Subject: bug#26591: 26.0.50; Using local emacs+tramp with remote emacsclient

From: [email-masked] (Peder O. Klingenberg)
Date: Sat, 29 Apr 2017 21:45:15 +0200

Eli Zaretskii <[email-masked]> writes:

> server-use-tcp is not described in the manual, so I think we should
> add its description somewhere, and then reference that place from this
> text.

I added a new node to the manual, "TCP Emacs server", and
collected/wrote documentation on the various related variables there.
Does this type of doc reorganization require its own NEWS entry?  I
didn't see the point, and so didn't write any.

As this is only tangentially related to the new feature, I made it into
a separate patch.  The updated feature patch applies on top of this
documentation patch, and references the new node.

> "/home" should be in @file, not @samp.  Also, I don't see "/home" used
> anywhere in the example, so something is missing here.

I have hopefully clarified the wording and fixed the tagging and typos.
I noticed while writing the TCP server doc that Emacs was capitalized
elsewhere in the docs, so I updated the capitalization in the paragraphs
on the new option.

Jeez, writing good docs is hard.  Criticisms welcome.  :)

> Why the test for argv[i] being an absolute file name?  And if relative
> file names cannot be supported, I think emacsclient should emit an
> error message rather than silently ignoring --tramp.

As I explained in my previous mail, both absolute and relative filenames
are supported.  There are no code changes in this updated patch set.

>From f5a4c2ef877a476a1f2bfb8f3eb07cba7c641234 Mon Sep 17 00:00:00 2001
From: "Peder O. Klingenberg" <[email-masked]>
Date: Sat, 29 Apr 2017 01:18:30 +0200
Subject: [PATCH] Improve documentation of TCP mode of server.el

* doc/emacs/misc.texi (TCP Emacs server): New subsection describing
the various knobs to tune server.el for TCP opereation.
(emacsclient Options): Reference "TCP Emacs server" from description of
--server-file.
---
 doc/emacs/misc.texi | 80 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 63 insertions(+), 17 deletions(-)

diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index bcc20a6db1..c8504fef49 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -1661,10 +1661,66 @@ Emacs Server
 signaled.)  Currently, this feature is mainly useful for developers.
 
 @menu
+* TCP Emacs server::     Listening to a TCP socket.
 * Invoking emacsclient:: Connecting to the Emacs server.
 * emacsclient Options::  Emacs client startup options.
 @end menu
 
+@node TCP Emacs server
+@subsection TCP Emacs server
+@cindex TCP Emacs server
+
+@vindex server-use-tcp
+  By default, the Emacs server will listen to a local unix domain
+socket.  In some cases it is useful to have it listen on a TCP socket
+instead.  Examples of such cases are operating systems like Microsoft
+Windows that don't support local sockets, and if you need to contact
+the Emacs server from a remote machine.  You can set
+@code{server-use-tcp} to non-@code{nil} to have Emacs listen on a TCP
+socket instead of a local socket.  This is the default if your OS does
+not support local sockets.
+
+@vindex server-host
+@vindex server-port
+  If the Emacs server is set to use TCP, it will by default listen to
+a random port on the localhost interface.  This can be changed to
+another interface and/or a fixed port using the variables
+@code{server-host} and @code{server-port}.
+
+@vindex server-auth-key
+  A TCP socket is not subject to file system permissions.  To retain
+some control over who can talk to a TCP Emacs server, the
+@command{emacsclient} program must send an authorization key to the
+server.  This key is normally randomly generated by the Emacs server.
+This is the recommended mode of operation.
+
+@findex server-generate-key
+  If needed, you can set it to a static value by setting the
+@code{server-auth-key} variable.  The key must consist of 64 ASCII
+printable characters except for space (this means characters from ! to
+~; or from code 33 to 126).  You can use @kbd{M-x server-generate-key}
+to get a random key.
+
+@vindex server-auth-dir
+@cindex server file
+  When you start a TCP Emacs server, Emacs creates a @dfn{server file}
+containing the TCP information to be used by @command{emacsclient} to
+connect to the server.  The variable @code{server-auth-dir} specifies
+the directory containing the server file; by default, this is
+@file{~/.emacs.d/server/}.  In the absence of a local socket with file
+permissions, it is the permissions of this directory that determines
+who can talk to the Emacs server.
+
+@cindex @env{EMACS_SERVER_FILE} environment variable
+  To tell @command{emacsclient} to connect to the server over TCP with a
+specific server file, use the @samp{-f} or @samp{--server-file}
+option, or set the @env{EMACS_SERVER_FILE} environment variable
+(@pxref{emacsclient Options}).  If @code{server-auth-dir} is set to a
+non-standard value, @command{emacsclient} needs an absolute path to the
+server file, as the default @code{server-auth-dir} is hardcoded in
+@command{emacsclient} as the base of relative filenames.
+
+
 @node Invoking emacsclient
 @subsection Invoking @code{emacsclient}
 @cindex @code{emacsclient} invocation
@@ -1810,25 +1866,15 @@ emacsclient Options
 
 @item -f @var{server-file}
 @itemx --server-file=@var{server-file}
-@cindex @env{EMACS_SERVER_FILE} environment variable
 Specify a @dfn{server file} for connecting to an Emacs server via TCP.
 
-An Emacs server usually uses a
-local socket to listen for connections.  Some operating systems,
-such as Microsoft Windows, do not support local sockets; in that case,
-the server communicates with @command{emacsclient} via TCP.
-
-@vindex server-auth-dir
-@cindex server file
-@vindex server-port
-When you start a TCP Emacs server, Emacs creates a @dfn{server file}
-containing the TCP information to be used by @command{emacsclient} to
-connect to the server.  The variable @code{server-auth-dir} specifies
-the directory containing the server file; by default, this is
-@file{~/.emacs.d/server/}.  To tell @command{emacsclient} to connect
-to the server over TCP with a specific server file, use the @samp{-f}
-or @samp{--server-file} option, or set the @env{EMACS_SERVER_FILE}
-environment variable.
+An Emacs server usually uses a local socket to listen for connections,
+but also supports connections over TCP.  To connect to a TCP Emacs
+server, @command{emacsclient} needs to read a @dfn{server file}
+containing the connection details of the Emacs server.  The name of
+this file is specified with this option, either as a file name
+relative to @file{~/.emacs.d/server} or as an absolute file name.
+@xref{TCP Emacs server}.
 
 @item -n
 @itemx --no-wait
-- 
2.11.0

>From 724e7d83948e7efd93f22c18d534321c461f6cbc Mon Sep 17 00:00:00 2001
From: "Peder O. Klingenberg" <[email-masked]>
Date: Fri, 21 Apr 2017 17:16:08 +0200
Subject: [PATCH] New option -T / --tramp for remote editing with emacsclient

In combination with existing functionality for having server.el
listen on tcp ports, enables emacsclient on a remote machine to
instruct the local emacs to open remote files via Tramp.  Useful with
remote programs that invoke EDITOR.

* lib-src/emacsclient.c (main, decode_options)
(print_help_and_exit, longopts): New option --tramp / -T which
specifies how emacs should use tramp to find remote files.
* doc/emacs/misc.texi (emacsclient Options): Document new
--tramp / -T options.

(Bug#26591)
---
 doc/emacs/misc.texi   | 34 +++++++++++++++++++++++++++++++++-
 etc/NEWS              |  6 ++++++
 lib-src/emacsclient.c | 20 ++++++++++++++++++--
 3 files changed, 57 insertions(+), 3 deletions(-)

diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index c8504fef49..3c6a192ca6 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -1720,7 +1720,6 @@ TCP Emacs server
 server file, as the default @code{server-auth-dir} is hardcoded in
 @command{emacsclient} as the base of relative filenames.
 
-
 @node Invoking emacsclient
 @subsection Invoking @code{emacsclient}
 @cindex @code{emacsclient} invocation
@@ -1918,6 +1917,39 @@ emacsclient Options
 server is using the graphical display, but if the Emacs server is
 running on a text terminal, it creates a new frame in the current text
 terminal.
+
+@item -T @var{tramp-prefix}
+@itemx --tramp-prefix=@var{tramp-prefix}
+@cindex @env{EMACSCLIENT_TRAMP} environment variable
+Prefix to add to filenames for Emacs to locate files on remote
+machines through TRAMP.  This is mostly useful in combination with
+using the Emacs server over TCP.  By ssh-forwarding the listening port
+and making the @var{server-file} available on a remote machine,
+programs on the remote machine can use @command{emacsclient} as
+@env{EDITOR}, but instead of starting Emacs on the remote machine, the
+files will be opened in the local Emacs through TRAMP.
+
+Setting the environment variable @env{EMACSCLIENT_TRAMP} has the same
+effect as using this option.  If both are specified, the explicit
+option will take precedence.
+
+For example, assume two hosts, @samp{local} and @samp{remote}, and
+that the local Emacs listens on tcp port 12345.  Assume further that
+@file{/home} is on a shared file system, so that the server file
+@file{~/.emacs.d/server/server} is readable on both hosts without
+further magic.
+
+@example
+local$ ssh -R12345:localhost:12345 remote
+remote$ export EDITOR="emacsclient \
+        --server-file=server \
+        --tramp=/ssh:remote:"
+remote$ $EDITOR /tmp/foo.txt #Should open in local emacs.
+@end example
+
+@xref{TCP Emacs server}, and @xref{Top, The Tramp Manual,,tramp, The
+Tramp Manual}.
+
 @end table
 
   The new graphical or text terminal frames created by the @samp{-c}
diff --git a/etc/NEWS b/etc/NEWS
index 76c9dbc331..4599efd7da 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -340,6 +340,12 @@ want to reverse the direction of the scroll, customize
 ** Emacsclient has a new option -u/--suppress-output.  The option
 suppresses display of return values from the server process.
 
++++
+** Emacsclient has a new option -T/--tramp.  This helps with using a
+local emacs as the target for a remote emacsclient.  With appropriate
+setup, one can now set EDITOR on a remote machine to emacsclient, and
+use the local emacs to edit remote files via Tramp.
+
 
 * Editing Changes in Emacs 26.1
 
diff --git a/lib-src/emacsclient.c b/lib-src/emacsclient.c
index 7b735dfb05..0661480f58 100644
--- a/lib-src/emacsclient.c
+++ b/lib-src/emacsclient.c
@@ -149,6 +149,9 @@ const char *socket_name = NULL;
 /* If non-NULL, the filename of the authentication file.  */
 const char *server_file = NULL;
 
+/* If non-NULL, the tramp prefix emacs must use to find the files.  */
+const char *tramp_prefix = NULL;
+
 /* PID of the Emacs server process.  */
 int emacs_pid = 0;
 
@@ -178,6 +181,7 @@ struct option longopts[] =
   { "server-file",	required_argument, NULL, 'f' },
   { "display",	required_argument, NULL, 'd' },
   { "parent-id", required_argument, NULL, 'p' },
+  { "tramp",	required_argument, NULL, 'T' },
   { 0, 0, 0, 0 }
 };
 
@@ -468,14 +472,15 @@ static void
 decode_options (int argc, char **argv)
 {
   alternate_editor = egetenv ("ALTERNATE_EDITOR");
+  tramp_prefix = egetenv ("EMACSCLIENT_TRAMP");
 
   while (1)
     {
       int opt = getopt_long_only (argc, argv,
 #ifndef NO_SOCKETS_IN_FILE_SYSTEM
-			     "VHnequa:s:f:d:F:tc",
+			     "VHnequa:s:f:d:F:tcT:",
 #else
-			     "VHnequa:f:d:F:tc",
+			     "VHnequa:f:d:F:tcT:",
 #endif
 			     longopts, 0);
 
@@ -554,6 +559,10 @@ decode_options (int argc, char **argv)
           frame_parameters = optarg;
           break;
 
+        case 'T':
+          tramp_prefix = optarg;
+          break;
+
 	default:
 	  message (true, "Try '%s --help' for more information\n", progname);
 	  exit (EXIT_FAILURE);
@@ -654,6 +663,9 @@ The following OPTIONS are accepted:\n\
 			Editor to fallback to if the server is not running\n"
 "			If EDITOR is the empty string, start Emacs in daemon\n\
 			mode and try connecting again\n"
+"-T PREFIX, --tramp=PREFIX\n\
+                        PREFIX to filenames emacs needs to use to find files\n\
+                        local to emacsclient\n"
 "\n\
 Report bugs with M-x report-emacs-bug.\n");
   exit (EXIT_SUCCESS);
@@ -1687,6 +1699,8 @@ main (int argc, char **argv)
         }
     }
   send_to_emacs (emacs_socket, "-dir ");
+  if (tramp_prefix)
+    quote_argument (emacs_socket, tramp_prefix);
   quote_argument (emacs_socket, cwd);
   send_to_emacs (emacs_socket, "/");
   send_to_emacs (emacs_socket, " ");
@@ -1791,6 +1805,8 @@ main (int argc, char **argv)
 #endif
 
           send_to_emacs (emacs_socket, "-file ");
+	  if (tramp_prefix && file_name_absolute_p (argv[i]))
+	    quote_argument (emacs_socket, tramp_prefix);
           quote_argument (emacs_socket, argv[i]);
           send_to_emacs (emacs_socket, " ");
         }
-- 
2.11.0

...Peder...