Implement federation room state snapshot endpoint

lib/matrix_server_web/error.ex

@@ -13,6 +13,7 @@ defmodule MatrixServerWeb.Error do
       {400, "M_INVALID_ROOM_STATE", "The request would leave the room in an invalid state."},
     unauthorized: {400, "M_UNAUTHORIZED", "The request was unauthorized."},
     invalid_param: {400, "M_INVALID_PARAM", "A request parameter was invalid."},
+    missing_param: {400, "M_MISSING_PARAM", "A request parameter is missing."},
     unknown_token: {401, "M_UNKNOWN_TOKEN", "Invalid access token."},
     missing_token: {401, "M_MISSING_TOKEN", "Access token required."},
     not_found: {404, "M_NOT_FOUND", "The requested resource was not found."},

lib/matrix_server_web/federation/controllers/event_controller.ex

@@ -25,11 +25,7 @@ defmodule MatrixServerWeb.Federation.EventController do
               |> put_status(200)
               |> json(data)
             else
-              put_error(
-                conn,
-                :unauthorized,
-                "Origin server is not allowed to see requested event."
-              )
+              put_error(conn, :unauthorized, "Origin server is not participating in room.")
             end
 
           _ ->
@@ -41,5 +37,44 @@ defmodule MatrixServerWeb.Federation.EventController do
     end
   end
 
-  def event(conn, _), do: put_error(conn, :bad_json)
+  def event(conn, _), do: put_error(conn, :missing_param)
+
+  def state(%Plug.Conn{assigns: %{origin: origin}} = conn, %{
+        "event_id" => event_id,
+        "room_id" => room_id
+      }) do
+    query =
+      Event
+      |> where([e], e.event_id == ^event_id and e.room_id == ^room_id)
+      |> preload(:room)
+
+    case Repo.one(query) do
+      %Event{room: room} = event ->
+        case RoomServer.get_room_server(room) do
+          {:ok, pid} ->
+            if RoomServer.server_in_room(pid, origin) do
+              {state_events, auth_chain} = RoomServer.get_state_at_event(pid, event)
+
+              data = %{
+                auth_chain: auth_chain,
+                pdus: state_events
+              }
+
+              conn
+              |> put_status(200)
+              |> json(data)
+            else
+              put_error(conn, :unauthorized, "Origin server is not participating in room.")
+            end
+
+          _ ->
+            put_error(conn, :unknown)
+        end
+
+      nil ->
+        put_error(conn, :not_found, "Event or room not found.")
+    end
+  end
+
+  def state(conn, _), do: put_error(conn, :missing_param)
 end

lib/matrix_server_web/federation/http_client.ex

@@ -66,6 +66,13 @@ defmodule MatrixServerWeb.Federation.HTTPClient do
     Tesla.get(client, path)
   end
 
+  def get_state(client, room_id, event_id) do
+    path =
+      RouteHelpers.event_path(Endpoint, :state, room_id) |> Tesla.build_url(event_id: event_id)
+
+    Tesla.get(client, path)
+  end
+
   defp tesla_request(method, client, path, request_schema) do
     with {:ok, %Tesla.Env{body: body}} <- Tesla.request(client, url: path, method: method),
          %Ecto.Changeset{valid?: true} = cs <- apply(request_schema, :changeset, [body]) do

lib/matrix_server_web/federation/transaction.ex

@@ -6,11 +6,11 @@ defmodule MatrixServerWeb.Federation.Transaction do
   @type edu :: any()
 
   @type t :: %__MODULE__{
-    origin: String.t(),
-    origin_server_ts: integer(),
-    pdus: [Event.t()],
-    edus: [edu()] | nil
-  }
+          origin: String.t(),
+          origin_server_ts: integer(),
+          pdus: [Event.t()],
+          edus: [edu()] | nil
+        }
 
   defstruct [:origin, :origin_server_ts, :pdus, :edus]
 

lib/matrix_server_web/router.ex

@@ -65,6 +65,7 @@ defmodule MatrixServerWeb.Router do
     scope "/v1" do
       get "/query/profile", QueryController, :profile
       get "/event/:event_id", EventController, :event
+      get "/state/:room_id", EventController, :state
     end
   end