Don't treat remote accepts/rejects as local.

Also, use specialized functions to get safe data.

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -95,6 +95,17 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
     end
   end
 
+  def reject(%{to: to, actor: actor, object: object} = params) do
+    # only accept false as false value
+    local = !(params[:local] == false)
+
+    with data <- %{"to" => to, "type" => "Reject", "actor" => actor, "object" => object},
+         {:ok, activity} <- insert(data, local),
+         :ok <- maybe_federate(activity) do
+      {:ok, activity}
+    end
+  end
+
   def update(%{to: to, cc: cc, actor: actor, object: object} = params) do
     # only accept false as false value
     local = !(params[:local] == false)

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -173,7 +173,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
          %User{local: true} = follower <- User.get_cached_by_ap_id(follow_activity["actor"]),
          follow_activity <- Utils.fetch_latest_follow(follower, followed),
          false <- is_nil(follow_activity),
-         {:ok, activity} <- ActivityPub.insert(data, true) do
+         {:ok, activity} <- ActivityPub.accept(%{to: follow_activity.data["to"], type: "Accept", actor: followed.ap_id, object: follow_activity.data["id"], local: false}) do
       if not User.following?(follower, followed) do
         {:ok, follower} = User.follow(follower, followed)
       end
@@ -192,7 +192,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
          %User{local: true} = follower <- User.get_cached_by_ap_id(follow_activity["actor"]),
          follow_activity <- Utils.fetch_latest_follow(follower, followed),
          false <- is_nil(follow_activity),
-         {:ok, activity} <- ActivityPub.insert(data, true) do
+         {:ok, activity} <- ActivityPub.accept(%{to: follow_activity.data["to"], type: "Accept", actor: followed.ap_id, object: follow_activity.data["id"], local: false}) do
       User.unfollow(follower, followed)
 
       {:ok, activity}

test/web/activity_pub/transmogrifier_test.exs

@@ -404,7 +404,10 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
       accept_data =
         Map.put(accept_data, "object", Map.put(accept_data["object"], "actor", follower.ap_id))
 
-      {:ok, %Activity{data: _}} = Transmogrifier.handle_incoming(accept_data)
+      {:ok, activity} = Transmogrifier.handle_incoming(accept_data)
+      refute activity.local
+
+      assert activity.data["object"] == follow_activity.data["id"]
 
       follower = Repo.get(User, follower.id)
 
@@ -425,7 +428,8 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
       accept_data =
         Map.put(accept_data, "object", Map.put(accept_data["object"], "actor", follower.ap_id))
 
-      {:ok, %Activity{data: _}} = Transmogrifier.handle_incoming(accept_data)
+      {:ok, activity} = Transmogrifier.handle_incoming(accept_data)
+      assert activity.data["object"] == follow_activity.data["id"]
 
       follower = Repo.get(User, follower.id)
 
@@ -444,7 +448,8 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
         |> Map.put("actor", followed.ap_id)
         |> Map.put("object", follow_activity.data["id"])
 
-      {:ok, %Activity{data: _}} = Transmogrifier.handle_incoming(accept_data)
+      {:ok, activity} = Transmogrifier.handle_incoming(accept_data)
+      assert activity.data["object"] == follow_activity.data["id"]
 
       follower = Repo.get(User, follower.id)
 
@@ -470,6 +475,25 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
       refute User.following?(follower, followed) == true
     end
 
+    test "it fails for incoming rejects which cannot be correlated" do
+      follower = insert(:user)
+      followed = insert(:user, %{info: %{"locked" => true}})
+
+      accept_data =
+        File.read!("test/fixtures/mastodon-reject-activity.json")
+        |> Poison.decode!()
+        |> Map.put("actor", followed.ap_id)
+
+      accept_data =
+        Map.put(accept_data, "object", Map.put(accept_data["object"], "actor", follower.ap_id))
+
+      :error = Transmogrifier.handle_incoming(accept_data)
+
+      follower = Repo.get(User, follower.id)
+
+      refute User.following?(follower, followed) == true
+    end
+
     test "it works for incoming rejects which are orphaned" do
       follower = insert(:user)
       followed = insert(:user, %{info: %{"locked" => true}})
@@ -487,7 +511,8 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
       reject_data =
         Map.put(reject_data, "object", Map.put(reject_data["object"], "actor", follower.ap_id))
 
-      {:ok, %Activity{data: _}} = Transmogrifier.handle_incoming(reject_data)
+      {:ok, activity} = Transmogrifier.handle_incoming(reject_data)
+      refute activity.local
 
       follower = Repo.get(User, follower.id)