Add `to` field in follow activities for better compatibility (#2829)

* Add `to` field in follow activities for better compatibility (fixes #2744)

* fix tests

crates/apub/assets/lemmy/activities/following/accept.json

@@ -1,7 +1,9 @@
 {
   "actor": "http://enterprise.lemmy.ml/c/main",
+  "to": ["http://ds9.lemmy.ml/u/lemmy_alpha"],
   "object": {
     "actor": "http://ds9.lemmy.ml/u/lemmy_alpha",
+    "to": ["http://enterprise.lemmy.ml/c/main"],
     "object": "http://enterprise.lemmy.ml/c/main",
     "type": "Follow",
     "id": "http://ds9.lemmy.ml/activities/follow/6abcd50b-b8ca-4952-86b0-a6dd8cc12866"

crates/apub/assets/lemmy/activities/following/follow.json

@@ -1,5 +1,6 @@
 {
   "actor": "http://ds9.lemmy.ml/u/lemmy_alpha",
+  "to": ["http://enterprise.lemmy.ml/c/main"],
   "object": "http://enterprise.lemmy.ml/c/main",
   "type": "Follow",
   "id": "http://ds9.lemmy.ml/activities/follow/6abcd50b-b8ca-4952-86b0-a6dd8cc12866"

crates/apub/assets/lemmy/activities/following/undo_follow.json

@@ -1,7 +1,9 @@
 {
   "actor": "http://ds9.lemmy.ml/u/lemmy_alpha",
+  "to": ["http://enterprise.lemmy.ml/c/main"],
   "object": {
     "actor": "http://ds9.lemmy.ml/u/lemmy_alpha",
+    "to": ["http://enterprise.lemmy.ml/c/main"],
     "object": "http://enterprise.lemmy.ml/c/main",
     "type": "Follow",
     "id": "http://ds9.lemmy.ml/activities/follow/dc2f1bc5-f3a0-4daa-a46b-428cbfbd023c"

crates/apub/src/activities/following/accept.rs

@@ -34,6 +34,7 @@ impl AcceptFollow {
     let person = follow.actor.clone().dereference(context).await?;
     let accept = AcceptFollow {
       actor: user_or_community.id().into(),
+      to: Some([person.id().into()]),
       object: follow,
       kind: AcceptType::Accept,
       id: generate_activity_id(
@@ -64,6 +65,9 @@ impl ActivityHandler for AcceptFollow {
   async fn verify(&self, context: &Data<LemmyContext>) -> Result<(), LemmyError> {
     verify_urls_match(self.actor.inner(), self.object.object.inner())?;
     self.object.verify(context).await?;
+    if let Some(to) = &self.to {
+      verify_urls_match(to[0].inner(), self.object.actor.inner())?;
+    }
     Ok(())
   }
 

crates/apub/src/activities/following/follow.rs

@@ -18,6 +18,7 @@ use crate::{
 use activitypub_federation::{
   config::Data,
   kinds::activity::FollowType,
+  protocol::verification::verify_urls_match,
   traits::{ActivityHandler, Actor},
 };
 use lemmy_api_common::{
@@ -44,6 +45,7 @@ impl Follow {
     Ok(Follow {
       actor: actor.id().into(),
       object: community.id().into(),
+      to: Some([community.id().into()]),
       kind: FollowType::Follow,
       id: generate_activity_id(
         FollowType::Follow,
@@ -93,6 +95,9 @@ impl ActivityHandler for Follow {
     if let UserOrCommunity::Community(c) = object {
       verify_person_in_community(&self.actor, &c, context).await?;
     }
+    if let Some(to) = &self.to {
+      verify_urls_match(to[0].inner(), self.object.inner())?;
+    }
     Ok(())
   }
 

crates/apub/src/activities/following/undo_follow.rs

@@ -32,6 +32,7 @@ impl UndoFollow {
     let object = Follow::new(actor, community, context)?;
     let undo = UndoFollow {
       actor: actor.id().into(),
+      to: Some([community.id().into()]),
       object,
       kind: UndoType::Undo,
       id: generate_activity_id(
@@ -62,6 +63,9 @@ impl ActivityHandler for UndoFollow {
     verify_urls_match(self.actor.inner(), self.object.actor.inner())?;
     verify_person(&self.actor, context).await?;
     self.object.verify(context).await?;
+    if let Some(to) = &self.to {
+      verify_urls_match(to[0].inner(), self.object.object.inner())?;
+    }
     Ok(())
   }
 

crates/apub/src/protocol/activities/following/accept.rs

@@ -1,4 +1,7 @@
-use crate::{objects::community::ApubCommunity, protocol::activities::following::follow::Follow};
+use crate::{
+  objects::{community::ApubCommunity, person::ApubPerson},
+  protocol::activities::following::follow::Follow,
+};
 use activitypub_federation::{fetch::object_id::ObjectId, kinds::activity::AcceptType};
 use serde::{Deserialize, Serialize};
 use url::Url;
@@ -7,6 +10,8 @@ use url::Url;
 #[serde(rename_all = "camelCase")]
 pub struct AcceptFollow {
   pub(crate) actor: ObjectId<ApubCommunity>,
+  /// Optional, for compatibility with platforms that always expect recipient field
+  pub(crate) to: Option<[ObjectId<ApubPerson>; 1]>,
   pub(crate) object: Follow,
   #[serde(rename = "type")]
   pub(crate) kind: AcceptType,

crates/apub/src/protocol/activities/following/follow.rs

@@ -7,6 +7,8 @@ use url::Url;
 #[serde(rename_all = "camelCase")]
 pub struct Follow {
   pub(crate) actor: ObjectId<ApubPerson>,
+  /// Optional, for compatibility with platforms that always expect recipient field
+  pub(crate) to: Option<[ObjectId<UserOrCommunity>; 1]>,
   pub(crate) object: ObjectId<UserOrCommunity>,
   #[serde(rename = "type")]
   pub(crate) kind: FollowType,

crates/apub/src/protocol/activities/following/undo_follow.rs

@@ -7,6 +7,8 @@ use url::Url;
 #[serde(rename_all = "camelCase")]
 pub struct UndoFollow {
   pub(crate) actor: ObjectId<ApubPerson>,
+  /// Optional, for compatibility with platforms that always expect recipient field
+  pub(crate) to: Option<[ObjectId<ApubPerson>; 1]>,
   pub(crate) object: Follow,
   #[serde(rename = "type")]
   pub(crate) kind: UndoType,