From 6b14cd64fcfd607d7a9a4e24e95c49cd3643cb8b Mon Sep 17 00:00:00 2001
From: geeksilva97 <edigleyssonsilva@gmail.com>
Date: Sat, 3 Feb 2024 18:49:37 -0300
Subject: [PATCH] return allow header

---
 src/cowboy_rest.erl         |  8 ++++++--
 test/rest_handler_SUITE.erl | 12 ++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/cowboy_rest.erl b/src/cowboy_rest.erl
index 003e5f9d..b5dc1196 100644
--- a/src/cowboy_rest.erl
+++ b/src/cowboy_rest.erl
@@ -328,7 +328,9 @@ uri_too_long(Req, State) ->
 allowed_methods(Req, State=#state{method=Method}) ->
 	case call(Req, State, allowed_methods) of
 		no_call when Method =:= <<"HEAD">>; Method =:= <<"GET">> ->
-			next(Req, State, fun malformed_request/2);
+			Allow = <<"HEAD, GET, OPTIONS">>,
+			Req2 = cowboy_req:set_resp_header(<<"allow">>, Allow, Req),
+			next(Req2, State, fun malformed_request/2);
 		no_call when Method =:= <<"OPTIONS">> ->
 			next(Req, State#state{allowed_methods=
 				[<<"HEAD">>, <<"GET">>, <<"OPTIONS">>]},
@@ -343,7 +345,9 @@ allowed_methods(Req, State=#state{method=Method}) ->
 		{List, Req2, State2} ->
 			case lists:member(Method, List) of
 				true when Method =:= <<"OPTIONS">> ->
-					next(Req2, State2#state{allowed_methods=List},
+					<< ", ", Allow/binary >> = << << ", ", M/binary >> || M <- List >>,
+					Req3 = cowboy_req:set_resp_header(<<"allow">>, Allow, Req2),
+					next(Req3, State2#state{allowed_methods=List},
 						fun malformed_request/2);
 				true ->
 					next(Req2, State2, fun malformed_request/2);
diff --git a/test/rest_handler_SUITE.erl b/test/rest_handler_SUITE.erl
index 510098f1..d43b8f16 100644
--- a/test/rest_handler_SUITE.erl
+++ b/test/rest_handler_SUITE.erl
@@ -778,6 +778,17 @@ last_modified_missing(Config) ->
 	false = lists:keyfind(<<"last-modified">>, 1, Headers),
 	ok.
 
+head_call(Config) ->
+	doc("A successful HEAD request to a simple handler results in "
+		"a 200 OK response with the allow header set. (RFC7231 4.3.7)"),
+	ConnPid = gun_open(Config),
+	Ref = gun:head(ConnPid, "/", [
+		{<<"accept-encoding">>, <<"gzip">>}
+	]),
+	{response, fin, 200, Headers} = gun:await(ConnPid, Ref),
+	{_, <<"HEAD, GET, OPTIONS">>} = lists:keyfind(<<"allow">>, 1, Headers),
+	ok.
+
 options_missing(Config) ->
 	doc("A successful OPTIONS request to a simple handler results in "
 		"a 200 OK response with the allow header set. (RFC7231 4.3.7)"),
@@ -799,6 +810,7 @@ provide_callback(Config) ->
 	]),
 	{response, nofin, 200, Headers} = gun:await(ConnPid, Ref),
 	{_, <<"text/plain">>} = lists:keyfind(<<"content-type">>, 1, Headers),
+	{_, <<"HEAD, GET, OPTIONS">>} = lists:keyfind(<<"allow">>, 1, Headers),
 	{ok, <<"This is REST!">>} = gun:await_body(ConnPid, Ref),
 	ok.