Add the required Date header in the HTTP replies.

The formatted date is generated and kept up to date regularly
by a gen_server process storing it in the cowboy_clock ets table.
Then it is retrieved by other processes simply by reading the table.

src/cowboy.app.src

@@ -16,7 +16,7 @@
 	{description, "Small, fast, modular HTTP server."},
 	{vsn, "0.1.0"},
 	{modules, []},
-	{registered, [cowboy_sup]},
+	{registered, [cowboy_clock, cowboy_sup]},
 	{applications, [
 		kernel,
 		stdlib

src/cowboy_clock.erl

@@ -0,0 +1,207 @@
+%% Copyright (c) 2011, Loïc Hoguin <essen@dev-extend.eu>
+%%
+%% Permission to use, copy, modify, and/or distribute this software for any
+%% purpose with or without fee is hereby granted, provided that the above
+%% copyright notice and this permission notice appear in all copies.
+%%
+%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+-module(cowboy_clock).
+-behaviour(gen_server).
+
+-export([start_link/0, stop/0, rfc1123/0]). %% API.
+-export([init/1, handle_call/3, handle_cast/2,
+	handle_info/2, terminate/2, code_change/3]). %% gen_server.
+
+%% @todo Use calendar types whenever they get exported.
+-type year()   :: non_neg_integer().
+-type month()  :: 1..12.
+-type day()    :: 1..31.
+-type hour()   :: 0..23.
+-type minute() :: 0..59.
+-type second() :: 0..59.
+-type daynum() :: 1..7.
+
+-type date() :: {year(), month(), day()}.
+-type time() :: {hour(), minute(), second()}.
+
+-type datetime() :: {date(), time()}.
+
+-record(state, {
+	universaltime = undefined :: undefined | datetime(),
+	rfc1123 = <<>> :: binary(),
+	tref = undefined :: undefined | timer:tref()
+}).
+
+-define(SERVER, ?MODULE).
+-define(TABLE, ?MODULE).
+
+-include_lib("eunit/include/eunit.hrl").
+
+%% API.
+
+-spec start_link() -> {ok, Pid::pid()}.
+start_link() ->
+	gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).
+
+-spec stop() -> stopped.
+stop() ->
+	gen_server:call(?SERVER, stop).
+
+-spec rfc1123() -> binary().
+rfc1123() ->
+	ets:lookup_element(?TABLE, rfc1123, 2).
+
+%% gen_server.
+
+init([]) ->
+	?TABLE = ets:new(?TABLE, [set, protected,
+		named_table, {read_concurrency, true}]),
+	T = erlang:universaltime(),
+	B = update_rfc1123(undefined, T, <<>>),
+	{ok, TRef} = timer:send_interval(10, update),
+	ets:insert(?TABLE, {rfc1123, B}),
+	{ok, #state{universaltime=T, rfc1123=B, tref=TRef}}.
+
+handle_call(stop, _From, State=#state{tref=TRef}) ->
+	{ok, cancel} = timer:cancel(TRef),
+	{stop, normal, stopped, State};
+
+handle_call(_Request, _From, State) ->
+	{reply, ignored, State}.
+
+handle_cast(_Msg, State) ->
+	{noreply, State}.
+
+handle_info(update, #state{universaltime=Prev, rfc1123=B1, tref=TRef}) ->
+	T = erlang:universaltime(),
+	B2 = update_rfc1123(Prev, T, B1),
+	ets:insert(?TABLE, {rfc1123, B2}),
+	{noreply, #state{universaltime=T, rfc1123=B2, tref=TRef}};
+
+handle_info(_Info, State) ->
+	{noreply, State}.
+
+terminate(_Reason, _State) ->
+	ok.
+
+code_change(_OldVsn, State, _Extra) ->
+	{ok, State}.
+
+%% Internal.
+
+-spec update_rfc1123(Prev::undefined | datetime(), Now::datetime(),
+	Bin::binary()) -> binary().
+update_rfc1123(Now, Now, Bin) ->
+	Bin;
+update_rfc1123({Date, {H, M, _}}, {Date, {H, M, S}},
+		<< Keep:23/binary, _/bits >>) ->
+	<< Keep/binary, (pad_int(S))/binary, " GMT" >>;
+update_rfc1123({Date, {H, _, _}}, {Date, {H, M, S}},
+		<< Keep:20/binary, _/bits >>) ->
+	<< Keep/binary, (pad_int(M))/binary, $:, (pad_int(S))/binary, " GMT" >>;
+update_rfc1123({Date, _}, {Date, {H, M, S}}, << Keep:17/binary, _/bits >>) ->
+	<< Keep/binary, (pad_int(H))/binary, $:, (pad_int(M))/binary,
+		$:, (pad_int(S))/binary, " GMT" >>;
+update_rfc1123({{Y, Mo, _}, _}, {Date = {Y, Mo, D}, {H, M, S}},
+		<< _:7/binary, Keep:10/binary, _/bits >>) ->
+	Wday = calendar:day_of_the_week(Date),
+	<< (weekday(Wday))/binary, ", ", (pad_int(D))/binary, Keep/binary,
+		(pad_int(H))/binary, $:, (pad_int(M))/binary,
+		$:, (pad_int(S))/binary, " GMT" >>;
+update_rfc1123({{Y, _, _}, _}, {Date = {Y, Mo, D}, {H, M, S}},
+		<< _:11/binary, Keep:6/binary, _/bits >>) ->
+	Wday = calendar:day_of_the_week(Date),
+	<< (weekday(Wday))/binary, ", ", (pad_int(D))/binary, " ",
+		(month(Mo))/binary, Keep/binary,
+		(pad_int(H))/binary, $:, (pad_int(M))/binary,
+		$:, (pad_int(S))/binary, " GMT" >>;
+update_rfc1123(_, {Date = {Y, Mo, D}, {H, M, S}}, _) ->
+	Wday = calendar:day_of_the_week(Date),
+	<< (weekday(Wday))/binary, ", ", (pad_int(D))/binary, " ",
+		(month(Mo))/binary, " ", (list_to_binary(integer_to_list(Y)))/binary,
+		" ", (pad_int(H))/binary, $:, (pad_int(M))/binary,
+		$:, (pad_int(S))/binary, " GMT" >>.
+
+%% Following suggestion by MononcQc on #erlounge.
+-spec pad_int(0..59) -> binary().
+pad_int(X) when X < 10 ->
+	<< $0, ($0 + X) >>;
+pad_int(X) ->
+	list_to_binary(integer_to_list(X)).
+
+-spec weekday(daynum()) -> binary().
+weekday(1) -> <<"Mon">>;
+weekday(2) -> <<"Tue">>;
+weekday(3) -> <<"Wed">>;
+weekday(4) -> <<"Thu">>;
+weekday(5) -> <<"Fri">>;
+weekday(6) -> <<"Sat">>;
+weekday(7) -> <<"Sun">>.
+
+-spec month(month()) -> binary().
+month( 1) -> <<"Jan">>;
+month( 2) -> <<"Feb">>;
+month( 3) -> <<"Mar">>;
+month( 4) -> <<"Apr">>;
+month( 5) -> <<"May">>;
+month( 6) -> <<"Jun">>;
+month( 7) -> <<"Jul">>;
+month( 8) -> <<"Aug">>;
+month( 9) -> <<"Sep">>;
+month(10) -> <<"Oct">>;
+month(11) -> <<"Nov">>;
+month(12) -> <<"Dec">>.
+
+%% Tests.
+
+-ifdef(TEST).
+
+update_rfc1123_test_() ->
+	Tests = [
+		{<<"Sat, 14 May 2011 14:25:33 GMT">>, undefined,
+			{{2011, 5, 14}, {14, 25, 33}}, <<>>},
+		{<<"Sat, 14 May 2011 14:25:33 GMT">>, {{2011, 5, 14}, {14, 25, 33}},
+			{{2011, 5, 14}, {14, 25, 33}}, <<"Sat, 14 May 2011 14:25:33 GMT">>},
+		{<<"Sat, 14 May 2011 14:25:34 GMT">>, {{2011, 5, 14}, {14, 25, 33}},
+			{{2011, 5, 14}, {14, 25, 34}}, <<"Sat, 14 May 2011 14:25:33 GMT">>},
+		{<<"Sat, 14 May 2011 14:26:00 GMT">>, {{2011, 5, 14}, {14, 25, 59}},
+			{{2011, 5, 14}, {14, 26,  0}}, <<"Sat, 14 May 2011 14:25:59 GMT">>},
+		{<<"Sat, 14 May 2011 15:00:00 GMT">>, {{2011, 5, 14}, {14, 59, 59}},
+			{{2011, 5, 14}, {15,  0,  0}}, <<"Sat, 14 May 2011 14:59:59 GMT">>},
+		{<<"Sun, 15 May 2011 00:00:00 GMT">>, {{2011, 5, 14}, {23, 59, 59}},
+			{{2011, 5, 15}, { 0,  0,  0}}, <<"Sat, 14 May 2011 23:59:59 GMT">>},
+		{<<"Wed, 01 Jun 2011 00:00:00 GMT">>, {{2011, 5, 31}, {23, 59, 59}},
+			{{2011, 6,  1}, { 0,  0,  0}}, <<"Tue, 31 May 2011 23:59:59 GMT">>},
+		{<<"Sun, 01 Jan 2012 00:00:00 GMT">>, {{2011, 5, 31}, {23, 59, 59}},
+			{{2012, 1,  1}, { 0,  0,  0}}, <<"Sat, 31 Dec 2011 23:59:59 GMT">>}
+	],
+	[{R, fun() -> R = update_rfc1123(P, N, B) end} || {R, P, N, B} <- Tests].
+
+pad_int_test_() ->
+	Tests = [
+		{ 0, <<"00">>}, { 1, <<"01">>}, { 2, <<"02">>}, { 3, <<"03">>},
+		{ 4, <<"04">>}, { 5, <<"05">>}, { 6, <<"06">>}, { 7, <<"07">>},
+		{ 8, <<"08">>}, { 9, <<"09">>}, {10, <<"10">>}, {11, <<"11">>},
+		{12, <<"12">>}, {13, <<"13">>}, {14, <<"14">>}, {15, <<"15">>},
+		{16, <<"16">>}, {17, <<"17">>}, {18, <<"18">>}, {19, <<"19">>},
+		{20, <<"20">>}, {21, <<"21">>}, {22, <<"22">>}, {23, <<"23">>},
+		{24, <<"24">>}, {25, <<"25">>}, {26, <<"26">>}, {27, <<"27">>},
+		{28, <<"28">>}, {29, <<"29">>}, {30, <<"30">>}, {31, <<"31">>},
+		{32, <<"32">>}, {33, <<"33">>}, {34, <<"34">>}, {35, <<"35">>},
+		{36, <<"36">>}, {37, <<"37">>}, {38, <<"38">>}, {39, <<"39">>},
+		{40, <<"40">>}, {41, <<"41">>}, {42, <<"42">>}, {43, <<"43">>},
+		{44, <<"44">>}, {45, <<"45">>}, {46, <<"46">>}, {47, <<"47">>},
+		{48, <<"48">>}, {49, <<"49">>}, {50, <<"50">>}, {51, <<"51">>},
+		{52, <<"52">>}, {53, <<"53">>}, {54, <<"54">>}, {55, <<"55">>},
+		{56, <<"56">>}, {57, <<"57">>}, {58, <<"58">>}, {59, <<"59">>}
+	],
+	[{I, fun() -> O = pad_int(I) end} || {I, O} <- Tests].
+
+-endif.

src/cowboy_http_req.erl

@@ -187,7 +187,8 @@ reply(Code, Headers, Body, Req=#http_req{socket=Socket,
 	Head = response_head(Code, Headers, [
 		{<<"Connection">>, atom_to_connection(Connection)},
 		{<<"Content-Length">>,
-			list_to_binary(integer_to_list(iolist_size(Body)))}
+			list_to_binary(integer_to_list(iolist_size(Body)))},
+		{<<"Date">>, cowboy_clock:rfc1123()}
 	]),
 	Transport:send(Socket, [Head, Body]),
 	{ok, Req#http_req{resp_state=done}}.
@@ -198,7 +199,8 @@ chunked_reply(Code, Headers, Req=#http_req{socket=Socket, transport=Transport,
 		resp_state=waiting}) ->
 	Head = response_head(Code, Headers, [
 		{<<"Connection">>, <<"close">>},
-		{<<"Transfer-Encoding">>, <<"chunked">>}
+		{<<"Transfer-Encoding">>, <<"chunked">>},
+		{<<"Date">>, cowboy_clock:rfc1123()}
 	]),
 	Transport:send(Socket, Head),
 	{ok, Req#http_req{resp_state=chunks}}.

src/cowboy_sup.erl

@@ -30,4 +30,6 @@ start_link() ->
 
 -spec init([]) -> term(). %% @todo These specs should be improved.
 init([]) ->
-	{ok, {{one_for_one, 10, 10}, []}}.
+	Procs = [{cowboy_clock, {cowboy_clock, start_link, []},
+		permanent, 5000, worker, dynamic}],
+	{ok, {{one_for_one, 10, 10}, Procs}}.