Clipboard Manager Specification
Responsibilities of clipboard managers
Clipboard managers will acquire ownership of a selection named CLIPBOARD_MANAGER, as described in section 1.2.6 of the ICCCM. Clipboard managers should comply with the conventions for "Manager Selections" described in section 2.8 of the ICCCM. The intent is for clients to be able to request a variety of information or services by issuing conversion requests on this selection.
Clipboard managers should support conversion of the SAVE_TARGETS target on their manager selection. This is a side-effect target, as described in ICCCM section 2.6.3.
When a clipboard manager receives a request to convert the manager selection to the target SAVE_TARGETS, the named property specifies a list of targets to convert the CLIPBOARD selection to. If the named property exists, it must be of type ATOM and contain the list of targets. If the named property does not exist, the list of targets should be obtained by converting the CLIPBOARD to the TARGETS target, excluding side effect targets like DELETE, INSERT_PROPERTY and INSERT_SELECTION and possibly reducing the list of targets further.
If the clipboard owner supports the TARGET_SIZES target, the clipboard manager may use that to determine how to handle the SAVE_TARGETS request, possibly refusing to save large amounts of data, or asking the user before doing so.
When handling SAVE_TARGETS, the clipboard manager should convert the CLIPBOARD selection to the selected targets. Then it should take over ownership of the CLIPBOARD selection and offer the saved conversion results under the same targets they were requested with. Note: It is important to not send the ?SelectionNotify finishing the SAVE_TARGETS conversion until all target transfers are complete, since the clipboard owner will quit upon receiving the ?SelectionNotify and may not wait for the incremental transfers (using the INCR mechanism) to complete.
Clipboard owners which support SAVE_TARGETS should include SAVE_TARGETS in their list of supported targets to indicate this. Clipboard managers are encouraged to use this information to support legacy clients.
Responsibilities of clipboard owners
If a client needs to exit while owning the CLIPBOARD selection, it should request the clipboard manager to take over the ownership of the clipboard, using the SAVE_TARGETS mechanism. If there is no clipboard manager, or if the SAVE_TARGETS conversion fails, the application should simply exit.
Clients which support the SAVE_TARGETS mechanism should announce this by listing SAVE_TARGETS as a target for the CLIPBOARD. In this context, SAVE_TARGETS is used purely as a "marker target". If another client tries to convert the CLIPBOARD to SAVE_TARGETS, the clipboard owner should treat it like a side effect target without any actual side effect.
In order to support peers who use the XFIXES extension to watch clipboard ownership changes, clipboard owners should reacquire the clipboard whenever the content or metadata (e.g the list of supported targets) changes.
In order to support clipboard managers who want to avoid storing large amounts of data, clipboard owners should support a target named TARGET_SIZES. When asked to convert the clipboard to TARGET_SIZES, the clipboard owner must set the named property to format 32, type ATOM, and fill it with a list of pairs of target atoms and integers. There should be exactly one list entry for each supported target, and the integer should be
- a. -1 for side effect targets, or
- b. an estimate of the size in bytes of the result of converting the current CLIPBOARD contents to the target, or
- c. 0 if it is too hard or impossible to determine the size, e.g. for MULTIPLE.