Rocket.Chat/packages/rocketchat-message-snippet/client/snippetMessage.js

Meteor.methods({
	snippetMessage: function(message) {
		if (typeof Meteor.userId() === 'undefined' || Meteor.userId() == null) {
			return false;
		}
		if ((typeof RocketChat.settings.get('Message_AllowSnippeting') === 'undefined') ||
			(RocketChat.settings.get('Message_AllowSnippeting') === null) ||
			(RocketChat.settings.get('Message_AllowSnippeting') === false)) {
			return false;
		}

		let room = RocketChat.models.Rooms.findOne({ _id: message.rid });

		if (Array.isArray(room.usernames) && room.usernames.indexOf(Meteor.user().username) === -1) {
			return false;
		}
		ChatMessage.update({
			_id: message._id
		}, {
			$set: {
				snippeted: true
			}
		});
	}
});