Add cowboy_req:inform/2,3

User code can now send as many 1xx responses as necessary.

src/cowboy_http2.erl

@@ -495,6 +495,13 @@ commands(State, Stream=#stream{local=idle}, [{error_response, StatusCode, Header
 	commands(State, Stream, [{response, StatusCode, Headers, Body}|Tail]);
 commands(State, Stream, [{error_response, _, _, _}|Tail]) ->
 	commands(State, Stream, Tail);
+%% Send an informational response.
+commands(State=#state{socket=Socket, transport=Transport, encode_state=EncodeState0},
+		Stream=#stream{id=StreamID, local=idle}, [{inform, StatusCode, Headers0}|Tail]) ->
+	Headers = Headers0#{<<":status">> => status(StatusCode)},
+	{HeaderBlock, EncodeState} = headers_encode(Headers, EncodeState0),
+	Transport:send(Socket, cow_http2:headers(StreamID, fin, HeaderBlock)),
+	commands(State#state{encode_state=EncodeState}, Stream, Tail);
 %% Send response headers.
 %%
 %% @todo Kill the stream if it sent a response when one has already been sent.

src/cowboy_req.erl

@@ -71,6 +71,8 @@
 -export([set_resp_body/2]).
 %% @todo set_resp_body/3 with a ContentType or even Headers argument, to set content headers.
 -export([has_resp_body/1]).
+-export([inform/2]).
+-export([inform/3]).
 -export([reply/2]).
 -export([reply/3]).
 -export([reply/4]).
@@ -685,6 +687,18 @@ has_resp_body(_) ->
 delete_resp_header(Name, Req=#{resp_headers := RespHeaders}) ->
 	Req#{resp_headers => maps:remove(Name, RespHeaders)}.
 
+-spec inform(cowboy:http_status(), req()) -> ok.
+inform(Status, Req) ->
+	inform(Status, #{}, Req).
+
+-spec inform(cowboy:http_status(), cowboy:http_headers(), req()) -> ok.
+inform(_, _, #{has_sent_resp := _}) ->
+	error(function_clause); %% @todo Better error message.
+inform(Status, Headers, #{pid := Pid, streamid := StreamID})
+		when is_integer(Status); is_binary(Status) ->
+	Pid ! {{Pid, StreamID}, {inform, Status, Headers}},
+	ok.
+
 -spec reply(cowboy:http_status(), Req) -> Req when Req::req().
 reply(Status, Req) ->
 	reply(Status, #{}, Req).
@@ -699,7 +713,7 @@ reply(Status, Headers, Req) ->
 -spec reply(cowboy:http_status(), cowboy:http_headers(), resp_body(), Req)
 	-> Req when Req::req().
 reply(_, _, _, #{has_sent_resp := _}) ->
-	error(function_clause);
+	error(function_clause); %% @todo Better error message.
 reply(Status, Headers, {sendfile, _, 0, _}, Req)
 		when is_integer(Status); is_binary(Status) ->
 	do_reply(Status, Headers#{

src/cowboy_stream_h.erl

@@ -119,6 +119,8 @@ info(_StreamID, {read_body_timeout, Ref}, State=#state{pid=Pid, read_body_ref=Re
 info(_StreamID, {read_body_timeout, _}, State) ->
 	{[], State};
 %% Response.
+info(_StreamID, Inform = {inform, _, _}, State) ->
+	{[Inform], State};
 info(_StreamID, Response = {response, _, _, _}, State) ->
 	{[Response], State};
 info(_StreamID, Headers = {headers, _, _}, State) ->