Design Idea: Support for copying multiple mime-types into the clipboard

[titaniumtraveler]

wl-clipboard is an incredible tool, but is currently not exposing the two capabilities that I absolutely love about the wayland clipboard:

• Having support for multiple mime-types
• And computing the actual values lazily

To solve both of these problems at once I would suggest to add a command wl-copy --watch <command>-subcommand with the following execution pattern:

First accept a list of mime-types. Either over the command line as list of -t <mime-type>, or over stdin the of wl-copy as newline separated list.

Then advertise that list as available clipboard, and when a copy-request is made, that mime-type is written to the stdin of <command>, which then is expected to reply via stdout.

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This design would make it incredibly easy to write for example shellscripte that compute file formats on-demand depending on what the client supports/requests.