "x11".
+				{only available when Vim is compiled with both
+				|+X11| and |+socketserver| features}
 
 
 Examples ~
@@ -105,7 +114,8 @@ specified name is not available, a postfix is applied until a free name is
 encountered, i.e. "gvim1" for the second invocation of gvim on a particular
 X-server.  The resulting name is available in the servername builtin variable
 |v:servername|.  The case of the server name is ignored, thus "gvim" and
-"GVIM" are considered equal.
+"GVIM" are considered equal.  Note if a socket server is being used, there are
+some differences, see |socketserver-differences|.
 
 When Vim is invoked with --remote, --remote-wait or --remote-send it will try
 to locate the server name determined by the invocation name and --servername
@@ -119,7 +129,8 @@ itself.  This way it is not necessary to know whether gvim is already started
 when sending command to it.
 
 The --serverlist argument will cause Vim to print a list of registered command
-servers on the standard output (stdout) and exit.
+servers on the standard output (stdout) and exit.  If a socket server is being
+used, there are caveats, see |socketserver-differences|.
 							*{server}*
 The {server} argument is used by several functions.  When this is an empty
 string then on Unix the default server name is used, which is "GVIM".  On
@@ -206,4 +217,64 @@ When using gvim, the --remote-wait only works properly this way: >
 
 	start /w gvim --remote-wait file.txt
 <
+==============================================================================
+3. Socket server specific items			    *socketserver-clientserver*
+				    *E1563* *E1564* *E1565* *E1566* *E1567*
+
+The communication between client and server is done using Unix domain sockets.
+These sockets are either placed in these directories in the following order of
+availability:
+    1. "$XDG_RUTIME_DIR/vim" if $XDG_RUNTIME_DIR is set in the environment.
+    2. "$TMPDIR/vim-[uid]", where "[uid]" is the uid of the user. This
+       directory will have the access permissions set to 700 so only the user
+       can read or write from/to it. If $TMPDIR is not set, "/tmp" is used.
+
+						    *socketserver-name*
+When specifying the server id/name, it can be taken as a generic name or an
+absolute or relative path.  If the server id starts with either a "/"
+(absolute) or "./" | "../" (relative), then it is taken as path to the socket.
+Otherwise the server id will be the filename of the socket which will be
+placed in the above common directories.  Note that a server id/name can only
+contain slashes "/" if it is taken as a path, so names such as "abc/dir" will
+be invalid.
+
+Socket server functionality is available in both GTK GUI and terminal versions of
+Vim.  Unless Vim is compiled with |+autoservername| feature, the socket server
+will have to started explicitly, just like X11, even in the GUI.
+
+If Vim crashes or does not exit cleanly, the socket server will not remove the
+socket file and it will be left around.  This is generally not a problem,
+because if a socket name is taken, Vim checks if the socket in its place is
+dead (not attached to any process), and can replace it instead of finding a
+new name.
+
+To send commands to a Vim socket server from another application, read the
+source file src/os_unix.c, there is detailed description of the protocol used.
+
+						    *socketserver-differences*
+Most of the functionality is the same as X11, however unlike X11, where the
+client does not need to be a server in order to communicate with another
+server, the socket server requires the server to be running even as a client.
+The exception is |serverlist()| or the |--serverlist| argument, which does not
+require the server to be running.
+
+Additionally, the server id or client id will not be a number like X11 or
+MS-Windows (shown in hex representation), instead it is the absolute path to
+the socket.  This can be seen via the |v:servername| variable.
+
+The |--serverlist| argument will act just like X11, however it only checks the
+given common directories above.  If a custom path is used for a socket, it
+will not be detected, such as a path either not in $XDG_RUNTIME_DIR or
+<$TMPDIR or /tmp>/vim of the |--serverlist| Vim process.
+
+If you have both |+socketserver| and |+X11| compiled, you will need to add
+|--clientserver| set to "socket" in combination with |--serverlist| to list
+the available servers.  You cannot list both types of backends in one command.
+
+						    *socketserver-x11*
+If Vim is compiled with both |+X11| and |+socketserver|, then deciding which
+backend to use is done at startup time, via the |--clientserver| argument.  By
+default if it is not specified, then X11 will be used.  A Vim instance using a
+socket server cannot communicate with one using X11.
+
  vim:tw=78:sw=4:ts=8:noet:ft=help:norl:

runtime/doc/tags

@@ -1497,6 +1497,7 @@ $quote	eval.txt	/*$quote*
 +scrollbind	various.txt	/*+scrollbind*
 +signs	various.txt	/*+signs*
 +smartindent	various.txt	/*+smartindent*
++socketserver	various.txt	/*+socketserver*
 +sodium	various.txt	/*+sodium*
 +sound	various.txt	/*+sound*
 +spell	various.txt	/*+spell*
@@ -1557,6 +1558,7 @@ $quote	eval.txt	/*$quote*
 --	starting.txt	/*--*
 ---	starting.txt	/*---*
 --clean	starting.txt	/*--clean*
+--clientserver	remote.txt	/*--clientserver*
 --cmd	starting.txt	/*--cmd*
 --echo-wid	starting.txt	/*--echo-wid*
 --gui-dialog-file	starting.txt	/*--gui-dialog-file*
@@ -4697,6 +4699,11 @@ E156	sign.txt	/*E156*
 E1560	vim9.txt	/*E1560*
 E1561	vim9.txt	/*E1561*
 E1562	options.txt	/*E1562*
+E1563	remote.txt	/*E1563*
+E1564	remote.txt	/*E1564*
+E1565	remote.txt	/*E1565*
+E1566	remote.txt	/*E1566*
+E1567	remote.txt	/*E1567*
 E157	sign.txt	/*E157*
 E158	sign.txt	/*E158*
 E159	sign.txt	/*E159*
@@ -10225,6 +10232,10 @@ slow-fast-terminal	term.txt	/*slow-fast-terminal*
 slow-start	starting.txt	/*slow-start*
 slow-terminal	term.txt	/*slow-terminal*
 socket-interface	channel.txt	/*socket-interface*
+socketserver-clientserver	remote.txt	/*socketserver-clientserver*
+socketserver-differences	remote.txt	/*socketserver-differences*
+socketserver-name	remote.txt	/*socketserver-name*
+socketserver-x11	remote.txt	/*socketserver-x11*
 sort()	builtin.txt	/*sort()*
 sorting	change.txt	/*sorting*
 sound-functions	usr_41.txt	/*sound-functions*

runtime/doc/various.txt

@@ -1,4 +1,4 @@
-*various.txt*   For Vim version 9.1.  Last change: 2025 Aug 06
+*various.txt*   For Vim version 9.1.  Last change: 2025 Aug 18
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -487,6 +487,8 @@ m  *+ruby/dyn*		Ruby interface |ruby-dynamic| |/dyn|
 T  *+scrollbind*	'scrollbind'
 N  *+signs*		|:sign|
 T  *+smartindent*	'smartindent'
+N  *+socketserver*	Unix only: socket server backend for clientserver
+			functionality
 H  *+sodium*		compiled with libsodium for better encryption support
 H  *+sound*		|sound_playevent()|, |sound_playfile()| functions, etc.
 N  *+spell*		spell checking support, see |spell|

runtime/doc/version9.txt

@@ -41745,6 +41745,10 @@ Others: ~
   Unicode 16.
 - Two additional digraphs have been added: LEFT ANGLE BRACKET "<[" and RIGHT
   ANGLE BRACKET "]>".
+- Support for Unix domain sockets have been added for the clientserver
+  feature, see |socketserver-clientserver|.
+
+Platform specific ~
 - MS-Winodws: Paths like "\Windows" and "/Windows" are now considered to be
   absolute paths (to the current drive) and no longer relative.
 
@@ -41849,6 +41853,7 @@ Options: ~
 
 Vim Arguments: ~
 |-Y|			Do not connect to the Wayland compositor.
+|--clientserver|	Specify backend  for clientserver functionality.
 
 
 ==============================================================================

runtime/doc/vim.1

@@ -499,7 +499,14 @@ List the names of all Vim servers that can be found.
 .TP
 \-\-servername {name}
 Use {name} as the server name.  Used for the current Vim, unless used with a
-\-\-remote argument, then it's the name of the server to connect to.
+\-\-remote argument, then it's the name of the server to connect to.  If the
+socketserver backend is being used, if the name starts with "/", "./", or "../",
+it is taken as either an absolute, relative or relative path to the socket.
+.TP
+\-\-clientserver {backend}
+Use {backend} as the backend for clientserver functionality, either "socket" or
+"x11" respectively.  Only available when compiled with both socketserver and X11
+features present
 .TP
 \-\-socketid {id}
 GTK GUI only: Use the GtkPlug mechanism to run gVim in another window.

runtime/doc/vim.man

@@ -378,7 +378,16 @@ OPTIONS
        --servername {name}
                    Use  {name}  as the server name.  Used for the current Vim,
                    unless used with a --remote argument, then it's the name of
-                   the server to connect to.
+                   the server to connect to.  If the socketserver  backend  is
+                   being used, if the name starts with "/", "./", or "../", it
+                   is  taken  as either an absolute, relative or relative path
+                   to the socket.
+
+       --clientserver {backend}
+                   Use {backend} as the backend for  clientserver  functional‐
+                   ity, either "socket" or "x11" respectively.  Only available
+                   when  compiled  with  both  socketserver  and  X11 features
+                   present
 
        --socketid {id}
                    GTK GUI only: Use the GtkPlug mechanism to run gVim in  an‐

runtime/plugin/rrhelper.vim

@@ -16,9 +16,10 @@ function SetupRemoteReplies()
   let max = argc()
 
   let id = expand("<client>")
-  if id == 0
+  if (type(id) == v:t_number && id == 0) || (type(id) == v:t_string && id == '')
     return
   endif
+
   while cnt < max
     " Handle same file from more clients and file being more than once
     " on the command line by encoding this stuff in the group name

runtime/syntax/vim.vim

@@ -2,7 +2,7 @@
 " Language:	   Vim script
 " Maintainer:	   Hirohito Higashi <h.east.727 ATMARK gmail.com>
 "	   Doug Kearns <dougkearns@gmail.com>
-" Last Change:	   2025 Aug 16
+" Last Change:	   2025 Aug 18
 " Former Maintainer: Charles E. Campbell
 
 " DO NOT CHANGE DIRECTLY.