thepraandClaude Opus 5.5
e6729c77e7
- Our public and unlisted posts state interactionPolicy.canQuote. The policy comes from the post, then the persona
(`source[quote_policy]`: public, followers or nobody; default public as the owner chose), and is always nobody for
followers-only posts and DMs.
- QuoteRequests are answered with Accept{result} naming a parrot-licence at /peasants/{name}/parrot-licences/{id}
(the route name the owner chose), or with Reject. Followers-only checks that the requester really follows.
- A licence is a QuoteAuthorization naming both posts; revoking it (POST /api/v1/statuses/:id/quotes/:quoting_id/revoke)
marks it 410, sends Delete{licence} to the quoter and the persona's followers, and revokes our own copy of the quote.
- A quote that arrives with one of our licences is accepted only if that licence is ours, unrevoked and names exactly
that quoting post. One persona quoting another gets a licence too.
- Mastodon API: quote_approval for our posts (automatic, followers, current_user), `quote_approval_policy` when posting,
PUT /api/v1/statuses/:id/interaction_policy, `source.quote_policy`.
Checked live: GoToSocial still accepts our posts with the policy stated, and leaves likes, replies and boosts open.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB
195 lines
13 KiB
Markdown
195 lines
13 KiB
Markdown
# Federation
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PrivaPub is an ActivityPub server written in C#. This document follows
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[FEP-67ff](https://codeberg.org/fediverse/fep/src/branch/main/fep/67ff/fep-67ff.md) and describes how it federates.
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## Supported federation protocols and standards
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- [ActivityPub](https://www.w3.org/TR/activitypub/) (server-to-server)
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- [WebFinger](https://webfinger.net/)
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- [HTTP Signatures](https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures), `rsa-sha256` / `hs2019` with RSA keys
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- [NodeInfo](https://nodeinfo.diaspora.software/) 2.0 and 2.1
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## Tested against
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- **GoToSocial 0.22.1, end to end.** It runs in a private network on the workstation (`tools/pasture/`) and is driven
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through its own client API. Checked both ways:
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- follows, including to a locked account;
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- public posts with a content warning;
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- replies with notifications;
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- likes and boosts;
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- direct messages;
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- edits and deletes;
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- unfollow.
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- **Mastodon, Misskey, Lemmy and PeerTube, by unit tests only.** The tests feed the parser documents written in each
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server's shape. No live exchange with any of them has run yet.
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## Supported FEPs
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- [FEP-67ff: FEDERATION.md](https://codeberg.org/fediverse/fep/src/branch/main/fep/67ff/fep-67ff.md)
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- [FEP-f1d5: NodeInfo in Fediverse Software](https://codeberg.org/fediverse/fep/src/branch/main/fep/f1d5/fep-f1d5.md)
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- [FEP-2c59: Discovery of a WebFinger address from an ActivityPub actor](https://codeberg.org/fediverse/fep/src/branch/main/fep/2c59/fep-2c59.md)
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- [FEP-1b12: Group federation](https://codeberg.org/fediverse/fep/src/branch/main/fep/1b12/fep-1b12.md) (communities; see "Groups")
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Planned (see `docs/ROADMAP.md`, phases P5 to P8, and the per-platform notes in `docs/INTEROP.md`): FEP-044f (quotes),
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FEP-9967 (polls), FEP-c0e0 (emoji reactions), FEP-9098 (custom emoji), FEP-7888 and FEP-f228 (threads), FEP-7628 (Move),
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FEP-8fcf (followers synchronisation), FEP-5feb (`indexable`), FEP-8967 (link attachments), FEP-521a and FEP-8b32 (keys
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and integrity proofs), FEP-ae0c (relays).
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## Actors
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Every account is an *avatar*: one private login can own several, and they are deliberately unlinkable. Nothing in an
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actor document, a collection, NodeInfo or a delivery relates two avatars of the same login.
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| Thing | Address |
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|---|---|
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| Actor (Person, Group, Application) | `/peasants/{name}` (`/users/{name}` redirects) |
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| Inbox | `/peasants/{name}/mouth` |
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| Outbox | `/peasants/{name}/anus` |
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| Shared inbox | `/human-centipede` |
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| Followers / following | `/peasants/{name}/groupies`, `/peasants/{name}/stalking` |
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| Objects | `/peasants/{name}/scribbles/{id}` |
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| Activities | `/peasants/{name}/grunts/{id}` |
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| Quote permissions (`QuoteAuthorization`) | `/peasants/{name}/parrot-licences/{id}` |
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| Direct-message context | `/peasants/{name}/whispers/{id}` |
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| Profile and post pages | `/@{name}`, `/@{name}/{id}` |
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The names are the project's own and are stable; resolve actors through WebFinger, not by guessing a path.
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- The key is `{actor}#main-key`, RSA 2048, served as SPKI PEM with `owner` set to the actor.
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- `published` on an actor is a whole day, chosen at random up to two weeks before the account was made, so two
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personas made on the same day do not share a date. `indexable` is `false`.
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- The instance actor is `/peasants/privapub` (type `Application`). It signs every fetch PrivaPub makes, so no avatar's key
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is used to read another server's content.
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## Groups
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A group is either a **community** or a **circle**.
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- A **community** follows [FEP-1b12](https://codeberg.org/fediverse/fep/src/branch/main/fep/1b12/fep-1b12.md). Posts
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addressed to it (in `to`, `cc` or `audience`) are accepted according to its posting policy (followers, anyone, or
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moderators only) and the group `Announce`s the whole activity, with `audience` set, to its followers. A new post is
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also announced as an object so Mastodon shows it. Updates and deletes of community content are announced too. A
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top-level post is a `Page` with a `name`. Members are counted at `/flock`; moderators are listed at `/wardens`, which
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the actor's `attributedTo` points to, with `postingRestrictedToMods` as Lemmy expects. A mention of a community posts into it.
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- A **circle** is private. Its actor is not discoverable and every follow is a request. Its posts are addressed to the
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circle and its members collection, delivered to each member's own inbox and never announced. They are served only
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to a signed request from a member, or from the instance actor of a member's server; anyone else gets 404. A
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Mastodon member's replies reach only the people they mention.
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- Announces from **remote** groups (Lemmy communities) are followed through to the activity: the object is fetched
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from its own origin, never taken from the announce.
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## Activities
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Received:
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| Activity | Effect |
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|---|---|
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| `Follow` | follows an avatar or community; `Accept` is sent unless the community approves members by hand |
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| `Accept{Follow}`, `Reject{Follow}` | completes or ends a follow an avatar requested |
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| `Undo{Follow, Like, Announce}` | reverses it |
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| `Create{Note, Article, Page, Question, Video, Audio, Event, ChatMessage, …}` | stored when a local avatar follows the author, is addressed or mentioned, when it replies to a local post, or when it is addressed to a community the author follows; a public parent is fetched to complete the thread |
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| `Update{Note}` | replaces the content; the previous version is kept |
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| `Update{Person}` | refetches the actor |
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| `Like` | counted and notified, on posts the liker could see |
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| `Dislike` | counted as a downvote (Lemmy, PieFed, Mbin, Friendica); `Undo` takes it back |
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| `EmojiReact`, `Like` with an emoji `content` | an emoji reaction (FEP-c0e0; Pleroma, Akkoma, Iceshrimp.NET, Misskey, Sharkey), Unicode or a custom emoji from its `tag`; a `Like` whose content is ❤ stays a favourite; `Undo` takes it back |
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| `Join` | answered with `Ignore`: PrivaPub hosts no events yet (FEP-8a8e) |
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| `Announce` | counted and notified for local posts; shown to followers of the announcer, with the original refetched from its origin |
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| `Delete` | deletes the object, or the actor and its follows; a deleted object id is remembered for 90 days, so a late `Create` cannot bring it back |
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| `Flag` | becomes a report for this server's moderators |
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Sent: `Follow`, `Undo{Follow}`, `Create{Note}`, `Create{Question}` and poll votes, `EmojiReact` and its `Undo`, `Update{Note}`, `Update{Person}`, `Delete{Tombstone}`, `Accept{Follow}`,
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`Reject{Follow}`, `Like`, `Announce` and their `Undo`, `Flag`. A deleted post answers 410 with a `Tombstone`.
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- **Attachments** are `Document`s with `mediaType`, `name` (alt text), `blurhash`, `focalPoint`, `width` and `height`.
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Uploaded files have all metadata removed.
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- **Pinned posts** are the actor's `featured` collection (`/trophies`); `featuredTags` is `/tattoos`.
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- **Blocks are sent.** A blocked remote account receives `Block` from the blocking account (and `Reject{Follow}` if it
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followed); an unblock sends `Undo{Block}`.
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- **Reports** are sent as `Flag` by the instance actor, never by the reporting account.
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A `Create`'s `Note` carries Mastodon's `content`, `contentMap`, `summary` and `sensitive`, plus `Mention` and `Hashtag`
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tags.
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**Polls** (FEP-9967) go out as a `Question` with `oneOf` or `anyOf`, each option's count in `replies.totalItems`,
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`endTime`, `votersCount`, and `closed` once it has ended. Incoming votes are `Create{Note{name, inReplyTo}}` with no
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content, one per choice, counted once per voter. Counts are refreshed with an `Update{Question}` at most every three
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minutes. Our own votes on other servers' polls are sent the same way to the poll's author only, without `published`.
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An incoming `Update` without a newer `updated` only refreshes counts and details; it is never recorded as an edit.
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**Quotes** (FEP-044f, with the older keys):
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- **Received.** A quote is read from `quote`, `quoteUrl`, `quoteUri`, `_misskey_quote` or a FEP-e232 `Link` tag.
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- With a `quoteAuthorization`, the stamp is fetched and must be a `QuoteAuthorization` on the quoted author's origin,
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attributed to them, naming exactly the two posts.
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- A FEP-044f `quote` without a stamp is pending until an `Update` brings one.
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- A quote made with the older keys only, by software that asks nobody, is shown when the quoted post is public.
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- A `Delete` of a stamp revokes the quote.
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- **Sent.** Our accounts quote with every key, plus the `RE:` fallback.
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- When the quoted post states an `interactionPolicy.canQuote` that allows us, `quote` is included and a `QuoteRequest`
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(with the quoting post as `instrument`) goes to the quoted author. The quote stays pending until their `Accept` brings a
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stamp we can verify; the post is then updated with `quoteAuthorization`.
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- Posts that state no policy are quoted the older way, without `quote`.
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- Quoting posts are also delivered to the quoted author.
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- **Quoting our accounts.** Our public and unlisted posts state `interactionPolicy.canQuote`. By default anyone may quote,
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automatically (as on Mastodon); an account can choose followers only or nobody, and so can each post.
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- A `QuoteRequest` is answered with `Accept{result}` naming a stamp at `/peasants/{name}/parrot-licences/{id}`, or
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with `Reject`.
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- A stamp is a `QuoteAuthorization` naming both posts. A revoked stamp answers 410 and is announced with
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`Delete{stamp}`.
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- Followers-only posts and DMs can never be quoted.
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**Custom emoji** (`Emoji` tags) are read on posts, display names, bios and profile fields, at most 64 per object.
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**Profiles** keep their header, profile fields, `manuallyApprovesFollowers`, `published`, `movedTo`, `indexable`,
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`memorial` and avatar and header descriptions. A post's title becomes `name` and is also the first, bold line of `content`, because Mastodon does not show
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`name`. A content warning without its own text uses the title, or "Content warning".
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Received `summary` is a content warning only on a `Note` or `Question`, or when `sensitive` is `true`. On an `Article`,
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`Page`, `Event`, `Video` or `Audio` it is an excerpt or description, kept as such and never hidden.
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Visibility is expressed in `to`/`cc` the way Mastodon does it: public, unlisted, followers-only and direct. Inbound
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followers-only posts are recognised by the author's own `followers` collection.
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## Link previews
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For a public post that links to a page, PrivaPub builds a preview card. It uses, in order:
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1. a Link attachment's own `preview` (FEP-8967) or the post's own image, title and summary;
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2. otherwise, the linked page, read once by the server between 0 and 60 seconds after the post arrives (never when
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someone reads it), with an `Accept: text/html` request that reads at most 512 KB, through the same address checks as
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every other fetch.
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The page's OpenGraph and Twitter tags give the title, description and image; the result is cached per address for 7
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days and shared by every account on the server. Images are served to clients only through PrivaPub's media proxy.
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`Federation:FetchLinkPreviews=false` turns page fetching off.
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## Local-only posts
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Posts with a location (shown to nearby users of this server) never leave the server, in any form.
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## Security rules a peer will notice
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- **Signatures.** Inbox POSTs must be signed over `(request-target)`, `host`, `digest` and `date` (or `(created)`). The
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date may be at most one hour old and fifteen minutes ahead. A bad signature gets 401, malformed input 400, an accepted
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activity 202, too many requests 429. Activities are processed after the 202.
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- **Origins.** An actor document is accepted only from the address it names as its `id`. A key only if its actor lists
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it with `owner` set to the actor and on the actor's origin. An activity's `id`, and any object it creates, updates or
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deletes, must be on its actor's origin. An embedded object from another origin is fetched from that origin.
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- **Fetching.** All fetches are signed by the instance actor. They go only to public addresses, follow at most three
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redirects and read at most 1 MB.
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- **HTML.** Received HTML is sanitised to Mastodon's allowlist.
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- **Keys we cannot fetch for now.** When a sender's key cannot be fetched because its server timed out or answered
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5xx, the inbox answers 503 with `Retry-After: 300` rather than 401.
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- **Activity ids.** `Create` and `Announce` ids dereference. `Follow`, `Like`, `Block` and the `Accept`, `Reject` and
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`Undo` that answer them do not, because serving them would reveal who follows, likes and blocks whom; they are always
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sent with their object embedded.
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- **Delivery.** Failed deliveries are retried with Mastodon's backoff (16 attempts). A host that keeps failing is paused,
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starting at an hour and growing to a week.
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## Known limitations
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- Our own posts carry no custom emoji: emoji are received and shown, not offered.
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- Remote media is fetched through this server's proxy when a local client displays it. Video and audio are streamed
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through it with byte ranges passed on, so a PeerTube file is never fetched whole for one viewer.
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- Collections expose counts, not members.
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- Only `rsa-sha256`-style keys are verified. RFC 9421 signatures are planned.
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