docs/src/contributing_apub_api_outline.md

   1 # Activitypub API outline
   2
   3 This document is targeted at developers who are familiar with the ActivityPub and ActivityStreams protocols. It gives a detailed outline of the actors, objects and activities used by Lemmy.
   4
   5 Before reading this, have a look at our [Federation Overview](contributing_federation_overview.md) to get an idea how Lemmy federation works on a high level.
   6
   7 Lemmy does not yet follow the ActivityPub spec in all regards. For example, we don't set a valid context indicating our context fields. We also ignore fields like `inbox`, `outbox` or `endpoints` for remote actors, and assume that everything is Lemmy. For an overview of deviations, read [#698](https://github.com/LemmyNet/lemmy/issues/698). They will be fixed in the near future.
   8
   9 Lemmy is also really inflexible when it comes to incoming activities and objects. They need to be exactly identical to the examples below. Things like having an array instead of a single value, or an object ID instead of the full object will result in an error.
  10
  11 In the following tables, "mandatory" refers to whether or not Lemmy will accept an incoming activity without this field. Lemmy itself will always include all non-empty fields.
  12
  13 <!-- toc -->
  14
  15 - [Actors](#actors)
  16   * [Community](#community)
  17   * [User](#user)
  18 - [Objects](#objects)
  19   * [Post](#post)
  20   * [Comment](#comment)
  21   * [Private Message](#private-message)
  22 - [Activities](#activities)
  23   * [Follow](#follow)
  24   * [Accept Follow](#accept-follow)
  25   * [Unfollow](#unfollow)
  26   * [Create or Update Post](#create-or-update-post)
  27   * [Create or Update Comment](#create-or-update-comment)
  28   * [Like Post or Comment](#like-post-or-comment)
  29   * [Dislike Post or Comment](#dislike-post-or-comment)
  30   * [Delete Post or Comment](#delete-post-or-comment)
  31   * [Remove Post or Comment](#remove-post-or-comment)
  32   * [Undo](#undo)
  33   * [Announce](#announce)
  34   * [Create or Update Private message](#create-or-update-private-message)
  35   * [Delete Private Message](#delete-private-message)
  36   * [Undo Delete Private Message](#undo-delete-private-message)
  37
  38 <!-- tocstop -->
  39
  40 ## Actors
  41
  42 ### Community
  43
  44 An automated actor. Users can send posts or comments to it, which the community forwards to its followers in the form of `Announce`.
  45
  46 Sends activities to user: `Accept/Follow`, `Announce`
  47
  48 Receives activities from user: `Follow`, `Undo/Follow`, `Create`, `Update`, `Like`, `Dislike`, `Remove` (only admin/mod), `Delete` (only creator), `Undo` (only for own actions)
  49
  50 ```json
  51 {
  52     "@context": "https://www.w3.org/ns/activitystreams",
  53     "id": "https://enterprise.lemmy.ml/c/main",
  54     "type": "Group",
  55     "preferredUsername": "main",
  56     "name": "The Main Community",
  57     "category": {
  58         "identifier": "1",
  59         "name": "Discussion"
  60     },
  61     "sensitive": false,
  62     "attributedTo": [
  63         "https://enterprise.lemmy.ml/u/picard",
  64         "https://enterprise.lemmy.ml/u/riker"
  65     ],
  66     "content": "Welcome to the default community!",
  67     "icon": {
  68         "type": "Image",
  69         "url": "https://enterprise.lemmy.ml/pictrs/image/Z8pFFb21cl.png"
  70     },
  71     "image": {
  72         "type": "Image",
  73         "url": "https://enterprise.lemmy.ml/pictrs/image/Wt8zoMcCmE.jpg"
  74     },
  75     "inbox": "https://enterprise.lemmy.ml/c/main/inbox",
  76     "outbox": "https://enterprise.lemmy.ml/c/main/outbox",
  77     "followers": "https://enterprise.lemmy.ml/c/main/followers",
  78     "endpoints": {
  79         "sharedInbox": "https://enterprise.lemmy.ml/inbox"
  80     },
  81     "published": "2020-10-06T17:27:43.282386+00:00",
  82     "updated": "2020-10-08T11:57:50.545821+00:00",
  83     "publicKey": {
  84         "id": "https://enterprise.lemmy.ml/c/main#main-key",
  85         "owner": "https://enterprise.lemmy.ml/c/main",
  86         "publicKeyPem": "-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA9JJ7Ybp/H7iXeLkWFepg\ny4PHyIXY1TO9rK3lIBmAjNnkNywyGXMgUiiVhGyN9yU7Km8aWayQsNHOkPL7wMZK\nnY2Q+CTQv49kprEdcDVPGABi6EbCSOcRFVaUjjvRHf9Olod2QP/9OtX0oIFKN2KN\nPIUjeKK5tw4EWB8N1i5HOuOjuTcl2BXSemCQLAlXerLjT8xCarGi21xHPaQvAuns\nHt8ye7fUZKPRT10kwDMapjQ9Tsd+9HeBvNa4SDjJX1ONskNh2j4bqHHs2WUymLpX\n1cgf2jmaXAsz6jD9u0wfrLPelPJog8RSuvOzDPrtwX6uyQOl5NK00RlBZwj7bMDx\nzwIDAQAB\n-----END PUBLIC KEY-----\n"
  87     }
  88 }
  89 ```
  90
  91 | Field Name | Mandatory | Description |
  92 |---|---|---|
  93 | `preferredUsername` | yes | Name of the actor |
  94 | `name` | yes | Title of the community |
  95 | `category` | yes | Hardcoded list of categories, see https://dev.lemmy.ml/api/v1/categories |
  96 | `sensitive` | yes | True indicates that all posts in the community are nsfw |
  97 | `attributedTo` | yes | First the community creator, then all the remaining moderators |
  98 | `content` | no | Text for the community sidebar, usually containing a description and rules |
  99 | `icon` | no | Icon, shown next to the community name |
 100 | `image` | no | Banner image, shown on top of the community page |
 101 | `inbox` | no | ActivityPub inbox URL |
 102 | `outbox` | no | ActivityPub outbox URL, only contains up to 20 latest posts, no comments, votes or other activities |
 103 | `followers` | no | Follower collection URL, only contains the number of followers, no references to individual followers |
 104 | `endpoints` | no | Contains URL of shared inbox |
 105 | `published` | no | Datetime when the community was first created |
 106 | `updated` | no | Datetime when the community was last changed |
 107 | `publicKey` | yes | The public key used to verify signatures from this actor |
 108
 109 ### User
 110
 111 A person, interacts primarily with the community where it sends and receives posts/comments. Can also create and moderate communities, and send private messages to other users.
 112
 113 Sends activities to Community: `Follow`, `Undo/Follow`, `Create`, `Update`, `Like`, `Dislike`, `Remove` (only admin/mod), `Delete` (only creator), `Undo` (only for own actions)
 114
 115 Receives activities from Community: `Accept/Follow`, `Announce`
 116
 117 Sends and receives activities from/to other users: `Create/Note`, `Update/Note`, `Delete/Note`, `Undo/Delete/Note` (all those related to private messages)
 118
 119 ```json
 120 {
 121     "@context": "https://www.w3.org/ns/activitystreams",
 122     "id": "https://enterprise.lemmy.ml/u/picard",
 123     "type": "Person",
 124     "preferredUsername": "picard",
 125     "name": "Jean-Luc Picard",
 126     "summary": "The user bio",
 127     "icon": {
 128         "type": "Image",
 129         "url": "https://enterprise.lemmy.ml/pictrs/image/DS3q0colRA.jpg"
 130     },
 131     "image": {
 132         "type": "Image",
 133         "url": "https://enterprise.lemmy.ml/pictrs/image/XenaYI5hTn.png"
 134     },
 135     "inbox": "https://enterprise.lemmy.ml/u/picard/inbox",
 136     "endpoints": {
 137         "sharedInbox": "https://enterprise.lemmy.ml/inbox"
 138     },
 139     "published": "2020-10-06T17:27:43.234391+00:00",
 140     "updated": "2020-10-08T11:27:17.905625+00:00",
 141     "publicKey": {
 142         "id": "https://enterprise.lemmy.ml/u/picard#main-key",
 143         "owner": "https://enterprise.lemmy.ml/u/picard",
 144         "publicKeyPem": "-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAyH9iH83+idw/T4QpuRSY\n5YgQ/T5pJCNxvQWb6qcCu3gEVigfbreqZKJpOih4YT36wu4GjPfoIkbWJXcfcEzq\nMEQoYbPStuwnklpN2zj3lRIPfGLht9CAlENLWikTUoW5kZLyU6UQtOGdT2b1hDuK\nsUEn67In6qYx6pal8fUbO6X3O2BKzGeofnXgHCu7QNIuH4RPzkWsLhvwqEJYP0zG\nodao2j+qmhKFsI4oNOUCGkdJejO7q+9gdoNxAtNNKilIOwUFBYXeZJb+XGlzo0X+\n70jdJ/xQCPlPlItU4pD/0FwPLtuReoOpMzLi20oDsPXJBvn+/NJaxqDINuywcN5p\n4wIDAQAB\n-----END PUBLIC KEY-----\n"
 145     }
 146 }
 147 ```
 148
 149 | Field Name | Mandatory | Description |
 150 |---|---|---|
 151 | `preferredUsername` | yes | Name of the actor |
 152 | `name` | no | The user's displayname |
 153 | `summary` | no | User bio |
 154 | `icon` | no | The user's avatar, shown next to the username |
 155 | `image` | no | The user's banner, shown on top of the profile |
 156 | `inbox` | no | ActivityPub inbox URL |
 157 | `endpoints` | no | Contains URL of shared inbox |
 158 | `published` | no | Datetime when the user signed up |
 159 | `updated` | no | Datetime when the user profile was last changed |
 160 | `publicKey` | yes | The public key used to verify signatures from this actor |
 161
 162 ## Objects
 163
 164 ### Post
 165
 166 A page with title, and optional URL and text content. The URL often leads to an image, in which case a thumbnail is included. Each post belongs to exactly one community.
 167
 168 ```json
 169 {
 170     "@context": "https://www.w3.org/ns/activitystreams",
 171     "id": "https://voyager.lemmy.ml/post/29",
 172     "type": "Page",
 173     "attributedTo": "https://voyager.lemmy.ml/u/picard",
 174     "to": "https://voyager.lemmy.ml/c/main",
 175     "summary": "Test thumbnail 2",
 176     "content": "blub blub",
 177     "url": "https://voyager.lemmy.ml:/pictrs/image/fzGwCsq7BJ.jpg",
 178     "image": {
 179         "type": "Image",
 180         "url": "https://voyager.lemmy.ml/pictrs/image/UejwBqrJM2.jpg"
 181     },
 182     "commentsEnabled": true,
 183     "sensitive": false,
 184     "stickied": false,
 185     "published": "2020-09-24T17:42:50.396237+00:00",
 186     "updated": "2020-09-24T18:31:14.158618+00:00"
 187 }
 188 ```
 189
 190 | Field Name | Mandatory | Description |
 191 |---|---|---|
 192 | `attributedTo` | yes | ID of the user which created this post |
 193 | `to` | yes | ID of the community where it was posted to |
 194 | `summary` | yes | Title of the post |
 195 | `content` | no | Body of the post |
 196 | `url` | no | An arbitrary link to be shared |
 197 | `image` | no | Thumbnail for `url`, only present if it is an image link |
 198 | `commentsEnabled` | yes | False indicates that the post is locked, and no comments can be added |
 199 | `sensitive` | yes | True marks the post as NSFW, blurs the thumbnail and hides it from users with NSFW settign disabled |
 200 | `stickied` | yes | True means that it is shown on top of the community |
 201 | `published` | no | Datetime when the post was created |
 202 | `updated` | no | Datetime when the post was edited (not present if it was never edited) |
 203
 204 ### Comment
 205
 206 A reply to a post, or reply to another comment. Contains only text (including references to other users or communities). Lemmy displays comments in a tree structure.
 207
 208 ```json
 209 {
 210     "@context": "https://www.w3.org/ns/activitystreams",
 211     "id": "https://enterprise.lemmy.ml/comment/95",
 212     "type": "Note",
 213     "attributedTo": "https://enterprise.lemmy.ml/u/picard",
 214     "to": "https://enterprise.lemmy.ml/c/main",
 215     "content": "mmmk",
 216     "inReplyTo": [
 217         "https://enterprise.lemmy.ml/post/38",
 218         "https://voyager.lemmy.ml/comment/73"
 219     ],
 220     "published": "2020-10-06T17:53:22.174836+00:00",
 221     "updated": "2020-10-06T17:53:22.174836+00:00"
 222 }
 223 ```
 224
 225 | Field Name | Mandatory | Description |
 226 |---|---|---|
 227 | `attributedTo` | yes | ID of the user who created the comment |
 228 | `to` | yes | Community where the comment was made |
 229 | `content` | yes | The comment text |
 230 | `inReplyTo` | yes | IDs of the post where this comment was made, and the parent comment. If this is a top-level comment, `inReplyTo` only contains the post |
 231 | `published` | no | Datetime when the comment was created |
 232 | `updated` | no | Datetime when the comment was edited (not present if it was never edited) |
 233
 234 ### Private Message
 235
 236 A direct message from one user to another. Can not include additional users. Threading is not implemented yet, so the `inReplyTo` field is missing.
 237
 238 ```json
 239 {
 240     "@context": "https://www.w3.org/ns/activitystreams",
 241     "id": "https://enterprise.lemmy.ml/private_message/34",
 242     "type": "Note",
 243     "attributedTo": "https://enterprise.lemmy.ml/u/picard",
 244     "to": "https://voyager.lemmy.ml/u/janeway",
 245     "content": "test",
 246     "published": "2020-10-08T19:10:46.542820+00:00",
 247     "updated": "2020-10-08T20:13:52.547156+00:00"
 248 }
 249 ```
 250
 251 | Field Name | Mandatory | Description |
 252 |---|---|---|
 253 | `attributedTo` | ID of the user who created this private message |
 254 | `to` | ID of the recipient |
 255 | `content` | yes | The text of the private message |
 256 | `published` | no | Datetime when the message was created |
 257 | `updated` | no | Datetime when the message was edited (not present if it was never edited) |
 258
 259 ## Activities
 260
 261 ### Follow
 262
 263 When the user clicks "Subscribe" in a community, a `Follow` is sent. The community automatically responds with an `Accept/Follow`.
 264
 265 Sent by: User
 266
 267 Sent to: Community
 268
 269 ```json
 270 {
 271     "@context": "https://www.w3.org/ns/activitystreams",
 272     "id": "https://enterprise.lemmy.ml/activities/follow/2e4784b7-4edf-4fa1-a352-674d5d5f8891",
 273     "type": "Follow",
 274     "actor": "https://enterprise.lemmy.ml/u/picard",
 275     "to": "https://ds9.lemmy.ml/c/main",
 276     "object": "https://ds9.lemmy.ml/c/main"
 277 }
 278 ```
 279
 280 | Field Name | Mandatory | Description |
 281 |---|---|---|
 282 | `actor` | yes | The user that is sending the follow request |
 283 | `object` | yes | The community to be followed |
 284
 285 ### Accept Follow
 286
 287 Automatically sent by the community in response to a `Follow`. At the same time, the community adds this user to its followers list.
 288
 289 Sent by: Community
 290
 291 Sent to: User
 292
 293 ```json
 294 {
 295     "@context": "https://www.w3.org/ns/activitystreams",
 296     "id": "https://ds9.lemmy.ml/activities/accept/5314bf7c-dab8-4b01-baf2-9be11a6a812e",
 297     "type": "Accept",
 298     "actor": "https://ds9.lemmy.ml/c/main",
 299     "to": "https://enterprise.lemmy.ml/u/picard",
 300     "object": {
 301         "@context": "https://www.w3.org/ns/activitystreams",
 302         "id": "https://enterprise.lemmy.ml/activities/follow/2e4784b7-4edf-4fa1-a352-674d5d5f8891",
 303         "type": "Follow",
 304         "object": "https://ds9.lemmy.ml/c/main",
 305         "actor": "https://enterprise.lemmy.ml/u/picard"
 306     }
 307 }
 308 ```
 309
 310 | Field Name | Mandatory | Description |
 311 |---|---|---|
 312 | `actor` | yes | The same community as in the `Follow` activity |
 313 | `to` | no | ID of the user which sent the `Follow` |
 314 | `object` | yes | The previously sent `Follow` activity |
 315
 316 ### Unfollow
 317
 318 Clicking on the unsubscribe button in a community causes an `Undo/Follow` to be sent. The community removes the user from its follower list after receiving it.
 319
 320 Sent by: User
 321
 322 Sent to: Community
 323
 324 ```json
 325 {
 326     "@context": "https://www.w3.org/ns/activitystreams",
 327     "id": "http://lemmy-alpha:8541/activities/undo/2c624a77-a003-4ed7-91cb-d502eb01b8e8",
 328     "type": "Undo",
 329     "actor": "http://lemmy-alpha:8541/u/lemmy_alpha",
 330     "to": "http://lemmy-beta:8551/c/main",
 331     "object": {
 332         "@context": "https://www.w3.org/ns/activitystreams",
 333         "id": "http://lemmy-alpha:8541/activities/follow/f0d732e7-b1e7-4857-a5e0-9dc83c3f7ee8",
 334         "type": "Follow",
 335         "actor": "http://lemmy-alpha:8541/u/lemmy_alpha",
 336         "object": "http://lemmy-beta:8551/c/main"
 337     }
 338 }
 339 ```
 340 ### Create or Update Post
 341
 342 When a user creates a new post, it is sent to the respective community. Editing a previously created post sends an almost identical activity, except the `type` being `Update`. We don't support mentions in posts yet.
 343
 344 Sent by: User
 345
 346 Sent to: Community
 347
 348 ```json
 349 {
 350     "@context": "https://www.w3.org/ns/activitystreams",
 351     "id": "https://enterprise.lemmy.ml/activities/create/6e11174f-501a-4531-ac03-818739bfd07d",
 352     "type": "Create",
 353     "actor": "https://enterprise.lemmy.ml/u/riker",
 354     "to": "https://www.w3.org/ns/activitystreams#Public",
 355     "cc": [
 356       "https://ds9.lemmy.ml/c/main/"
 357     ],
 358     "object": ...
 359 }
 360 ```
 361
 362 | Field Name | Mandatory | Description |
 363 |---|---|---|
 364 | `type` | yes | either `Create` or `Update` |
 365 | `cc` | yes | Community where the post is being made |
 366 | `object` | yes | The post being created |
 367
 368 ### Create or Update Comment
 369
 370 A reply to a post, or to another comment. Can contain mentions of other users. Editing a previously created post sends an almost identical activity, except the `type` being `Update`.
 371
 372 Sent by: User
 373
 374 Sent to: Community
 375
 376 ```json
 377 {
 378     "@context": "https://www.w3.org/ns/activitystreams",
 379     "id": "https://enterprise.lemmy.ml/activities/create/6f52d685-489d-4989-a988-4faedaed1a70",
 380     "type": "Create",
 381     "actor": "https://enterprise.lemmy.ml/u/riker",
 382     "to": "https://www.w3.org/ns/activitystreams#Public",
 383     "tag": [{
 384         "type": "Mention",
 385         "name": "@sisko@ds9.lemmy.ml",
 386         "href": "https://ds9.lemmy.ml/u/sisko"
 387     }],
 388     "cc": [
 389         "https://ds9.lemmy.ml/c/main/",
 390         "https://ds9.lemmy.ml/u/sisko"
 391     ],
 392     "object": ...
 393 }
 394 ```
 395
 396 | Field Name | Mandatory | Description |
 397 |---|---|---|
 398 | `tag` | no | List of users which are mentioned in the comment (like `@user@example.com`) |
 399 | `cc` | yes | Community where the post is being made, the user being replied to (creator of the parent post/comment), as well as any mentioned users |
 400 | `object` | yes | The comment being created |
 401
 402 ### Like Post or Comment
 403
 404 An upvote for a post or comment.
 405
 406 Sent by: User
 407
 408 Sent to: Community
 409
 410 ```json
 411 {
 412     "@context": "https://www.w3.org/ns/activitystreams",
 413     "id": "https://enterprise.lemmy.ml/activities/like/8f3f48dd-587d-4624-af3d-59605b7abad3",
 414     "type": "Like",
 415     "actor": "https://enterprise.lemmy.ml/u/riker",
 416     "to": "https://www.w3.org/ns/activitystreams#Public",
 417     "cc": [
 418         "https://ds9.lemmy.ml/c/main/"
 419     ],
 420     "object": ...
 421 }
 422 ```
 423
 424 | Field Name | Mandatory | Description |
 425 |---|---|---|
 426 | `cc` | yes | ID of the community where the post/comment is |
 427 | `object` | yes | The post or comment being upvoted |
 428
 429 ### Dislike Post or Comment
 430
 431 A downvote for a post or comment.
 432
 433 Sent by: User
 434
 435 Sent to: Community
 436
 437 ```json
 438 {
 439     "@context": "https://www.w3.org/ns/activitystreams",
 440     "id": "https://enterprise.lemmy.ml/activities/dislike/fd2b8e1d-719d-4269-bf6b-2cadeebba849",
 441     "type": "Dislike",
 442     "actor": "https://enterprise.lemmy.ml/u/riker",
 443     "to": "https://www.w3.org/ns/activitystreams#Public",
 444     "cc": [
 445       "https://ds9.lemmy.ml/c/main/"
 446     ],
 447     "object": ...
 448 }
 449 ```
 450
 451 | Field Name | Mandatory | Description |
 452 |---|---|---|
 453 | `cc` | yes | ID of the community where the post/comment is |
 454 | `object` | yes | The post or comment being upvoted |
 455
 456 ### Delete Post or Comment
 457
 458 Deletes a previously created post or comment. This can only be done by the original creator of that post/comment.
 459
 460 Sent by: User
 461
 462 Sent to: Community
 463
 464 ```json
 465 {
 466     "@context": "https://www.w3.org/ns/activitystreams",
 467     "id": "https://enterprise.lemmy.ml/activities/delete/f1b5d57c-80f8-4e03-a615-688d552e946c",
 468     "type": "Delete",
 469     "actor": "https://enterprise.lemmy.ml/u/riker",
 470     "to": "https://www.w3.org/ns/activitystreams#Public",
 471     "cc": [
 472         "https://enterprise.lemmy.ml/c/main/"
 473     ],
 474     "object": "https://enterprise.lemmy.ml/post/32"
 475 }
 476 ```
 477
 478 | Field Name | Mandatory | Description |
 479 |---|---|---|
 480 | `cc` | yes | ID of the community where the post/comment is |
 481 | `object` | yes | ID of the post or comment being deleted |
 482
 483 ### Remove Post or Comment
 484
 485 Removes a post or comment. This can only be done by a community mod, or by an admin on the instance where the community is hosted.
 486
 487 Sent by: User
 488
 489 Sent to: Community
 490
 491 ```json
 492 {
 493     "@context": "https://www.w3.org/ns/activitystreams",
 494     "id": "https://ds9.lemmy.ml/activities/remove/aab93b8e-3688-4ea3-8212-d00d29519218",
 495     "type": "Remove",
 496     "actor": "https://ds9.lemmy.ml/u/sisko",
 497     "to": "https://www.w3.org/ns/activitystreams#Public",
 498     "cc": [
 499         "https://ds9.lemmy.ml/c/main/"
 500     ],
 501     "object": "https://enterprise.lemmy.ml/comment/32"
 502 }
 503 ```
 504
 505 | Field Name | Mandatory | Description |
 506 |---|---|---|
 507 | `cc` | yes | ID of the community where the post/comment is |
 508 | `object` | yes | ID of the post or comment being removed |
 509
 510 ### Undo
 511
 512 Reverts a previous activity, can only be done by the `actor` of `object`. In case of a `Like` or `Dislike`, the vote count is changed back. In case of a `Delete` or `Remove`, the post/comment is restored. The `object` is regenerated from scratch, as such the activity ID and other fields are different.
 513
 514 Sent by: User
 515
 516 Sent to: Community
 517
 518 ```json
 519 {
 520   "@context": "https://www.w3.org/ns/activitystreams",
 521   "id": "https://ds9.lemmy.ml/activities/undo/70ca5fb2-e280-4fd0-a593-334b7f8a5916",
 522   "type": "Undo",
 523   "actor": "https://ds9.lemmy.ml/u/sisko",
 524   "to": "https://www.w3.org/ns/activitystreams#Public",
 525   "cc": [
 526     "https://ds9.lemmy.ml/c/main/"
 527   ],
 528   "object": ...
 529 }
 530 ```
 531
 532 | Field Name | Mandatory | Description |
 533 |---|---|---|
 534 | `object` | yes | Any `Like`, `Dislike`, `Delete` or `Remove` activity as described above |
 535
 536 ### Announce
 537
 538 When the community receives a post or comment activity, it wraps that into an `Announce` and sends it to all followers.
 539
 540 Sent by: Community
 541
 542 Sent to: User
 543
 544 ```json
 545 {
 546   "@context": "https://www.w3.org/ns/activitystreams",
 547   "id": "https://ds9.lemmy.ml/activities/announce/b98382e8-6cb1-469e-aa1f-65c5d2c31cc4",
 548   "type": "Announce",
 549   "actor": "https://ds9.lemmy.ml/c/main",
 550   "to": "https://www.w3.org/ns/activitystreams#Public",
 551   "cc": [
 552     "https://ds9.lemmy.ml/c/main/followers"
 553   ],
 554   "object": ...
 555 }
 556 ```
 557
 558 | Field Name | Mandatory | Description |
 559 |---|---|---|
 560 | `object` | yes | Any `Create`, `Update`, `Like`, `Dislike`, `Delete` `Remove` or `Undo` activity as described above |
 561
 562 ### Create or Update Private message
 563
 564 Creates a new private message between two users.
 565
 566 Sent by: User
 567
 568 Sent to: User
 569
 570 ```json
 571 {
 572     "@context": "https://www.w3.org/ns/activitystreams",
 573     "id": "https://ds9.lemmy.ml/activities/create/202daf0a-1489-45df-8d2e-c8a3173fed36",
 574     "type": "Create",
 575     "actor": "https://ds9.lemmy.ml/u/sisko",
 576     "to": "https://enterprise.lemmy.ml/u/riker/inbox",
 577     "object": ...
 578 }
 579 ```
 580
 581 | Field Name | Mandatory | Description |
 582 |---|---|---|
 583 | `type` | yes | Either `Create` or `Update` |
 584
 585 ### Delete Private Message
 586
 587 Deletes a previous private message.
 588
 589 Sent by: User
 590
 591 Sent to: User
 592
 593 ```json
 594 {
 595     "@context": "https://www.w3.org/ns/activitystreams",
 596     "id": "https://ds9.lemmy.ml/activities/delete/2de5a5f3-bf26-4949-a7f5-bf52edfca909",
 597     "type": "Delete",
 598     "actor": "https://ds9.lemmy.ml/u/sisko",
 599     "to": "https://enterprise.lemmy.ml/u/riker/inbox",
 600     "object": "https://ds9.lemmy.ml/private_message/341"
 601 }
 602 ```
 603
 604 ### Undo Delete Private Message
 605
 606 Restores a previously deleted private message. The `object` is regenerated from scratch, as such the activity ID and other fields are different.
 607
 608 Sent by: User
 609
 610 Sent to: User
 611
 612 ```json
 613 {
 614     "@context": "https://www.w3.org/ns/activitystreams",
 615     "id": "https://ds9.lemmy.ml/activities/undo/b24bc56d-5db1-41dd-be06-3f1db8757842",
 616     "type": "Undo",
 617     "actor": "https://ds9.lemmy.ml/u/sisko",
 618     "to": "https://enterprise.lemmy.ml/u/riker/inbox",
 619     "object": ...
 620 }
 621 ```