From 99cdf742d4366e835fd827749eb6638d5f56ba9b Mon Sep 17 00:00:00 2001
From: Felix Ableitner <me@nutomic.com>
Date: Wed, 25 Sep 2024 13:21:20 +0200
Subject: [PATCH] Ignore NotFound errors when receiving activities (fixes
 #2240)

---
 Cargo.lock                  |  1 +
 crates/apub/src/http/mod.rs | 15 +++++++++++----
 crates/utils/Cargo.toml     |  2 ++
 crates/utils/src/error.rs   | 28 ++++++++++++++++++++--------
 4 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index a799d9d6f..c49ae5274 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2795,6 +2795,7 @@ dependencies = [
 name = "lemmy_utils"
 version = "0.19.6-beta.7"
 dependencies = [
+ "activitypub_federation",
  "actix-web",
  "anyhow",
  "cfg-if",
diff --git a/crates/apub/src/http/mod.rs b/crates/apub/src/http/mod.rs
index dad39881f..ed3026e6e 100644
--- a/crates/apub/src/http/mod.rs
+++ b/crates/apub/src/http/mod.rs
@@ -17,7 +17,7 @@ use lemmy_db_schema::{
   source::{activity::SentActivity, community::Community},
   CommunityVisibility,
 };
-use lemmy_utils::error::{LemmyErrorType, LemmyResult};
+use lemmy_utils::error::{LemmyError, LemmyErrorType, LemmyResult};
 use serde::{Deserialize, Serialize};
 use std::{ops::Deref, time::Duration};
 use tokio::time::timeout;
@@ -43,9 +43,16 @@ pub async fn shared_inbox(
   // avoid taking a long time to process an incoming activity when a required data fetch times out.
   // In this case our own instance would timeout and be marked as dead by the sender. Better to
   // consider the activity broken and move on.
-  timeout(INCOMING_ACTIVITY_TIMEOUT, receive_fut)
-    .await
-    .map_err(|_| LemmyErrorType::InboxTimeout)?
+  let res = timeout(INCOMING_ACTIVITY_TIMEOUT, receive_fut).await;
+
+  match res {
+    // Ignore NotFound error, usually means that the sending actor was deleted and sent a delete
+    // activity: https://github.com/LemmyNet/lemmy/issues/2240
+    Ok(Err(LemmyError {error_type: LemmyErrorType::NotFound, ..})) => Ok(HttpResponse::Ok().finish()),
+    // Top-level error means we hit the send timeout
+    Err(_) => Err(LemmyErrorType::InboxTimeout.into()),
+    Ok(other) => other,
+  }
 }
 
 /// Convert the data to json and turn it into an HTTP Response with the correct ActivityPub
diff --git a/crates/utils/Cargo.toml b/crates/utils/Cargo.toml
index f0369f7e9..6f6059160 100644
--- a/crates/utils/Cargo.toml
+++ b/crates/utils/Cargo.toml
@@ -47,6 +47,7 @@ full = [
   "dep:uuid",
   "dep:itertools",
   "dep:markdown-it",
+  "dep:activitypub_federation"
 ]
 
 [dependencies]
@@ -80,6 +81,7 @@ lettre = { version = "0.11.8", default-features = false, features = [
 markdown-it = { version = "0.6.1", optional = true }
 ts-rs = { workspace = true, optional = true }
 enum-map = { workspace = true, optional = true }
+activitypub_federation = { workspace = true, optional = true }
 cfg-if = "1"
 clearurls = { version = "0.0.4", features = ["linkify"] }
 
diff --git a/crates/utils/src/error.rs b/crates/utils/src/error.rs
index e03ff2e23..b0cfcc9ce 100644
--- a/crates/utils/src/error.rs
+++ b/crates/utils/src/error.rs
@@ -198,10 +198,14 @@ cfg_if! {
     {
       fn from(t: T) -> Self {
         let cause = t.into();
-        let error_type = match cause.downcast_ref::<diesel::result::Error>() {
-          Some(&diesel::NotFound) => LemmyErrorType::NotFound,
-          _ => LemmyErrorType::Unknown(format!("{}", &cause))
-      };
+        let error_type = if let Some(&diesel::NotFound) = cause.downcast_ref::<diesel::result::Error>() {
+          LemmyErrorType::NotFound
+        } else if let Some(activitypub_federation::error::Error::NotFound) = cause.downcast_ref::<activitypub_federation::error::Error>() {
+          LemmyErrorType::NotFound
+        }
+        else {
+          LemmyErrorType::Unknown(format!("{}", &cause))
+        };
         LemmyError {
           error_type,
           inner: cause,
@@ -231,11 +235,15 @@ cfg_if! {
     impl actix_web::error::ResponseError for LemmyError {
       fn status_code(&self) -> actix_web::http::StatusCode {
         if self.error_type == LemmyErrorType::IncorrectLogin {
-          return actix_web::http::StatusCode::UNAUTHORIZED;
+          actix_web::http::StatusCode::UNAUTHORIZED
         }
-        match self.inner.downcast_ref::<diesel::result::Error>() {
-          Some(diesel::result::Error::NotFound) => actix_web::http::StatusCode::NOT_FOUND,
-          _ => actix_web::http::StatusCode::BAD_REQUEST,
+        else if let Some(&diesel::NotFound) = self.inner.downcast_ref::<diesel::result::Error>() {
+          actix_web::http::StatusCode::NOT_FOUND
+        } else if let Some(activitypub_federation::error::Error::NotFound) = self.inner.downcast_ref::<activitypub_federation::error::Error>() {
+          actix_web::http::StatusCode::NOT_FOUND
+        }
+        else {
+          actix_web::http::StatusCode::BAD_REQUEST
         }
       }
 
@@ -320,6 +328,10 @@ cfg_if! {
         assert_eq!(LemmyErrorType::NotFound, not_found_error.error_type);
         assert_eq!(404, not_found_error.status_code());
 
+        let apub_not_found_error = LemmyError::from(activitypub_federation::error::Error::NotFound);
+        assert_eq!(LemmyErrorType::NotFound, apub_not_found_error.error_type);
+        assert_eq!(404, apub_not_found_error.status_code());
+
         let other_error = LemmyError::from(diesel::result::Error::NotInTransaction);
         assert!(matches!(other_error.error_type, LemmyErrorType::Unknown{..}));
         assert_eq!(400, other_error.status_code());