clipmon

clipmon, or clipboard monitor is a wayland helper that:

1. It keeps the selection when the application that copied exits. Normally, when the copying application exits, the selection is lost and this can be rather annoying. Keeping the selection around matches what is normally expected to happen on a modern desktop. This feature is stable.
2. Shows a notification when an application pastes a selection. This is intended as a security measure: when an untrusted application (ideally sandboxed) snooping on the clipboard, the user will quickly by notified of what's going on. This feature is WIP.

The initial intention was meretly the second feature, but due to limitations of the underlying Wayland protocol, it's necessary to implement a clipboard monitor to achieve this.

Build

To build use cargo build. You can also quickly run this with cargo run.

Design

• We use the wlr-data-control-unstable-v1 wayland protocol.
• As soon as an application copies data into a selection, we copy this data and claim the clipboard ourselves.
• Because only foreground applications can take a selection, it should not be possible for another application to try and read data before we do.
• When another application tries to paste a selection, we receive that request, and can show a notification before sending any data. not implemented

Additionally, clipmon avoids ever writing copied data to disk, since highly sensitive information can go through a clipboard, and that could lead to unintentional leaks.

Debugging

Use WAYLAND_DEBUG=1 to see all wayland events -- that's usually most of what's needed to debug clipmon.

Caveats

In order to keep clipboard selections, clipmon needs to read any selection that's copied.

This means that if you copy a line of text, clipmon need to read this entire text and create an in-memory copy of it, so that when the original application exist, clipmon still has its copy in-memory. When copying text this is usually under 1kB of memory, but when you copy an image, the original application might expose that selection as multiple formats (jpeg/png/ico/bmp, etc). In order to avoid any data loss, clipmon must copy all these formats, which can potentially be a few megabytes or RAM.

Memory containing copied data may be swapped; preventing that is not yet implemented.

When two selections are taken ("copied") in extremely quick succession, it's possible that race conditions may occur. This is due to design limitations of the underlying wayland protocol, but should not realistically happen in real life scenario since it needs to happen too fast for a human operator to trigger the issue. This cannot be fixed without changes to the underlying Wayland protocol.

Development

Send patches on the mailing list and bugs reports to the issue tracker. Feel free to join #whynothugo on Libera Chat. If you find this tool useful, leave a tip.

LICENCE

clipmon is open sourced under the ISC licence. See LICENCE for details.