Improving session restore functionality

[Aetf]

Overview

Shpool currently has a session restore feature that uses an in-memory terminal emulator implementation to record shell output, and then generate appropriate format codes and data to restore the last known screen state when a user reconnects. There are some issues with the current functionality that we would like to address.

Problem

The current in-memory terminal crate we use, shpool_vt100, has some issues. In particular, it does not use a very memory efficient representation of the terminal, and a lack of correct text wrapping supports means we need to make each line 10k characters long. Worse than the excessive resource consumption though is the fact that not all control sequences are correctly handled, resulting in output being occasionally mangled.

List of control sequences we may consider support:

• 44

• any other?

Potential Solution

Fixing the shpool_vt100 crate and replacing it with a new crate, which could either be written from the ground up or extracted from one of several existing rust terminals.

Currently wezterm-term looks promising, but it is not published to crates.io, and we need more investigation to see if it actually fits shpool's use case.

Other terminals considered:

• Zellij - modern tmux
  • Not a full terminal emulator state machine, just relevant control sequences (cursor movements, color, etc) (Terminal Pane and Grid)
    • In grid.rs: osc, esc, oci dispatch
• Tab - terminal workspace tabs, now died, doesn’t seem to have terminal emulation
  • No terminal emulator, just enough scrollback buffer management with filtering on a few sequences: https://github.com/austinjones/tab-rs/blob/main/tab-daemon/src/service/pty/scrollback.rs
• https://github.com/asciinema/asciinema Terminal session recorder
  • https://docs.asciinema.org/how-it-works/
  • Captures all terminal outputs using pty, timestamped and saved to a portable format asciicast.
  • no interpretation of control sequences
  • handles resize event WezTerm - terminal emulator and multiplexer https://github.com/wez/wezterm/tree/main/term
• Alacritty
  • its terminal component is published: https://crates.io/crates/alacritty_terminal

[Aetf]

+@ethanpailes @jalberss

[Aetf]

I'll try to integrate wezterm-term, and @jalberss will give alacritty a try. We will see which one works better, or we need to write one from scratch after all.

In the end of the day, if we end up with both. We can have a selection of backends for the user to choose.