Re: X11-Forwarding

[Andreas Schneider <asn@xxxxxxxxxxxxxx>]

On Monday, April 18, 2022 11:26:23 AM CEST Klaus Schlitt wrote:
> Hi,

Hi Klaus,

die you see the MR to add an X11 example implementation?

https://gitlab.com/libssh/libssh-mirror/-/merge_requests/236

Cheers,

	Andreas

> I want to forward the X11 output from the remote application (e.g.
> xterm) to my local computer.
>  From the libssh tutorial, I have used this code fragment to do so:
> 
>      ssh_channel x11channel;
>      rc = ssh_channel_request_pty(channel);
>      if (rc != SSH_OK) return rc;
>      rc = ssh_channel_change_pty_size(channel, 80, 24);
>      if (rc != SSH_OK) return rc;
> 
>      int displayNr = 100;
>      rc = ssh_channel_request_x11(channel, 0, NULL, NULL, displayNr);
>      if (rc != SSH_OK) return rc;
> 
>      rc = ssh_channel_request_shell(channel);
>      if (rc != SSH_OK) return rc;
> 
>      x11channel = ssh_channel_accept_x11(channel, 3000);
>      if (x11channel == NULL) return -1;
> 
> My callback function, which is called at the time,
> ssh_channel_accept_x11() is executed, looks like:
> static ssh_channel my_channel_open_request_x11_callback(ssh_session
> session, const char* originator_address, int originator_port, void*
> userdata)
> {
>      ssh_channel channel = ssh_channel_new(session);
>      return channel;
> }
> 
> My expectation was, that the ssh_channel, provided by
> ssh_channel_accept_x11(), must be used then to do the ssh request from
> where the X11 output will be redirected to my local computer.
> Problem:
> After the specified timeout (3000 ms in my example), the function
> ssh_channel_accept_x11() returns NULL, although the return value of the
> callback function was not NULL.
> 
>  From the console log "channel" shows the newly created ssh channel from
> the callback function:
> [2022/04/18 10:33:34.651892, 2] grow_window: growing window (channel
> 43:0) to 1280000 bytes
> session            = 0x16C9138
> originator_address = ::1
> originator_port    = 40528
> userdata           = 016D9ED8
> channel            = 0x16D9E60
> [2022/04/18 10:33:40.551005, 2] grow_window:  growing window (channel
> 44:3) to 1280000 bytes
> [2022/04/18 10:33:43.951259, 1] ssh_channel_accept:  No channel request
> of this type from server
> [2022/04/18 10:38:10.603076, 1] channel_request:  Channel request exec
> failed
> 
> The problem seems to be:
> "No channel request of this type from server"
> 
> What is wrong with my implementation?
> The complete example can be found here:
> http://kschlitt.bplaced.net/LibsshTestX11.cpp
> 
> My goal is to open the X11 window on my local computer where cygwin-x is
> installed.
>      rc = ssh_channel_request_exec(channel, "xterm -display
> localhost:100.0");
> 
> Is my approach correct for this goal?
> If I use the same display number, which other cygwin xterm windows have
> already set, then the X11 windows is opened on my local computer by
> executing the command ("xterm").
> Problem with this solution:
> How to know the display number to use for this purpose?
> 
> Thanks,
> Klaus


-- 
Andreas Schneider                 asn@xxxxxxxxxxxxxx
GPG-ID:     8DFF53E18F2ABC8D8F3C92237EE0FC4DCC014E3D