update tcp_connection example

.formatter.exs

@@ -1,4 +1,4 @@
 # Used by "mix format"
 [
-  inputs: ["{mix,.formatter}.exs", "{config,lib,test,integration_test}/**/*.{ex,exs}"]
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test,examples,integration_test}/**/*.{ex,exs}"]
 ]

examples/tcp_connection/lib/tcp_connection.ex

@@ -64,6 +64,8 @@ defmodule TCPConnection do
 
     case :gen_tcp.connect(host, port, socket_opts, timeout) do
       {:ok, sock} ->
+        # Monitor the socket so we can react to it being closed. See handle_info/2.
+        _ref = :inet.monitor(sock)
         {:ok, {sock, <<>>}}
 
       {:error, reason} ->
@@ -143,6 +145,13 @@ defmodule TCPConnection do
     end
   end
 
+  # The handle_info callback is optional and can be removed if not needed.
+  # Here it is used to react to `:inet.monitor/1` messages which arrive
+  # when socket gets closed while the connection is idle.
+  def handle_info({:DOWN, _ref, _type, sock, _info}, {sock, _buffer} = s) do
+    {:disconnect, TCPConnection.Error.exception({:idle, :closed}), s}
+  end
+
   @impl true
   def handle_close(_, _, s) do
     {:ok, nil, s}