246 lines
17 KiB
Markdown
Executable file
246 lines
17 KiB
Markdown
Executable file
---
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gitea: none
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title: WordPress/ActivityPub
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lang: en
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authors:
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- André Menrath
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- ruru
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include_toc: true
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---
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This document describes proposals for the evolvment of the [WordPress ActivityPub plugin](https://github.com/Automattic/WordPress-ActivityPub/) in the field of the interaction with other WordPress plugins that may add additional ActivityPub features.
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# Terms used
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The following terms are used:
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## Content related
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- **post type:** post types and custom post types within WordPress
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- **Object Type:** ActivityPub [object type](https://www.w3.org/TR/activitystreams-vocabulary/#object-types)
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- **Transformers:** a piece of code that converts items of particular WordPress post types to an ActivityPub object. For example a transformer that can transform:
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- every post type to a `Note`
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- `post` or `page` to `Note`, `Article`, `Image`, `Audio` or `Article` depending on the [post-format](https://wordpress.org/documentation/article/post-formats/)
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- `tribe_events` (Event post the of [The Event Calendar](https://wordpress.org/plugins/the-events-calendar/)) to `Event`
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- `podcast` (Podcast post of [Podlove Podcast Publisher](https://github.com/podlove/podlove-publisher)) to `PodcastEpisode` as ([proposed and implemented by Castopod](https://code.castopod.org/adaures/castopod/-/blob/main/app/Libraries/PodcastEpisode.php))
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## Actor related
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- **Actors:** ActivityPub [Actor Objects](https://www.w3.org/TR/activitypub/#actor-objects)
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- **Actor Types:** ActivityPub [Actor Types](https://www.w3.org/TR/activitystreams-vocabulary/#actor-types)
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- **WordPress actor types:** Things on WordPress that can be mapped to actors:
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- WordPress users →`Person`
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- Whole Blog →`Application` or `Group`
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- post types → e.g. `Organization`
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- custom definitions → custom actor types
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- **Mapping:** Which WordPress actor types are actually are mapped to any ActivityPub actors at all and to which one.
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## General
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- **publish/dispatch:** Sending a `Create`, `Update` or `Announce` [Activity](https://www.w3.org/TR/activitypub/#create-activity-outbox).
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# Principals of the changes proposed to the ActivityPub plugin
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The WordPress ActivityPub plugin
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- should be aware (or even control) the whole chain from creating some content within WordPress to being published via ActivityPub. For sure, it should be the only plugin that directly sends and receives ActivityPub.
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- should not get any more complex by default, the out-of-the box functionality/features and simplicity should be similar to version 1.0.0.
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- offers other plugins the possibility to register custom transformers.
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- (maybe) offers other plugins the possibility to register new WordPress actor types, e.g. the `tribe_organizer` post type of [The Event Calendar](https://wordpress.org/plugins/the-events-calendar/).
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- handles the controls collisions of actor names:
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* collisions that are already present during activation of a WordPress actor type on the settings page
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* collisions that happen afterwards (e.g. a new user registering with the same username as the blog-wide actor)
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* (maybe) show notifications/warnings when using an actor name which has been used and followed by in the past, as there may be issues due to caching of the old public key.
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- maybe distinguishes between the default admin user interface and advanced sections which give the user more fine-grained control:
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* transformer management
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* actor management
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# Goals
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## Goals of the WordPress Event Fedeartion project
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The event federations project goal is make it possible that events created within an event plugin can federate properly as an ActivityPub object with Type `Event` along with all the meta-data belonging to the event, as found in common ActivityPub implementations, e.g. of Mobilizon, in order to ensure maximum compatibly between those services.
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## Tangential Objectives:
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Nevertheless, we see a lot of other cases that can benefit, if the primary goals of the event federation project are achieved this using a modularized approach as proposed below. The following list indicates examples what might be those other benefits:
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- Other types of content get federated in a more feature rich way:
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- `PodcastEpisode` [as proposed by CastoPod](https://code.castopod.org/adaures/castopod/-/blob/main/app/Libraries/PodcastEpisode.php)
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- `Question`
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- `Product`
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- ...
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- ActivityPub offers features how to deal with multilingual content ([contentMap - see Example 115](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-contentmap)) which could be implemented differently by multilingual and translation plugins (example search for the current use of `->set_content_map` within the ActivityPub plugin).
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**Note:** CastoPop, to give an example, has currently decided that podcast episodes will not be sent to followers as a `Create` activity directly containing the `PodcastEpisode` object, but will send a `Note` which is linking to the `PodcastEpisode`, because most Fediverse implementations currently ignore by default all object types they don't know. This is likely the same reason [flohmarkt](https://codeberg.org/grindhold/flohmarkt) is currently also using the `Note` and not `Product` even though that one would be available in the offical specification.
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# Transformer Management
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## User Interface
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### Current situation
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The admin user interface in v1.0.0 lets one choose to which object type all post get transformed to. The options are:
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* [x] Note (default) - Should work with most platforms.
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* [ ] Article - The presentation of the "Article" might change on different platforms.
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* [ ] WordPress Post-Format - Maps the WordPress Post-Format to the ActivityPub Object Type.
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### Proposal
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All publicly accessible WordPress post types can become active for ActivityPub federation when selecting a transformer available for the relevant post type. The transformer determines the target ActivityPub object type, which can vary depending on variables like the post type or post format. If there is no specific transformer available for a given post type, it cannot be assigned through the user interface.
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| | Note | Post-Format | The Events Calendar Transformer | Custom Event Transformer |
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| ----------------- |:----:|:-----------:|:-------------------------------:|:------------------------:|
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| **post** | X | O | - | - |
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| **page** | O | O | - | - |
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| **tribe_events** | O | - | X | O |
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| **custom_event** | O | - | - | O |
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| **...** | O | - | - | - |
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**x:** Available transformers
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**y:** Public and non-password protected WordPress post types
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**Note:** Only one or zero selections can be made in each row.
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- For any custom post type, if there is a custom transformer registered, indicate that one should be selected as default (or select it right ahead?).
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- Should not differ too much from the current view: Maybe completely hide the current activity object type part of the settings and only show the buttons for `enable` and `disable` and move the transformer table to an advanced settings page.
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- Maybe make the tables more advanced and cleary show the origin of the transformer (built-in, etc.) and maybe a Pop-Up with a description, or even a link to a configuration page of the transformer.
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## Backend
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Currently, only one hard-coded transformer exists in `includes/transformer/class post.php` ([Source](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/transformer/class-post.php)).
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```php
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/**
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* WordPress Post Transformer
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*
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* The Post Transformer is responsible for transforming a WP_Post object into different othe
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* Object-Types.
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*
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* Currently supported are:
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*
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* - Activitypub\Activity\Base_Object
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*/
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class Post {
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...
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/**
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* Transforms the WP_Post object to an ActivityPub Object
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*
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* @see \Activitypub\Activity\Base_Object
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*
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* @return \Activitypub\Activity\Base_Object The ActivityPub Object
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*/
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public function to_object() {
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...
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```
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A solution could be to define a transformer interface and let the transformers be implementations.
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```php
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interface Transformer {
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public function get_supported_post_types(): array;
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public function get_transformer_info(): array;
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public function to_object(WP_Post $post);
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....
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}
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```
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Use WordPress's hook system or a public API function to let other plugins register their custom transformer implementations to the ActivityPub plugin.
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**Problem:** With the design above the transformer does a lot and leaves a lot of responsibility to the developer implementing it.
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**Possible alternatives and solutions:**
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- The ActivityPub plugin could provide reusable Traits for common tasks.
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- Highly unlikely: The ActivityPub plugin provides an even more height level framework for adding transformers. For example for events the ActivityPub plugin could provide a built-in transformer to the object type `Event` which only needs a mapping (might make things harder, instead of making them easier). See Appendix.
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- Don't use an interface with implementations, (miss)use class extensions.
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# Mapping: Actors and Dispatching
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More comprehensive actor management would benefit our project aims and potentially meet the needs of others in the future. Nevertheless, **its importance is considerably lower than that of Transformer management**. In the future, the following factors may become more important when larger websites should be using the ActivityPub plugin.
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## Current situation
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Currently, the admin user interface in v1.0.0 gives very limited options.
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```
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- [ ] Enable `blog`-actor
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- [ ] Enable `author`-actors
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```
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Note that depending on which options are enabled, the method of federating via ActivityPub varies significantly:
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- If the `blog`-actor is enabled, but the `author`-actors are not, posts are attributed and created by the blog actor.
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- If both are enabled the `blog`-actor will announce (boosting) the posts of the
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`author`-actors.
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Currently the whole logic controlling this is written within the `Activity_Dispatcher` [class](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/class-activity-dispatcher.php#L21) which is currently triggered only within the `Scheduler` [class](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/class-scheduler.php#L14-L15).
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Furthermore, although a blog actor is available, the ActivityPub plugin is still written in such a way that WordPress users are the default ActivityPub actors. This also reflects in things like the class which is responsible for the actor lookup is still called `Users` and yet handles the `Blog` and the `Application` user too, see the [Source](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/collection/class-users.php).
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## Possibilities
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ActivityPub knows several [actor types](https://www.w3.org/TR/activitystreams-core/#actors):
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- `Application`
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- `Group`
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- `Organization`
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- `Person`
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- `Service`
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The specifications allow for a lot of flexibility in their use. As WordPress websites serve a variety of tasks and goals, providing more detailed capabilities and options in this area **may prove challenging to accomplish in a user-friendly manner**.
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## What features does our event federation project need?
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- For maximum Mobilizon compatibility we would love to have simply an actor of type `Application`, preferable called `@relay@wordpress.site`, that announces all events. Nonetheless, in theory, a Mobilizon instance should have the capability to follow any other actor as well. More or less this can already be achieved with the current blog-actor.
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- Additionally, for example, organizers in [The Event Calendar](https://wordpress.org/plugins/the-events-calendar/) could also offer their own actor of type `Organizer` or `Group` to publicize events (getting referred to via [attributedTo](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attributedto)) if the `author`-actors are enabled, or create events (being the [actor](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-actor) directly) if the `author`-actors are not enabled.
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- Optional: As events are sometimes published a long time before they start, adding the possibility that events get announced again at a scheduled time before the start, e.g. by sending an `Announce` activity.
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## Other features
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Other WordPress actor types might have valid use cases, like actors for categories, or specific post types in general: "I only want to see the blog updates, but I do not want to spam my timeline with each product they post on their site, even if they choose to federate them."
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**Problems:**
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- Overall complexity may lead to programming and usage errors.
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- Naming collisions become more likely. See below.
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- Who is the `actor`, who is the `attributedTo`, who is just sending an `Announce` of a post?
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## Proposed starting point for evaluating use cases
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We keep in mind that every post type shall only ever send as a `Create` Activity once by one single actor.
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**User Interface:**
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| | users | tribe_organizers | custom | blog | category |
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| -----------------|:-----:|:----------------:|:------:|:-----:|:--------:|
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| **post** | C | O | O | A | A |
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| **page** | C | O | O | A | O |
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| **tribe_events** | O | C | - | A | 0 |
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| **product** | O | - | C | 0 | 0 |
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**x:** WordPress actor-types
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**y:** WordPress post types
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**C:** Create - can only be assigned once per row
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**A:** Announce - can be assigned multiple times per row, but only if a Create has been assigned before
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**user:** the WordPress user publishing or updating something
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**all:** blog-wide actor, everything that is published (like a relay)
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**custom:** e.g. only a certain post_type that gets announced with this actor
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**tribe_organizers:** only posts by one organizer
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- Only allow setting something to `Announce`, when a `Create` is already set.
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- Maybe forbid, that a user can automatically announce a post, because it's the "lowest level".
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## Actor collisions
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Each ActivityPub actor must have a [unique ID](https://www.w3.org/TR/activitypub/#obj-id). In our case this is a HTTPS URI.
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But in reality [webfinger](https://webfinger.net/) is used: `@actor-name@instance.tld`. Actors like Persons and Groups and Applications have Public Keys attached to them, as well as their ID is probably cached by most software. So assigning some actor-name to something new also can cause unintended behavior.
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If multiple plugins want to individually federate their content (like events, products and blog posts or even the built-in WordPress categories), they must be able to have something like an actor API, the ActivityPub plugin can register. The ActivityPub plugin being the main coordinator is necessary because actors are globally unique.
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- For existing (collision was created before the installation/activation of the plugin)
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- For new collisions (collision was/will be created after the installation/activation of the plugin)
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It seems like it is the best if collisions are avoided in the first place by encouraging the use of prefixes, like `category_<category>`.
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Anyway it seems the question has to be raised wheter activitypub should store a history of all past and currently mapped actors.
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### Existing collisions
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- **Easy:** Either we just tell the user to resolve all conflicts before a WordPress actor type can be activated at all
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- **Complex:** We let him choose alternatives for conflicts.
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### New collisions
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- **Easy** Forbid the saving of new users or posts that would conflict with an existing actor.
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- **Complex** ...
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## Conclusion
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- Anyway it seems the question has to be raised whether the ActivityPub plugin should store a history of all past and currently mapped actors.
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- Additionally, shouldn't the user have a detailed overview in each case if the actor management should get more complex?
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# Appendix
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## The approach of youtube-dl
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[youtube-dl](https://github.com/ytdl-org/youtube-dl) is solving a similar problem with "extractors" that return data to the processing-chain of youtube-dl. They provide a base class that includes useful functions for common issues e.g. automatic testing, geo-bypassing, login/cookie/header management. The most [basic extractor](https://github.com/ytdl-org/youtube-dl#adding-support-for-a-new-site) is about 40 lines of code.
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They can also chain extractors recursivly, like a extractor for mastodon videos, that gets the video from the post and returns the source of the video, that could be youtube, vimeo or anything else youtube-dl supports.
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