Added service for delivering activities

ref https://linear.app/tryghost/issue/MOM-120

This will allow us to deliver Follow activities to other sites

ghost/ghost/src/core/activitypub/tell-the-world.service.test.ts

@@ -0,0 +1,51 @@
+import assert from 'assert';
+import {Activity} from './activity.entity';
+import {Actor} from './actor.entity';
+import {TheWorld} from './tell-the-world.service';
+import {URI} from './uri.object';
+import nock from 'nock';
+
+describe('TheWorld', function () {
+    describe('deliverActivity', function () {
+        beforeEach(function () {
+            nock.disableNetConnect();
+        });
+        afterEach(function () {
+            nock.enableNetConnect();
+        });
+        it('Can deliver the activity to the inbox of the desired recipient', async function () {
+            const service = new TheWorld(new URL('https://base.com'));
+
+            const actor = Actor.create({
+                username: 'Testing'
+            });
+
+            const toFollow = new URI('https://main.ghost.org/activitypub/actor/deadbeefdeadbeefdeadbeef');
+
+            const activity = new Activity({
+                type: 'Follow',
+                activity: null,
+                actor: actor.actorId,
+                object: {
+                    id: toFollow
+                },
+                to: toFollow
+            });
+
+            const actorFetch = nock('https://main.ghost.org')
+                .get('/activitypub/actor/deadbeefdeadbeefdeadbeef')
+                .reply(200, {
+                    inbox: 'https://main.ghost.org/activitypub/inbox/deadbeefdeadbeefdeadbeef'
+                });
+
+            const activityDelivery = nock('https://main.ghost.org')
+                .post('/activitypub/inbox/deadbeefdeadbeefdeadbeef')
+                .reply(201, {});
+
+            await service.deliverActivity(activity, actor);
+
+            assert(actorFetch.isDone(), 'Expected actor to be fetched');
+            assert(activityDelivery.isDone(), 'Expected activity to be delivered');
+        });
+    });
+});

ghost/ghost/src/core/activitypub/tell-the-world.service.ts

@@ -0,0 +1,61 @@
+import {Inject} from '@nestjs/common';
+import {Activity} from './activity.entity';
+import {Actor} from './actor.entity';
+
+export class TheWorld {
+    constructor(
+        @Inject('ActivityPubBaseURL') private readonly url: URL
+    ) {}
+
+    async deliverActivity(activity: Activity, actor: Actor): Promise<void> {
+        const recipients = await this.getRecipients(activity);
+        for (const recipient of recipients) {
+            const data = await this.fetchForActor(recipient.href, actor);
+            if ('inbox' in data && typeof data.inbox === 'string') {
+                const inbox = new URL(data.inbox);
+                await this.sendActivity(inbox, activity, actor);
+            }
+        }
+    }
+
+    private async sendActivity(to: URL, activity: Activity, from: Actor) {
+        const request = new Request(to.href, {
+            method: 'POST',
+            headers: {
+                'Content-Type': 'application/ld+json'
+            },
+            body: JSON.stringify(activity.getJSONLD(this.url))
+        });
+        const signedRequest = await from.sign(request, this.url);
+        await fetch(signedRequest);
+    }
+
+    private async getRecipients(activity: Activity): Promise<URL[]>{
+        const json = activity.getJSONLD(this.url);
+        const recipients = [];
+        if (json.to) {
+            recipients.push(new URL(json.to));
+        }
+        return recipients;
+    }
+
+    private async fetchForActor(uri: string, actor: Actor) {
+        const request = new Request(uri, {
+            headers: {
+                Accept: 'application/ld+json'
+            }
+        });
+
+        const signedRequest = await actor.sign(request, this.url);
+
+        const result = await fetch(signedRequest);
+
+        const json = await result.json();
+
+        if (typeof json !== 'object' || json === null) {
+            throw new Error('Could not read data');
+        }
+
+        return json;
+    }
+}