MediaWiki draw.io editor extension

This is a MediaWiki extension that integrates the draw.io flow chart editor and allows inline editing of charts.

Warnings

Please read these warnings carefully before use:

The default editor functionality is loaded from draw.io (for configuration options see below). This code only provides integration.
Be aware that draw.io is an online service and while this plugin integrates the editor using an iframe and communicates with it only locally in your browser (javascript postMessage), it cannot guarantee that the code loaded from draw.io will not upload any data to foreign servers. This may be a privacy concern. Read the Privacy section for more information. When in doubt, don't use draw.io or this module. You have been warned!
This plugin is quite new and probably still has bugs, so it may or may not work with your installation.

Features

draw.io chart creation and editing.
SVG and PNG support. The file type can be configured globally and changed on a per-image basis.
Inline Editing and javascript uploads on save, you never leave or reload the wiki page.
Image files are transparently stored in the standard wiki file store, you don't need to worry about them.
Versioning is provided by the file store.
Draw.io original XML data is stored within the image files, so only one file must be stored per chart.
Supports multiple charts per page.
Supports relative and fixed chart dimensions.

Requirements

When you intend to use SVG which is recommended, you might want to install Extension:NativeSvgHandler too. Also you need a browser that supports SVG.
While displaying charts may work in older browsers, especially when using PNG (SVG is default and recommended), saving charts requires a fairly recent browser.
The drawings produced by the draw.io editor make use of the xhtml namespace in SVG files. This namespace is not allowed for file uploads in MediaWiki 1.26 and later. So if you want to use SVG with this extension, you need to use a MediaWiki that is older or you need to patch it (see Installation). Hopefully this requirement is only temporary. She this issue and the one on Wikimedia's phabricator.

Installation

Clone this plugin into a folder named DrawioEditor within your wiki's extensions folder:

cd /where/your/wiki/is/extensions
git clone https://github.com/mgeb/mediawiki-drawio-editor DrawioEditor

Activate the plugin in LocalSettings.php:

wfLoadExtension( 'DrawioEditor' );

If you want so use SVG (recommended) and the version of your MediaWiki is 1.26 or newer, you need to add the namespace http://www.w3.org/1999/xhtml to $validNamespacesin includes/upload/UploadBase.php. See Requirements for more information on why this is currently needed.

Configuration

$wgDrawioEditorBackendUrl

To avoid the mentioned privacy concerns, you can change the URL of the editor using this setting in LocalSettings.php (i.e. use the officially provided docker image from jgraph/docker-drawio as server). The URL given here is used to load the draw.io/diagrams.net editor components embedded in an iframe, WARNING: changing this URL is officially not supported, but works, only change this for testing purpose or if know what you are doing! The default value is https://embed.diagrams.net.

Usage

Add a chart

Add the following tag to any wiki page to insert a draw.io chart:
```
{{#drawio:ChartName}}
```
ChartName must be unique and will be used as the basename for the backing file.
Save the wiki page.
Since no chart exists at this point, a placeholder will be shown where you've put the drawio tag. Click on the Edit link at the top right of it.
Draw your chart, click Save to save and Exit to leave Edit mode.

Edit a chart

Each chart will have an Edit lilnk at it's top right. Click it to get back into the editor. Click Save to save and Exit to get out of the editor. If a wiki page has multiple charts, only one can be edited at the same time.

View or revert to old versions

On each save, a new version of the backing file will be added to the wiki file store. You can get there by clicking the chart while you're not editing. There you can look at and revert to old versions like with any file uploaded to the wiki.

Options

Options are appended to the tag separated by |. For example:

{{#drawio:ChartName|type=svg|max-width=500px}}

Chart dimensions

While the defaults are good under most circumstances, it may be necessary to control how your chart is displayed. The following options can be used for that:

width: Sets the chart width. Defaults to 100%.
max-width: Set the maximum chart width if width is relative. Defaults to chart.
height: Sets the chart height. Defaults to auto. Usually not used.

These option take any absolute CSS length value as argument, for example:

400px
80%
auto

The keyword chart has a special meaning and stands for the actual size of the chart. When the chart is saved, the image dimensions are automatically adjusted. Usually it's preferable to use chart instead of a fixed pixel value.

The default behaviour is the let the chart scale (width=100% and height=auto) until it reaches its actual width stored in the chart (max-width=chart).

If you want it to scale further or less, you can adjust max_width manually. Use none to allow infinite scaling.

If you just want a fixed width, set width to chart or some fixed CSS value and leave height on auto. Unless you need a fixed sized image area before the image is actually loaded or really need to scale based on height, there is usually no point in setting height. If you set it you probably should set width to auto, or when setting both use chart so you don't need to update the values manually every time your image changes.

Examples

Let the chart scale until it reaches its actual width (default):

{{#drawio:ChartName}}

Same as:

{{#drawio:ChartName|width=100%|max-width=chart|height=auto}}

Let the chart scale until it's 800 px wide:
```
{{#drawio:ChartName|max-width=800px}}
```
Let the chart scale infinitely:
```
{{#drawio:ChartName|max-width=none}}
```
Fixed width:
```
{{#drawio:ChartName|width=600px}}
```
Fixed width using the actual chart width:
```
{{#drawio:ChartName|width=chart}}
```
Fixed height and width using the actual chart dimensions:
```
{{#drawio:ChartName|width=chart|height=chart}}
```

File type

The file type to be used can be set to either png or svg. The default is svg unless you set $wgDrawioEditorImageType to png in LocalSettings.php.

{{#drawio:ChartName|type=png}}

Use an Object Tag

MediaWiki normally embeds images inside <img> tags and links them to their description page. If you want to use SVG multimedia functions (e.g. links) it has to be embedded as <object>. This can be set using the interactive attribute or generally by enabling $wgDrawioEditorImageInteractive = true in LocalSettings.php.

{{#drawio:ChartName|interactive}}

Privacy

As mentioned in the Warnings Section above, there are some privacy concerns when using this plugin (or draw.io in general). Carefully read the information below, especially when you're running a wiki in a private environment.

draw.io may change it's code at any time, so the everything below could be outdated by the time you read it.

Referrer Leak

The draw.io editor is loaded within an iframe when you click the Edit link for a chart. At this point your browser loads all draw.io code from draw.io servers. While it is running in an iframe and has no access to your wiki page contents or any other resources, your browser may still send a referrer containing the current wiki page's URL to the draw.io servers, which may or may not be a problem in your environment. The wiki setting $wgReferrerPolicy may help you with this, but only for modern browsers.

Chart Data Privacy

Obviously the chart data must be passed to the draw.io application. The plugin uses the draw.io embed mode and passes the data to draw.io running in an iframe using javascript's postMessage(). This part happens locally, the data does not leave your browser. Currently, there does not seem to be any interaction with the draw.io servers while editing, which is good but of course this could change at any time without you or your wiki's users noticing. When saving, the file data is prepared (exported) by the iframe and passed back to this plugin (again) using postMessage(). The plugin then safely uploads the new version to the wiki file store. While the data passing happens locally and uploading is safe because it's done by this plugin in the main window context, the draw.io data export code running in the iframe seems to require interaction with draw.io servers in some cases.

One example is when you are using the Safari browser and save a chart which uses type png (see Options above). That process does not seem to be entirely implemented in javascript and needs the draw.io servers to generate the PNG data. This means your chart data leaves the browser. It is sent SSL encrypted and the draw.io folks probably don't care about your chart, but of course it's up to you to decide wether you can accept his or not. SVG does not seem to have that problem, at least in Chrome, Firefox and Safari, so I recommend using that. There may be other circumstances under which data leaves the browser. If this is a concern, you should check wether your use cases trigger such uploads, or not use this plugin and draw.io at all.

Again, be aware that the draw.io code running in the iframe may change its behavior at any time without you noticing. While that code has no access to your wiki, it may cause your chart data to be leaked. If this is a concern, don't use this plugin.

Links

https://www.mediawiki.org/wiki/Extension:DrawioEditor

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