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Connection closing and detaching

A session can have one or more open windows, or it can be in a detached state, in which case the process (and pty) still exist, along with preserved state that can be used to attach a new window to the session. Onc can also attach a new window to a session that has open windows, in which case the open windows can provide the state needed to create the new window.

Preserved state is currently represented in two parts: a snapshot (the DOM slightly sanitized and serialized, plus terminal state properties), and a replay log: the session output sent to the terminal since the last snapshot.

For each session, the sever maintains a detach-count, which is rougly the number of windows that have been explictly closed. This is also the number of attaches “pending“ before a session is closed. When a new non-detached session is created, the detach-count is zero; when a window is detached, the detach-count is incremented; it a window is connected to an existing session, the detach-count is decremented. (If a new session is created in detached state, should the initial connect-count be zero or one?)

A connection (between session and window) can be closed in 4 ways:

• Session process exits, perhaps because the user typed exit. The server sends all windows a request to close themselves.
• User explicitly closed window (menu item or close button). If the detach-count is zero, the session is terminated. ((Possible actions: Exit process and close window; detach process and close window; ask user. Latter may depend on whether “process is running” (as checked by Gnome Terminal, Konsole).))
• User explicitly requests the session be detached. The detach-count is incremented
• Connection closes for unknown reason, such as network failure, or laptop sleep. Treat as a detach. The detach-count is incremented.