Ignore Announce() activity if repost already exists but with a different object ID

src/activitypub/handlers/announce.rs

@@ -65,8 +65,16 @@ pub async fn handle_announce(
         },
     };
     let repost_data = PostCreateData::repost(post_id, Some(repost_object_id));
-    create_post(db_client, &author.id, repost_data).await?;
+    match create_post(db_client, &author.id, repost_data).await {
-    Ok(Some(NOTE))
+        Ok(_) => Ok(Some(NOTE)),
+        Err(DatabaseError::AlreadyExists("post")) => {
+            // Ignore activity if repost already exists (with a different
+            // object ID, or due to race condition in a handler).
+            log::warn!("repost already exists");
+            Ok(None)
+        },
+        Err(other_error) => Err(other_error.into()),
+    }
 }
 
 #[cfg(test)]

src/models/posts/queries.rs

@@ -82,6 +82,7 @@ pub async fn create_post(
             &data.created_at,
         ],
     ).await.map_err(catch_unique_violation("post"))?;
+    // Return NotFound error if reply/repost is not allowed
     let post_row = maybe_post_row.ok_or(DatabaseError::NotFound("post"))?;
     let db_post: DbPost = post_row.try_get("post")?;
     // Create links to attachments
@@ -175,7 +176,7 @@ pub async fn create_post(
             ).await?;
             notified_users.push(in_reply_to_author.id);
         };
-    }
+    };
     if let Some(repost_of_id) = &db_post.repost_of_id {
         update_repost_count(&transaction, repost_of_id, 1).await?;
         let repost_of_author = get_post_author(&transaction, repost_of_id).await?;