Redmine wiki external filter plugin


This plugin allows defining macros that process macro argument using external filter program and render its result in Redmine wiki.

For every filter two macros are defined: <macro> and <macro>_include. The first one directly processes its argument using filter, while the second one assumes its argument is wiki page name, so it reads that wiki page content and processes it using the filter.

Macros already bundled with current release are listed below, but adding new ones is typically as easy as adding several lines in plugin config file.


  1. It’s recommended (but not required) to install popen4 library first as without it plugin is unable to capture stderr output of external command, so it might be hard to debug it if things go wrong.
  2. Get sources from github.
  3. See Installing a plugin on Redmine site.
  4. Copy wiki_external_filter.yml from config folder of plugin directory to the config folder of your redmine installation.
  5. After installation it’s strongly recommended to go to plugin settings and configure caching: Administration → Plugins → Wiki External Filter Plugin: Configure and follow instructions. Note that RoR file-based caching suggested by default does not implement proper cache expiration: you should either setup a cron task to clean cache or do it manually from time to time.
  6. To successfully use macros with argument expressions, it’s necessary to patch wiki formatting routine so that it preserves macros arguments.

    Redmine 1.3.0: apply redmine-1.3.0-macros-escaping.patch to the Redmine core and go to step 7.

    Redmine 1.0.2: apply this patch to the Redmine core and go to step 7, there’s no need to patch individual wiki formatters anymore.

    Redmine 0.9. if you use Markdown Extra, switch to the following fork of redmine_markdown_extra_formatter that contains all necessary changes. This patch is for older Markdown Extra formatter version and should not be used for new installations.

    Note: if you install Markdown Extra formatter - you should enable it in Administration → Settings → General → Text formatting.

    If you use wiki formatter other than Markdown Extra (including default Textile formatter) you will have to change your wiki formatter yourselves as follows:

    • Change MACROS_RE regexp not to stop too early - in the issue description Textile wiki formatter is mentioned, but in fact this change should be done for whatever wiki formatter you use.
    • Change arguments parsing - again, should be done for whatever wiki formatter you use.
    • For some of the formatters escaping should be avoided for macro arguments, see how it is done for Markdown Extra wiki formatter.

    Preliminary version of patch for Textile support was made available by Yuya Nishihara, according to the author “It works but really messy” but I haven’t tested it so cannot comment on it.

  7. To allow passing attachments names as macros arguments Redmine core should be patched accordingly:

    Redmine 1.3.0: redmine-1.3.0-attachments.patch.

    Redmine 1.0.2: redmine-1.0.2-attachments.patch.

    Redmine 0.9. redmine-attachments-in-macros.patch.

Specific filters installation instructions are below.

Prefedined Macros


PlantUML is a tool to render UML diagrams from their textual representation. It’s assumed that it can be invoked via wrapper /usr/bin/plantuml, here’s its example content:

/usr/bin/java -jar /usr/share/plantuml/lib/plantuml.jar ${@}

Result is rendered as PNG file. SVG support seems to be under development for PlantUML but so far looks like it’s still unusable.

Gentoo ebuild is attached.

Example of usage:

Alice -> Bob: Authentication Request
alt successful case
  Bob -> Alice: Authentication Accepted
else some kind of failure
  Bob -> Alice: Authentication Failure
    loop 1000 times
      Alice -> Bob: DNS Attack
else Another type of failure
  Bob -> Alice: Please repeat

Rendered output:

PlantUML output


Graphviz is a tool for graph-like structures visualization. It’s assumed that it can be called as /usr/bin/dot.

Result is rendered as SVG image or PNG fallback if SVG is not supported by your browser.

Example of usage:

digraph finite_state_machine {
    node [shape = doublecircle]; LR_0 LR_3 LR_4 LR_8;
    node [shape = circle];
    LR_0 -> LR_2 [ label = "SS(B)" ];
    LR_0 -> LR_1 [ label = "SS(S)" ];
    LR_1 -> LR_3 [ label = "S($end)" ];
    LR_2 -> LR_6 [ label = "SS(b)" ];
    LR_2 -> LR_5 [ label = "SS(a)" ];
    LR_2 -> LR_4 [ label = "S(A)" ];
    LR_5 -> LR_7 [ label = "S(b)" ];
    LR_5 -> LR_5 [ label = "S(a)" ];
    LR_6 -> LR_6 [ label = "S(b)" ];
    LR_6 -> LR_5 [ label = "S(a)" ];
    LR_7 -> LR_8 [ label = "S(b)" ];
    LR_7 -> LR_5 [ label = "S(a)" ];
    LR_8 -> LR_6 [ label = "S(b)" ];
    LR_8 -> LR_5 [ label = "S(a)" ];

Rendered output:

Graphviz output


Combination of Ritex: a Ruby WebTeX to MathML converter and SVGMath that takes WebTeX formula specification as input and produces SVG file as output.

Both ritex and SVGMath require some patches/wrappers.

Additionally working installation of xmllint from libxml2 with configured MathML catalog is required: for Gentoo use this ebuild.

Gentoo ebuilds for ritex and svgmath are attached.

Example of usage:

G(y) = \left\{\array{ 1 - e^{-\lambda x} & \text{ if } y \geq 0 \\ 0 & \text{ if } y < 0 }\right.

Rendered output:

Ritex output

video and video_url

These macros use ffmpeg to convert any supported video file to FLV format and display it on wiki using FlowPlayer flash player. video macro takes file path on server as its input, as well as attachments names from current wiki page, while video_url expects full URL to the video to convert & show.

Splash images for videos are generated automatically from the first frame of the video.

Multiple videos per page are supported, player instance is attached to the selected video as in this example.

Required packages installed:

  • ffmpeg
  • RMagick
  • wget - for video_url only.

Example of usage:






Rendered output (before player is embedded by clicking on the image, using Flowplayer video demo file):

Video output


Fortune is a simple program that displays a random message from a database of quotations.

Not strictly a filter on its own (as it does not require any input), but it plays nice with external filtering approach and is fun to use, hence it’s here

Example of usage:


Rendered output:

Fortune output

Third-Party macros


This macro provides Syntax diagrams support, thanks to Siamak Haschemi, see his blog for details and macro code.

Writing new macros

New macros can easily be added via wiki_external_filter.yml config file.

Every macro may have multiple commands processing the same input - for example for video macro two commands are used: first one extracts thumbnail and second one converts the video.

Commands use standard Unix approach for filtering: input is fed to the command via stdin and output is read on stdout. If command return status is zero, content type is assumed to be of content_type specified in config, otherwise it’s assumed to be plain error text together with stderr content.

You can use prolog/epilog config parameters to add standard text before/after actual macro content passed to filter.

Additionally, cache_seconds parameter specifies the number of seconds commands output result should be cached, use zero to disable caching for this macro.

The way filter output is visualized is controlled via app/views/wiki_external_filter/macro_*.html.erb files. The view to use is selected by template macro option in config. The view can use all commands outputs for particular macro.

replace_attachments tells plugin that it should parse the text passed to the macro and replace all occurrences of strings matching attachments names with their physical paths on disk.

Macro argument is de-escaped via CGI.unescapeHTML call prior to being fed to filter.

Current bugs/issues

  1. Either Redmine core (if you use default wiki engine) or your custom wiki engine plugin requires patching to get things work. In fact, the whole wiki formatting design as of now seems to be quite messy.
  2. SVG support is more complex it should have been if all browsers had played by the rules - currently quite some trickery with different XHTML elements/CSS tricks is used to show SVGs properly in major browsers. Of course, there’s not that much that can be done for IE as it does not support SVG at all, but now at least the plugin substitutes raster fall-back image for IE if it is available.
  3. For formula support, theoretically ritex alone is sufficient if you have MathML-capable browser, however in practice there are too many issues with this approach: for example Firefox (actually the onlt MathML-capable browser so far, it seems) requires specific DOCTYPE additions that Redmine currently lacks; additionally, Redmine emits text/html, while Firefox expects text/xml in order to parse MathML. Changing content type alone is not sufficient as Redmine HTML output does not pass more strict checks required for XML output. Hence, the double conversion (WebTeX to MathML and then MathML to SVG) is necessary. Once (if ever?) MathML support matures in other browser, possibly this can be revisited.
  4. SVGs could have been embedded into HTML page directly (thus allowing to use redmine links there) but I’m afraid there are similar problems as with MathML embedding attempts.
  5. RoR caching support is a mess: no way to expire old files from file-based cache??? Are you joking???

Additional info

  1. Somewhat similar plugins (although with narrower scope) are graphviz plugin and latex plugin. Graphviz functionality is mostly covered by current version of wiki_external_filter. Latex is not, but only due to the fact I do not have latex installed nor currently have a need in that: adding macro that performs latex filtering should be trivial.