Resolve federated objects from other instances via redirect (fixes #3129) (#4073)

* Resolve federated objects from other instances via redirect (fixes #3129)

* restore domain check using library change

* add test case, update apub lib

---------

Co-authored-by: Dessalines <dessalines@users.noreply.github.com>

api_tests/src/post.spec.ts

@@ -39,7 +39,7 @@ import {
   loginUser,
 } from "./shared";
 import { PostView } from "lemmy-js-client/dist/types/PostView";
-import { LemmyHttp } from "lemmy-js-client";
+import { LemmyHttp, ResolveObject } from "lemmy-js-client";
 
 let betaCommunity: CommunityView | undefined;
 
@@ -556,3 +556,26 @@ test("Report a post", async () => {
   expect(betaReport.original_post_body).toBe(alphaReport.original_post_body);
   expect(betaReport.reason).toBe(alphaReport.reason);
 });
+
+test("Fetch post via redirect", async () => {
+  let alphaPost = await createPost(alpha, betaCommunity!.community.id);
+  expect(alphaPost.post_view.post).toBeDefined();
+  // Make sure that post is liked on beta
+  const betaPost = await waitForPost(
+    beta,
+    alphaPost.post_view.post,
+    res => res?.counts.score === 1,
+  );
+
+  expect(betaPost).toBeDefined();
+  expect(betaPost.post?.ap_id).toBe(alphaPost.post_view.post.ap_id);
+
+  // Fetch post from url on beta instance instead of ap_id
+  let q = `http://lemmy-beta:8551/post/${betaPost.post.id}`;
+  let form: ResolveObject = {
+    q,
+  };
+  let gammaPost = await gamma.resolveObject(form);
+  expect(gammaPost).toBeDefined();
+  expect(gammaPost.post?.post.ap_id).toBe(alphaPost.post_view.post.ap_id);
+});

crates/apub/src/http/comment.rs

 use crate::{
-  http::{create_apub_response, create_apub_tombstone_response, err_object_not_local},
+  http::{create_apub_response, create_apub_tombstone_response, redirect_remote_object},
   objects::comment::ApubComment,
 };
 use activitypub_federation::{config::Data, traits::Object};
@@ -23,7 +23,7 @@ pub(crate) async fn get_apub_comment(
   let id = CommentId(info.comment_id.parse::<i32>()?);
   let comment: ApubComment = Comment::read(&mut context.pool(), id).await?.into();
   if !comment.local {
-    Err(err_object_not_local())
+    Ok(redirect_remote_object(&comment.ap_id))
   } else if !comment.deleted && !comment.removed {
     create_apub_response(&comment.into_json(&context).await?)
   } else {

crates/apub/src/http/mod.rs

@@ -11,10 +11,10 @@ use activitypub_federation::{
   FEDERATION_CONTENT_TYPE,
 };
 use actix_web::{web, web::Bytes, HttpRequest, HttpResponse};
-use http::StatusCode;
+use http::{header::LOCATION, StatusCode};
 use lemmy_api_common::context::LemmyContext;
-use lemmy_db_schema::source::activity::SentActivity;
-use lemmy_utils::error::{LemmyError, LemmyErrorType, LemmyResult};
+use lemmy_db_schema::{newtypes::DbUrl, source::activity::SentActivity};
+use lemmy_utils::error::{LemmyError, LemmyResult};
 use serde::{Deserialize, Serialize};
 use std::ops::Deref;
 use url::Url;
@@ -64,8 +64,10 @@ fn create_apub_tombstone_response<T: Into<Url>>(id: T) -> LemmyResult<HttpRespon
   )
 }
 
-fn err_object_not_local() -> LemmyError {
-  LemmyErrorType::ObjectNotLocal.into()
+fn redirect_remote_object(url: &DbUrl) -> HttpResponse {
+  let mut res = HttpResponse::PermanentRedirect();
+  res.insert_header((LOCATION, url.as_str()));
+  res.finish()
 }
 
 #[derive(Deserialize)]

crates/apub/src/http/post.rs

 use crate::{
-  http::{create_apub_response, create_apub_tombstone_response, err_object_not_local},
+  http::{create_apub_response, create_apub_tombstone_response, redirect_remote_object},
   objects::post::ApubPost,
 };
 use activitypub_federation::{config::Data, traits::Object};
@@ -23,7 +23,7 @@ pub(crate) async fn get_apub_post(
   let id = PostId(info.post_id.parse::<i32>()?);
   let post: ApubPost = Post::read(&mut context.pool(), id).await?.into();
   if !post.local {
-    Err(err_object_not_local())
+    Ok(redirect_remote_object(&post.ap_id))
   } else if !post.deleted && !post.removed {
     create_apub_response(&post.into_json(&context).await?)
   } else {

docker/federation/docker-compose.yml

@@ -2,7 +2,7 @@ version: "3.7"
 
 x-ui-default: &ui-default
   init: true
-  image: dessalines/lemmy-ui:0.18.4
+  image: dessalines/lemmy-ui:0.19.0-rc.3
   # assuming lemmy-ui is cloned besides lemmy directory
   # build:
   #   context: ../../../lemmy-ui

docker/federation/start-local-instances.bash

@@ -8,4 +8,4 @@ for Item in alpha beta gamma delta epsilon ; do
   sudo chown -R 991:991 volumes/pictrs_$Item
 done
 
-sudo docker compose up
+sudo docker compose up --build