signature: drop unecessary round trip over user

We already got the key.

lib/pleroma/signature.ex

@@ -9,24 +9,11 @@ defmodule Pleroma.Signature do
   alias Pleroma.User.SigningKey
   require Logger
 
-  def key_id_to_actor_id(key_id) do
-    case SigningKey.key_id_to_ap_id(key_id) do
-      nil ->
-        # hm, we SHOULD have gotten this in the pipeline before we hit here!
-        Logger.error("Could not figure out who owns the key #{key_id}")
-        {:error, :key_owner_not_found}
-
-      key ->
-        {:ok, key}
-    end
-  end
-
   def fetch_public_key(conn) do
     with %{"keyId" => kid} <- HTTPSignatures.signature_for_conn(conn),
-         {:ok, %SigningKey{}} <- SigningKey.get_or_fetch_by_key_id(kid),
-         {:ok, actor_id} <- key_id_to_actor_id(kid),
-         {:ok, public_key} <- User.get_public_key_for_ap_id(actor_id) do
-      {:ok, public_key}
+         {:ok, %SigningKey{} = sk} <- SigningKey.get_or_fetch_by_key_id(kid),
+         {:ok, decoded_key} <- SigningKey.public_key_decoded(sk) do
+      {:ok, decoded_key}
     else
       e ->
         {:error, e}
@@ -35,10 +22,10 @@ def fetch_public_key(conn) do
 
   def refetch_public_key(conn) do
     with %{"keyId" => kid} <- HTTPSignatures.signature_for_conn(conn),
-         {:ok, %SigningKey{}} <- SigningKey.get_or_fetch_by_key_id(kid),
-         {:ok, actor_id} <- key_id_to_actor_id(kid),
-         {:ok, public_key} <- User.get_public_key_for_ap_id(actor_id) do
-      {:ok, public_key}
+         # TODO: force a refetch of stale keys (perhaps with a backoff time based on updated_at)
+         {:ok, %SigningKey{} = sk} <- SigningKey.get_or_fetch_by_key_id(kid),
+         {:ok, decoded_key} <- SigningKey.public_key_decoded(sk) do
+      {:ok, decoded_key}
     else
       e ->
         {:error, e}

lib/pleroma/user.ex

@@ -2068,17 +2068,6 @@ defp create_service_actor(uri, nickname) do
 
   defdelegate public_key(user), to: SigningKey
 
-  def get_public_key_for_ap_id(ap_id) do
-    with {:ok, %User{} = user} <- get_or_fetch_by_ap_id(ap_id),
-         {:ok, public_key} <- SigningKey.public_key(user) do
-      {:ok, public_key}
-    else
-      e ->
-        Logger.error("Could not get public key for #{ap_id}.\n#{inspect(e)}")
-        {:error, e}
-    end
-  end
-
   @doc "Gets or fetch a user by uri or nickname."
   @spec get_or_fetch(String.t()) :: {:ok, User.t()} | {:error, String.t()}
   def get_or_fetch("http://" <> _host = uri), do: get_or_fetch_by_ap_id(uri)

lib/pleroma/user/signing_key.ex

@@ -115,24 +115,18 @@ def private_pem_to_public_pem(private_pem) do
     {:ok, :public_key.pem_encode([public_key])}
   end
 
-  @spec public_key(User.t()) :: {:ok, binary()} | {:error, String.t()}
+  @spec public_key(__MODULE__) :: {:ok, binary()} | {:error, String.t()}
   @doc """
-  Given a user, return the public key for that user in binary format.
+  Return public key data in binary format.
   """
-  def public_key(%User{} = user) do
-    case Repo.preload(user, :signing_key) do
-      %User{signing_key: %__MODULE__{public_key: public_key_pem}} ->
-        key =
+  def public_key_decoded(%__MODULE__{public_key: public_key_pem}) do
+    decoded =
       public_key_pem
       |> :public_key.pem_decode()
       |> hd()
       |> :public_key.pem_entry_decode()
 
-        {:ok, key}
-
-      _ ->
-        {:error, "key not found"}
-    end
+    {:ok, decoded}
   end
 
   def public_key(_), do: {:error, "key not found"}

lib/pleroma/web/plugs/http_signature_plug.ex

@@ -8,8 +8,8 @@ defmodule Pleroma.Web.Plugs.HTTPSignaturePlug do
 
   use Pleroma.Web, :verified_routes
   alias Pleroma.Activity
-  alias Pleroma.Signature
   alias Pleroma.Instances
+  alias Pleroma.User.SigningKey
   require Logger
 
   @cachex Pleroma.Config.get([:cachex, :provider], Cachex)
@@ -140,15 +140,17 @@ defp maybe_require_signature(conn), do: conn
 
   defp signature_host(conn) do
     with {:key_id, %{"keyId" => kid}} <- {:key_id, HTTPSignatures.signature_for_conn(conn)},
-         {:actor_id, {:ok, actor_id}} <- {:actor_id, Signature.key_id_to_actor_id(kid)} do
+         {:actor_id, actor_id, _} when actor_id != nil <-
+           {:actor_id, SigningKey.key_id_to_ap_id(kid), kid} do
       actor_id
     else
       {:key_id, e} ->
         Logger.error("Failed to extract key_id from signature: #{inspect(e)}")
         nil
 
-      {:actor_id, e} ->
-        Logger.error("Failed to extract actor_id from signature: #{inspect(e)}")
+      {:actor_id, _, kid} ->
+        # SigningKeys SHOULD have been fetched before this gets called!
+        Logger.error("Failed to extract actor_id from signature: signing key #{kid} not known")
         nil
     end
   end

test/pleroma/signature_test.exs

@@ -114,16 +114,6 @@ test "it returns signature headers" do
     end
   end
 
-  describe "key_id_to_actor_id/1" do
-    test "it reverses the key id to actor id" do
-      user =
-        insert(:user)
-        |> with_signing_key()
-
-      assert Signature.key_id_to_actor_id(user.signing_key.key_id) == {:ok, user.ap_id}
-    end
-  end
-
   describe "signed_date" do
     test "it returns formatted current date" do
       with_mock(NaiveDateTime, utc_now: fn -> ~N[2019-08-23 18:11:24.822233] end) do

test/pleroma/user_test.exs

@@ -1820,10 +1820,6 @@ test "unsuggests a user" do
     end
   end
 
-  test "get_public_key_for_ap_id fetches a user that's not in the db" do
-    assert {:ok, _key} = User.get_public_key_for_ap_id("http://mastodon.example.org/users/admin")
-  end
-
   describe "per-user rich-text filtering" do
     test "html_filter_policy returns default policies, when rich-text is enabled" do
       user = insert(:user)