Implement ObjectDatabase.valid?/1.

lib/xgit/lib/object_database.ex

@@ -51,6 +51,7 @@ defmodule Xgit.Lib.ObjectDatabase do
   An object database stores one or more git objects, indexed by their unique
   `ObjectId`.
   """
+  use GenServer
 
   require Logger
 
@@ -79,6 +80,16 @@ defmodule Xgit.Lib.ObjectDatabase do
     end
   end
 
+  @doc ~S"""
+  Returns `true` if the argument is a PID representing a valid `ObjectDatabase` process.
+  """
+  def valid?(database) when is_pid(database) do
+    Process.alive?(database) &&
+      GenServer.call(database, :valid_object_database?) == :valid_object_database
+  end
+
+  def valid?(_), do: false
+
   # TO DO: https://github.com/elixir-git/xgit/issues/132
 
   # /**
@@ -603,6 +614,9 @@ defmodule Xgit.Lib.ObjectDatabase do
   #   return null;
   # }
 
+  def handle_call(:valid_object_database?, _from, state),
+    do: {:reply, :valid_object_database, state}
+
   def handle_call(:exists?, _from, {mod, mod_state}) do
     case mod.handle_exists?(mod_state) do
       {true, mod_state} -> {:reply, true, {mod, mod_state}}

test/xgit/internal/storage/file/object_directory_test.exs

@@ -69,6 +69,7 @@ defmodule Xgit.Internal.Storage.File.ObjectDirectoryTest do
     assert {:ok, pid} = ObjectDirectory.start_link(config: Config.new(), objects: extra_dir)
     assert is_pid(pid)
 
+    assert ObjectDatabase.valid?(pid) == true
     assert ObjectDatabase.exists?(pid) == false
     assert :ok = ObjectDatabase.create(pid)
     assert ObjectDatabase.exists?(pid) == true