Background

We are developing a cross-platform application with SSH support. For safety concerns, we prefer to use ssh client provided by system (rather than introduce 3rd-party dependence).

We've successfully started a SSH session with pseudo terminal ( ssh -tt ... ) and pipe its data, which works, but the size of pseudo terminal is always 0 * 0, and which cause some full-screen applications like nano or htop to fallback to default size, causing some unexpected behaviors.

We query the tty size using this command:

stty size

We also use nano and htop as full-screen size validators.

Imperfect methods

In below text, {cols} and {rows} represents real columns and rows respectively.

One possible solution we found is that sending stty columns {cols} rows {rows} command into SSH can force it to change into specified size, but this is raw text command and will be taken as text imput, so when user open a text editor and resized the window.. boom, the file will be corrupted.

Another approach is to use ANSI escape code, \x1B[8;{rows};{cols}t (\x1B is equivalent to \e). This works well in real terminal (non-PTY ones, using command like echo -e "\e[8;30;120t"), but on pseudo terminals this can't be recognized as a whole, causing something left behind as raw text. A worse situation is that even we typed the same command into PTY to try manually applying this setting, it also makes no difference, the tty size is till 0 * 0.

Thoughts

So the only left way we found seems to be sending signals to ssh process itself, either through fcntl.ioutil with TIOCSWINSZ equivalents (we are using Tauri to build this application so an implementation in rust is recommended, we are seeking for nix package), or sending a SIGWINCH signal. Unfortunately, these methods are all unix-based, which seems unapplicable for Windows.

We seems to find implementation of similar functionalities like pty_change_window_size or definition of W32_SIGWINCH, but TTY PTY support in Windows OpenSSH section in wiki seems to be native based, which should be enough for common users, but seems not covering our situation.

We've searched many documents but found little information, so we don't know whether these are the best practices, or we can use some other modern methods to achieve this requirement. If you've any ideas of implementing this, or just happen to face similar situations, don't hesitate to leave a message.

Thanks for your concern and sincere help. 🙏