Treat iolist of empty binaries as empty body

Normally when the request body is empty, `handle_body` is only called for POST and PUT requests, since other methods shouldn't have `Content-Type` and `Content-Length` headers for empty bodies. But one case is missed in the empty body detection, an iolist containing empty binaries. The [gleam hackney wrapper](https://github.com/gleam-lang/hackney) represents empty bodies as `[<<>>]`, triggering this bug and causing gleam-lang/hackney#5.

This PR expands the empty body detection to check if the result of `iolist_to_binary` is empty.

Author: pvsr

src/hackney_request.erl

@@ -99,12 +99,18 @@ perform(Client0, {Method0, Path0, Headers0, Body0}) ->
                                                                     Size, Boundary, Client0);
                                             <<>> when Method =:= <<"POST">> orelse Method =:= <<"PUT">> ->
                                               handle_body(Headers2, ReqType0, Body0, Client0);
-                                            [] when Method =:= <<"POST">> orelse Method =:= <<"PUT">> ->
-                                              handle_body(Headers2, ReqType0, Body0, Client0);
                                             <<>> ->
                                               {Headers2, ReqType0, Body0, Client0};
-                                            [] ->
-                                              {Headers2, ReqType0, Body0, Client0};
+                                            _ when is_list(Body0) ->
+                                              Body1 = iolist_to_binary(Body0),
+                                              case Body1 of
+                                                <<>> when Method =:= <<"POST">> orelse Method =:= <<"PUT">> ->
+                                                  handle_body(Headers2, ReqType0, Body1, Client0);
+                                                <<>> ->
+                                                  {Headers2, ReqType0, Body1, Client0};
+                                                _ ->
+                                                  handle_body(Headers2, ReqType0, Body1, Client0)
+                                              end;
                                             _ ->
                                               handle_body(Headers2, ReqType0, Body0, Client0)
                                           end,
@@ -370,13 +376,6 @@ handle_body(Headers, ReqType0, Body0, Client) ->
                             S = hackney_headers_new:get_value(<<"content-length">>, Headers),
                             {S, CT, Body0};
 
-                          _ when is_list(Body0) -> % iolist case
-                            Body1 = iolist_to_binary(Body0),
-                            S = erlang:byte_size(Body1),
-                            CT = hackney_headers_new:get_value(
-                                   <<"content-type">>, Headers, <<"application/octet-stream">>
-                                  ),
-                            {S, CT, Body1};
                           _ when is_binary(Body0) ->
                             S = erlang:byte_size(Body0),
                             CT = hackney_headers_new:get_value(

test/hackney_integration_tests.erl

@@ -20,6 +20,10 @@ all_tests() ->
   % fun relative_redirect_request_no_follow/0,
    fun relative_redirect_request_follow/0,
    fun test_duplicate_headers/0,
+   fun test_post_includes_content_length_with_body/0,
+   fun test_post_includes_content_length_with_empty_body/0,
+   fun test_get_includes_content_length_with_body/0,
+   fun test_get_excludes_content_length_with_empty_body/0,
    fun test_custom_host_headers/0,
    fun async_request/0,
    fun async_head_request/0,
@@ -186,6 +190,45 @@ test_custom_host_headers() ->
   ReqHeaders = proplists:get_value(<<"headers">>, Obj),
   ?assertEqual(<<"myhost.com">>, proplists:get_value(<<"Host">>, ReqHeaders)).
 
+test_post_includes_content_length_with_body() ->
+    URL = <<"http://localhost:8000/post">>,
+    Body = <<"{\"test\": \"ok\" }">>,
+    Options = [with_body],
+    {ok, 200, _H, JsonBody} = hackney:post(URL, [], Body, Options),
+    Obj = jsone:decode(JsonBody, [{object_format, proplist}]),
+    ReqHeaders = proplists:get_value(<<"headers">>, Obj),
+    ?assertEqual(<<"15">>, proplists:get_value(<<"Content-Length">>, ReqHeaders)).
+
+test_post_includes_content_length_with_empty_body() ->
+    URL = <<"http://localhost:8000/post">>,
+    Body = <<>>,
+    Options = [with_body],
+    {ok, 200, _H, JsonBody} = hackney:post(URL, [], Body, Options),
+    Obj = jsone:decode(JsonBody, [{object_format, proplist}]),
+    ReqHeaders = proplists:get_value(<<"headers">>, Obj),
+    ?assertEqual(<<"0">>, proplists:get_value(<<"Content-Length">>, ReqHeaders)).
+
+test_get_includes_content_length_with_body() ->
+    URL = <<"http://localhost:8000/post">>,
+    Body = <<"{\"test\": \"ok\" }">>,
+    Options = [with_body],
+    {ok, 200, _H, JsonBody} = hackney:post(URL, [], Body, Options),
+    Obj = jsone:decode(JsonBody, [{object_format, proplist}]),
+    ReqHeaders = proplists:get_value(<<"headers">>, Obj),
+    ?assertEqual(<<"15">>, proplists:get_value(<<"Content-Length">>, ReqHeaders)).
+
+test_get_excludes_content_length_with_empty_body() ->
+    URL = <<"http://localhost:8000/get">>,
+    EmptyBodies = [<<>>, [], [<<>>]],
+    Options = [with_body],
+    lists:foreach(fun(Body) ->
+        {ok, 200, _H, JsonBody} = hackney:get(URL, [], Body, Options),
+        Obj = jsone:decode(JsonBody, [{object_format, proplist}]),
+        ReqHeaders = proplists:get_value(<<"headers">>, Obj),
+        ?assertEqual(undefined, proplists:get_value(<<"Content-Type">>, ReqHeaders)),
+        ?assertEqual(undefined, proplists:get_value(<<"Content-Length">>, ReqHeaders))
+    end, EmptyBodies).
+
 test_frees_manager_ets_when_body_is_in_client() ->
     URL = <<"http://localhost:8000/get">>,
     BeforeCount = ets:info(hackney_manager_refs, size),