Currently writing a clipboard manager[1], I've seen some things as well.
- So far ran into two applications which don't even implement the X11 clipboard specification (ICCCM section 2) correctly - xsel and Emacs (patches submitted).
- By far the worst offense I've seen in clipboard privacy on the Linux desktop is RedHat's virt-manager. It sends your clipboard AND selection content to all virtual machines, even when they are not focused, with no indication that it's happening, and with no GUI option to turn it off. This is at odds with the common practice of running untrusted code in virtual machines.
- X11 being network-transparent makes its protocol fairly malleable, so it's not difficult to bolt some privacy on top. hax11[2] has an option to restrict access to the primary selection for configured applications (though, for truly malicious applications, you may find X11's security model generally lacking).
I've always wanted an application dedicated to managing the clipboard. It would provide security and even offer interchange conversion that existing apps do not implement. For example: Copying HTML in Windows it has an associated mime type that receiving applications can recognize and choose to convert from.
I've always wanted a clipboard/paste manager - with history - like this, that would allow me to copy, manipulate, and paste or share that data to another application.
I don't know how this would look, but even the ability to pop open my paste manager and look at the copied contents, filter it, or split the text, or (silly stuff) convert text to emoji'fied content, or take a screenshot of that (text to bitmap), and create a new entry within the paste manager. For some of my friends it would be awesome to have a hex editor in there.
Perhaps there are 2 focuses: Isolating what is copied from applications until the user chooses to expose it, and the history function. Being able to send it to another app for manipulation and pulling it back is a 2nd responsibility. It would be /suave/ to have this all in the same GUI brought up by the compositor, though.
For Windows, there is "ClipboardFusion" by Binary Fortress, which acts as a scriptable clipboard manager, and could tick most of your boxes.
I'm not sure how possible it would be on Windows for a third party app to perform isolation - maybe if it registers a hook for when clipboard content changes which is somehow guaranteed to run first before other applications and any hooks they may have, it could swallow the event and clear the clipboard so other processes can't see it, and then do something similar with paste events maybe?
While not scriptable and not super advanced, Windows 10 and Windows 11 have a native visual clipboard manager with history and some other basic features. And it works quite well.
Try pressing Win+V, and the OS will give you a prompt to enable clipboard manager in settings. Once you enabled it (has to be done once), next time you press Win+V, a panel will slide out from the right side, and you can see the last N entries in your clipboard (which could include text, images, etc.). You can pick anything from there and paste it, and you can also pin any item there so that it won’t be overwritten when the clipboard reaches the limit and starts writing over.
This replacement keyboard for Android saves clips and allows the user to select and paste them into any application. Most importantly, it allows the user to delete the contents of the clipboard. It also allows the user to "pin" certain clips to be retained for future pasting. Clip storage.
If one needs a further reason to replace the keyboard, consider that the default keyboard on Google phones, Gboard, tries to phone home to Google. A keyboard that expects internet access. Incredible.
While it's not what you're looking for, a lot of people also don't know that windows has a built-in copy paste history if you use windows+v instead of ctrl-v.
That's quiet handy too, but a fast cry from what you've proposed there
- So far ran into two applications which don't even implement the X11 clipboard specification (ICCCM section 2) correctly - xsel and Emacs (patches submitted).
- By far the worst offense I've seen in clipboard privacy on the Linux desktop is RedHat's virt-manager. It sends your clipboard AND selection content to all virtual machines, even when they are not focused, with no indication that it's happening, and with no GUI option to turn it off. This is at odds with the common practice of running untrusted code in virtual machines.
- X11 being network-transparent makes its protocol fairly malleable, so it's not difficult to bolt some privacy on top. hax11[2] has an option to restrict access to the primary selection for configured applications (though, for truly malicious applications, you may find X11's security model generally lacking).
[1]: https://news.ycombinator.com/item?id=29808487 [2]: https://github.com/CyberShadow/hax11