BUG: tsshd rendering on reconnect

[eejd]

relative to mosh, when returning to a tsshd connection, tmux (non-command mode) has rendering update problems. I.e. tmux status like gets repeated 2 or 3 times until char sent, update returns, then recovers.

[kitknox]

First let me start with a brief summary of the architectural differences. In the mosh scenario it has mosh-server always keeping a server side view of the currently fully rendered window. This is what then syncs back to the client. The upside is a client that can quickly reach a consistent state. The downside is that mosh-server owns the view and you lose all sorts of other things including the client side scrollback.

In the tssh case it doesn’t parse and keep a view of the terminal, it is keeping the transport virtually alive for us to be able to reattach to. While a client is disconnected if the terminal continues to update it will buffer that data to burst back on reconnect up to a point and then starts to discard data. @lonnywong has done a lot of work recently to improve the latency for tssh data to start flowing again for both KCP and QUIC modes. In practice most of my sessions are flowing again within 1 to 2 seconds, with some being basically instant.

On the rootshell side when we enter the background we attempt a final flush of each tabs scrollback history for the primary and alternate screen, encrypt it, and save it to disk. When coming back if the app restarted we first replay the primary and alt screen data into each tab. We then restore the tssh connectivity and allow it to render anything it has in its buffer. tssh then inject a SIGWINCH (Signal Windows Change) to signal to whatever is running in the terminal to redraw the current screen.

In control mode if no data was discarded the tmux delta updates just catch us back up as soon as data starts to flow and everything is fully consistent. If the app terminated, or if tsshd exceeded its buffer size and discarded, then we request a fresh scrollback history from tmux for each pane and re-render those to result in a fully consistent state.

With all of that as background when you are experiencing a rendering update issue, was the terminal in question idle while the connection was away, or had a fair bit of activity?

[lonnywong]

@eejd I actually just released tsshd v0.1.9 today. Could you please update to this latest version and see if the tmux rendering issue is improved or resolved?

[kitknox]

@eejd Are you still having issues after upgrading?