Ensure socket owner always exits (#266)

lib/redix/connection.ex

@@ -271,9 +271,13 @@ defmodule Redix.Connection do
           {:keep_state, data, actions}
 
         {:error, _reason} ->
-          # The socket owner will get a closed message at some point, so we just move to the
-          # disconnected state.
+          # The socket owner is not guaranteed to get a "closed" message, even if we close the
+          # socket here. So, we move to the disconnected state but also notify the owner that
+          # sending failed. If the owner already got the "closed" message, it exited so this
+          # message goes nowere, otherwise the socket owner will exit and notify the connection.
+          # See https://github.com/whatyouhide/redix/issues/265.
           :ok = data.transport.close(data.socket)
+          send(data.socket_owner, {:send_errored, self()})
           {:next_state, :disconnected, data}
       end
     else

lib/redix/socket_owner.ex

@@ -50,6 +50,19 @@ defmodule Redix.SocketOwner do
     end
   end
 
+  # The connection is notifying the socket owner that sending failed. If the socket owner
+  # gets this, it can stop normally without waiting for the "closed"/"error" network
+  # message from the socket.
+  def handle_info({:send_errored, conn}, %__MODULE__{conn: conn} = state) do
+    error =
+      case state.transport do
+        :ssl -> {:ssl_error, :closed}
+        :gen_tcp -> {:tcp_error, :closed}
+      end
+
+    stop(error, state)
+  end
+
   def handle_info({transport, socket, data}, %__MODULE__{socket: socket} = state)
       when transport in [:tcp, :ssl] do
     :ok = setopts(state, socket, active: :once)