The onresponse hook now receives 4 arguments, including the body

We do not always provide the body however. It is not available
when using chunked replies, or when using set_resp_body_fun.

src/cowboy_protocol.erl

@@ -34,7 +34,7 @@
 %%   any dispatching is done. Host info, path info and bindings are thus
 %%   not available at this point.</dd>
 %%  <dt>onresponse</dt><dd>Optional fun that allows replacing a response
-%%   sent by the application based on its status code or headers.</dd>
+%%   sent by the application.</dd>
 %%  <dt>timeout</dt><dd>Time in milliseconds before an idle
 %%   connection is closed. Defaults to 5000 milliseconds.</dd>
 %% </dl>
@@ -56,7 +56,7 @@
 
 -type onrequest_fun() :: fun((Req) -> Req).
 -type onresponse_fun() ::
-	fun((cowboy_http:status(), cowboy_http:headers(), Req) -> Req).
+	fun((cowboy_http:status(), cowboy_http:headers(), iodata(), Req) -> Req).
 
 -export_type([onrequest_fun/0]).
 -export_type([onresponse_fun/0]).

src/cowboy_req.erl

@@ -1108,7 +1108,7 @@ response(Status, Headers, RespHeaders, DefaultHeaders, Body, Req=#http_req{
 	FullHeaders = response_merge_headers(Headers, RespHeaders, DefaultHeaders),
 	Req2 = case OnResponse of
 		undefined -> Req;
-		OnResponse -> OnResponse(Status, FullHeaders,
+		OnResponse -> OnResponse(Status, FullHeaders, Body,
 			%% Don't call 'onresponse' from the hook itself.
 			Req#http_req{resp_headers=[], resp_body= <<>>,
 				onresponse=undefined})

test/http_SUITE.erl

@@ -188,7 +188,7 @@ init_per_group(onresponse, Config) ->
 	{ok, _} = cowboy:start_http(onresponse, 100, [{port, Port}], [
 		{dispatch, init_dispatch(Config)},
 		{max_keepalive, 50},
-		{onresponse, fun onresponse_hook/3},
+		{onresponse, fun onresponse_hook/4},
 		{timeout, 500}
 	]),
 	{ok, Client} = cowboy_client:init([]),
@@ -623,7 +623,7 @@ onresponse_reply(Config) ->
 	{error, closed} = cowboy_client:response_body(Client3).
 
 %% Hook for the above onresponse tests.
-onresponse_hook(_, Headers, Req) ->
+onresponse_hook(_, Headers, _, Req) ->
 	{ok, Req2} = cowboy_req:reply(
 		<<"777 Lucky">>, [{<<"x-hook">>, <<"onresponse">>}|Headers], Req),
 	Req2.