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36c0a2 Ralph Thesen 2026-08-30 20:08:01
Add plugins page documenting installation and hooks
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# Plugins
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An Otter Wiki can be extended with plugins. It uses
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[pluggy](https://pluggy.readthedocs.io/en/stable/) to expose a set of function
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hooks that a plugin implements to add or change behaviour, from rewriting
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markdown before it is rendered to injecting HTML into the sidebar or reacting
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to page changes.
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> [!NOTE]
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> The plugin API is experimental and still limited. If you want to write a
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> plugin and cannot find a matching hook, please open an
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> [issue](https://github.com/redimp/otterwiki/issues).
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## What a plugin is
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A plugin is a normal, pip-installable Python package that registers one or more
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hook implementations. In practice that means three things:
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- a class whose methods are decorated with `@hookimpl`,
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- a call to `plugin_manager.register(...)` so the wiki finds it,
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- an `otterwiki` entry point in the package metadata.
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The smallest complete example, the `noemojis` plugin, strips emojis from every
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page before it is rendered:
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```python
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from otterwiki.plugins import hookimpl, plugin_manager
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class NoEmojiPlugin:
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@hookimpl
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def renderer_markdown_preprocess(self, md):
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return self.emojis.sub('', md)
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# needed so the plugin_manager finds the plugin
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plugin_manager.register(NoEmojiPlugin())
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```
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with a `pyproject.toml` that declares the entry point:
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```toml
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[project.entry-points.otterwiki]
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noemojis = "otterwiki_noemojis"
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```
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A plugin that surfaces `info()` and `help()` also appears in the in-app plugin
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help at [/-/help/plugins](/-/help/plugins), next to the built-in embeddings.
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## Installing a plugin
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A plugin must be installed into the same (virtual) environment that runs the
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flask app.
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### In the docker image
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On container start `entrypoint.sh` installs every plugin directory it finds
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under `/app-data/plugins/` and `/plugins/` with `pip install -U .`. So there
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are two ways to deploy a plugin:
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- drop the plugin directory into `plugins/` inside the volume that already
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holds your `app-data` (alongside `db.sqlite` and `repository`), or
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- keep your plugins in a separate directory and mount it into the container at
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`/plugins`.
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For example, mounting a plugins directory next to the usual app-data volume:
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```yaml
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services:
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otterwiki:
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image: redimp/otterwiki:2
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volumes:
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- ./app-data:/app-data
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- ./plugins:/plugins
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```
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> [!NOTE]
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> A plugin with dependencies that are not already in the image will fail to
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> install. In that case build a custom image that bundles the plugin and its
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> requirements. In environments with `SELINUX=enforcing` the bind mounts need
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> adjusting, see the [[FAQ|FAQ#environments-with-selinux]].
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### From a source install
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Activate the virtual environment that runs the app and install the plugin
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directory into it:
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```bash
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venv/bin/pip install .
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```
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### Uninstalling
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From a source install run `pip uninstall <plugin-name>`. For the docker image,
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remove the plugin directory and recreate the container for a clean environment.
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## Developing Plugins
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TODO
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### Available hooks
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The authoritative list of hooks, with full signatures and documentation, is the
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`OtterWikiPluginSpec` class in
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[otterwiki/plugins.py](https://github.com/redimp/otterwiki/blob/main/otterwiki/plugins.py).
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A plugin implements only the hooks it needs. Grouped by purpose:
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**Setup**
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- `setup(app, db, storage)` receives the Flask app, database and git storage to initialise the plugin.
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**Rendering (pre/post processing)**
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- `renderer_markdown_preprocess(md)` transforms the raw markdown before rendering (chained across plugins).
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- `renderer_html_postprocess(html)` transforms the HTML after the page has been rendered.
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- `renderer_javascript()` adds JavaScript to the rendered page.
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- `page_view_htmlcontent_postprocess(html, page)` transforms a page's rendered content just before display.
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- `page_render_context(page, preview)` receives the page currently being rendered, and whether it is a preview.
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**Embeddings**
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- `embedding_parse(embedding, options, args)` parses an embedding and returns its HTML.
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- `embedding_render(embedding, args)` renders a `{{name ...}}` embedding to HTML.
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**Template injection points**
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- `template_html_head_inject(page)` injects HTML into the `<head>`.
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- `template_html_body_inject(page)` injects HTML before the closing `</body>`.
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- `template_html_sidebar_left_inject(page)` appends HTML to the left sidebar (menu and page index).
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- `template_html_sidebar_right_inject(page)` appends HTML to the right sidebar (the "On this page" block).
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**Per-element rendering**
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- `renderer_process_link(...)` modifies each rendered markdown link.
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- `renderer_process_image(...)` modifies each rendered image.
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- `renderer_process_heading(...)` modifies each rendered heading.
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- `renderer_process_wikilink(...)` modifies each rendered WikiLink.
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**Repository and page events**
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- `repository_changed(changed_files)` reacts to any repository change, including the git web server and automatic pulls (read-only).
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- `page_saved(pagepath, content, author, message)` runs after a page's content changed.
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- `page_deleted(pagepath, author, message)` runs after a page was deleted.
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- `page_renamed(old_pagepath, new_pagepath, author, message)` runs after a page was renamed.
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**Info and help**
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- `info()` returns `(name, description, category)` used to group the plugin in the user help.
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- `help(plugin)` returns the plugin's documentation shown under `/-/help`.
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- `help_category_prelude(category)` returns introductory text for a help category.
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**Static CSS**
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- `static_css()` returns CSS added to every page via the layout template.
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**URL routes**
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- `url_request(plugin, extra, method, values)` handles requests to `/-/plugin/<name>/<extra>`.
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- `url_admin_request(plugin, extra, method, values)` handles admin requests to `/-/admin/plugin/<name>/<extra>`.
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**Sidebar page index**
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- `sidebar_page_index_filter_entries(entries, mode)` filters the sidebar page index entries in place.
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- `sidebar_page_index_sort_entries(entries, mode)` sorts the sidebar page index entries in place.
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## Example plugins
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Six worked examples live in
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[docs/plugin_examples](https://github.com/redimp/otterwiki/tree/main/docs/plugin_examples)
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in the source repository. Each is a self-contained package you can copy as a
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starting point, and they come with a `docker-compose.yaml` for trying them out
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and a test suite.
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- [noemojis](https://github.com/redimp/otterwiki/tree/main/docs/plugin_examples/plugin_noemojis) removes all emojis from pages.
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- [htmlinjection](https://github.com/redimp/otterwiki/tree/main/docs/plugin_examples/plugin_htmlinjection) demonstrates the HTML injection and per-element rendering hooks.
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- [referencingpages](https://github.com/redimp/otterwiki/tree/main/docs/plugin_examples/plugin_referencingpages) shows which pages reference the current page via WikiLinks.
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- [sidebarpageindex](https://github.com/redimp/otterwiki/tree/main/docs/plugin_examples/plugin_sidebarpageindex) demonstrates the sidebar page index filter and sort hooks.
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- [authorsignature](https://github.com/redimp/otterwiki/tree/main/docs/plugin_examples/plugin_authorsignature) adds a footer with the original author and last editor.
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- [redlinks](https://github.com/redimp/otterwiki/tree/main/docs/plugin_examples/plugin_redlinks) marks WikiLinks to non-existent pages in red, like MediaWiki's redlinks.