From a3d81dd911b39877dc07d993912c14a2271646aa Mon Sep 17 00:00:00 2001
From: Daniel Holmgren <dtholmgren@gmail.com>
Date: Fri, 3 Nov 2023 16:55:50 -0500
Subject: [PATCH] Prevent thread loops (#1813)

* prevent thread loops

* include original uri

* tidy

* tweak

* last tweak

* last tweak i swear

* wording
---
 .../src/api/app/bsky/feed/getPostThread.ts    | 20 +++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/packages/bsky/src/api/app/bsky/feed/getPostThread.ts b/packages/bsky/src/api/app/bsky/feed/getPostThread.ts
index 1480e54ac1a..0e31107d052 100644
--- a/packages/bsky/src/api/app/bsky/feed/getPostThread.ts
+++ b/packages/bsky/src/api/app/bsky/feed/getPostThread.ts
@@ -255,11 +255,15 @@ const getThreadData = async (
       .orderBy('sortAt', 'desc')
       .execute(),
   ])
-  const parentsByUri = parents.reduce((acc, parent) => {
-    return Object.assign(acc, { [parent.postUri]: parent })
+  // prevent self-referential loops
+  const includedPosts = new Set<string>([uri])
+  const parentsByUri = parents.reduce((acc, post) => {
+    return Object.assign(acc, { [post.uri]: post })
   }, {} as Record<string, FeedRow>)
   const childrenByParentUri = children.reduce((acc, child) => {
     if (!child.replyParent) return acc
+    if (includedPosts.has(child.uri)) return acc
+    includedPosts.add(child.uri)
     acc[child.replyParent] ??= []
     acc[child.replyParent].push(child)
     return acc
@@ -269,7 +273,12 @@ const getThreadData = async (
   return {
     post,
     parent: post.replyParent
-      ? getParentData(parentsByUri, post.replyParent, parentHeight)
+      ? getParentData(
+          parentsByUri,
+          includedPosts,
+          post.replyParent,
+          parentHeight,
+        )
       : undefined,
     replies: getChildrenData(childrenByParentUri, uri, depth),
   }
@@ -277,16 +286,19 @@ const getThreadData = async (
 
 const getParentData = (
   postsByUri: Record<string, FeedRow>,
+  includedPosts: Set<string>,
   uri: string,
   depth: number,
 ): PostThread | ParentNotFoundError | undefined => {
   if (depth < 1) return undefined
+  if (includedPosts.has(uri)) return undefined
+  includedPosts.add(uri)
   const post = postsByUri[uri]
   if (!post) return new ParentNotFoundError(uri)
   return {
     post,
     parent: post.replyParent
-      ? getParentData(postsByUri, post.replyParent, depth - 1)
+      ? getParentData(postsByUri, includedPosts, post.replyParent, depth - 1)
       : undefined,
     replies: [],
   }