New plugin: Stickers

This plugin implements XEP-0449 and allows the user to send and receive stickers. Sticker packs that are not published on the user's account can be uploaded and published on sign-in, if configured. The same holds true for stickers that are published on the user's account but not locally present, except that they are downloaded on sign-in. Animated stickers, though currently only GIFs, are also supported with the ability to turn off animations.

The button that shows a menu for selecting the sticker to send is also searchable and updates when a new sticker pack gets added. It searches for matchin in either a sticker's "description" (desc) or one of its "suggests".

When a sticker is not known, the sticker pack gets automatically downloaded and added. This, however, can be turned off. In that case, a button is shown that asks the user if the sticker pack should be downloaded.

As just deleting the folder containing the sticker pack does not delete it from the account, this plugin also features a UI for removing sticker packs:

There are, however, currently two problems:

• The stickers are always sent unencrypted. At least with OMEMO, all non-whitelisted tags are filtered out before sending.
• As a rework of the conversation view is currently in progress, I would have to rewrite the plugin a bit when that MR is merged.

I should note that the plugin does not support importing or creating sticker packs. For my testing purposes I have created a script that takes a JSON representation of a sticker pack - that this plugin uses internally - and updates it so that the plugin can work with it. I feel like it is out of scope of the plugin, or at least of this first MR.

Under Linux the plugin requires stickers to be located at ~/.local/share/gajim/plugins_data/stickers/<sticker pack ID>/<sticker file>. The folder must contain a info.json file that describes the sticker pack and looks like this:

{
  "id": "0c58051a78fcd4ecf982f136",
  "name": "A sticker pack",
  "summary": "A description",
  "stickers": [
    {
      "type": "image/png",
      "hashes": [
        {
          "algo": "sha-256",
          "value": "8b76e01a4cd9ef8b3d63541459b1718b62c6073271b4e14cd0a9d3155964f13b"
        }
      ],
      "size": "14015",
      "dimension": "113x110",
      "desc": ":grin:",
      "suggests": [":blobgrin:"],
      "filename": "grin.png",
      "url": ""
    },
    [...]
  ]
}

The URL attribute of a sticker can be left empty as the plugin updates it automatically when the sticker pack has been published.

I tested this plugin on two Linux machines and it works. It requires a Gajim version newer than a290db02.