feat: handle QUIT command

The client uses the QUIT command to terminate the session.  The
server MUST acknowledge the QUIT command and then close the
connection to the client.  This is the preferred method for a client
to indicate that it has finished all of its transactions with the
NNTP server.

src/gen_nntp.erl

@@ -146,6 +146,14 @@ handle_info(timeout, #client{module =Module, transport = Transport} = Client) ->
   Transport:send(Socket, "200 Service available, posting allowed\r\n"),
   {noreply, Client};
 
+% The client uses the QUIT command to terminate the session. The server
+% MUST acknowledge the QUIT command and then close the connection to
+% the client.
+handle_info({tcp, Socket, <<"QUIT\r\n">>}, #client{transport = Transport} = Client) ->
+  Transport:send(Socket, <<"205 Connection closing\r\n">>),
+  Transport:close(Socket),
+  {noreply, Client};
+
 handle_info({tcp, Socket, Line}, Client) ->
   #client{transport = Transport, module = Module, state = State} = Client,
   ok = Transport:setopts(Socket, [{active, once}]),

test/gen_nntp_test.exs

@@ -75,12 +75,18 @@ defmodule GenNNTPTest do
 
       opts = [:binary, packet: :line, active: false]
       {:ok, socket} = :gen_tcp.connect('localhost', 119, opts)
-      %{socket: socket}
+      {:ok, greeting} = :gen_tcp.recv(socket, 0, 1000)
+      %{socket: socket, greeting: greeting}
     end
 
-    test "MUST send a 200 greeting", %{socket: socket} do
-      {:ok, data} = :gen_tcp.recv(socket, 0, 1000)
-      assert data =~ ~r/^200 /
+    test "MUST send a 200 greeting", %{greeting: greeting} do
+      assert greeting =~ ~r/^200 /
+    end
+
+    test "MUST send a 205 if the client sends QUIT", %{socket: socket} do
+      :ok = :gen_tcp.send(socket, "QUIT\r\n")
+      {:ok, data} = :gen_tcp.recv(socket, 0)
+      assert data =~ ~r/^205 /
     end
 
   end