RFR: 8280982: [Wayland] [XWayland] java.awt.Robot taking screenshots [v7]

[Alexander Zvegintsev]

On Thu, 25 May 2023 16:29:39 GMT, Alexander Zvegintsev <azvegint at openjdk.org> wrote:

>> Modern Linux systems often come with [Wayland](https://wayland.freedesktop.org/) by default.
>> This comes with some difficulties, and one of them is the inability to get screenshots from the system.
>> This is because we now use the [X Window System API](https://en.wikipedia.org/wiki/X_Window_System) to capture screenshots and it cannot access data outside the [XWayland server](https://wayland.freedesktop.org/xserver.html) 
>> 
>> But this functionality is a very important part of automated testing.
>> 
>> 
>> At the moment there are two obvious solutions to this problem, and both use [xdg-desktop-portal](https://github.com/flatpak/xdg-desktop-portal):
>> 
>> 1. [org.freedesktop.portal.Screenshot DBUS API](https://flatpak.github.io/xdg-desktop-portal/#gdbus-org.freedesktop.portal.Screenshot)
>> It has several drawbacks though:
>> + It saves a screenshot to disk, which must be read and deleted(may add some delays depending on the type of a disk drive).
>> + There is no way to disable the visual "screen flash" after screenshot
>> + It asks a user confirmation to save a screenshot. This confirmation can be saved on Gnome 43+. 
>> Since we would like Ubuntu 22.04 LTS which comes with Gnome 42 this option is not acceptable for us because it would require user confirmation for each screenshot.
>> But we still can consider this option as a fallback.
>> 
>> 
>> 
>> 2. [org.freedesktop.portal.ScreenCast](https://flatpak.github.io/xdg-desktop-portal/#gdbus-org.freedesktop.portal.ScreenCast)
>> It typically used by applications that need to capture the contents of the user's screen or a specific window for the purpose of sharing, recording, or streaming.
>> This might be a bit of overkill, but it avoids several of the problems mentioned in the Screenshot API.
>> 
>> + implementation is more complicated comparing to Screenshot API
>> + no intermediate file, screenshot data can be obtained from memory
>> + Permission to make screenshots can be stored with [`restore_token`](https://flatpak.github.io/xdg-desktop-portal/#gdbus-method-org-freedesktop-portal-ScreenCast.SelectSources)
>> 
>> 
>> So this PR adds the ability to take screenshots using the ScreenCast API. This functionality is currently disabled by default.
>> 
>> This change also introduces some new behavior for the robot:
>> A system window now appears asking for confirmation from the user to capture the screen.
>> + The user can refuse the screen capture completely. In this case a security exception will be thrown.
>> + The user can allow...
>
> Alexander Zvegintsev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   rework token storage

Token storage now does not use Preferences API and serialization.
(there were some problems with missing token during automated testing).

Properties API is now used:
No more writing to file if token data was not updated.
Detect external changes to the file, and update the token data if it was updated.
If we can't save the data, we can still use the received token, but we won't keep it between runs.

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PR Comment: https://git.openjdk.org/jdk/pull/13803#issuecomment-1563212589