Added handler for incoming likes (#33)

refs [AP-283](https://linear.app/tryghost/issue/AP-283/handle-incoming-likes)

Added handler for incoming likes that adds the like activity to the actors
inbox and persists any relevant data to the database.

features/handle-like.feature

@@ -0,0 +1,10 @@
+Feature: Like(Article)
+  We want to handle Like(Article) activities in the Inbox
+
+  Scenario: We recieve a Like(Article) activity from someone we follow
+    Given an Actor "Alice"
+    And an Actor "Bob"
+    And a "Create(Article)" Activity "A" by "Alice"
+    And a "Like(A)" Activity "L" by "Bob"
+    When "Bob" sends "L" to the Inbox
+    Then "L" is in our Inbox

features/step_definitions/stepdefs.js

@@ -60,6 +60,20 @@ async function createActivity(activityType, object, actor, remote = true) {
             actor: actor,
         };
     }
+
+    if (activityType === 'Like') {
+        return {
+            '@context': [
+                'https://www.w3.org/ns/activitystreams',
+                'https://w3id.org/security/data-integrity/v1',
+            ],
+            'type': 'Like',
+            'id': 'http://wiremock:8080/like/1',
+            'to': 'as:Public',
+            'object': object,
+            actor: actor,
+        };
+    }
 }
 
 async function createActor(name = 'Test', remote = true) {

src/app.ts

@@ -17,6 +17,7 @@ import {
     Update,
     Announce,
     Context,
+    Like,
 } from '@fedify/fedify';
 import { federation } from '@fedify/fedify/x/hono';
 import { Hono, Context as HonoContext } from 'hono';
@@ -47,6 +48,7 @@ import {
     createDispatcher,
     updateDispatcher,
     handleAnnounce,
+    handleLike
 } from './dispatchers';
 
 import { followAction, inboxHandler, postPublishedWebhook, siteChangedWebhook } from './handlers';
@@ -115,6 +117,8 @@ inboxListener
     .on(Create, ensureCorrectContext(handleCreate))
     .onError(inboxErrorHandler)
     .on(Announce, ensureCorrectContext(handleAnnounce))
+    .onError(inboxErrorHandler)
+    .on(Like, ensureCorrectContext(handleLike))
     .onError(inboxErrorHandler);
 
 fedify

src/dispatchers.ts

@@ -15,6 +15,7 @@ import {
     Actor,
     Object as APObject,
     Recipient,
+    Like,
 } from '@fedify/fedify';
 import { v4 as uuidv4 } from 'uuid';
 import { addToList } from './kv-helpers';
@@ -229,6 +230,69 @@ export async function handleAnnounce(
     await addToList(ctx.data.db, ['inbox'], announce.id.href);
 }
 
+export async function handleLike(
+    ctx: Context<ContextData>,
+    like: Like,
+) {
+    console.log('Handling Like');
+
+    // Validate like
+    if (!like.id) {
+        console.log('Invalid Like - no id');
+        return;
+    }
+
+    if (!like.objectId) {
+        console.log('Invalid Like - no object id');
+        return;
+    }
+
+    // Validate sender
+    const sender = await like.getActor(ctx);
+
+    if (sender === null || sender.id === null) {
+        console.log('Sender missing, exit early');
+        return;
+    }
+
+    // Lookup liked object - If not found in globalDb, perform network lookup
+    let object = null;
+    let existing = await ctx.data.globaldb.get([like.objectId.href]) ?? null;
+
+    if (!existing) {
+        console.log('Object not found in globalDb, performing network lookup');
+
+        object = await like.getObject();
+    }
+
+    // Validate object
+    if (!existing && !object) {
+        console.log('Invalid Like - could not find object');
+        return;
+    }
+
+    if (object && !object.id) {
+        console.log('Invalid Like - could not find object id');
+        return;
+    }
+
+    // Persist like
+    const likeJson = await like.toJsonLd();
+    ctx.data.globaldb.set([like.id.href], likeJson);
+
+    // Persist object if not already persisted
+    if (!existing && object && object.id) {
+        console.log('Storing object in globalDb');
+
+        const objectJson = await object.toJsonLd();
+
+        ctx.data.globaldb.set([object.id.href], objectJson);
+    }
+
+    // Add to inbox
+    await addToList(ctx.data.db, ['inbox'], like.id.href);
+}
+
 export async function inboxErrorHandler(
     ctx: Context<ContextData>,
     error: unknown,