feat: connect/3 to connect to NNTP server

Similar to `gen_tcp:connect/3` but also wait for server's greeting
before returning.

include/gen_nntp.hrl

@@ -1,5 +1,7 @@
 -type name() :: atom() | {'local', term()} | {'global', term()} | {'via', module(), term()}.
 -type option() ::
   {'name', name()}
-  | {'port', pos_integer()}.
+  | {'port', port_number()}.
 -type on_start() :: {'ok', pid()} | 'ignore' |  {'error', {'already_started', pid()} | term()}.
+-type address() :: inet:socket_address() | inet:hostname() | binary().
+-type port_number() :: inet:port_number().

lib/gen_nntp.ex

@@ -23,6 +23,11 @@ defmodule GenNNTP do
   @spec stop(module()) :: :ok
   defdelegate stop(ref), to: :gen_nntp
 
+  @doc """
+  Connects to a NNTP server.
+  """
+  defdelegate connect(address \\ "localhost", port \\ 119, options \\ []), to: :gen_nntp
+
   @callback init(any()) ::
     {:ok, state} | {:ok, state, timeout | :hibernate} |
     :ignore | {:stop, reason :: term}

src/gen_nntp.erl

@@ -5,7 +5,11 @@
 %% API
 -export([
   start/3,
-  stop/1
+  stop/1,
+  connect/0,
+  connect/1,
+  connect/2,
+  connect/3
 ]).
 
 %% gen_server callbacks
@@ -92,6 +96,38 @@ stop(Ref) ->
     _:_ -> ok
   end.
 
+%%-------------------------------------------------------------------
+%% @doc Connects to a NNTP server.
+%%
+%% @end
+%%-------------------------------------------------------------------
+-spec connect() -> {ok, socket(), Greeting :: binary()} | {error, Reason :: timeout | inet:posix()}.
+connect() ->
+  connect("localhost", 119, []).
+
+-spec connect(address()) -> {ok, socket(), Greeting :: binary()} | {error, Reason :: timeout | inet:posix()}.
+connect(Address) ->
+  connect(Address, 119, []).
+
+-spec connect(address(), port_number()) -> {ok, socket(), Greeting :: binary()} | {error, Reason :: timeout | inet:posix()}.
+connect(Address, Port) ->
+  connect(Address, Port, []).
+
+-spec connect(address(), port_number(), [gen_tcp:connect_option()]) -> {ok, socket(), Greeting :: binary()} | {error, Reason :: timeout | inet:posix()}.
+connect(Address, Port, Options) when is_binary(Address) ->
+  connect(binary_to_list(Address), Port, Options);
+
+connect(Address, Port, _Options) ->
+  % @TODO: Merge default options with user-supplied options.
+  Options = [binary, {packet, line}, {active, false}],
+  case gen_tcp:connect(Address, Port, Options) of
+    {ok, Socket} ->
+      {ok, Greeting} = gen_tcp:recv(Socket, 0, 1000),
+      {ok, Socket, Greeting};
+    {error, Reason} ->
+      {error, Reason}
+  end.
+
 %% ==================================================================
 %% ranch_protocol Callbacks
 %% ==================================================================

src/gen_nntp_internal.hrl

@@ -1 +1,2 @@
 -type state() :: term().
+-type socket() :: gen_tcp:socket().

test/gen_nntp_test.exs

@@ -41,6 +41,40 @@ defmodule GenNNTPTest do
 
   end
 
+  describe "connect/3" do
+
+    test "connects to a NNTP server" do
+      GenNNTP.start(TestNNTPServer, [], [])
+      assert {:ok, _socket, _greeting} = GenNNTP.connect("localhost", 119, [])
+    end
+
+    test "error if fail to connect to NNTP server" do
+      assert {:error, :econnrefused} = GenNNTP.connect("localhost", 119, [])
+    end
+
+    test "receives a greeting after connecting" do
+      GenNNTP.start(TestNNTPServer, [], [])
+      assert {:ok, _socket, greeting} = GenNNTP.connect("localhost", 119, [])
+      assert greeting =~ ~r/^20[0,1] /
+    end
+
+    test "connect/2 default to empty options" do
+      GenNNTP.start(TestNNTPServer, [], [])
+      assert {:ok, _socket, _greeting} = GenNNTP.connect("localhost", 119)
+    end
+
+    test "connect/1 default to port 119" do
+      GenNNTP.start(TestNNTPServer, [], [])
+      assert {:ok, _socket, _greeting} = GenNNTP.connect("localhost")
+    end
+
+    test "connect/0 default to localhost" do
+      GenNNTP.start(TestNNTPServer, [], [])
+      assert {:ok, _socket, _greeting} = GenNNTP.connect()
+    end
+
+  end
+
   describe "@callback init/1" do
 
     test "is called when a client connects to it" do