Extract authorization functions from state resolution

Add function to get room server's pid

lib/matrix_server/quick_check.ex

@@ -0,0 +1,14 @@
+defmodule MatrixServer.QuickCheck do
+  import Ecto.Query
+
+  alias MatrixServer.{Repo, Room, Account, RoomServer}
+  alias MatrixServerWeb.API.CreateRoom
+
+  def create_room do
+    account = Repo.one!(from a in Account, limit: 1)
+    input = %CreateRoom{}
+    %Room{id: room_id} = Repo.insert!(Room.create_changeset(input))
+    {:ok, pid} = RoomServer.get_room_server(room_id)
+    RoomServer.create_room(pid, account, input)
+  end
+end

lib/matrix_server/room_server.ex

@@ -3,71 +3,102 @@ defmodule MatrixServer.RoomServer do
 
   import Ecto.Query
 
-  alias MatrixServer.{Repo, Room, Event, Account, StateResolution}
+  alias MatrixServer.{Repo, Room, Event, StateResolution}
   alias MatrixServerWeb.API.CreateRoom
+  alias MatrixServer.StateResolution.Authorization
 
   @registry MatrixServer.RoomServer.Registry
   @supervisor MatrixServer.RoomServer.Supervisor
 
-  def create_room(input, account) do
-    %Room{id: room_id} = room = Repo.insert!(Room.create_changeset(input))
-
-    opts = [
-      name: {:via, Registry, {@registry, room_id}},
-      input: input,
-      account: account,
-      room: room
-    ]
-
-    DynamicSupervisor.start_child(@supervisor, {__MODULE__, opts})
-  end
+  ### Interface
 
   def start_link(opts) do
     {name, opts} = Keyword.pop(opts, :name)
     GenServer.start_link(__MODULE__, opts, name: name)
   end
 
+  # Get room server pid, or spin one up for the room.
+  # If the room does not exist, return an error.
+  def get_room_server(room_id) do
+    case Repo.one(from r in Room, where: r.id == ^room_id) do
+      nil ->
+        {:error, :not_found}
+
+      %Room{} ->
+        case Registry.lookup(@registry, room_id) do
+          [{pid, _}] ->
+            {:ok, pid}
+
+          [] ->
+            opts = [
+              name: {:via, Registry, {@registry, room_id}},
+              room_id: room_id
+            ]
+
+            DynamicSupervisor.start_child(@supervisor, {__MODULE__, opts})
+        end
+    end
+  end
+
+  def create_room(pid, account, input) do
+    GenServer.call(pid, {:create_room, account, input})
+  end
+
+  ### Implementation
+
   @impl true
   def init(opts) do
-    room = Keyword.fetch!(opts, :room)
-    input = Keyword.fetch!(opts, :input)
-    account = Keyword.fetch!(opts, :account)
+    room_id = Keyword.fetch!(opts, :room_id)
 
-    Repo.transaction(fn ->
-      with {:ok, create_room_id, state_set, room} <-
-             room_creation_create_room(account, input, room),
-           {:ok, join_creator_id, state_set, room} <-
-             room_creation_join_creator(account, room, state_set, [create_room_id]),
-           {:ok, pl_id, state_set, room} <-
-             room_creation_power_levels(
-               account,
-               room,
-               state_set,
-               [create_room_id, join_creator_id]
-             ),
-           {:ok, _, state_set, room} <-
-             room_creation_preset(account, input, room, state_set, [
-               create_room_id,
-               join_creator_id,
-               pl_id
-             ]),
-           {:ok, _, state_set, room} <-
-             room_creation_name(account, input, room, state_set, [
-               create_room_id,
-               join_creator_id,
-               pl_id
-             ]),
-           {:ok, _, state_set, room} <-
-             room_creation_topic(account, input, room, state_set, [
-               create_room_id,
-               join_creator_id,
-               pl_id
-             ]) do
-        {:ok, %{room: room, state_set: state_set}}
-      else
-        _ -> {:error, :validation}
-      end
-    end)
+    {:ok, %{room_id: room_id, state_set: %{}}}
+  end
+
+  @impl true
+  def handle_call({:create_room, account, input}, _from, %{room_id: room_id} = state) do
+    result =
+      Repo.transaction(fn ->
+        # TODO: power_level_content_override, initial_state, invite, invite_3pid
+        with room <- Repo.one!(from r in Room, where: r.id == ^room_id),
+             {:ok, create_room_id, state_set, room} <-
+               room_creation_create_room(account, input, room),
+             {:ok, join_creator_id, state_set, room} <-
+               room_creation_join_creator(account, room, state_set, [create_room_id]),
+             {:ok, pl_id, state_set, room} <-
+               room_creation_power_levels(
+                 account,
+                 room,
+                 state_set,
+                 [create_room_id, join_creator_id]
+               ),
+             {:ok, _, state_set, room} <-
+               room_creation_preset(account, input, room, state_set, [
+                 create_room_id,
+                 join_creator_id,
+                 pl_id
+               ]),
+             {:ok, _, state_set, room} <-
+               room_creation_name(account, input, room, state_set, [
+                 create_room_id,
+                 join_creator_id,
+                 pl_id
+               ]),
+             {:ok, _, state_set, _} <-
+               room_creation_topic(account, input, room, state_set, [
+                 create_room_id,
+                 join_creator_id,
+                 pl_id
+               ]) do
+          state_set
+        else
+          reason ->
+            Repo.rollback(reason)
+        end
+      end)
+
+    case result do
+      {:ok, state_set} -> {:reply, :ok, %{state | state_set: state_set}}
+      {:error, reason} -> {:reply, {:error, reason}, state}
+    end
   end
 
   defp room_creation_create_room(account, %CreateRoom{room_version: room_version}, room) do
@@ -177,11 +208,11 @@ defmodule MatrixServer.RoomServer do
     event = %Event{event | prev_events: forward_extremities}
 
     if Event.prevalidate(event) do
-      if StateResolution.is_authorized_by_auth_events(event) do
+      if Authorization.authorized_by_auth_events?(event) do
         state_set = StateResolution.resolve(event, false)
 
-        if StateResolution.is_authorized(event, state_set) do
-          if StateResolution.is_authorized(event, current_state_set) do
+        if Authorization.authorized?(event, state_set) do
+          if Authorization.authorized?(event, current_state_set) do
             # We assume here that the event is always a forward extremity.
             room = Room.update_forward_extremities(event, room)
             {:ok, event} = Repo.insert(event)
@@ -200,9 +231,4 @@ defmodule MatrixServer.RoomServer do
       {:error, :invalid}
     end
   end
-
-  def testing do
-    account = Repo.one!(from a in Account, limit: 1)
-    create_room(%CreateRoom{name: "Sneed", topic: "City slickers"}, account)
-  end
 end

lib/matrix_server/state_resolution.ex

@@ -2,6 +2,7 @@ defmodule MatrixServer.StateResolution do
   import Ecto.Query
 
   alias MatrixServer.{Repo, Event, Room}
+  alias MatrixServer.StateResolution.Authorization
 
   def resolve(event), do: resolve(event, true)
 
@@ -35,17 +36,6 @@ defmodule MatrixServer.StateResolution do
     end
   end
 
-  def is_authorized_by_auth_events(%Event{auth_events: auth_event_ids} = event) do
-    # We assume the auth events are validated beforehand.
-    state_set =
-      Event
-      |> where([e], e.event_id in ^auth_event_ids)
-      |> Repo.all()
-      |> Enum.reduce(%{}, &update_state_set/2)
-
-    is_authorized(event, state_set)
-  end
-
   def resolve_forward_extremities(%Event{room_id: room_id}) do
     room_events =
       Event
@@ -63,278 +53,6 @@ defmodule MatrixServer.StateResolution do
     |> do_resolve(room_events)
   end
 
-  def is_authorized(%Event{type: "m.room.create", prev_events: prev_events}, %{}),
-    do: prev_events == []
-
-  # Check rule: 5.2.1
-  def is_authorized(%Event{type: "m.room.member", state_key: state_key}, %{
-        {"m.room.create", ""} => %Event{content: %{"creator" => creator}}
-      }),
-      do: state_key == creator
-
-  def is_authorized(
-        %Event{type: "m.room.member", sender: sender, content: %{"membership" => "join"}},
-        state_set
-      ) do
-    join_rule = get_join_rule(state_set)
-    membership = get_membership(sender, state_set)
-
-    # Check rules: 5.2.3, 5.2.4, 5.2.5
-    cond do
-      membership == "ban" -> false
-      join_rule == "invite" -> membership in ["invite", "join"]
-      join_rule == "public" -> true
-      true -> false
-    end
-  end
-
-  # TODO: rule 5.3.1
-  def is_authorized(
-        %Event{
-          type: "m.room.member",
-          content: %{"membership" => "invite", "third_party_invite" => _}
-        },
-        _
-      ),
-      do: false
-
-  def is_authorized(
-        %Event{
-          type: "m.room.member",
-          sender: sender,
-          content: %{"membership" => "invite"},
-          state_key: state_key
-        },
-        state_set
-      ) do
-    sender_membership = get_membership(sender, state_set)
-    target_membership = get_membership(state_key, state_set)
-    power_levels = get_power_levels(state_set)
-
-    # Check rules: 5.3.2, 5.3.3, 5.3.4
-    cond do
-      sender_membership != "join" -> false
-      target_membership in ["join", "ban"] -> false
-      has_power_level(sender, power_levels, :invite) -> true
-      true -> false
-    end
-  end
-
-  def is_authorized(
-        %Event{
-          type: "m.room.member",
-          sender: sender,
-          content: %{"membership" => "leave"},
-          state_key: sender
-        },
-        state_set
-      ) do
-    # Check rule: 5.4.1
-    get_membership(sender, state_set) in ["invite", "join"]
-  end
-
-  def is_authorized(
-        %Event{
-          type: "m.room.member",
-          sender: sender,
-          content: %{"membership" => "leave"},
-          state_key: state_key
-        },
-        state_set
-      ) do
-    sender_membership = get_membership(sender, state_set)
-    target_membership = get_membership(state_key, state_set)
-    power_levels = get_power_levels(state_set)
-    sender_pl = get_user_power_level(sender, power_levels)
-    target_pl = get_user_power_level(state_key, power_levels)
-
-    # Check rules: 5.4.2, 5.4.3, 5.4.4
-    cond do
-      sender_membership != "join" -> false
-      target_membership == "ban" and not has_power_level(sender, power_levels, :ban) -> false
-      has_power_level(sender, power_levels, :kick) and target_pl < sender_pl -> true
-      true -> false
-    end
-  end
-
-  def is_authorized(
-        %Event{
-          type: "m.room.member",
-          sender: sender,
-          content: %{"membership" => "ban"},
-          state_key: state_key
-        },
-        state_set
-      ) do
-    sender_membership = get_membership(sender, state_set)
-    power_levels = get_power_levels(state_set)
-    sender_pl = get_user_power_level(sender, power_levels)
-    target_pl = get_user_power_level(state_key, power_levels)
-
-    # Check rules: 5.5.1, 5.5.2
-    cond do
-      sender_membership != "join" -> false
-      has_power_level(sender, power_levels, :ban) and target_pl < sender_pl -> true
-      true -> false
-    end
-  end
-
-  # Check rule: 5.6
-  def is_authorized(%Event{type: "m.room.member"}, _), do: false
-
-  def is_authorized(%Event{sender: sender} = event, state_set) do
-    # Check rule: 6
-    get_membership(sender, state_set) == "join" and _is_authorized(event, state_set)
-  end
-
-  defp _is_authorized(%Event{type: "m.room.third_party_invite", sender: sender}, state_set) do
-    # Check rule: 7.1
-    has_power_level(sender, state_set, :invite)
-  end
-
-  defp _is_authorized(%Event{state_key: state_key, sender: sender} = event, state_set) do
-    power_levels = get_power_levels(state_set)
-
-    # Check rules: 8, 9
-    cond do
-      not has_power_level(sender, power_levels, {:event, event}) -> false
-      String.starts_with?(state_key, "@") and state_key != sender -> false
-      true -> __is_authorized(event, state_set)
-    end
-  end
-
-  defp __is_authorized(
-         %Event{type: "m.room.power_levels", sender: sender, content: content},
-         state_set
-       ) do
-    current_pls = get_power_levels(state_set)
-    new_pls = content
-    sender_pl = get_user_power_level(sender, new_pls)
-
-    # Check rules: 10.2, 10.3, 10.4, 10.5
-    cond do
-      not is_map_key(state_set, {"m.room.power_levels", ""}) -> true
-      not authorize_power_levels(sender, sender_pl, current_pls, new_pls) -> false
-      true -> true
-    end
-  end
-
-  # TODO: Rule 11
-
-  defp __is_authorized(_, _), do: true
-
-  defp authorize_power_levels(
-         user,
-         user_pl,
-         %{"events" => current_events, "users" => current_users} = current_pls,
-         %{"events" => new_events, "users" => new_users} = new_pls
-       ) do
-    keys = ["users_default", "events_default", "state_default", "ban", "redact", "kick", "invite"]
-
-    valid_power_level_key_changes(Map.take(current_pls, keys), Map.take(new_pls, keys), user_pl) and
-      valid_power_level_key_changes(current_events, new_events, user_pl) and
-      valid_power_level_key_changes(current_users, new_users, user_pl) and
-      valid_power_level_users_changes(current_users, new_users, user, user_pl)
-  end
-
-  defp has_power_level(user, power_levels, action) do
-    user_pl = get_user_power_level(user, power_levels)
-    action_pl = get_action_power_level(action, power_levels)
-
-    user_pl >= action_pl
-  end
-
-  defp get_user_power_level(user, %{"users" => users}) when is_map_key(users, user),
-    do: users[user]
-
-  defp get_user_power_level(_, %{"users_default" => pl}), do: pl
-  defp get_user_power_level(_, _), do: 0
-
-  defp get_action_power_level(:invite, %{"invite" => pl}), do: pl
-  defp get_action_power_level(:invite, _), do: 50
-  defp get_action_power_level(:ban, %{"ban" => pl}), do: pl
-  defp get_action_power_level(:ban, _), do: 50
-  defp get_action_power_level(:redact, %{"redact" => pl}), do: pl
-  defp get_action_power_level(:redact, _), do: 50
-
-  defp get_action_power_level({:event, %Event{type: type}}, %{"events" => events})
-       when is_map_key(events, type),
-       do: events[type]
-
-  defp get_action_power_level({:event, event}, power_levels) do
-    if Event.is_state_event(event) do
-      case power_levels do
-        %{"state_default" => pl} -> pl
-        %{} -> 50
-        _ -> 0
-      end
-    else
-      case power_levels do
-        %{"events_default" => pl} -> pl
-        _ -> 0
-      end
-    end
-  end
-
-  defp get_power_levels(state_set) do
-    case state_set[{"m.room.power_levels", ""}] do
-      %Event{content: content} -> content
-      nil -> nil
-    end
-  end
-
-  defp get_join_rule(state_set) do
-    case state_set[{"m.room.join_rules", ""}] do
-      %Event{content: %{"join_rule" => join_rule}} -> join_rule
-      nil -> nil
-    end
-  end
-
-  defp get_membership(user, state_set) do
-    case state_set[{"m.room.member", user}] do
-      %Event{content: %{"membership" => membership}} -> membership
-      nil -> nil
-    end
-  end
-
-  defp valid_power_level_key_changes(l1, l2, user_pl) do
-    set1 = MapSet.new(l1)
-    set2 = MapSet.new(l2)
-
-    MapSet.difference(
-      MapSet.union(set1, set2),
-      MapSet.intersection(set1, set2)
-    )
-    |> Enum.group_by(&elem(&1, 0), &elem(&1, 1))
-    |> Enum.all?(fn {_k, values} ->
-      Enum.all?(values, &(&1 <= user_pl))
-    end)
-  end
-
-  defp valid_power_level_users_changes(current_users, new_users, user, user_pl) do
-    set1 = MapSet.new(current_users)
-    set2 = MapSet.new(new_users)
-
-    MapSet.difference(
-      MapSet.union(set1, set2),
-      MapSet.intersection(set1, set2)
-    )
-    |> Enum.all?(fn
-      {_k, values} when length(values) != 2 -> true
-      {k, _} when k == user -> true
-      {_k, [old_value, _]} -> old_value != user_pl
-    end)
-  end
-
-  def testing do
-    %Event{content: content} = event = Event.power_levels("room1", "charlie")
-    event = %Event{event | content: %{content | "ban" => 0}}
-
-    event
-    |> Map.put(:prev_events, ["b", "fork"])
-    |> Map.put(:auth_events, ["create", "join_charlie", "b"])
-  end
-
   defp do_resolve([], _), do: %{}
 
   defp do_resolve(state_sets, room_events) do
@@ -541,23 +259,23 @@ defmodule MatrixServer.StateResolution do
 
   defp iterative_auth_checks(events, state_set, room_events) do
     Enum.reduce(events, state_set, fn event, acc ->
-      if is_authorized2(event, acc, room_events), do: update_state_set(event, acc), else: acc
+      if authorized?(event, acc, room_events), do: update_state_set(event, acc), else: acc
     end)
   end
 
-  defp update_state_set(
+  def update_state_set(
          %Event{type: event_type, state_key: state_key} = event,
          state_set
        ) do
     Map.put(state_set, {event_type, state_key}, event)
   end
 
-  defp is_authorized2(%Event{auth_events: auth_event_ids} = event, state_set, room_events) do
+  defp authorized?(%Event{auth_events: auth_event_ids} = event, state_set, room_events) do
     state_set =
       auth_event_ids
       |> Enum.map(&room_events[&1])
       |> Enum.reduce(state_set, &update_state_set/2)
 
-    is_authorized(event, state_set)
+    Authorization.authorized?(event, state_set)
   end
 end

lib/matrix_server/state_resolution/authorization.ex

@@ -0,0 +1,280 @@
+defmodule MatrixServer.StateResolution.Authorization do
+  import MatrixServer.StateResolution
+  import Ecto.Query
+
+  alias MatrixServer.{Repo, Event}
+
+  def authorized?(%Event{type: "m.room.create", prev_events: prev_events}, %{}),
+    do: prev_events == []
+
+  # Check rule: 5.2.1
+  def authorized?(%Event{type: "m.room.member", state_key: state_key}, %{
+        {"m.room.create", ""} => %Event{content: %{"creator" => creator}}
+      }),
+      do: state_key == creator
+
+  def authorized?(
+        %Event{type: "m.room.member", sender: sender, content: %{"membership" => "join"}},
+        state_set
+      ) do
+    join_rule = get_join_rule(state_set)
+    membership = get_membership(sender, state_set)
+
+    # Check rules: 5.2.3, 5.2.4, 5.2.5
+    cond do
+      membership == "ban" -> false
+      join_rule == "invite" -> membership in ["invite", "join"]
+      join_rule == "public" -> true
+      true -> false
+    end
+  end
+
+  # TODO: rule 5.3.1
+  def authorized?(
+        %Event{
+          type: "m.room.member",
+          content: %{"membership" => "invite", "third_party_invite" => _}
+        },
+        _
+      ),
+      do: false
+
+  def authorized?(
+        %Event{
+          type: "m.room.member",
+          sender: sender,
+          content: %{"membership" => "invite"},
+          state_key: state_key
+        },
+        state_set
+      ) do
+    sender_membership = get_membership(sender, state_set)
+    target_membership = get_membership(state_key, state_set)
+    power_levels = get_power_levels(state_set)
+
+    # Check rules: 5.3.2, 5.3.3, 5.3.4
+    cond do
+      sender_membership != "join" -> false
+      target_membership in ["join", "ban"] -> false
+      has_power_level(sender, power_levels, :invite) -> true
+      true -> false
+    end
+  end
+
+  def authorized?(
+        %Event{
+          type: "m.room.member",
+          sender: sender,
+          content: %{"membership" => "leave"},
+          state_key: sender
+        },
+        state_set
+      ) do
+    # Check rule: 5.4.1
+    get_membership(sender, state_set) in ["invite", "join"]
+  end
+
+  def authorized?(
+        %Event{
+          type: "m.room.member",
+          sender: sender,
+          content: %{"membership" => "leave"},
+          state_key: state_key
+        },
+        state_set
+      ) do
+    sender_membership = get_membership(sender, state_set)
+    target_membership = get_membership(state_key, state_set)
+    power_levels = get_power_levels(state_set)
+    sender_pl = get_user_power_level(sender, power_levels)
+    target_pl = get_user_power_level(state_key, power_levels)
+
+    # Check rules: 5.4.2, 5.4.3, 5.4.4
+    cond do
+      sender_membership != "join" -> false
+      target_membership == "ban" and not has_power_level(sender, power_levels, :ban) -> false
+      has_power_level(sender, power_levels, :kick) and target_pl < sender_pl -> true
+      true -> false
+    end
+  end
+
+  def authorized?(
+        %Event{
+          type: "m.room.member",
+          sender: sender,
+          content: %{"membership" => "ban"},
+          state_key: state_key
+        },
+        state_set
+      ) do
+    sender_membership = get_membership(sender, state_set)
+    power_levels = get_power_levels(state_set)
+    sender_pl = get_user_power_level(sender, power_levels)
+    target_pl = get_user_power_level(state_key, power_levels)
+
+    # Check rules: 5.5.1, 5.5.2
+    cond do
+      sender_membership != "join" -> false
+      has_power_level(sender, power_levels, :ban) and target_pl < sender_pl -> true
+      true -> false
+    end
+  end
+
+  # Check rule: 5.6
+  def authorized?(%Event{type: "m.room.member"}, _), do: false
+
+  def authorized?(%Event{sender: sender} = event, state_set) do
+    # Check rule: 6
+    get_membership(sender, state_set) == "join" and _authorized?(event, state_set)
+  end
+
+  defp _authorized?(%Event{type: "m.room.third_party_invite", sender: sender}, state_set) do
+    # Check rule: 7.1
+    has_power_level(sender, state_set, :invite)
+  end
+
+  defp _authorized?(%Event{state_key: state_key, sender: sender} = event, state_set) do
+    power_levels = get_power_levels(state_set)
+
+    # Check rules: 8, 9
+    cond do
+      not has_power_level(sender, power_levels, {:event, event}) -> false
+      String.starts_with?(state_key, "@") and state_key != sender -> false
+      true -> __authorized?(event, state_set)
+    end
+  end
+
+  defp __authorized?(
+         %Event{type: "m.room.power_levels", sender: sender, content: content},
+         state_set
+       ) do
+    current_pls = get_power_levels(state_set)
+    new_pls = content
+    sender_pl = get_user_power_level(sender, new_pls)
+
+    # Check rules: 10.2, 10.3, 10.4, 10.5
+    cond do
+      not is_map_key(state_set, {"m.room.power_levels", ""}) -> true
+      not authorize_power_levels(sender, sender_pl, current_pls, new_pls) -> false
+      true -> true
+    end
+  end
+
+  # TODO: Rule 11
+
+  defp __authorized?(_, _), do: true
+
+  defp get_power_levels(state_set) do
+    case state_set[{"m.room.power_levels", ""}] do
+      %Event{content: content} -> content
+      nil -> nil
+    end
+  end
+
+  defp get_join_rule(state_set) do
+    case state_set[{"m.room.join_rules", ""}] do
+      %Event{content: %{"join_rule" => join_rule}} -> join_rule
+      nil -> nil
+    end
+  end
+
+  defp get_membership(user, state_set) do
+    case state_set[{"m.room.member", user}] do
+      %Event{content: %{"membership" => membership}} -> membership
+      nil -> nil
+    end
+  end
+
+  defp has_power_level(user, power_levels, action) do
+    user_pl = get_user_power_level(user, power_levels)
+    action_pl = get_action_power_level(action, power_levels)
+
+    user_pl >= action_pl
+  end
+
+  defp get_user_power_level(user, %{"users" => users}) when is_map_key(users, user),
+    do: users[user]
+
+  defp get_user_power_level(_, %{"users_default" => pl}), do: pl
+  defp get_user_power_level(_, _), do: 0
+
+  defp get_action_power_level(:invite, %{"invite" => pl}), do: pl
+  defp get_action_power_level(:invite, _), do: 50
+  defp get_action_power_level(:ban, %{"ban" => pl}), do: pl
+  defp get_action_power_level(:ban, _), do: 50
+  defp get_action_power_level(:redact, %{"redact" => pl}), do: pl
+  defp get_action_power_level(:redact, _), do: 50
+
+  defp get_action_power_level({:event, %Event{type: type}}, %{"events" => events})
+       when is_map_key(events, type),
+       do: events[type]
+
+  defp get_action_power_level({:event, event}, power_levels) do
+    if Event.is_state_event(event) do
+      case power_levels do
+        %{"state_default" => pl} -> pl
+        %{} -> 50
+        _ -> 0
+      end
+    else
+      case power_levels do
+        %{"events_default" => pl} -> pl
+        _ -> 0
+      end
+    end
+  end
+
+  defp authorize_power_levels(
+         user,
+         user_pl,
+         %{"events" => current_events, "users" => current_users} = current_pls,
+         %{"events" => new_events, "users" => new_users} = new_pls
+       ) do
+    keys = ["users_default", "events_default", "state_default", "ban", "redact", "kick", "invite"]
+
+    valid_power_level_key_changes(Map.take(current_pls, keys), Map.take(new_pls, keys), user_pl) and
+      valid_power_level_key_changes(current_events, new_events, user_pl) and
+      valid_power_level_key_changes(current_users, new_users, user_pl) and
+      valid_power_level_users_changes(current_users, new_users, user, user_pl)
+  end
+
+  defp valid_power_level_key_changes(l1, l2, user_pl) do
+    set1 = MapSet.new(l1)
+    set2 = MapSet.new(l2)
+
+    MapSet.difference(
+      MapSet.union(set1, set2),
+      MapSet.intersection(set1, set2)
+    )
+    |> Enum.group_by(&elem(&1, 0), &elem(&1, 1))
+    |> Enum.all?(fn {_k, values} ->
+      Enum.all?(values, &(&1 <= user_pl))
+    end)
+  end
+
+  defp valid_power_level_users_changes(current_users, new_users, user, user_pl) do
+    set1 = MapSet.new(current_users)
+    set2 = MapSet.new(new_users)
+
+    MapSet.difference(
+      MapSet.union(set1, set2),
+      MapSet.intersection(set1, set2)
+    )
+    |> Enum.all?(fn
+      {_k, values} when length(values) != 2 -> true
+      {k, _} when k == user -> true
+      {_k, [old_value, _]} -> old_value != user_pl
+    end)
+  end
+
+  def authorized_by_auth_events?(%Event{auth_events: auth_event_ids} = event) do
+    # We assume the auth events are validated beforehand.
+    state_set =
+      Event
+      |> where([e], e.event_id in ^auth_event_ids)
+      |> Repo.all()
+      |> Enum.reduce(%{}, &update_state_set/2)
+
+    authorized?(event, state_set)
+  end
+end

lib/matrix_server_web/controllers/room_controller.ex

@@ -4,6 +4,7 @@ defmodule MatrixServerWeb.RoomController do
   import MatrixServerWeb.Plug.Error
   import Ecto.Changeset
 
+  alias MatrixServer.{Repo, Room, RoomServer}
   alias MatrixServerWeb.API.{CreateRoom}
   alias Ecto.Changeset
   alias Plug.Conn
@@ -11,9 +12,12 @@ defmodule MatrixServerWeb.RoomController do
   def create(%Conn{assigns: %{account: account}} = conn, params) do
     case CreateRoom.changeset(params) do
       %Changeset{valid?: true} = cs ->
-        cs
-        |> apply_changes()
-        |> MatrixServer.RoomServer.create_room(account)
+        input = apply_changes(cs)
+
+        # TODO: refactor
+        %Room{id: room_id} = Repo.insert!(Room.create_changeset(input))
+        {:ok, pid} = RoomServer.get_room_server(room_id)
+        RoomServer.create_room(pid, account, input)
 
         conn
         |> put_status(200)