Rework and improve the decompress stream handler

The read buffer was changed into an iovec to avoid doing
too many binary concatenations and allocations.

Decompression happens transparently: when decoding gzip,
the content-encoding header is removed (we only decode
when "gzip" is the only encoding so nothing remains).

We always add a content_decoded key to the Req object.
This key contains a list of codings that were decoded,
in the reverse order in which they were. Currently it
can only be empty or contain <<"gzip">> but future
improvements or user handlers may see it contain more
values.

The option to disable decompression was renamed to
decompress_enabled and defaults to true.

It is no longer possible to enable/disable decompression
in the middle of reading the body: this ensures that the
data we pass forward is always valid.

Various smaller improvements were made to the code,
tests and manual pages.

doc/src/guide/streams.asciidoc

@@ -66,9 +66,9 @@ enabled by default. It is a good example for writing your
 own handlers that will modify responses.
 
 link:man:cowboy_decompress_h(3)[cowboy_decompress_h] will
-automatically decompress requests when possible. It is not
+automatically decompress request bodies when possible.
-enabled by default. It is a good example for writing your
+It is not enabled by default. It is a good example for
-own handlers that will modify requests.
+writing your own handlers that will modify requests.
 
 link:man:cowboy_metrics_h(3)[cowboy_metrics_h] gathers
 metrics about a stream then passes them to a configurable

doc/src/manual/cowboy_app.asciidoc

@@ -36,6 +36,7 @@ Stream handlers:
 
 * link:man:cowboy_stream_h(3)[cowboy_stream_h(3)] - Default stream handler
 * link:man:cowboy_compress_h(3)[cowboy_compress_h(3)] - Compress stream handler
+* link:man:cowboy_decompress_h(3)[cowboy_decompress_h(3)] - Decompress stream handler
 * link:man:cowboy_metrics_h(3)[cowboy_metrics_h(3)] - Metrics stream handler
 * link:man:cowboy_tracer_h(3)[cowboy_tracer_h(3)] - Tracer stream handler
 

doc/src/manual/cowboy_decompress_h.asciidoc

@@ -7,18 +7,26 @@ cowboy_decompress_h - Decompress stream handler
 == Description
 
 The module `cowboy_decompress_h` decompresses request bodies
-automatically when the server supports it. Requests will
+automatically when the server supports it.
-only be decompressed when their compression ratio is lower
+
-than the configured limit. Mismatch of the content and
+The only compression algorithm currently supported is the
-`content-encoding` is rejected with `400 Bad Request`.
+gzip algorithm. Another limitation is that decompression
+is only attempted when gzip is the only content-encoding
+in the request.
+
+This stream handler always adds a field to the Req object
+with the name `content_decoded` which is treated as a
+list of decoded content-encoding values. Currently this
+list may only contain the `<<"gzip">>` binary if content
+was decoded; or be empty otherwise.
 
 == Options
 
 [source,erlang]
 ----
 opts() :: #{
-	decompress_ratio_limit => non_neg_integer(),
+	decompress_enabled => boolean(),
-	decompress_ignore => boolean()
+	decompress_ratio_limit => non_neg_integer()
 }
 ----
 
@@ -28,17 +36,21 @@ The default value is given next to the option name:
 
 decompress_ratio_limit (20)::
 The max ratio of the compressed and decompressed body
-before it is rejected with `413 Payload Too Large`.
+before it is rejected with a `413 Payload Too Large`
+error response.
 +
 This option can be updated at any time using the
 `set_options` stream handler command.
 
-decompress_ignore (false)::
+decompress_enabled (true)::
 
-Whether the handler will be ignored.
+Whether the handler is enabled by default.
 +
-This option can be updated at any time using the
+This option can be updated using the `set_options`
-`set_options` stream handler command.
+stream handler command. This allows disabling
+decompression for the current stream. Attempts
+to enable or disable decompression after starting
+to read the body will be ignored.
 
 == Events
 

src/cowboy_decompress_h.erl

@@ -1,3 +1,18 @@
+%% Copyright (c) 2024, jdamanalo <joshuadavid.agustin@manalo.ph>
+%% Copyright (c) 2024, Loïc Hoguin <essen@ninenines.eu>
+%%
+%% Permission to use, copy, modify, and/or distribute this software for any
+%% purpose with or without fee is hereby granted, provided that the above
+%% copyright notice and this permission notice appear in all copies.
+%%
+%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
 -module(cowboy_decompress_h).
 -behavior(cowboy_stream).
 
@@ -9,21 +24,27 @@
 
 -record(state, {
 	next :: any(),
+	enabled :: boolean(),
 	ratio_limit :: non_neg_integer() | undefined,
-	ignore = false :: boolean(),
 	compress = undefined :: undefined | gzip,
 	inflate = undefined :: undefined | zlib:zstream(),
 	is_reading = false :: boolean(),
-	read_body_buffer = <<>> :: binary(),
+
+	%% We use a list of binaries to avoid doing unnecessary
+	%% memory allocations when inflating. We convert to binary
+	%% when we propagate the data. The data must be reversed
+	%% before converting to binary or inflating: this is done
+	%% via the buffer_to_binary/buffer_to_iovec functions.
+	read_body_buffer = [] :: [binary()],
 	read_body_is_fin = nofin :: nofin | {fin, non_neg_integer()}
 }).
 
 -spec init(cowboy_stream:streamid(), cowboy_req:req(), cowboy:opts())
 	-> {cowboy_stream:commands(), #state{}}.
-init(StreamID, Req, Opts) ->
+init(StreamID, Req0, Opts) ->
+	Enabled = maps:get(decompress_enabled, Opts, true),
 	RatioLimit = maps:get(decompress_ratio_limit, Opts, 20),
-	Ignore = maps:get(decompress_ignore, Opts, false),
+	{Req, State} = check_and_update_req(Req0),
-	State = check_req(Req),
 	Inflate = case State#state.compress of
 		undefined ->
 			undefined;
@@ -33,48 +54,46 @@ init(StreamID, Req, Opts) ->
 			Z
 	end,
 	{Commands, Next} = cowboy_stream:init(StreamID, Req, Opts),
-	fold(Commands, State#state{next=Next, ratio_limit=RatioLimit, ignore=Ignore,
+	fold(Commands, State#state{next=Next, enabled=Enabled,
-		inflate=Inflate}).
+		ratio_limit=RatioLimit, inflate=Inflate}).
 
 -spec data(cowboy_stream:streamid(), cowboy_stream:fin(), cowboy_req:resp_body(), State)
 	-> {cowboy_stream:commands(), State} when State::#state{}.
 data(StreamID, IsFin, Data, State=#state{next=Next0, inflate=undefined}) ->
 	{Commands, Next} = cowboy_stream:data(StreamID, IsFin, Data, Next0),
 	fold(Commands, State#state{next=Next, read_body_is_fin=IsFin});
-data(StreamID, IsFin, Data, State=#state{next=Next0, ignore=true, read_body_buffer=Buffer}) ->
+data(StreamID, IsFin, Data, State=#state{next=Next0, enabled=false, read_body_buffer=Buffer}) ->
 	{Commands, Next} = cowboy_stream:data(StreamID, IsFin,
-		<< Buffer/binary, Data/binary >>, Next0),
+		buffer_to_binary([Data|Buffer]), Next0),
 	fold(Commands, State#state{next=Next, read_body_is_fin=IsFin});
 data(StreamID, IsFin, Data, State0=#state{next=Next0, ratio_limit=RatioLimit,
-		inflate=Z, is_reading=true, read_body_buffer=Buffer0}) ->
+		inflate=Z, is_reading=true, read_body_buffer=Buffer}) ->
-	Buffer = << Buffer0/binary, Data/binary >>,
+	case inflate(Z, RatioLimit, buffer_to_iovec([Data|Buffer])) of
-	case inflate(Z, RatioLimit, Buffer) of
+		{error, ErrorType} ->
-		{error, Type} ->
+			zlib:close(Z),
-			Status = case Type of
+			Status = case ErrorType of
-				data -> 400;
+				data_error -> 400;
-				size -> 413
+				size_error -> 413
 			end,
 			Commands = [
 				{error_response, Status, #{<<"content-length">> => <<"0">>}, <<>>},
 				stop
 			],
-			fold(Commands, State0#state{inflate=undefined});
+			fold(Commands, State0#state{inflate=undefined, read_body_buffer=[]});
 		{ok, Inflated} ->
 			State = case IsFin of
 				nofin ->
 					State0;
 				fin ->
-					zlib:inflateEnd(Z),
 					zlib:close(Z),
 					State0#state{inflate=undefined}
 			end,
 			{Commands, Next} = cowboy_stream:data(StreamID, IsFin, Inflated, Next0),
-			fold(Commands, State#state{next=Next, read_body_buffer= <<>>,
+			fold(Commands, State#state{next=Next, read_body_buffer=[],
 				read_body_is_fin=IsFin})
 	end;
-data(_, IsFin, Data, State=#state{read_body_buffer=Buffer0}) ->
+data(_, IsFin, Data, State=#state{read_body_buffer=Buffer}) ->
-	Buffer = << Buffer0/binary, Data/binary >>,
+	{[], State#state{read_body_buffer=[Data|Buffer], read_body_is_fin=IsFin}}.
-	{[], State#state{read_body_buffer=Buffer, read_body_is_fin=IsFin}}.
 
 -spec info(cowboy_stream:streamid(), any(), State)
 	-> {cowboy_stream:commands(), State} when State::#state{}.
@@ -86,12 +105,19 @@ info(StreamID, Info={CommandTag, _, _, _, _}, State=#state{next=Next0, read_body
 	{Commands0, Next1} = cowboy_stream:info(StreamID, Info, Next0),
 	{Commands, Next} = data(StreamID, IsFin, <<>>, State#state{next=Next1, is_reading=true}),
 	fold(Commands ++ Commands0, Next);
-info(StreamID, Info={set_options, Opts}, State=#state{next=Next0,
+info(StreamID, Info={set_options, Opts}, State0=#state{next=Next0,
-		ignore=Ignore0, ratio_limit=RatioLimit0}) ->
+		enabled=Enabled0, ratio_limit=RatioLimit0, is_reading=IsReading}) ->
-	Ignore = maps:get(decompress_ignore, Opts, Ignore0),
+	Enabled = maps:get(decompress_enabled, Opts, Enabled0),
 	RatioLimit = maps:get(decompress_ratio_limit, Opts, RatioLimit0),
 	{Commands, Next} = cowboy_stream:info(StreamID, Info, Next0),
-	fold(Commands, State#state{next=Next, ignore=Ignore, ratio_limit=RatioLimit});
+	%% We can't change the enabled setting after we start reading,
+	%% otherwise the data becomes garbage. Changing the setting
+	%% is not treated as an error, it is just ignored.
+	State = case IsReading of
+		true -> State0;
+		false -> State0#state{enabled=Enabled}
+	end,
+	fold(Commands, State#state{next=Next, ratio_limit=RatioLimit});
 info(StreamID, Info, State=#state{next=Next0}) ->
 	{Commands, Next} = cowboy_stream:info(StreamID, Info, Next0),
 	fold(Commands, State#state{next=Next}).
@@ -112,31 +138,49 @@ early_error(StreamID, Reason, PartialReq, Resp, Opts) ->
 
 %% Internal.
 
-check_req(Req) ->
+%% Check whether the request needs content decoding, and if it does
+%% whether it fits our criteria for decoding. We also update the
+%% Req to indicate whether content was decoded.
+%%
+%% We always set the content_decoded value in the Req because it
+%% indicates whether content decoding was attempted.
+%%
+%% A malformed content-encoding header results in no decoding.
+check_and_update_req(Req=#{headers := Headers}) ->
+	ContentDecoded = maps:get(content_decoded, Req, []),
 	try cowboy_req:parse_header(<<"content-encoding">>, Req) of
-		undefined ->
+		%% We only automatically decompress when gzip is the only
-			#state{compress=undefined};
+		%% encoding used. Since it's the only encoding used, we
-		Encodings ->
+		%% can remove the header entirely before passing the Req
-			case [E || E=(<<"gzip">>) <- Encodings] of
+		%% forward.
-				[] ->
+		[<<"gzip">>] ->
-					#state{compress=undefined};
+			{Req#{
+				headers => maps:remove(<<"content-encoding">>, Headers),
+				content_decoded => [<<"gzip">>|ContentDecoded]
+			}, #state{compress=gzip}};
 		_ ->
-					#state{compress=gzip}
+			{Req#{content_decoded => ContentDecoded},
-			end
+				#state{compress=undefined}}
-	catch
+	catch _:_ ->
-		_:_ ->
+		{Req#{content_decoded => ContentDecoded},
-			#state{compress=undefined}
+			#state{compress=undefined}}
 	end.
 
+buffer_to_iovec(Buffer) ->
+	lists:reverse(Buffer).
+
+buffer_to_binary(Buffer) ->
+	iolist_to_binary(lists:reverse(Buffer)).
+
 fold(Commands, State) ->
 	fold(Commands, State, []).
 
 fold([], State, Acc) ->
 	{lists:reverse(Acc), State};
-fold([{response, Status, Headers0, Body}|Tail], State=#state{ignore=false}, Acc) ->
+fold([{response, Status, Headers0, Body}|Tail], State=#state{enabled=true}, Acc) ->
 	Headers = add_accept_encoding(Headers0),
 	fold(Tail, State, [{response, Status, Headers, Body}|Acc]);
-fold([{headers, Status, Headers0} | Tail], State=#state{ignore=false}, Acc) ->
+fold([{headers, Status, Headers0} | Tail], State=#state{enabled=true}, Acc) ->
 	Headers = add_accept_encoding(Headers0),
 	fold(Tail, State, [{headers, Status, Headers}|Acc]);
 fold([Command|Tail], State, Acc) ->
@@ -146,7 +190,7 @@ add_accept_encoding(Headers=#{<<"accept-encoding">> := AcceptEncoding}) ->
 	try cow_http_hd:parse_accept_encoding(iolist_to_binary(AcceptEncoding)) of
 		List ->
 			case lists:keyfind(<<"gzip">>, 1, List) of
-				%% gzip is excluded but this handler is not ignored; we replace.
+				%% gzip is excluded but this handler is enabled; we replace.
 				{_, 0} ->
 					Replaced = lists:keyreplace(<<"gzip">>, 1, List, {<<"gzip">>, 1000}),
 					Codings = build_accept_encoding(Replaced),
@@ -167,18 +211,20 @@ add_accept_encoding(Headers=#{<<"accept-encoding">> := AcceptEncoding}) ->
 					end
 			end
 	catch _:_ ->
+		%% The accept-encoding header is invalid. Probably empty. We replace it with ours.
 		Headers#{<<"accept-encoding">> => <<"gzip">>}
 	end;
 add_accept_encoding(Headers) ->
 	Headers#{<<"accept-encoding">> => <<"gzip">>}.
 
-%% From cowlib, maybe expose?
+%% @todo From cowlib, maybe expose?
 qvalue_to_iodata(0) -> <<"0">>;
 qvalue_to_iodata(Q) when Q < 10 -> [<<"0.00">>, integer_to_binary(Q)];
 qvalue_to_iodata(Q) when Q < 100 -> [<<"0.0">>, integer_to_binary(Q)];
 qvalue_to_iodata(Q) when Q < 1000 -> [<<"0.">>, integer_to_binary(Q)];
 qvalue_to_iodata(1000) -> <<"1">>.
 
+%% @todo Should be added to Cowlib.
 build_accept_encoding([{ContentCoding, Q}|Tail]) ->
 	Weight = iolist_to_binary(qvalue_to_iodata(Q)),
 	Acc = <<ContentCoding/binary, ";q=", Weight/binary>>,
@@ -195,20 +241,14 @@ inflate(Z, RatioLimit, Data) ->
 	try
 		{Status, Output} = zlib:safeInflate(Z, Data),
 		Size = iolist_size(Output),
-		do_inflate(Z, Size, byte_size(Data) * RatioLimit, Status, [Output])
+		do_inflate(Z, Size, iolist_size(Data) * RatioLimit, Status, [Output])
 	catch
 		error:data_error ->
-			zlib:close(Z),
+			{error, data_error}
-			{error, data}
 	end.
 
-do_inflate(Z, Size, Limit, Status, _) when Size > Limit ->
+do_inflate(_, Size, Limit, _, _) when Size > Limit ->
-	case Status of
+	{error, size_error};
-		continue -> ok;
-		finished -> zlib:inflateEnd(Z)
-	end,
-	zlib:close(Z),
-	{error, size};
 do_inflate(Z, Size0, Limit, continue, Acc) ->
 	{Status, Output} = zlib:safeInflate(Z, []),
 	Size = Size0 + iolist_size(Output),

test/decompress_SUITE.erl

@@ -1,3 +1,17 @@
+%% Copyright (c) 2024, jdamanalo <joshuadavid.agustin@manalo.ph>
+%%
+%% Permission to use, copy, modify, and/or distribute this software for any
+%% purpose with or without fee is hereby granted, provided that the above
+%% copyright notice and this permission notice appear in all copies.
+%%
+%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
 -module(decompress_SUITE).
 -compile(export_all).
 -compile(nowarn_export_all).
@@ -50,14 +64,8 @@ init_compress_opts(Config) ->
 
 init_routes(_) ->
 	[{'_', [
-		{"/echo/:what", decompress_h, []},
+		{"/echo/:what", decompress_h, echo},
-		{"/header", decompress_h, header_command},
+		{"/test/:what", decompress_h, test}
-		{"/invalid-header", decompress_h, invalid_header},
-		{"/accept-identity", decompress_h, accept_identity},
-		{"/reject-explicit-header", decompress_h, reject_explicit_header},
-		{"/reject-implicit-header", decompress_h, reject_implicit_header},
-		{"/accept-explicit-header", decompress_h, accept_explicit_header},
-		{"/accept-implicit-header", decompress_h, accept_implicit_header}
 	]}].
 
 %% Internal.
@@ -92,49 +100,91 @@ do_create_gzip_bomb(Z, N) ->
 %% Tests.
 
 content_encoding_none(Config) ->
-	doc("Send no content-encoding; get echo."),
+	doc("Requests without content-encoding are processed normally."),
 	Body = <<"test">>,
-	{200, _, Body} = do_post("/echo/normal",
+	{200, _, Body} = do_post("/echo/normal", [], Body, Config),
-		[{<<"content-encoding">>, <<";">>}], Body, Config),
+	%% The content-encoding header would be propagated,
+	%% but there was no content-encoding header to propagate.
+	{200, _, <<"undefined">>} = do_post("/test/content-encoding", [], Body, Config),
+	%% The content_decoded list is empty.
+	{200, _, <<"[]">>} = do_post("/test/content-decoded", [], Body, Config),
 	ok.
 
 content_encoding_malformed(Config) ->
-	doc("Send malformed content-encoding; get echo."),
+	doc("Requests with a malformed content-encoding are processed "
+		"as if no content-encoding was sent."),
 	Body = <<"test">>,
 	{200, _, Body} = do_post("/echo/normal",
 		[{<<"content-encoding">>, <<";">>}], Body, Config),
+	%% The content-encoding header is propagated.
+	{200, _, <<";">>} = do_post("/test/content-encoding",
+		[{<<"content-encoding">>, <<";">>}], Body, Config),
+	%% The content_decoded list is empty.
+	{200, _, <<"[]">>} = do_post("/test/content-decoded",
+		[{<<"content-encoding">>, <<";">>}], Body, Config),
 	ok.
 
 content_encoding_not_supported(Config) ->
-	doc("Send content-encoding: compress (unsupported by Cowboy); get echo."),
+	doc("Requests with an unsupported content-encoding are processed "
+		"as if no content-encoding was sent."),
 	Body = <<"test">>,
 	{200, _, Body} = do_post("/echo/normal",
 		[{<<"content-encoding">>, <<"compress">>}], Body, Config),
+	%% The content-encoding header is propagated.
+	{200, _, <<"compress">>} = do_post("/test/content-encoding",
+		[{<<"content-encoding">>, <<"compress">>}], Body, Config),
+	%% The content_decoded list is empty.
+	{200, _, <<"[]">>} = do_post("/test/content-decoded",
+		[{<<"content-encoding">>, <<"compress">>}], Body, Config),
 	ok.
 
-content_encoding_wrong(Config) ->
+content_encoding_multiple(Config) ->
-	doc("Send content-encoding and unencoded body; get 400."),
+	doc("Requests with multiple content-encoding values are processed "
+		"as if no content-encoding was sent."),
+	Body = <<"test">>,
+	{200, _, Body} = do_post("/echo/normal",
+		[{<<"content-encoding">>, <<"gzip, compress">>}], Body, Config),
+	%% The content-encoding header is propagated.
+	{200, _, <<"gzip, compress">>} = do_post("/test/content-encoding",
+		[{<<"content-encoding">>, <<"gzip, compress">>}], Body, Config),
+	%% The content_decoded list is empty.
+	{200, _, <<"[]">>} = do_post("/test/content-decoded",
+		[{<<"content-encoding">>, <<"gzip, compress">>}], Body, Config),
+	ok.
+
+decompress(Config) ->
+	doc("Requests with content-encoding set to gzip and gzipped data "
+		"are transparently decompressed."),
+	Data = <<"test">>,
+	Body = zlib:gzip(Data),
+	{200, _, Data} = do_post("/echo/normal",
+		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
+	%% The content-encoding header is NOT propagated.
+	{200, _, <<"undefined">>} = do_post("/test/content-encoding",
+		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
+	%% The content_decoded list contains <<"gzip">>.
+	{200, _, <<"[<<\"gzip\">>]">>} = do_post("/test/content-decoded",
+		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
+	ok.
+
+decompress_error(Config) ->
+	doc("Requests with content-encoding set to gzip but the data "
+		"cannot be decoded are rejected with a 400 Bad Request error."),
 	Body = <<"test">>,
 	{400, _, _} = do_post("/echo/normal",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
 	ok.
 
-decompress(Config) ->
-	doc("Send content-encoding and encoded body; get decompressed response."),
-	Data = <<"test">>,
-	Body = zlib:gzip(Data),
-	{200, _, Data} = do_post("/echo/normal",
-		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
-	ok.
-
 decompress_stream(Config) ->
-	doc("Stream encoded body; get decompressed response."),
+	doc("Requests with content-encoding set to gzip and gzipped data "
+		"are transparently decompressed, even when the data is streamed."),
 	%% Handler read length 1KB. Compressing 3KB should be enough to trigger more.
 	Data = crypto:strong_rand_bytes(3000),
 	Body = zlib:gzip(Data),
 	Size = byte_size(Body),
 	ConnPid = gun_open(Config),
-	Ref = gun:post(ConnPid, "/echo/normal", [{<<"content-encoding">>, <<"gzip">>}]),
+	Ref = gun:post(ConnPid, "/echo/normal",
+		[{<<"content-encoding">>, <<"gzip">>}]),
 	gun:data(ConnPid, Ref, nofin, binary:part(Body, 0, Size div 2)),
 	timer:sleep(1000),
 	gun:data(ConnPid, Ref, fin, binary:part(Body, Size div 2, Size div 2 + Size rem 2)),
@@ -144,12 +194,23 @@ decompress_stream(Config) ->
 		fin -> {ok, <<>>}
 	end,
 	gun:close(ConnPid),
-	{200, _, Data} = do_post("/echo/normal",
+	%% The content-encoding header is NOT propagated.
-		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
+	ConnPid2 = gun_open(Config),
-	ok.
+	Ref2 = gun:post(ConnPid2, "/test/content-encoding",
+		[{<<"content-encoding">>, <<"gzip">>}]),
+	{response, nofin, 200, _} = gun:await(ConnPid2, Ref2),
+	{ok, <<"undefined">>} = gun:await_body(ConnPid2, Ref2),
+	gun:close(ConnPid2),
+	%% The content_decoded list contains <<"gzip">>.
+	ConnPid3 = gun_open(Config),
+	Ref3 = gun:post(ConnPid3, "/test/content-decoded",
+		[{<<"content-encoding">>, <<"gzip">>}]),
+	{response, nofin, 200, _} = gun:await(ConnPid3, Ref3),
+	{ok, <<"[<<\"gzip\">>]">>} = gun:await_body(ConnPid3, Ref3),
+	gun:close(ConnPid3).
 
-opts_decompress_ignore(Config0) ->
+opts_decompress_enabled_false(Config0) ->
-	doc("Confirm that the decompress_ignore option can be set."),
+	doc("Confirm that the decompress_enabled option can be set."),
 	Fun = case config(ref, Config0) of
 		HTTPS when HTTPS =:= https_compress; HTTPS =:= https -> init_https;
 		H2 when H2 =:= h2_compress; H2 =:= h2 -> init_http2;
@@ -158,28 +219,75 @@ opts_decompress_ignore(Config0) ->
 	Config = cowboy_test:Fun(?FUNCTION_NAME, #{
 		env => #{dispatch => cowboy_router:compile(init_routes(Config0))},
 		stream_handlers => [cowboy_decompress_h, cowboy_stream_h],
-		decompress_ignore => true
+		decompress_enabled => false
 	}, Config0),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
 	try
-		{200, _, Body} = do_post("/echo/normal",
+		{200, Headers, Body} = do_post("/echo/normal",
-			[{<<"content-encoding">>, <<"gzip">>}], Body, Config)
+			[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
+		%% We do not set accept-encoding when we are disabled.
+		false = lists:keyfind(<<"accept-encoding">>, 1, Headers)
 	after
 		cowboy:stop_listener(?FUNCTION_NAME)
 	end.
 
-set_options_decompress_ignore(Config) ->
+set_options_decompress_enabled_false(Config) ->
-	doc("Confirm that the decompress_ignore option can be dynamically
+	doc("Confirm that the decompress_enabled option can be dynamically "
-		set to true and the data received is not decompressed."),
+		"set to false and the data received is not decompressed."),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
-	{200, _, Body} = do_post("/echo/decompress_ignore",
+	{200, Headers, Body} = do_post("/echo/decompress_disable",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
+	%% We do not set accept-encoding when we are disabled.
+	false = lists:keyfind(<<"accept-encoding">>, 1, Headers),
 	ok.
 
+set_options_decompress_disable_in_the_middle(Config) ->
+	doc("Confirm that setting the decompress_enabled option dynamically "
+		"to false after starting to read the body does not disable decompression "
+		"and the data received is decompressed."),
+	Data = rand:bytes(1000000),
+	Body = zlib:gzip(Data),
+	%% Since we were not ignoring before starting to read,
+	%% we receive the entire body decompressed.
+	{200, Headers, Data} = do_post("/test/disable-in-the-middle",
+		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
+	%% We do set accept-encoding when we are enabled,
+	%% even if an attempt to disable in the middle is ignored.
+	{_, _} = lists:keyfind(<<"accept-encoding">>, 1, Headers),
+	ok.
+
+set_options_decompress_enable_in_the_middle(Config0) ->
+	doc("Confirm that setting the decompress_enabled option dynamically "
+		"to true after starting to read the body does not enable decompression "
+		"and the data received is not decompressed."),
+	Fun = case config(ref, Config0) of
+		HTTPS when HTTPS =:= https_compress; HTTPS =:= https -> init_https;
+		H2 when H2 =:= h2_compress; H2 =:= h2 -> init_http2;
+		_ -> init_http
+	end,
+	Config = cowboy_test:Fun(?FUNCTION_NAME, #{
+		env => #{dispatch => cowboy_router:compile(init_routes(Config0))},
+		stream_handlers => [cowboy_decompress_h, cowboy_stream_h],
+		decompress_enabled => false
+	}, Config0),
+	Data = rand:bytes(1000000),
+	Body = zlib:gzip(Data),
+	try
+		%% Since we were ignoring before starting to read,
+		%% we receive the entire body compressed.
+		{200, Headers, Body} = do_post("/test/enable-in-the-middle",
+			[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
+		%% We do not set accept-encoding when we are disabled,
+		%% even if an attempt to enable in the middle is ignored.
+		false = lists:keyfind(<<"accept-encoding">>, 1, Headers)
+	after
+		cowboy:stop_listener(?FUNCTION_NAME)
+	end.
+
 opts_decompress_ratio_limit(Config0) ->
-	doc("Confirm that the decompress_ignore option can be set"),
+	doc("Confirm that the decompress_ratio_limit option can be set."),
 	Fun = case config(ref, Config0) of
 		HTTPS when HTTPS =:= https_compress; HTTPS =:= https -> init_https;
 		H2 when H2 =:= h2_compress; H2 =:= h2 -> init_http2;
@@ -190,7 +298,8 @@ opts_decompress_ratio_limit(Config0) ->
 		stream_handlers => [cowboy_decompress_h, cowboy_stream_h],
 		decompress_ratio_limit => 1
 	}, Config0),
-	%% Data must be big enough for compression to be effective, so that ratio_limit=1 will fail.
+	%% Data must be big enough for compression to be effective,
+	%% so that ratio_limit=1 will fail.
 	Data = <<0:800>>,
 	Body = zlib:gzip(Data),
 	try
@@ -202,7 +311,8 @@ opts_decompress_ratio_limit(Config0) ->
 
 set_options_decompress_ratio_limit(Config) ->
 	doc("Confirm that the decompress_ratio_limit option can be dynamically set."),
-	%% Data must be big enough for compression to be effective, so that ratio_limit=1 will fail.
+	%% Data must be big enough for compression to be effective,
+	%% so that ratio_limit=1 will fail.
 	Data = <<0:800>>,
 	Body = zlib:gzip(Data),
 	{413, _, _} = do_post("/echo/decompress_ratio_limit",
@@ -210,19 +320,16 @@ set_options_decompress_ratio_limit(Config) ->
 	ok.
 
 gzip_bomb(Config) ->
-	doc("Send body compressed with suspiciously large ratio; get 413."),
+	doc("Confirm that requests are rejected with a 413 Payload Too Large "
+		"error when the ratio limit is exceeded."),
 	Body = create_gzip_bomb(),
 	{413, _, _} = do_post("/echo/normal",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
 	ok.
 
-%% RFC 9110. Section 12.5.3. 3. When sent by a server in a response,
-%% Accept-Encoding provides information about which content codings are
-%% preferred in the content of a subsequent request to the same resource.
-%%
-%% Set or add gzip
 set_accept_encoding_response(Config) ->
-	doc("Header accept-encoding must be set on valid response command."),
+	doc("Header accept-encoding must be set on valid response command. "
+		"(RFC9110 12.5.3)"),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
 	{200, Headers, Data} = do_post("/echo/normal",
@@ -231,97 +338,79 @@ set_accept_encoding_response(Config) ->
 	ok.
 
 set_accept_encoding_header(Config) ->
-	doc("Header accept-encoding must be set on valid header command."),
+	doc("Header accept-encoding must be set on valid header command. "
+		"(RFC9110 12.5.3)"),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
-	{200, Headers, Data} = do_post("/header",
+	{200, Headers, Data} = do_post("/test/header-command",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
 	{_, <<"gzip">>} = lists:keyfind(<<"accept-encoding">>, 1, Headers),
 	ok.
 
 add_accept_encoding_header_valid(Config) ->
-	doc("Header accept-encoding must be added on valid accept-encoding."),
+	doc("Supported content codings must be added to the accept-encoding "
+		"header if it already exists. (RFC9110 12.5.3)"),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
-	{200, Headers, Data} = do_post("/accept-identity",
+	{200, Headers, Data} = do_post("/test/accept-identity",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
 	{_, <<"identity, gzip">>} = lists:keyfind(<<"accept-encoding">>, 1, Headers),
 	ok.
 
 override_accept_encoding_header_invalid(Config) ->
-	doc("Header accept-encoding must override invalid accept-encoding."),
+	doc("When the stream handler cannot parse the accept-encoding header "
+		"found in the response, it overrides it."),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
-	{200, Headers, Data} = do_post("/invalid-header",
+	{200, Headers, Data} = do_post("/test/invalid-header",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
 	{_, <<"gzip">>} = lists:keyfind(<<"accept-encoding">>, 1, Headers),
 	ok.
 
-%% RFC 9110. Section 12.5.3. 10.3. If the representation's content coding is
-%% one of the content codings listed in the Accept-Encoding field value, then
-%% it is acceptable unless it is accompanied by a qvalue of 0.
-%%
-%% gzip must not have a qvalue of 0 when the handler is used. Set to 1.
 override_accept_encoding_excluded(Config) ->
-	doc("Header accept-encoding must override when explicitly excluded."),
+	doc("The stream handler must ensure that the content encodings "
+		"it supports are not marked as unsupported in response headers. "
+		"The stream handler enables gzip when explicitly excluded. "
+		"(RFC9110 12.5.3)"),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
-	{200, Headers, Data} = do_post("/reject-explicit-header",
+	{200, Headers, Data} = do_post("/test/reject-explicit-header",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
 	{_, <<"identity;q=1, gzip;q=1">>} = lists:keyfind(<<"accept-encoding">>, 1, Headers),
 	ok.
 
-%% RFC 9110. Section 12.5.3. 10.2. If the representation has no content coding,
+%% *;q=0 will reject codings that are not listed. Supported codings
-%% then it is acceptable by default unless specifically excluded by the
+%% must always be enabled when the handler is used.
-%% Accept-Encoding field stating either "identity;q=0" or "*;q=0" wihout a more
-%% specific entry for "identity".
-%%
-%% *;q=0 will reject codings that are not listed. Specific entry gzip must
-%% always be listed when the handler is used. Add gzip.
 add_accept_encoding_excluded(Config) ->
-	doc("Header accept-encoding must added when implicitly excluded."),
+	doc("The stream handler must ensure that the content encodings "
+		"it supports are not marked as unsupported in response headers. "
+		"The stream handler enables gzip when implicitly excluded (*;q=0). "
+		"(RFC9110 12.5.3)"),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
-	{200, Headers, Data} = do_post("/reject-implicit-header",
+	{200, Headers, Data} = do_post("/test/reject-implicit-header",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
 	{_, <<"gzip;q=1, identity;q=1, *;q=0">>} = lists:keyfind(<<"accept-encoding">>, 1, Headers),
 	ok.
 
 no_override_accept_coding_set_explicit(Config) ->
-	doc("Confirm that accept-encoding is not overridden when explicitly set."),
+	doc("Confirm that accept-encoding is not overridden when the "
+		"content encodings it supports are explicitly set. "
+		"(RFC9110 12.5.3)"),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
-	{200, Headers, Data} = do_post("/accept-explicit-header",
+	{200, Headers, Data} = do_post("/test/accept-explicit-header",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
 	{_, <<"identity, gzip;q=0.5">>} = lists:keyfind(<<"accept-encoding">>, 1, Headers),
 	ok.
 
 no_override_accept_coding_set_implicit(Config) ->
-	doc("Confirm that accept-encoding is not overridden when implicitly set."),
+	doc("Confirm that accept-encoding is not overridden when the "
+		"content encodings it supports are implicitly set. "
+		"(RFC9110 12.5.3)"),
 	Data = <<"test">>,
 	Body = zlib:gzip(Data),
-	{200, Headers, Data} = do_post("/accept-implicit-header",
+	{200, Headers, Data} = do_post("/test/accept-implicit-header",
 		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
 	{_, <<"identity, *;q=0.5">>} = lists:keyfind(<<"accept-encoding">>, 1, Headers),
 	ok.
-
-%% RFC 9110. Section 12.5.3. 10.1. If no Accept-Encoding header field is in the
-%% request, any content coding is considered acceptable by the user agent.
-%%
-%% Don't add anything on error or when that handler is not used.
-no_set_accept_encoding(Config) ->
-	doc("No header accept-encoding on invalid responses."),
-	Body = <<"test">>,
-	{400, Headers, _} = do_post("/echo/normal",
-		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
-	false = lists:keyfind(<<"accept-encoding">>, 1, Headers),
-	ok.
-
-no_set_accept_encoding_ignore(Config) ->
-	doc("Confirm that no accept-encoding is set when stream is ignored."),
-	Data = <<"test">>,
-	Body = zlib:gzip(Data),
-	{200, Headers, Body} = do_post("/echo/decompress_ignore",
-		[{<<"content-encoding">>, <<"gzip">>}], Body, Config),
-	false = lists:keyfind(<<"accept-encoding">>, 1, Headers),
-	ok.

test/handlers/decompress_h.erl

@@ -5,10 +5,10 @@
 
 -export([init/2]).
 
-init(Req0, State=[]) ->
+init(Req0, State=echo) ->
 	case cowboy_req:binding(what, Req0) of
-		<<"decompress_ignore">> ->
+		<<"decompress_disable">> ->
-			cowboy_req:cast({set_options, #{decompress_ignore => true}}, Req0);
+			cowboy_req:cast({set_options, #{decompress_enabled => false}}, Req0);
 		<<"decompress_ratio_limit">> ->
 			cowboy_req:cast({set_options, #{decompress_ratio_limit => 0.5}}, Req0);
 		<<"normal">> -> ok
@@ -16,47 +16,63 @@ init(Req0, State=[]) ->
 	{ok, Body, Req1} = read_body(Req0),
 	Req = cowboy_req:reply(200, #{}, Body, Req1),
 	{ok, Req, State};
-
+init(Req0, State=test) ->
-init(Req0, State=header_command) ->
+	Req = test(Req0, cowboy_req:binding(what, Req0)),
-	{ok, Body, Req1} = read_body(Req0),
-	Req2 = cowboy_req:stream_reply(200, #{}, Req1),
-	Req = cowboy_req:stream_body(Body, fin, Req2),
-	{ok, Req, State};
-
-init(Req0, State=accept_identity) ->
-	{ok, Body, Req1} = read_body(Req0),
-	Req = cowboy_req:reply(200, #{<<"accept-encoding">> => <<"identity">>}, Body, Req1),
-	{ok, Req, State};
-
-init(Req0, State=invalid_header) ->
-	{ok, Body, Req1} = read_body(Req0),
-	Req = cowboy_req:reply(200, #{<<"accept-encoding">> => <<";">>}, Body, Req1),
-	{ok, Req, State};
-
-init(Req0, State=reject_explicit_header) ->
-	{ok, Body, Req1} = read_body(Req0),
-	Req = cowboy_req:reply(200, #{<<"accept-encoding">> => <<"identity, gzip;q=0">>},
-		Body, Req1),
-	{ok, Req, State};
-
-init(Req0, State=reject_implicit_header) ->
-	{ok, Body, Req1} = read_body(Req0),
-	Req = cowboy_req:reply(200, #{<<"accept-encoding">> => <<"identity, *;q=0">>},
-		Body, Req1),
-	{ok, Req, State};
-
-init(Req0, State=accept_explicit_header) ->
-	{ok, Body, Req1} = read_body(Req0),
-	Req = cowboy_req:reply(200, #{<<"accept-encoding">> => <<"identity, gzip;q=0.5">>},
-		Body, Req1),
-	{ok, Req, State};
-
-init(Req0, State=accept_implicit_header) ->
-	{ok, Body, Req1} = read_body(Req0),
-	Req = cowboy_req:reply(200, #{<<"accept-encoding">> => <<"identity, *;q=0.5">>},
-		Body, Req1),
 	{ok, Req, State}.
 
+test(Req, <<"content-encoding">>) ->
+	cowboy_req:reply(200, #{},
+		cowboy_req:header(<<"content-encoding">>, Req, <<"undefined">>),
+		Req);
+test(Req, <<"content-decoded">>) ->
+	cowboy_req:reply(200, #{},
+		io_lib:format("~0p", [maps:get(content_decoded, Req, undefined)]),
+		Req);
+test(Req0, <<"disable-in-the-middle">>) ->
+	{Status, Data, Req1} = cowboy_req:read_body(Req0, #{length => 1000}),
+	cowboy_req:cast({set_options, #{decompress_enabled => false}}, Req1),
+	{ok, Body, Req} = do_read_body(Status, Req1, Data),
+	cowboy_req:reply(200, #{}, Body, Req);
+test(Req0, <<"enable-in-the-middle">>) ->
+	{Status, Data, Req1} = cowboy_req:read_body(Req0, #{length => 1000}),
+	cowboy_req:cast({set_options, #{decompress_enabled => true}}, Req1),
+	{ok, Body, Req} = do_read_body(Status, Req1, Data),
+	cowboy_req:reply(200, #{}, Body, Req);
+test(Req0, <<"header-command">>) ->
+	{ok, Body, Req1} = read_body(Req0),
+	Req = cowboy_req:stream_reply(200, #{}, Req1),
+	cowboy_req:stream_body(Body, fin, Req);
+test(Req0, <<"accept-identity">>) ->
+	{ok, Body, Req} = read_body(Req0),
+	cowboy_req:reply(200,
+		#{<<"accept-encoding">> => <<"identity">>},
+		Body, Req);
+test(Req0, <<"invalid-header">>) ->
+	{ok, Body, Req} = read_body(Req0),
+	cowboy_req:reply(200,
+		#{<<"accept-encoding">> => <<";">>},
+		Body, Req);
+test(Req0, <<"reject-explicit-header">>) ->
+	{ok, Body, Req} = read_body(Req0),
+	cowboy_req:reply(200,
+		#{<<"accept-encoding">> => <<"identity, gzip;q=0">>},
+		Body, Req);
+test(Req0, <<"reject-implicit-header">>) ->
+	{ok, Body, Req} = read_body(Req0),
+	cowboy_req:reply(200,
+		#{<<"accept-encoding">> => <<"identity, *;q=0">>},
+		Body, Req);
+test(Req0, <<"accept-explicit-header">>) ->
+	{ok, Body, Req} = read_body(Req0),
+	cowboy_req:reply(200,
+		#{<<"accept-encoding">> => <<"identity, gzip;q=0.5">>},
+		Body, Req);
+test(Req0, <<"accept-implicit-header">>) ->
+	{ok, Body, Req} = read_body(Req0),
+	cowboy_req:reply(200,
+		#{<<"accept-encoding">> => <<"identity, *;q=0.5">>},
+		Body, Req).
+
 read_body(Req0) ->
 	{Status, Data, Req} = cowboy_req:read_body(Req0, #{length => 1000}),
 	do_read_body(Status, Req, Data).