Re: Shell-quoting issue for sshx/scpx on MS Windows

[Jim Porter]

On Fri, Apr 9, 2021 at 12:28 AM Michael Albinus <michael.albinus@gmx.de> wrote:
> What I'm thinking for a longer time is to enable remote processes on MS
> Windows, as remote target. AFAIK there is also an OpenSSH server for
> that beast, so it must be possible to start remote processes via ssh
> from a local Emacs running on, let's say, Linux.

There is, and I've tinkered with connecting via Tramp to an MS Windows
server running OpenSSH. However, when using ssh from a local MS
Windows client, I need to use the sshx method or Tramp hangs (this is
mentioned in the Tramp manual: "sshx is useful for MS Windows users
when ssh triggers an error about allocating a pseudo tty."). This
works fine when the server is Linux, but on MS Windows, running "ssh
-t" results in the Windows OpenSSH server replying with a bunch of
ANSI escapes that (I think) confuses Tramp.

There's a Github issue about this[1] that includes the following
helpful description:

"Due to a historical mistake, we gave Win32 applications full
read/write access to any rectangular region in the entire scrollback
buffer--including the viewport. To offer maximum compatibility for
those applications² the hosting APIs clear the screen by default,
unless the application requests cursor position inheritance¹.

"¹ This works by sending DSR-CPR and awaiting CPR. It won't work
without a compliant terminal emulator."

Perhaps Tramp can reply with the appropriate ANSI escape in this case
to make things work. Or perhaps not. I haven't had a chance to dig
into this very deeply, but when I get the time, I'll try to collect
some logs and narrow down the problem so I can send the results to the
list.

> The smb method must be extended for this, but that shall be
> possible. ATM, smb-like connections use winexe for remote processes on
> MS Windows. But I don't know whether this is really used by somebody,
> and winexe doesn't seem to be maintained anymore. I even don't know
> whether it is cooperating with MS Windows 10. WDYT?

I haven't spent much time looking at the smb method, since it would
require a bit more setup when using from an MS Windows client (I don't
have smbclient installed). While I use Tramp on both MS Windows and
Linux, I've only ever had a need to connect *to* an MS Windows server
when I'm running MS Windows locally too.

The smb method is surely useful for connecting to MS Windows servers
that don't have OpenSSH server installed. However, the OpenSSH
client/server are easy to install on MS Windows now, so it might make
sense to focus improvements for Tramp+Windows on the sshx/scpx
methods. These methods have been very reliable for me when connecting
from MS Windows, so hopefully it won't be too complicated to work
around the strangeness described above when connecting to an MS
Windows server.

- Jim

[1] https://github.com/PowerShell/Win32-OpenSSH/issues/1738