From: Felix Ableitner <me@nutomic.com>
Date: Fri, 23 Oct 2020 12:29:56 +0000 (+0200)
Subject: Ignore incoming activities which have been received before (ref #1220)
X-Git-Url: http://these/git/%7B%60%24%7BwebArchiveUrl%7D/%22%7B%7D/%22https:/hacktivis.me/README.es.md?a=commitdiff_plain;h=6d17d5ead2d429edcdd13ee462dfa999771985f3;p=lemmy.git

Ignore incoming activities which have been received before (ref #1220)
---

diff --git a/lemmy_apub/src/activities/receive/comment.rs b/lemmy_apub/src/activities/receive/comment.rs
index e7efe814..3fe9c0b2 100644
--- a/lemmy_apub/src/activities/receive/comment.rs
+++ b/lemmy_apub/src/activities/receive/comment.rs
@@ -73,7 +73,7 @@ pub(crate) async fn receive_create_comment(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(create, &user, context, request_counter).await?;
+  announce_if_community_is_local(create, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -131,7 +131,7 @@ pub(crate) async fn receive_update_comment(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(update, &user, context, request_counter).await?;
+  announce_if_community_is_local(update, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -183,7 +183,7 @@ pub(crate) async fn receive_like_comment(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(like, &user, context, request_counter).await?;
+  announce_if_community_is_local(like, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -241,7 +241,7 @@ pub(crate) async fn receive_dislike_comment(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(dislike, &user, context, request_counter).await?;
+  announce_if_community_is_local(dislike, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -276,8 +276,7 @@ pub(crate) async fn receive_delete_comment(
     websocket_id: None,
   });
 
-  let user = get_actor_as_user(&delete, context, request_counter).await?;
-  announce_if_community_is_local(delete, &user, context, request_counter).await?;
+  announce_if_community_is_local(delete, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
diff --git a/lemmy_apub/src/activities/receive/comment_undo.rs b/lemmy_apub/src/activities/receive/comment_undo.rs
index 4d6ca29b..ec61b111 100644
--- a/lemmy_apub/src/activities/receive/comment_undo.rs
+++ b/lemmy_apub/src/activities/receive/comment_undo.rs
@@ -57,7 +57,7 @@ pub(crate) async fn receive_undo_like_comment(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(undo, &user, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -109,7 +109,7 @@ pub(crate) async fn receive_undo_dislike_comment(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(undo, &user, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -145,8 +145,7 @@ pub(crate) async fn receive_undo_delete_comment(
     websocket_id: None,
   });
 
-  let user = get_actor_as_user(&undo, context, request_counter).await?;
-  announce_if_community_is_local(undo, &user, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -182,7 +181,6 @@ pub(crate) async fn receive_undo_remove_comment(
     websocket_id: None,
   });
 
-  let mod_ = get_actor_as_user(&undo, context, request_counter).await?;
-  announce_if_community_is_local(undo, &mod_, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
diff --git a/lemmy_apub/src/activities/receive/community.rs b/lemmy_apub/src/activities/receive/community.rs
index a79a85ee..80aad5e7 100644
--- a/lemmy_apub/src/activities/receive/community.rs
+++ b/lemmy_apub/src/activities/receive/community.rs
@@ -1,4 +1,4 @@
-use crate::activities::receive::{announce_if_community_is_local, get_actor_as_user};
+use crate::activities::receive::announce_if_community_is_local;
 use activitystreams::activity::{Delete, Remove, Undo};
 use actix_web::HttpResponse;
 use lemmy_db::{community::Community, community_view::CommunityView};
@@ -33,8 +33,7 @@ pub(crate) async fn receive_delete_community(
     websocket_id: None,
   });
 
-  let user = get_actor_as_user(&delete, context, request_counter).await?;
-  announce_if_community_is_local(delete, &user, context, request_counter).await?;
+  announce_if_community_is_local(delete, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -95,8 +94,7 @@ pub(crate) async fn receive_undo_delete_community(
     websocket_id: None,
   });
 
-  let user = get_actor_as_user(&undo, context, request_counter).await?;
-  announce_if_community_is_local(undo, &user, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -128,7 +126,6 @@ pub(crate) async fn receive_undo_remove_community(
     websocket_id: None,
   });
 
-  let mod_ = get_actor_as_user(&undo, context, request_counter).await?;
-  announce_if_community_is_local(undo, &mod_, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
diff --git a/lemmy_apub/src/activities/receive/mod.rs b/lemmy_apub/src/activities/receive/mod.rs
index 59c55519..2756fd14 100644
--- a/lemmy_apub/src/activities/receive/mod.rs
+++ b/lemmy_apub/src/activities/receive/mod.rs
@@ -39,7 +39,6 @@ where
 /// community, the activity is announced to all community followers.
 async fn announce_if_community_is_local<T, Kind>(
   activity: T,
-  user: &User_,
   context: &LemmyContext,
   request_counter: &mut i32,
 ) -> Result<(), LemmyError>
@@ -62,7 +61,7 @@ where
 
   if community.local {
     community
-      .send_announce(activity.into_any_base()?, &user, context)
+      .send_announce(activity.into_any_base()?, context)
       .await?;
   }
   Ok(())
diff --git a/lemmy_apub/src/activities/receive/post.rs b/lemmy_apub/src/activities/receive/post.rs
index 60fa8db1..0753b838 100644
--- a/lemmy_apub/src/activities/receive/post.rs
+++ b/lemmy_apub/src/activities/receive/post.rs
@@ -51,7 +51,7 @@ pub(crate) async fn receive_create_post(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(create, &user, context, request_counter).await?;
+  announce_if_community_is_local(create, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -89,7 +89,7 @@ pub(crate) async fn receive_update_post(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(update, &user, context, request_counter).await?;
+  announce_if_community_is_local(update, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -134,7 +134,7 @@ pub(crate) async fn receive_like_post(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(like, &user, context, request_counter).await?;
+  announce_if_community_is_local(like, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -185,7 +185,7 @@ pub(crate) async fn receive_dislike_post(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(dislike, &user, context, request_counter).await?;
+  announce_if_community_is_local(dislike, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -214,8 +214,7 @@ pub(crate) async fn receive_delete_post(
     websocket_id: None,
   });
 
-  let user = get_actor_as_user(&delete, context, request_counter).await?;
-  announce_if_community_is_local(delete, &user, context, request_counter).await?;
+  announce_if_community_is_local(delete, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
diff --git a/lemmy_apub/src/activities/receive/post_undo.rs b/lemmy_apub/src/activities/receive/post_undo.rs
index dea1a621..bee56d86 100644
--- a/lemmy_apub/src/activities/receive/post_undo.rs
+++ b/lemmy_apub/src/activities/receive/post_undo.rs
@@ -52,7 +52,7 @@ pub(crate) async fn receive_undo_like_post(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(undo, &user, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -98,7 +98,7 @@ pub(crate) async fn receive_undo_dislike_post(
     websocket_id: None,
   });
 
-  announce_if_community_is_local(undo, &user, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -127,8 +127,7 @@ pub(crate) async fn receive_undo_delete_post(
     websocket_id: None,
   });
 
-  let user = get_actor_as_user(&undo, context, request_counter).await?;
-  announce_if_community_is_local(undo, &user, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
 
@@ -158,7 +157,6 @@ pub(crate) async fn receive_undo_remove_post(
     websocket_id: None,
   });
 
-  let mod_ = get_actor_as_user(&undo, context, request_counter).await?;
-  announce_if_community_is_local(undo, &mod_, context, request_counter).await?;
+  announce_if_community_is_local(undo, context, request_counter).await?;
   Ok(HttpResponse::Ok().finish())
 }
diff --git a/lemmy_apub/src/activities/send/community.rs b/lemmy_apub/src/activities/send/community.rs
index f8d03579..446ce6f3 100644
--- a/lemmy_apub/src/activities/send/community.rs
+++ b/lemmy_apub/src/activities/send/community.rs
@@ -95,7 +95,7 @@ impl ActorType for Community {
       .set_to(public())
       .set_many_ccs(vec![self.get_followers_url()?]);
 
-    send_to_community_followers(delete, self, context, None).await?;
+    send_to_community_followers(delete, self, context).await?;
     Ok(())
   }
 
@@ -121,7 +121,7 @@ impl ActorType for Community {
       .set_to(public())
       .set_many_ccs(vec![self.get_followers_url()?]);
 
-    send_to_community_followers(undo, self, context, None).await?;
+    send_to_community_followers(undo, self, context).await?;
     Ok(())
   }
 
@@ -134,7 +134,7 @@ impl ActorType for Community {
       .set_to(public())
       .set_many_ccs(vec![self.get_followers_url()?]);
 
-    send_to_community_followers(remove, self, context, None).await?;
+    send_to_community_followers(remove, self, context).await?;
     Ok(())
   }
 
@@ -155,7 +155,7 @@ impl ActorType for Community {
       .set_to(public())
       .set_many_ccs(vec![self.get_followers_url()?]);
 
-    send_to_community_followers(undo, self, context, None).await?;
+    send_to_community_followers(undo, self, context).await?;
     Ok(())
   }
 
@@ -164,7 +164,6 @@ impl ActorType for Community {
   async fn send_announce(
     &self,
     activity: AnyBase,
-    sender: &User_,
     context: &LemmyContext,
   ) -> Result<(), LemmyError> {
     let mut announce = Announce::new(self.actor_id.to_owned(), activity);
@@ -174,13 +173,7 @@ impl ActorType for Community {
       .set_to(public())
       .set_many_ccs(vec![self.get_followers_url()?]);
 
-    send_to_community_followers(
-      announce,
-      self,
-      context,
-      Some(sender.get_shared_inbox_url()?),
-    )
-    .await?;
+    send_to_community_followers(announce, self, context).await?;
 
     Ok(())
   }
diff --git a/lemmy_apub/src/activities/send/user.rs b/lemmy_apub/src/activities/send/user.rs
index 6055a178..c4d287a5 100644
--- a/lemmy_apub/src/activities/send/user.rs
+++ b/lemmy_apub/src/activities/send/user.rs
@@ -121,7 +121,6 @@ impl ActorType for User_ {
   async fn send_announce(
     &self,
     _activity: AnyBase,
-    _sender: &User_,
     _context: &LemmyContext,
   ) -> Result<(), LemmyError> {
     unimplemented!()
diff --git a/lemmy_apub/src/activity_queue.rs b/lemmy_apub/src/activity_queue.rs
index 839cf667..c8c8af37 100644
--- a/lemmy_apub/src/activity_queue.rs
+++ b/lemmy_apub/src/activity_queue.rs
@@ -74,24 +74,19 @@ pub async fn send_to_community_followers<T, Kind>(
   activity: T,
   community: &Community,
   context: &LemmyContext,
-  sender_shared_inbox: Option<Url>,
 ) -> Result<(), LemmyError>
 where
   T: AsObject<Kind> + Extends<Kind> + Debug + BaseExt<Kind>,
   Kind: Serialize,
   <T as Extends<Kind>>::Error: From<serde_json::Error> + Send + Sync + 'static,
 {
-  // dont send to the local instance, nor to the instance where the activity originally came from,
-  // because that would result in a database error (same data inserted twice)
-  let community_shared_inbox = community.get_shared_inbox_url()?;
   let follower_inboxes: Vec<Url> = community
     .get_follower_inboxes(context.pool())
     .await?
     .iter()
-    .filter(|inbox| Some(inbox) != sender_shared_inbox.as_ref().as_ref())
-    .filter(|inbox| inbox != &&community_shared_inbox)
-    .filter(|inbox| check_is_apub_id_valid(inbox).is_ok())
     .unique()
+    .filter(|inbox| inbox.host_str() != Some(&Settings::get().hostname))
+    .filter(|inbox| check_is_apub_id_valid(inbox).is_ok())
     .map(|inbox| inbox.to_owned())
     .collect();
   debug!(
@@ -133,7 +128,7 @@ where
   // if this is a local community, we need to do an announce from the community instead
   if community.local {
     community
-      .send_announce(activity.into_any_base()?, creator, context)
+      .send_announce(activity.into_any_base()?, context)
       .await?;
   } else {
     let inbox = community.get_shared_inbox_url()?;
@@ -223,7 +218,8 @@ where
   // This is necessary because send_comment and send_comment_mentions
   // might send the same ap_id
   if insert_into_db {
-    insert_activity(actor.user_id(), activity.clone(), true, pool).await?;
+    let id = activity.id().context(location_info!())?;
+    insert_activity(id, actor.user_id(), activity.clone(), true, pool).await?;
   }
 
   for i in inboxes {
diff --git a/lemmy_apub/src/inbox/community_inbox.rs b/lemmy_apub/src/inbox/community_inbox.rs
index 6cef1d03..ffc5f6d7 100644
--- a/lemmy_apub/src/inbox/community_inbox.rs
+++ b/lemmy_apub/src/inbox/community_inbox.rs
@@ -3,6 +3,7 @@ use crate::{
   check_is_apub_id_valid,
   extensions::signatures::verify_signature,
   fetcher::get_or_fetch_and_upsert_user,
+  inbox::{get_activity_id, is_activity_already_known},
   insert_activity,
   ActorType,
 };
@@ -80,6 +81,11 @@ pub async fn community_inbox(
 
   verify_signature(&request, &user)?;
 
+  let activity_id = get_activity_id(&activity, user_uri)?;
+  if is_activity_already_known(context.pool(), &activity_id).await? {
+    return Ok(HttpResponse::Ok().finish());
+  }
+
   let any_base = activity.clone().into_any_base()?;
   let kind = activity.kind().context(location_info!())?;
   let user_id = user.id;
@@ -88,7 +94,14 @@ pub async fn community_inbox(
     ValidTypes::Undo => handle_undo_follow(any_base, user, community, &context).await,
   };
 
-  insert_activity(user_id, activity.clone(), false, context.pool()).await?;
+  insert_activity(
+    &activity_id,
+    user_id,
+    activity.clone(),
+    false,
+    context.pool(),
+  )
+  .await?;
   res
 }
 
diff --git a/lemmy_apub/src/inbox/mod.rs b/lemmy_apub/src/inbox/mod.rs
index 41a1b7ff..e2305b44 100644
--- a/lemmy_apub/src/inbox/mod.rs
+++ b/lemmy_apub/src/inbox/mod.rs
@@ -1,3 +1,37 @@
+use activitystreams::base::{BaseExt, Extends};
+use anyhow::Context;
+use lemmy_db::{activity::Activity, DbPool};
+use lemmy_structs::blocking;
+use lemmy_utils::{location_info, LemmyError};
+use serde::{export::fmt::Debug, Serialize};
+use url::Url;
+
 pub mod community_inbox;
 pub mod shared_inbox;
 pub mod user_inbox;
+
+pub(crate) fn get_activity_id<T, Kind>(activity: &T, creator_uri: &Url) -> Result<Url, LemmyError>
+where
+  T: BaseExt<Kind> + Extends<Kind> + Debug,
+  Kind: Serialize,
+  <T as Extends<Kind>>::Error: From<serde_json::Error> + Send + Sync + 'static,
+{
+  let creator_domain = creator_uri.host_str().context(location_info!())?;
+  let activity_id = activity.id(creator_domain)?;
+  Ok(activity_id.context(location_info!())?.to_owned())
+}
+
+pub(crate) async fn is_activity_already_known(
+  pool: &DbPool,
+  activity_id: &Url,
+) -> Result<bool, LemmyError> {
+  let activity_id = activity_id.to_string();
+  let existing = blocking(pool, move |conn| {
+    Activity::read_from_apub_id(&conn, &activity_id)
+  })
+  .await?;
+  match existing {
+    Ok(_) => Ok(true),
+    Err(_) => Ok(false),
+  }
+}
diff --git a/lemmy_apub/src/inbox/shared_inbox.rs b/lemmy_apub/src/inbox/shared_inbox.rs
index da26d748..4457a1a6 100644
--- a/lemmy_apub/src/inbox/shared_inbox.rs
+++ b/lemmy_apub/src/inbox/shared_inbox.rs
@@ -42,6 +42,7 @@ use crate::{
   check_is_apub_id_valid,
   extensions::signatures::verify_signature,
   fetcher::get_or_fetch_and_upsert_actor,
+  inbox::{get_activity_id, is_activity_already_known},
   insert_activity,
   ActorType,
 };
@@ -104,6 +105,11 @@ pub async fn shared_inbox(
   let actor = get_or_fetch_and_upsert_actor(&actor_id, &context, request_counter).await?;
   verify_signature(&request, actor.as_ref())?;
 
+  let activity_id = get_activity_id(&activity, &actor_id)?;
+  if is_activity_already_known(context.pool(), &activity_id).await? {
+    return Ok(HttpResponse::Ok().finish());
+  }
+
   let any_base = activity.clone().into_any_base()?;
   let kind = activity.kind().context(location_info!())?;
   let res = match kind {
@@ -119,7 +125,14 @@ pub async fn shared_inbox(
     ValidTypes::Undo => receive_undo(&context, any_base, actor_id, request_counter).await,
   };
 
-  insert_activity(actor.user_id(), activity.clone(), false, context.pool()).await?;
+  insert_activity(
+    &activity_id,
+    actor.user_id(),
+    activity.clone(),
+    false,
+    context.pool(),
+  )
+  .await?;
   res
 }
 
@@ -142,6 +155,9 @@ async fn receive_announce(
 
   let inner_id = object.id().context(location_info!())?.to_owned();
   check_is_apub_id_valid(&inner_id)?;
+  if is_activity_already_known(context.pool(), &inner_id).await? {
+    return Ok(HttpResponse::Ok().finish());
+  }
 
   match kind {
     Some("Create") => receive_create(context, object, inner_id, request_counter).await,
diff --git a/lemmy_apub/src/inbox/user_inbox.rs b/lemmy_apub/src/inbox/user_inbox.rs
index e89aba14..653a447c 100644
--- a/lemmy_apub/src/inbox/user_inbox.rs
+++ b/lemmy_apub/src/inbox/user_inbox.rs
@@ -3,6 +3,7 @@ use crate::{
   check_is_apub_id_valid,
   extensions::signatures::verify_signature,
   fetcher::{get_or_fetch_and_upsert_actor, get_or_fetch_and_upsert_community},
+  inbox::{get_activity_id, is_activity_already_known},
   insert_activity,
   ActorType,
   FromApub,
@@ -83,6 +84,11 @@ pub async fn user_inbox(
   let actor = get_or_fetch_and_upsert_actor(actor_uri, &context, request_counter).await?;
   verify_signature(&request, actor.as_ref())?;
 
+  let activity_id = get_activity_id(&activity, actor_uri)?;
+  if is_activity_already_known(context.pool(), &activity_id).await? {
+    return Ok(HttpResponse::Ok().finish());
+  }
+
   let any_base = activity.clone().into_any_base()?;
   let kind = activity.kind().context(location_info!())?;
   let res = match kind {
@@ -101,7 +107,14 @@ pub async fn user_inbox(
     }
   };
 
-  insert_activity(actor.user_id(), activity.clone(), false, context.pool()).await?;
+  insert_activity(
+    &activity_id,
+    actor.user_id(),
+    activity.clone(),
+    false,
+    context.pool(),
+  )
+  .await?;
   res
 }
 
diff --git a/lemmy_apub/src/lib.rs b/lemmy_apub/src/lib.rs
index 4a1413b3..14bc6f21 100644
--- a/lemmy_apub/src/lib.rs
+++ b/lemmy_apub/src/lib.rs
@@ -22,7 +22,7 @@ use activitystreams::{
 };
 use activitystreams_ext::{Ext1, Ext2};
 use anyhow::{anyhow, Context};
-use lemmy_db::{activity::do_insert_activity, user::User_, DbPool};
+use lemmy_db::{activity::Activity, user::User_, DbPool};
 use lemmy_structs::blocking;
 use lemmy_utils::{location_info, settings::Settings, LemmyError};
 use lemmy_websocket::LemmyContext;
@@ -195,7 +195,6 @@ pub trait ActorType {
   async fn send_announce(
     &self,
     activity: AnyBase,
-    sender: &User_,
     context: &LemmyContext,
   ) -> Result<(), LemmyError>;
 
@@ -249,16 +248,18 @@ pub trait ActorType {
 /// Store a sent or received activity in the database, for logging purposes. These records are not
 /// persistent.
 pub async fn insert_activity<T>(
+  ap_id: &Url,
   user_id: i32,
-  data: T,
+  activity: T,
   local: bool,
   pool: &DbPool,
 ) -> Result<(), LemmyError>
 where
   T: Serialize + std::fmt::Debug + Send + 'static,
 {
+  let ap_id = ap_id.to_string();
   blocking(pool, move |conn| {
-    do_insert_activity(conn, user_id, &data, local)
+    Activity::insert(conn, ap_id, user_id, &activity, local)
   })
   .await??;
   Ok(())
diff --git a/lemmy_db/src/activity.rs b/lemmy_db/src/activity.rs
index 37f86c4b..539820fc 100644
--- a/lemmy_db/src/activity.rs
+++ b/lemmy_db/src/activity.rs
@@ -12,6 +12,7 @@ use std::{
 #[table_name = "activity"]
 pub struct Activity {
   pub id: i32,
+  pub ap_id: String,
   pub user_id: i32,
   pub data: Value,
   pub local: bool,
@@ -22,6 +23,7 @@ pub struct Activity {
 #[derive(Insertable, AsChangeset)]
 #[table_name = "activity"]
 pub struct ActivityForm {
+  pub ap_id: String,
   pub user_id: i32,
   pub data: Value,
   pub local: bool,
@@ -53,30 +55,39 @@ impl Crud<ActivityForm> for Activity {
   }
 }
 
-pub fn do_insert_activity<T>(
-  conn: &PgConnection,
-  user_id: i32,
-  data: &T,
-  local: bool,
-) -> Result<Activity, IoError>
-where
-  T: Serialize + Debug,
-{
-  debug!("inserting activity for user {}: ", user_id);
-  debug!("{}", serde_json::to_string_pretty(&data)?);
-  let activity_form = ActivityForm {
-    user_id,
-    data: serde_json::to_value(&data)?,
-    local,
-    updated: None,
-  };
-  let result = Activity::create(&conn, &activity_form);
-  match result {
-    Ok(s) => Ok(s),
-    Err(e) => Err(IoError::new(
-      ErrorKind::Other,
-      format!("Failed to insert activity into database: {}", e),
-    )),
+impl Activity {
+  pub fn insert<T>(
+    conn: &PgConnection,
+    ap_id: String,
+    user_id: i32,
+    data: &T,
+    local: bool,
+  ) -> Result<Self, IoError>
+  where
+    T: Serialize + Debug,
+  {
+    debug!("inserting activity for user {}: ", user_id);
+    debug!("{}", serde_json::to_string_pretty(&data)?);
+    let activity_form = ActivityForm {
+      ap_id,
+      user_id,
+      data: serde_json::to_value(&data)?,
+      local,
+      updated: None,
+    };
+    let result = Activity::create(&conn, &activity_form);
+    match result {
+      Ok(s) => Ok(s),
+      Err(e) => Err(IoError::new(
+        ErrorKind::Other,
+        format!("Failed to insert activity into database: {}", e),
+      )),
+    }
+  }
+
+  pub fn read_from_apub_id(conn: &PgConnection, object_id: &str) -> Result<Self, Error> {
+    use crate::schema::activity::dsl::*;
+    activity.filter(ap_id.eq(object_id)).first::<Self>(conn)
   }
 }
 
@@ -125,16 +136,24 @@ mod tests {
 
     let inserted_creator = User_::create(&conn, &creator_form).unwrap();
 
+    let ap_id =
+      "https://enterprise.lemmy.ml/activities/delete/f1b5d57c-80f8-4e03-a615-688d552e946c";
     let test_json: Value = serde_json::from_str(
       r#"{
-    "street": "Article Circle Expressway 1",
-    "city": "North Pole",
-    "postcode": "99705",
-    "state": "Alaska"
-}"#,
+    "@context": "https://www.w3.org/ns/activitystreams",
+    "id": "https://enterprise.lemmy.ml/activities/delete/f1b5d57c-80f8-4e03-a615-688d552e946c",
+    "type": "Delete",
+    "actor": "https://enterprise.lemmy.ml/u/riker",
+    "to": "https://www.w3.org/ns/activitystreams#Public",
+    "cc": [
+        "https://enterprise.lemmy.ml/c/main/"
+    ],
+    "object": "https://enterprise.lemmy.ml/post/32"
+    }"#,
     )
     .unwrap();
     let activity_form = ActivityForm {
+      ap_id: ap_id.to_string(),
       user_id: inserted_creator.id,
       data: test_json.to_owned(),
       local: true,
@@ -144,6 +163,7 @@ mod tests {
     let inserted_activity = Activity::create(&conn, &activity_form).unwrap();
 
     let expected_activity = Activity {
+      ap_id: ap_id.to_string(),
       id: inserted_activity.id,
       user_id: inserted_creator.id,
       data: test_json,
@@ -153,9 +173,11 @@ mod tests {
     };
 
     let read_activity = Activity::read(&conn, inserted_activity.id).unwrap();
+    let read_activity_by_apub_id = Activity::read_from_apub_id(&conn, ap_id).unwrap();
     User_::delete(&conn, inserted_creator.id).unwrap();
 
     assert_eq!(expected_activity, read_activity);
+    assert_eq!(expected_activity, read_activity_by_apub_id);
     assert_eq!(expected_activity, inserted_activity);
   }
 }
diff --git a/lemmy_db/src/schema.rs b/lemmy_db/src/schema.rs
index c446edd9..c755009b 100644
--- a/lemmy_db/src/schema.rs
+++ b/lemmy_db/src/schema.rs
@@ -1,6 +1,7 @@
 table! {
     activity (id) {
         id -> Int4,
+        ap_id -> Text,
         user_id -> Int4,
         data -> Jsonb,
         local -> Bool,