Fix HTTP/2 server push

Cowboy was encoding the headers then decoding them when initializing
the request. The problem is that the encoding and decoding contexts
are not the same. Now, Cowboy will directly use the headers it
received in the push command for the new request. This is also
more efficient.

I am surprised it worked at all considering the issue.

src/cowboy_http2.erl

@@ -332,7 +332,7 @@ frame(State=#state{client_streamid=LastStreamID}, {headers, StreamID, _, _, _})
 %% Single HEADERS frame headers block.
 frame(State, {headers, StreamID, IsFin, head_fin, HeaderBlock}) ->
 	%% @todo We probably need to validate StreamID here and in 4 next clauses.
-	stream_init(State, StreamID, IsFin, HeaderBlock);
+	stream_decode_init(State, StreamID, IsFin, HeaderBlock);
 %% HEADERS frame starting a headers block. Enter continuation mode.
 frame(State, {headers, StreamID, IsFin, head_nofin, HeaderBlockFragment}) ->
 	State#state{parse_state={continuation, StreamID, IsFin, HeaderBlockFragment}};
@@ -340,7 +340,7 @@ frame(State, {headers, StreamID, IsFin, head_nofin, HeaderBlockFragment}) ->
 frame(State, {headers, StreamID, IsFin, head_fin,
 		_IsExclusive, _DepStreamID, _Weight, HeaderBlock}) ->
 	%% @todo Handle priority.
-	stream_init(State, StreamID, IsFin, HeaderBlock);
+	stream_decode_init(State, StreamID, IsFin, HeaderBlock);
 %% HEADERS frame starting a headers block. Enter continuation mode.
 frame(State, {headers, StreamID, IsFin, head_nofin,
 		_IsExclusive, _DepStreamID, _Weight, HeaderBlockFragment}) ->
@@ -411,7 +411,7 @@ frame(State, {continuation, _, _, _}) ->
 
 continuation_frame(State=#state{parse_state={continuation, StreamID, IsFin, HeaderBlockFragment0}},
 		{continuation, StreamID, head_fin, HeaderBlockFragment1}) ->
-	stream_init(State#state{parse_state=normal}, StreamID, IsFin,
+	stream_decode_init(State#state{parse_state=normal}, StreamID, IsFin,
 		<< HeaderBlockFragment0/binary, HeaderBlockFragment1/binary >>);
 continuation_frame(State=#state{parse_state={continuation, StreamID, IsFin, HeaderBlockFragment0}},
 		{continuation, StreamID, head_nofin, HeaderBlockFragment1}) ->
@@ -529,21 +529,24 @@ commands(State0=#state{socket=Socket, transport=Transport, server_streamid=Promi
 	Authority = case {Scheme, Port} of
 		{<<"http">>, 80} -> Host;
 		{<<"https">>, 443} -> Host;
-		_ -> [Host, $:, integer_to_binary(Port)]
+		_ -> iolist_to_binary([Host, $:, integer_to_binary(Port)])
 	end,
 	PathWithQs = case Qs of
 		<<>> -> Path;
 		_ -> [Path, $?, Qs]
 	end,
-	Headers = Headers0#{<<":method">> => Method,
-			<<":scheme">> => Scheme,
-			<<":authority">> => Authority,
-			<<":path">> => PathWithQs},
+	%% We need to make sure the header value is binary before we can
+	%% pass it to stream_req_init, as it expects them to be flat.
+	Headers1 = maps:map(fun(_, V) -> iolist_to_binary(V) end, Headers0),
+	Headers = Headers1#{
+		<<":method">> => Method,
+		<<":scheme">> => Scheme,
+		<<":authority">> => Authority,
+		<<":path">> => iolist_to_binary(PathWithQs)},
 	{HeaderBlock, EncodeState} = headers_encode(Headers, EncodeState0),
 	Transport:send(Socket, cow_http2:push_promise(StreamID, PromisedStreamID, HeaderBlock)),
-	%% @todo iolist_to_binary(HeaderBlock) isn't optimal. Need a shortcut.
-	State = stream_init(State0#state{server_streamid=PromisedStreamID + 2, encode_state=EncodeState},
-		PromisedStreamID, fin, iolist_to_binary(HeaderBlock)),
+	State = stream_req_init(State0#state{server_streamid=PromisedStreamID + 2,
+		encode_state=EncodeState}, PromisedStreamID, fin, Headers),
 	commands(State, Stream, Tail);
 commands(State=#state{socket=Socket, transport=Transport, remote_window=ConnWindow},
 		Stream=#stream{id=StreamID, remote_window=StreamWindow},
@@ -699,61 +702,60 @@ terminate_all_streams([#stream{id=StreamID, state=StreamState}|Tail], Reason, Ch
 
 %% Stream functions.
 
-stream_init(State0=#state{ref=Ref, socket=Socket, transport=Transport, peer=Peer, decode_state=DecodeState0},
-		StreamID, IsFin, HeaderBlock) ->
+stream_decode_init(State=#state{socket=Socket, transport=Transport,
+		decode_state=DecodeState0}, StreamID, IsFin, HeaderBlock) ->
 	%% @todo Add clause for CONNECT requests (no scheme/path).
 	try headers_decode(HeaderBlock, DecodeState0) of
-		{Headers0=#{
-				<<":method">> := Method,
-				<<":scheme">> := Scheme,
-				<<":authority">> := Authority,
-				<<":path">> := PathWithQs}, DecodeState} ->
-			State = State0#state{decode_state=DecodeState},
-			Headers = maps:without([<<":method">>, <<":scheme">>, <<":authority">>, <<":path">>], Headers0),
-			BodyLength = case Headers of
-				_ when IsFin =:= fin ->
-					0;
-				#{<<"content-length">> := <<"0">>} ->
-					0;
-				#{<<"content-length">> := BinLength} ->
-					Length = try
-						cow_http_hd:parse_content_length(BinLength)
-					catch _:_ ->
-						terminate(State0, {stream_error, StreamID, protocol_error,
-							'The content-length header is invalid. (RFC7230 3.3.2)'})
-						%% @todo Err should terminate here...
-					end,
-					Length;
-				_ ->
-					undefined
-			end,
-			{Host, Port} = cow_http_hd:parse_host(Authority),
-			{Path, Qs} = cow_http:parse_fullpath(PathWithQs),
-			Req = #{
-				ref => Ref,
-				pid => self(),
-				streamid => StreamID,
-				peer => Peer,
-				method => Method,
-				scheme => Scheme,
-				host => Host,
-				port => Port,
-				path => Path,
-				qs => Qs,
-				version => 'HTTP/2',
-				headers => Headers,
-				has_body => IsFin =:= nofin,
-				body_length => BodyLength
-			},
-			stream_handler_init(State, StreamID, IsFin, idle, Req);
+		{Headers=#{<<":method">> := _, <<":scheme">> := _,
+				<<":authority">> := _, <<":path">> := _}, DecodeState} ->
+			stream_req_init(State#state{decode_state=DecodeState}, StreamID, IsFin, Headers);
 		{_, DecodeState} ->
 			Transport:send(Socket, cow_http2:rst_stream(StreamID, protocol_error)),
-			State0#state{decode_state=DecodeState}
+			State#state{decode_state=DecodeState}
 	catch _:_ ->
-		terminate(State0, {connection_error, compression_error,
+		terminate(State, {connection_error, compression_error,
 			'Error while trying to decode HPACK-encoded header block. (RFC7540 4.3)'})
 	end.
 
+stream_req_init(State=#state{ref=Ref, peer=Peer}, StreamID, IsFin, Headers0=#{
+		<<":method">> := Method, <<":scheme">> := Scheme,
+		<<":authority">> := Authority, <<":path">> := PathWithQs}) ->
+	Headers = maps:without([<<":method">>, <<":scheme">>, <<":authority">>, <<":path">>], Headers0),
+	BodyLength = case Headers of
+		_ when IsFin =:= fin ->
+			0;
+		#{<<"content-length">> := <<"0">>} ->
+			0;
+		#{<<"content-length">> := BinLength} ->
+			try
+				cow_http_hd:parse_content_length(BinLength)
+			catch _:_ ->
+				terminate(State, {stream_error, StreamID, protocol_error,
+					'The content-length header is invalid. (RFC7230 3.3.2)'})
+			end;
+		_ ->
+			undefined
+	end,
+	{Host, Port} = cow_http_hd:parse_host(Authority),
+	{Path, Qs} = cow_http:parse_fullpath(PathWithQs),
+	Req = #{
+		ref => Ref,
+		pid => self(),
+		streamid => StreamID,
+		peer => Peer,
+		method => Method,
+		scheme => Scheme,
+		host => Host,
+		port => Port,
+		path => Path,
+		qs => Qs,
+		version => 'HTTP/2',
+		headers => Headers,
+		has_body => IsFin =:= nofin,
+		body_length => BodyLength
+	},
+	stream_handler_init(State, StreamID, IsFin, idle, Req).
+
 stream_handler_init(State=#state{opts=Opts,
 		local_settings=#{initial_window_size := RemoteWindow},
 		remote_settings=#{initial_window_size := LocalWindow}},