This is half a fix for #874
This patch introduces a new config flag:
- MediaConvertTgs
These need to be treated independently from the existing
MediaConvertWebPToPNG flag because Tgs→WebP results in an
*animated* WebP, and the WebP→PNG converter can't handle
animated WebP files yet.
Furthermore, some platforms (like discord) don't even support
animated WebP files, so the user may want to fall back to
static PNGs (not APNGs).
The final reason why this is only half a fix is that this
introduces an external dependency, namely lottie, to be
installed like this:
$ pip3 install lottie cairosvg
This patch works by writing the tgs to a temporary file in /tmp,
calling lottie to convert it (this conversion may take several seconds!),
and then deleting the temporary file.
The temporary file is absolutely necessary, as lottie refuses to
work on non-seekable files.
If anyone comes up with a reasonable use case where /tmp is
unavailable, I can add yet another config option for that, if desired.
Telegram will bail out if the option is configured but lottie isn't found.
An extra avatarMap (cache) is created for mattermost and telegram.
If MediaServerUpload is configured, the avatar images of users are downloaded the first time a
user sends a message.
If this download succeeds a message with EVENT_AVATAR_DOWNLOAD is sent to the originating protocol.
This message also contains a SHA field (in msg.Extra["file"]), if this is not empty, the sha will
be added to the avatarMap. (so we now have a userid-sha cache)
Next time this user sends a message, the MediaServerUpload/sha/userid.png URL will be used as the
avatar field.
