Add {set_options, #{metrics_user_data := Map}}

This allows giving custom metadata to the metrics stream handler.
This can be useful to for example provide the name of the
module handling the request which is only known after routing.
But any user data is allowed.

When called multiple times the user data maps are merged.

3 files changed, 43 insertions, 14 deletions

diff --git a/src/cowboy_metrics_h.erl b/src/cowboy_metrics_h.erl
index 309afde..4107aac 100644
--- a/src/cowboy_metrics_h.erl
+++ b/src/cowboy_metrics_h.erl
@@ -102,7 +102,10 @@
 	%% Length of the request and response bodies. This does
 	%% not include the framing.
 	req_body_length => non_neg_integer(),
-	resp_body_length => non_neg_integer()
+	resp_body_length => non_neg_integer(),
+
+	%% Additional metadata set by the user.
+	user_data => map()
 }.
 -export_type([metrics/0]).
 
@@ -126,7 +129,8 @@
 	procs = #{} :: proc_metrics(),
 	informational = [] :: [informational_metrics()],
 	req_body_length = 0 :: non_neg_integer(),
-	resp_body_length = 0 :: non_neg_integer()
+	resp_body_length = 0 :: non_neg_integer(),
+	user_data = #{} :: map()
 }).
 
 -spec init(cowboy_stream:streamid(), cowboy_req:req(), cowboy:opts())
@@ -255,6 +259,14 @@ fold([{data, fin, Data}|Tail], State=#state{resp_body_length=RespBodyLen}) ->
 		resp_end=RespEnd,
 		resp_body_length=RespBodyLen + resp_body_length(Data)
 	});
+fold([{set_options, SetOpts}|Tail], State0=#state{user_data=OldUserData}) ->
+	State = case SetOpts of
+		#{metrics_user_data := NewUserData} ->
+			State0#state{user_data=maps:merge(OldUserData, NewUserData)};
+		_ ->
+			State0
+	end,
+	fold(Tail, State);
 fold([_|Tail], State) ->
 	fold(Tail, State).
 
@@ -263,7 +275,7 @@ terminate(StreamID, Reason, #state{next=Next, callback=Fun,
 		req=Req, resp_status=RespStatus, resp_headers=RespHeaders, ref=Ref,
 		req_start=ReqStart, req_body_start=ReqBodyStart,
 		req_body_end=ReqBodyEnd, resp_start=RespStart, resp_end=RespEnd,
-		procs=Procs, informational=Infos,
+		procs=Procs, informational=Infos, user_data=UserData,
 		req_body_length=ReqBodyLen, resp_body_length=RespBodyLen}) ->
 	Res = cowboy_stream:terminate(StreamID, Reason, Next),
 	ReqEnd = erlang:monotonic_time(),
@@ -284,7 +296,8 @@ terminate(StreamID, Reason, #state{next=Next, callback=Fun,
 		procs => Procs,
 		informational => lists:reverse(Infos),
 		req_body_length => ReqBodyLen,
-		resp_body_length => RespBodyLen
+		resp_body_length => RespBodyLen,
+		user_data => UserData
 	},
 	Fun(Metrics),
 	Res.
diff --git a/test/handlers/set_options_h.erl b/test/handlers/set_options_h.erl
index 1cefe92..ef88a6f 100644
--- a/test/handlers/set_options_h.erl
+++ b/test/handlers/set_options_h.erl
@@ -32,4 +32,9 @@ set_options(<<"idle_timeout_long">>, Req0, State) ->
 	#{pid := Pid, streamid := StreamID} = Req0,
 	Pid ! {{Pid, StreamID}, {set_options, #{idle_timeout => 60000}}},
 	{_, Body, Req} = cowboy_req:read_body(Req0),
-	{ok, cowboy_req:reply(200, #{}, Body, Req), State}.
+	{ok, cowboy_req:reply(200, #{}, Body, Req), State};
+set_options(<<"metrics_user_data">>, Req, State) ->
+	%% @todo This should be replaced by a cowboy_req:cast/cowboy_stream:cast.
+	#{pid := Pid, streamid := StreamID} = Req,
+	Pid ! {{Pid, StreamID}, {set_options, #{metrics_user_data => #{handler => ?MODULE}}}},
+	{ok, cowboy_req:reply(200, #{}, <<"Hello world!">>, Req), State}.
diff --git a/test/metrics_SUITE.erl b/test/metrics_SUITE.erl
index 4ead60c..d9ff7ea 100644
--- a/test/metrics_SUITE.erl
+++ b/test/metrics_SUITE.erl
@@ -76,6 +76,7 @@ init_routes(_) -> [
 		{"/default", default_h, []},
 		{"/full/:key", echo_h, []},
 		{"/resp/:key[/:arg]", resp_h, []},
+		{"/set_options/:key", set_options_h, []},
 		{"/ws_echo", ws_echo, []}
 	]}
 ].
@@ -98,9 +99,13 @@ do_metrics_callback() ->
 
 hello_world(Config) ->
 	doc("Confirm metrics are correct for a normal GET request."),
-	do_get("/", Config).
+	do_get("/", #{}, Config).
 
-do_get(Path, Config) ->
+user_data(Config) ->
+	doc("Confirm user data can be attached to metrics."),
+	do_get("/set_options/metrics_user_data", #{handler => set_options_h}, Config).
+
+do_get(Path, UserData, Config) ->
 	%% Perform a GET request.
 	ConnPid = gun_open(Config),
 	Ref = gun:get(ConnPid, Path, [
@@ -153,7 +158,8 @@ do_get(Path, Config) ->
 				streamid := 1,
 				reason := normal,
 				req := #{},
-				informational := []
+				informational := [],
+				user_data := UserData
 			} = Metrics,
 			%% All good!
 			ok
@@ -216,7 +222,8 @@ post_body(Config) ->
 				streamid := 1,
 				reason := normal,
 				req := #{},
-				informational := []
+				informational := [],
+				user_data := #{}
 			} = Metrics,
 			%% All good!
 			ok
@@ -273,7 +280,8 @@ no_resp_body(Config) ->
 				streamid := 1,
 				reason := normal,
 				req := #{},
-				informational := []
+				informational := [],
+				user_data := #{}
 			} = Metrics,
 			%% All good!
 			ok
@@ -361,7 +369,7 @@ do_early_error_request_line(Config) ->
 %% This test is identical to normal GET except for the handler.
 stream_reply(Config) ->
 	doc("Confirm metrics are correct for long polling."),
-	do_get("/resp/stream_reply2/200", Config).
+	do_get("/resp/stream_reply2/200", #{}, Config).
 
 ws(Config) ->
 	case config(protocol, Config) of
@@ -421,7 +429,8 @@ do_ws(Config) ->
 						<<"sec-websocket-accept">> := _
 					},
 					time := _
-				}]
+				}],
+				user_data := #{}
 			} = Metrics,
 			%% All good!
 			ok
@@ -487,7 +496,8 @@ error_response(Config) ->
 				streamid := 1,
 				reason := {internal_error, {'EXIT', _Pid, {crash, _StackTrace}}, 'Stream process crashed.'},
 				req := #{},
-				informational := []
+				informational := [],
+				user_data := #{}
 			} = Metrics,
 			%% All good!
 			ok
@@ -546,7 +556,8 @@ error_response_after_reply(Config) ->
 				streamid := 1,
 				reason := {internal_error, {'EXIT', _Pid, {crash, _StackTrace}}, 'Stream process crashed.'},
 				req := #{},
-				informational := []
+				informational := [],
+				user_data := #{}
 			} = Metrics,
 			%% All good!
 			ok