From afa8ecfb17b017888cbe7f207678fccdfb170004 Mon Sep 17 00:00:00 2001
From: svemagie <869694+svemagie@users.noreply.github.com>
Date: Sun, 17 May 2026 09:50:41 +0200
Subject: [PATCH] feat: backfill recent posts from remote outbox on follow (max
 20)

---
 index.js               |  10 ++++
 lib/outbox-backfill.js | 118 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 128 insertions(+)
 create mode 100644 lib/outbox-backfill.js

diff --git a/index.js b/index.js
index 5610b23..51e6c26 100644
--- a/index.js
+++ b/index.js
@@ -120,6 +120,7 @@ import { logActivity } from "./lib/activity-log.js";
 import { batchBroadcast } from "./lib/batch-broadcast.js";
 import { resolveAuthor } from "./lib/resolve-author.js";
 import { scheduleCleanup } from "./lib/timeline-cleanup.js";
+import { backfillFromOutbox } from "./lib/outbox-backfill.js";
 import { runSeparateMentionsMigration } from "./lib/migrations/separate-mentions.js";
 import { loadBlockedServersToRedis } from "./lib/storage/server-blocks.js";
 import { scheduleKeyRefresh } from "./lib/key-refresh.js";
@@ -743,6 +744,15 @@ export default class ActivityPubEndpoint {
 
       console.info(`[ActivityPub] Sent Follow to ${actorUrl}`);
 
+      // Backfill recent posts from the remote outbox — fire-and-forget
+      backfillFromOutbox({
+        actorUrl,
+        remoteActor,
+        ctx,
+        handle,
+        collections: this._collections,
+      }).catch(() => {});
+
       await logActivity(this._collections.ap_activities, {
         direction: "outbound",
         type: "Follow",
diff --git a/lib/outbox-backfill.js b/lib/outbox-backfill.js
new file mode 100644
index 0000000..7722e67
--- /dev/null
+++ b/lib/outbox-backfill.js
@@ -0,0 +1,118 @@
+/**
+ * Outbox backfill — fetch recent posts from a remote actor's outbox
+ * and store them in the local ap_timeline after a follow.
+ *
+ * Runs asynchronously (fire-and-forget) — never blocks followActor().
+ * Fetches at most one page (limit 20) from the outbox's `first` page.
+ * Uses extractObjectData() from timeline-store for consistent normalization.
+ */
+
+import { Note, Article, Create, Announce } from "@fedify/fedify/vocab";
+import { extractObjectData } from "./timeline-store.js";
+import { addTimelineItem } from "./storage/timeline.js";
+
+/**
+ * Fetch up to `limit` recent posts from `actorUrl`'s AP outbox and
+ * store them in ap_timeline. Non-blocking — call without await.
+ *
+ * @param {object} options
+ * @param {string} options.actorUrl - Remote actor AP URL
+ * @param {object} options.remoteActor - Resolved Fedify actor object
+ * @param {object} options.ctx - Fedify context (for documentLoader)
+ * @param {string} options.handle - Local actor handle (for signed fetches)
+ * @param {object} options.collections - MongoDB collections
+ * @param {number} [options.limit=20] - Max posts to backfill
+ */
+export async function backfillFromOutbox({ actorUrl, remoteActor, ctx, handle, collections, limit = 20 }) {
+  if (!collections?.ap_timeline) return;
+
+  try {
+    const documentLoader = await ctx.getDocumentLoader({ identifier: handle });
+
+    // Fetch outbox collection
+    const outbox = await remoteActor.getOutbox({ documentLoader }).catch(() => null);
+    if (!outbox) return;
+
+    // Collect activity items — try direct items first, then first-page
+    const activities = [];
+    let itemSource = null;
+    try {
+      // Some servers return a directly-iterable collection without pagination
+      const direct = outbox.getItems?.({ documentLoader });
+      if (direct) itemSource = direct;
+    } catch { /* not directly iterable */ }
+
+    if (!itemSource) {
+      // Paginated — navigate to first page
+      const firstPage = await outbox.getFirst({ documentLoader }).catch(() => null);
+      if (firstPage?.getItems) itemSource = firstPage.getItems({ documentLoader });
+    }
+
+    if (!itemSource) return;
+
+    try {
+      for await (const item of itemSource) {
+        activities.push(item);
+        if (activities.length >= limit) break;
+      }
+    } catch {
+      // Partial read is fine — use what we got
+    }
+
+    if (activities.length === 0) return;
+
+    let stored = 0;
+    for (const activity of activities) {
+      try {
+        // Only handle Create(Note/Article) and Announce activities
+        let object = null;
+        let boostedBy = null;
+
+        if (activity instanceof Create) {
+          object = await activity.getObject({ documentLoader }).catch(() => null);
+        } else if (activity instanceof Announce) {
+          object = await activity.getObject({ documentLoader }).catch(() => null);
+          if (object) {
+            // For boosts: actor info comes from the remote actor we just followed
+            boostedBy = {
+              name: remoteActor.name?.toString() || remoteActor.preferredUsername?.toString() || "",
+              url: actorUrl,
+              photo: "",
+              handle: "",
+            };
+          }
+        }
+
+        if (!object || !(object instanceof Note || object instanceof Article)) continue;
+
+        const uid = object.id?.href;
+        if (!uid) continue;
+
+        // Skip if already in timeline
+        const exists = await collections.ap_timeline.findOne({ uid }, { projection: { _id: 1 } });
+        if (exists) continue;
+
+        const item = await extractObjectData(object, {
+          documentLoader,
+          actorFallback: remoteActor,
+          boostedBy,
+          boostedAt: boostedBy ? new Date().toISOString() : undefined,
+        });
+
+        // Ensure visibility field (extractObjectData doesn't set it)
+        if (!item.visibility) item.visibility = "public";
+
+        await addTimelineItem({ ap_timeline: collections.ap_timeline }, item);
+        stored++;
+      } catch {
+        // Skip individual item errors — keep going
+      }
+    }
+
+    if (stored > 0) {
+      console.info(`[ActivityPub] Outbox backfill: stored ${stored} posts from ${actorUrl}`);
+    }
+  } catch (error) {
+    console.warn(`[ActivityPub] Outbox backfill failed for ${actorUrl}:`, error?.message);
+  }
+}