Added API endpoint to repost a post (#302)

ref https://linear.app/ghost/issue/AP-702

- added `POST /actions/reposts/:id` endpoint to repost a post
- "Repost" is the equivalent of the "Announce" activity in the ActivityPub vocabulary, or "Boost" in the Mastodon vocabulary

features/repost-activity.feature

@@ -0,0 +1,32 @@
+Feature: Reposting a post
+  In order to share content with my followers
+  As a user
+  I want to be able to repost a post in my feed
+
+  Scenario: Reposting a post that has not been reposted before
+    Given an Actor "Person(Alice)"
+    And we follow "Alice"
+    And the request is accepted
+    And a "Accept(Follow(Alice))" Activity "Accept" by "Alice"
+    And "Alice" sends "Accept" to the Inbox
+    And "Accept" is in our Inbox
+    And a "Create(Note)" Activity "Note" by "Alice"
+    And "Alice" sends "Note" to the Inbox
+    And "Note" is in our Inbox
+    When we repost the object "Note"
+    Then a "Announce(Note)" activity is sent to "Alice"
+
+  Scenario: Reposting an post that has been reposted before
+    Given an Actor "Person(Alice)"
+    And we follow "Alice"
+    And the request is accepted
+    And a "Accept(Follow(Alice))" Activity "Accept" by "Alice"
+    And "Alice" sends "Accept" to the Inbox
+    And "Accept" is in our Inbox
+    And a "Create(Note)" Activity "Note" by "Alice"
+    And "Alice" sends "Note" to the Inbox
+    And "Note" is in our Inbox
+    And we repost the object "Note"
+    Then the request is accepted
+    Then we repost the object "Note"
+    Then the request is rejected with a 409

features/step_definitions/stepdefs.js

@@ -773,6 +773,16 @@ Then('the object {string} should not be liked', async function (name) {
     assert(found.object.liked !== true);
 });
 
+When('we repost the object {string}', async function (name) {
+    const id = this.objects[name].id;
+    this.response = await fetchActivityPub(
+        `http://fake-ghost-activitypub/.ghost/activitypub/actions/repost/${encodeURIComponent(id)}`,
+        {
+            method: 'POST',
+        },
+    );
+});
+
 async function getObjectInCollection(objectName, collectionType) {
     const initialResponse = await fetchActivityPub(
         `http://fake-ghost-activitypub/.ghost/activitypub/${collectionType}/index`,

src/app.ts

@@ -44,6 +44,7 @@ import { client } from './db';
 import {
     acceptDispatcher,
     actorDispatcher,
+    announceDispatcher,
     articleDispatcher,
     createAcceptHandler,
     createAnnounceHandler,
@@ -76,6 +77,7 @@ import {
 import { FeedService } from './feed/feed.service';
 import {
     createFollowActionHandler,
+    createRepostActionHandler,
     createUnfollowActionHandler,
     getSiteDataHandler,
     inboxHandler,
@@ -380,7 +382,11 @@ fedify.setObjectDispatcher(
     '/.ghost/activitypub/undo/{id}',
     spanWrapper(undoDispatcher),
 );
-
+fedify.setObjectDispatcher(
+    Announce,
+    '/.ghost/activitypub/announce/{id}',
+    spanWrapper(announceDispatcher),
+);
 fedify.setNodeInfoDispatcher(
     '/.ghost/activitypub/nodeinfo/2.1',
     spanWrapper(nodeInfoDispatcher),
@@ -798,6 +804,11 @@ app.post(
     requireRole(GhostRole.Owner),
     spanWrapper(replyAction),
 );
+app.post(
+    '/.ghost/activitypub/actions/repost/:id',
+    requireRole(GhostRole.Owner),
+    spanWrapper(createRepostActionHandler(accountService)),
+);
 app.post(
     '/.ghost/activitypub/actions/note',
     requireRole(GhostRole.Owner),

src/dispatchers.ts

@@ -3,7 +3,7 @@ import {
     Accept,
     Activity,
     type Actor,
-    type Announce,
+    Announce,
     Article,
     type Context,
     Create,
@@ -1300,6 +1300,18 @@ export async function likeDispatcher(
     return Like.fromJsonLd(exists);
 }
 
+export async function announceDispatcher(
+    ctx: RequestContext<ContextData>,
+    data: Record<'id', string>,
+) {
+    const id = ctx.getObjectUri(Announce, data);
+    const exists = await ctx.data.globaldb.get([id.href]);
+    if (!exists) {
+        return null;
+    }
+    return Announce.fromJsonLd(exists);
+}
+
 export async function undoDispatcher(
     ctx: RequestContext<ContextData>,
     data: Record<'id', string>,

src/handlers.ts

@@ -1,6 +1,7 @@
 import { createHash } from 'node:crypto';
 import {
     type Actor,
+    Announce,
     Create,
     Follow,
     Like,
@@ -571,3 +572,88 @@ export async function inboxHandler(
         },
     );
 }
+
+export function createRepostActionHandler(accountService: AccountService) {
+    return async function repostAction(
+        ctx: Context<{ Variables: HonoContextVariables }>,
+    ) {
+        const id = ctx.req.param('id');
+        const apCtx = fedify.createContext(ctx.req.raw as Request, {
+            db: ctx.get('db'),
+            globaldb: ctx.get('globaldb'),
+            logger: ctx.get('logger'),
+        });
+
+        const objectToRepost = await lookupObject(apCtx, id);
+        if (!objectToRepost) {
+            return new Response(null, {
+                status: 404,
+            });
+        }
+
+        const announceId = apCtx.getObjectUri(Announce, {
+            id: createHash('sha256')
+                .update(objectToRepost.id!.href)
+                .digest('hex'),
+        });
+
+        if (await ctx.get('globaldb').get([announceId.href])) {
+            return new Response(null, {
+                status: 409,
+            });
+        }
+
+        const actor = await apCtx.getActor(ACTOR_DEFAULT_HANDLE); // TODO This should be the actor making the request
+
+        const announce = new Announce({
+            id: announceId,
+            actor: actor,
+            object: objectToRepost,
+            to: PUBLIC_COLLECTION,
+            cc: apCtx.getFollowersUri(ACTOR_DEFAULT_HANDLE),
+        });
+
+        const announceJson = await announce.toJsonLd();
+
+        await ctx.get('globaldb').set([announce.id!.href], announceJson);
+        await addToList(ctx.get('db'), ['reposted'], announce.id!.href);
+
+        // Add to the actor's outbox
+        await addToList(ctx.get('db'), ['outbox'], announce.id!.href);
+
+        // Send the announce activity
+        let attributionActor: Actor | null = null;
+        if (objectToRepost.attributionId) {
+            attributionActor = await lookupActor(
+                apCtx,
+                objectToRepost.attributionId.href,
+            );
+        }
+        if (attributionActor) {
+            apCtx.sendActivity(
+                { handle: ACTOR_DEFAULT_HANDLE },
+                attributionActor,
+                announce,
+                {
+                    preferSharedInbox: true,
+                },
+            );
+        }
+
+        apCtx.sendActivity(
+            { handle: ACTOR_DEFAULT_HANDLE },
+            'followers',
+            announce,
+            {
+                preferSharedInbox: true,
+            },
+        );
+
+        return new Response(JSON.stringify(announceJson), {
+            headers: {
+                'Content-Type': 'application/activity+json',
+            },
+            status: 200,
+        });
+    };
+}