docs/app/extensions/groups/page.mdx

export const metadata = {
    title: 'Groups Extension',
    description: 'Groups are a way to organize users and notes into communities.'
}

# Groups Extension

Groups are a way to organize users and notes into communities. They can be used for any purpose, such as forums, blogs, image galleries, video sharing, audio sharing, and messaging. They are similar to Discord's channels or Matrix's rooms. {{ className: 'lead' }}

Refer to [Note](/entities/note#entity-definition)'s `group` property for how notes can be associated with groups.

## Entity Definition

<Row>
    <Col>
        <Properties name="Group">
            <Property name="type" type="string" required={true}>
                Must be `pub.versia:groups/Group`.
            </Property>
            <Property name="name" type="ContentFormat" required={false} typeLink="/structures/content-format">
               Group name/title.
               
               Text only (`text/plain`, `text/html`, etc).
            </Property>
            <Property name="description" type="ContentFormat" required={false} typeLink="/structures/content-format">
                Short description of the group's contents and purpose.
                
                Text only (`text/plain`, `text/html`, etc).
            </Property>
            <Property name="open" type="boolean" required={false}>
                Whether the group is open to all users or requires approval to join.

                <Note>
                    **This is meant as a UI hint** and does not guarantee that group subscriptions will be accepted or rejected.

                    It is similar to a [User](/entities/user)'s `manually_approves_followers` field.
                </Note>
            </Property>
            <Property name="members" type="URI" required={true} typeLink="/types#uri">
                URI of the group's members list. [URI Collection](/structures/collection#uri-collection) of [Users](/entities/user).
            </Property>
            <Property name="notes" type="URI" required={false} typeLink="/types#uri">
                URI of the group's associated notes. [URI Collection](/structures/collection#uri-collection) of [Notes](/entities/note).
            </Property>
        </Properties>
    </Col>

    <Col sticky>

    ```jsonc {{ title: "Example Group" }}
    {
        "type": "pub.versia:groups/Group",
        "id": "ed480922-b095-4f09-9da5-c995be8f5960",
        "name": {
            "text/html": {
                "content": "The <strong>Woozy</strong> fan club"
            }
        },
        "description": {
            "text/plain": {
                "content": "A group for fans of the Woozy emoji."
            }
        },
        "open": false
    }
    ```

    </Col>
</Row>

## Subscribing to Groups

[Users](/entities/user) may "subscribe" to a Group in order to receive all [Notes](/entities/note) posted to it. The mechanism by which federation is handled is described at [the end of this document](#federation).

First, a [User](/entities/user) must send a `GroupSubscribe` activity to the group. The group will then respond with either a `GroupSubscribeAccept` or a `GroupSubscribeReject` activity.

If the group accepts the subscription, the user will receive all notes posted to the group. If the group rejects the subscription, the user will not receive any notes posted to the group.

### GroupSubscribe

Indicates that a [User](/entities/user) wishes to subscribe to a group.

<Row>
    <Col>
        <Properties name="GroupSubscribe">
            <Property name="type" type="string" required={true}>
                Must be `pub.versia:groups/Subscribe`.
            </Property>
            <Property name="uri" type="null" required={false}>
                This is a [**Transient Entity**](/entities#transient-entities) and does not have a URI.
            </Property>
            <Property name="subscriber" type="URI" required={true} typeLink="/types#uri">
                URI of the [User](/entities/user) subscribing to the group.
            </Property>
            <Property name="group" type="URI" required={true} typeLink="/types#uri">
                URI of the group to subscribe to.
            </Property>
        </Properties>
    </Col>

    <Col sticky>

    ```jsonc {{ title: "Example GroupSubscribe" }}
    {
        "type": "pub.versia:groups/Subscribe",
        "id": "9a7e9345-4e4a-4d5a-8301-4dbbfe777ca0",
        "subscriber": "e9277471-8aa1-4d40-a3d0-0878e818ccdc",
        "group": "example.com:ed480922-b095-4f09-9da5-c995be8f5960",
        "created_at": "2021-01-01T00:00:00Z"
    }
    ```

    </Col>
</Row>

### GroupUnsubscribe

Indicates that a [User](/entities/user) wishes to unsubscribe from a group.

<Row>
    <Col>
        <Properties name="GroupUnsubscribe">
            <Property name="type" type="string" required={true}>
                Must be `pub.versia:groups/Unsubscribe`.
            </Property>
            <Property name="uri" type="null" required={false}>
                This is a [**Transient Entity**](/entities#transient-entities) and does not have a URI.
            </Property>
            <Property name="subscriber" type="URI" required={true} typeLink="/types#uri">
                URI of the [User](/entities/user) unsubscribing from the group.
            </Property>
            <Property name="group" type="URI" required={true} typeLink="/types#uri">
                URI of the group to unsubscribe from.
            </Property>
        </Properties>
    </Col>

    <Col sticky>

    ```jsonc {{ title: "Example GroupUnsubscribe" }}
    {
        "type": "pub.versia:groups/Unsubscribe",
        "id": "9a7e9345-4e4a-4d5a-8301-4dbbfe777ca0",
        "subscriber": "e9277471-8aa1-4d40-a3d0-0878e818ccdc",
        "group": "example.com:ed480922-b095-4f09-9da5-c995be8f5960",
        "created_at": "2021-01-01T00:00:00Z"
    }
    ```

    </Col>
</Row>

### GroupSubscribeAccept

Indicates that a [Group](#entity-definition) has accepted a [User](/entities/user)'s subscription request. Should be signed by the instance hosting the group.

<Row>
    <Col>
        <Properties name="GroupSubscribeAccept">
            <Property name="type" type="string" required={true}>
                Must be `pub.versia:groups/SubscribeAccept`.
            </Property>
            <Property name="uri" type="null" required={false}>
                This is a [**Transient Entity**](/entities#transient-entities) and does not have a URI.
            </Property>
            <Property name="subscriber" type="URI" required={true} typeLink="/types#uri">
                URI of the [User](/entities/user) subscribing to the group.
            </Property>
            <Property name="group" type="URI" required={true} typeLink="/types#uri">
                URI of the group that accepted the subscription.
            </Property>
        </Properties>
    </Col>

    <Col sticky>

    ```jsonc {{ title: "Example GroupSubscribeAccept" }}
    {
        "type": "pub.versia:groups/SubscribeAccept",
        "id": "9a7e9345-4e4a-4d5a-8301-4dbbfe777ca0",
        "subscriber": "e9277471-8aa1-4d40-a3d0-0878e818ccdc",
        "group": "example.com:ed480922-b095-4f09-9da5-c995be8f5960",
        "created_at": "2021-01-01T00:00:00Z"
    }
    ```

    </Col>
</Row>

### GroupSubscribeReject

Indicates that a [Group](#entity-definition) has rejected a [User](/entities/user)'s subscription request. Should be signed by the instance hosting the group.

<Row>
    <Col>
        <Properties name="GroupSubscribeReject">
            <Property name="type" type="string" required={true}>
                Must be `pub.versia:groups/SubscribeReject`.
            </Property>
            <Property name="uri" type="null" required={false}>
                This is a [**Transient Entity**](/entities#transient-entities) and does not have a URI.
            </Property>
            <Property name="subscriber" type="URI" required={true} typeLink="/types#uri">
                URI of the [User](/entities/user) subscribing to the group.
            </Property>
            <Property name="group" type="URI" required={true} typeLink="/types#uri">
                URI of the group that rejected the subscription.
            </Property>
        </Properties>
    </Col>

    <Col sticky>

    ```jsonc {{ title: "Example GroupSubscribeReject" }}
    {
        "type": "pub.versia:groups/SubscribeReject",
        "id": "9a7e9345-4e4a-4d5a-8301-4dbbfe777ca0",
        "subscriber": "e9277471-8aa1-4d40-a3d0-0878e818ccdc",
        "group": "example.com:ed480922-b095-4f09-9da5-c995be8f5960",
        "created_at": "2021-01-01T00:00:00Z"
    }
    ```

    </Col>
</Row>

## Federation

Group federation represents a particularly challenging problem, as it requires a way to make sure every single [Note](/entities/note) posted to it is delivered to every single member of the group.

All [Notes](/entities/note) posted to a group (using the `group` field) must be sent to its instance's [shared inbox](/federation#inboxes). Groups do not have an inbox of their own.

Once this is done, the group's instance must then federate this [Note](/entities/note) to every member of the group. However, this cannot be done the "normal way", as the group's instance does not have the private key to [sign](/signatures) the [Note](/entities/note).

### GroupFederate

The `GroupFederate` entity allows a group to federate a note to all of its members, without needing to sign the note itself. It contains a URI to the note being federated, which must be fetched by the receiving instances. This entity is signed by the group's instance.

<Row>
    <Col>
        <Properties name="GroupFederate">
            <Property name="type" type="string" required={true}>
                Must be `pub.versia:groups/Federate`.
            </Property>
            <Property name="uri" type="null" required={false}>
                This is a [**Transient Entity**](/entities#transient-entities) and does not have a URI.
            </Property>
            <Property name="note" type="URI" required={true} typeLink="/types#uri">
                URI of the note to federate.
            </Property>
            <Property name="group" type="URI" required={true} typeLink="/types#uri">
                URI of the group federating the note.
            </Property>
        </Properties>
    </Col>

    <Col sticky>

    ```jsonc {{ title: "Example GroupFederate" }}
    {
        "type": "pub.versia:groups/Federate",
        "id": "9a7e9345-4e4a-4d5a-8301-4dbbfe777ca0",
        "note": "c5aa65fa-0356-4029-b61c-6b237e5d1393",
        "group": "example.com:ed480922-b095-4f09-9da5-c995be8f5960",
        "created_at": "2021-01-01T00:00:00Z"
    }
    ```

    </Col>
</Row>