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.

1 files changed, 57 insertions, 41 deletions

diff --git a/test/handlers/decompress_h.erl b/test/handlers/decompress_h.erl
index 346200b..deb6de0 100644
--- a/test/handlers/decompress_h.erl
+++ b/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">> ->
-			cowboy_req:cast({set_options, #{decompress_ignore => true}}, Req0);
+		<<"decompress_disable">> ->
+			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
@@ -16,46 +16,62 @@ init(Req0, State=[]) ->
 	{ok, Body, Req1} = read_body(Req0),
 	Req = cowboy_req:reply(200, #{}, Body, Req1),
 	{ok, Req, State};
+init(Req0, State=test) ->
+	Req = test(Req0, cowboy_req:binding(what, Req0)),
+	{ok, Req, State}.
 
-init(Req0, State=header_command) ->
-	{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) ->
+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:reply(200, #{<<"accept-encoding">> => <<"identity, *;q=0.5">>},
-		Body, Req1),
-	{ok, Req, State}.
+	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}),