Merge pull request #7 from danielwhite/fix-exposed-headers

Use a single header for Access-Control-Expose-Headers

Author: danielwhite

src/cowboy_cors.erl

@@ -139,9 +139,9 @@ exposed_headers(Req, State) ->
 
 set_exposed_headers(Req, []) ->
     Req;
-set_exposed_headers(Req, [Header|Tail]) ->
-    Req1 = cowboy_req:set_resp_header(<<"access-control-expose-headers">>, Header, Req),
-    set_exposed_headers(Req1, Tail).
+set_exposed_headers(Req, Headers) ->
+    Bin = header_list(Headers),
+    cowboy_req:set_resp_header(<<"access-control-expose-headers">>, Bin, Req).
 
 %% allow_credentials/1 should return true or false.
 allow_credentials(Req, State) ->
@@ -195,3 +195,12 @@ terminate(Req, #state{env = Env}) ->
 -spec error_terminate(cowboy_req:req(), #state{}) -> no_return().
 error_terminate(_Req, _State) ->
     erlang:throw({?MODULE, error}).
+
+%% create a comma-separated list for a header value
+header_list(Values) ->
+    header_list(Values, <<>>).
+
+header_list([Value], Acc) ->
+    <<Acc/binary, Value/binary>>;
+header_list([Value | Rest], Acc) ->
+    header_list(Rest, <<Acc/binary, Value/binary, ",">>).

test/cors_SUITE.erl

@@ -17,6 +17,7 @@
 -export([standard_options/1]).
 -export([simple_allowed_get/1]).
 -export([simple_allowed_credentials_get/1]).
+-export([simple_exposed_headers/1]).
 -export([actual_options/1]).
 -export([preflight_method/1]).
 -export([preflight_allowed_method/1]).
@@ -46,6 +47,7 @@ groups() ->
                            standard_options,
                            simple_allowed_get,
                            simple_allowed_credentials_get,
+                           simple_exposed_headers,
                            actual_options,
                            preflight_method,
                            preflight_allowed_method,
@@ -168,6 +170,21 @@ simple_allowed_credentials_get(Config) ->
     {_, Origin} = lists:keyfind(<<"access-control-allow-origin">>, 1, Headers),
     {_, <<"true">>} = lists:keyfind(<<"access-control-allow-credentials">>, 1, Headers).
 
+simple_exposed_headers(Config) ->
+    Origin = <<"http://example.com">>,
+    Exposed = [<<"x-first">>, <<"x-second">>],
+    {ok, 204, Headers, _} =
+        request(<<"GET">>,
+                [{<<"Origin">>, Origin}],
+                [{allowed_origins, Origin},
+                 {allowed_methods, <<"GET">>},
+                 {exposed_headers, Exposed}],
+                Config),
+    {_, Origin} = lists:keyfind(<<"access-control-allow-origin">>, 1, Headers),
+    {_, ExposedList} = lists:keyfind(<<"access-control-expose-headers">>, 1, Headers),
+    Exposed = cowboy_http:nonempty_list(ExposedList, fun cowboy_http:token/2),
+    false = lists:keyfind(<<"access-control-allow-credentials">>, 1, Headers).
+
 actual_options(Config) ->
     %% OPTIONS request without Access-Control-Request-Method is not a pre-flight request.
     Origin = <<"http://example.com">>,