aboutsummaryrefslogtreecommitdiffstats
path: root/src/cowboy_http_protocol.erl
blob: c5a6f7f8a74f62dd6bb3f2299a02d76b076b76a5 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
%% Copyright (c) 2011, Loïc Hoguin <[email protected]>
%% Copyright (c) 2011, Anthony Ramine <[email protected]>
%%
%% 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.

%% @doc HTTP protocol handler.
%%
%% The available options are:
%% <dl>
%%  <dt>dispatch</dt><dd>The dispatch list for this protocol.</dd>
%%  <dt>max_empty_lines</dt><dd>Max number of empty lines before a request.
%%   Defaults to 5.</dd>
%%  <dt>timeout</dt><dd>Time in milliseconds before an idle
%%   connection is closed. Defaults to 5000 milliseconds.</dd>
%%  <dt>urldecode</dt><dd>Function and options argument to use when decoding
%%   URL encoded strings. Defaults to `{fun cowboy_http:urldecode/2, crash}'.
%%   </dd>
%% </dl>
%%
%% Note that there is no need to monitor these processes when using Cowboy as
%% an application as it already supervises them under the listener supervisor.
%%
%% @see cowboy_dispatcher
%% @see cowboy_http_handler
-module(cowboy_http_protocol).
-behaviour(cowboy_protocol).

-export([start_link/4]). %% API.
-export([init/4, parse_request/1, handler_loop/3]). %% FSM.

-include("http.hrl").
-include_lib("eunit/include/eunit.hrl").

-record(state, {
	listener :: pid(),
	socket :: inet:socket(),
	transport :: module(),
	dispatch :: cowboy_dispatcher:dispatch_rules(),
	handler :: {module(), any()},
	onrequest :: undefined | fun((#http_req{}) -> #http_req{}),
	urldecode :: {fun((binary(), T) -> binary()), T},
	req_empty_lines = 0 :: integer(),
	max_empty_lines :: integer(),
	req_keepalive = 1 :: integer(),
	max_keepalive :: integer(),
	max_line_length :: integer(),
	timeout :: timeout(),
	buffer = <<>> :: binary(),
	hibernate = false :: boolean(),
	loop_timeout = infinity :: timeout(),
	loop_timeout_ref :: undefined | reference()
}).

%% API.

%% @doc Start an HTTP protocol process.
-spec start_link(pid(), inet:socket(), module(), any()) -> {ok, pid()}.
start_link(ListenerPid, Socket, Transport, Opts) ->
	Pid = spawn_link(?MODULE, init, [ListenerPid, Socket, Transport, Opts]),
	{ok, Pid}.

%% FSM.

%% @private
-spec init(pid(), inet:socket(), module(), any()) -> ok.
init(ListenerPid, Socket, Transport, Opts) ->
	Dispatch = proplists:get_value(dispatch, Opts, []),
	MaxEmptyLines = proplists:get_value(max_empty_lines, Opts, 5),
	MaxKeepalive = proplists:get_value(max_keepalive, Opts, infinity),
	MaxLineLength = proplists:get_value(max_line_length, Opts, 4096),
	OnRequest = proplists:get_value(onrequest, Opts),
	Timeout = proplists:get_value(timeout, Opts, 5000),
	URLDecDefault = {fun cowboy_http:urldecode/2, crash},
	URLDec = proplists:get_value(urldecode, Opts, URLDecDefault),
	ok = cowboy:accept_ack(ListenerPid),
	wait_request(#state{listener=ListenerPid, socket=Socket, transport=Transport,
		dispatch=Dispatch, max_empty_lines=MaxEmptyLines,
		max_keepalive=MaxKeepalive, max_line_length=MaxLineLength,
		timeout=Timeout, onrequest=OnRequest, urldecode=URLDec}).

%% @private
-spec parse_request(#state{}) -> ok.
%% We limit the length of the Request-line to MaxLength to avoid endlessly
%% reading from the socket and eventually crashing.
parse_request(State=#state{buffer=Buffer, max_line_length=MaxLength}) ->
	case erlang:decode_packet(http_bin, Buffer, []) of
		{ok, Request, Rest} -> request(Request, State#state{buffer=Rest});
		{more, _Length} when byte_size(Buffer) > MaxLength ->
			error_terminate(413, State);
		{more, _Length} -> wait_request(State);
		{error, _Reason} -> error_terminate(400, State)
	end.

-spec wait_request(#state{}) -> ok.
wait_request(State=#state{socket=Socket, transport=Transport,
		timeout=T, buffer=Buffer}) ->
	case Transport:recv(Socket, 0, T) of
		{ok, Data} -> parse_request(State#state{
			buffer= << Buffer/binary, Data/binary >>});
		{error, _Reason} -> terminate(State)
	end.

-spec request({http_request, cowboy_http:method(), cowboy_http:uri(),
	cowboy_http:version()}, #state{}) -> ok.
request({http_request, _Method, _URI, Version}, State)
		when Version =/= {1, 0}, Version =/= {1, 1} ->
	error_terminate(505, State);
%% We still receive the original Host header.
request({http_request, Method, {absoluteURI, _Scheme, _Host, _Port, Path},
		Version}, State) ->
	request({http_request, Method, {abs_path, Path}, Version}, State);
request({http_request, Method, {abs_path, AbsPath}, Version},
		State=#state{socket=Socket, transport=Transport,
		urldecode={URLDecFun, URLDecArg}=URLDec}) ->
	URLDecode = fun(Bin) -> URLDecFun(Bin, URLDecArg) end,
	{Path, RawPath, Qs} = cowboy_dispatcher:split_path(AbsPath, URLDecode),
	ConnAtom = version_to_connection(Version),
	parse_header(#http_req{socket=Socket, transport=Transport,
		connection=ConnAtom, pid=self(), method=Method, version=Version,
		path=Path, raw_path=RawPath, raw_qs=Qs, urldecode=URLDec}, State);
request({http_request, Method, '*', Version},
		State=#state{socket=Socket, transport=Transport, urldecode=URLDec}) ->
	ConnAtom = version_to_connection(Version),
	parse_header(#http_req{socket=Socket, transport=Transport,
		connection=ConnAtom, pid=self(), method=Method, version=Version,
		path='*', raw_path= <<"*">>, raw_qs= <<>>, urldecode=URLDec}, State);
request({http_request, _Method, _URI, _Version}, State) ->
	error_terminate(501, State);
request({http_error, <<"\r\n">>},
		State=#state{req_empty_lines=N, max_empty_lines=N}) ->
	error_terminate(400, State);
request({http_error, <<"\r\n">>}, State=#state{req_empty_lines=N}) ->
	parse_request(State#state{req_empty_lines=N + 1});
request(_Any, State) ->
	error_terminate(400, State).

-spec parse_header(#http_req{}, #state{}) -> ok.
parse_header(Req, State=#state{buffer=Buffer, max_line_length=MaxLength}) ->
	case erlang:decode_packet(httph_bin, Buffer, []) of
		{ok, Header, Rest} -> header(Header, Req, State#state{buffer=Rest});
		{more, _Length} when byte_size(Buffer) > MaxLength ->
			error_terminate(413, State);
		{more, _Length} -> wait_header(Req, State);
		{error, _Reason} -> error_terminate(400, State)
	end.

-spec wait_header(#http_req{}, #state{}) -> ok.
wait_header(Req, State=#state{socket=Socket,
		transport=Transport, timeout=T, buffer=Buffer}) ->
	case Transport:recv(Socket, 0, T) of
		{ok, Data} -> parse_header(Req, State#state{
			buffer= << Buffer/binary, Data/binary >>});
		{error, timeout} -> error_terminate(408, State);
		{error, closed} -> terminate(State)
	end.

-spec header({http_header, integer(), cowboy_http:header(), any(), binary()}
	| http_eoh, #http_req{}, #state{}) -> ok.
header({http_header, _I, 'Host', _R, RawHost}, Req=#http_req{
		transport=Transport, host=undefined}, State) ->
	RawHost2 = cowboy_bstr:to_lower(RawHost),
	case catch cowboy_dispatcher:split_host(RawHost2) of
		{Host, RawHost3, undefined} ->
			Port = default_port(Transport:name()),
			parse_header(Req#http_req{
				host=Host, raw_host=RawHost3, port=Port,
				headers=[{'Host', RawHost3}|Req#http_req.headers]}, State);
		{Host, RawHost3, Port} ->
			parse_header(Req#http_req{
				host=Host, raw_host=RawHost3, port=Port,
				headers=[{'Host', RawHost3}|Req#http_req.headers]}, State);
		{'EXIT', _Reason} ->
			error_terminate(400, State)
	end;
%% Ignore Host headers if we already have it.
header({http_header, _I, 'Host', _R, _V}, Req, State) ->
	parse_header(Req, State);
header({http_header, _I, 'Connection', _R, Connection},
		Req=#http_req{headers=Headers}, State) ->
	Req2 = Req#http_req{headers=[{'Connection', Connection}|Headers]},
	{ConnTokens, Req3}
		= cowboy_http_req:parse_header('Connection', Req2),
	ConnAtom = cowboy_http:connection_to_atom(ConnTokens),
	parse_header(Req3#http_req{connection=ConnAtom}, State);
header({http_header, _I, Field, _R, Value}, Req, State) ->
	Field2 = format_header(Field),
	parse_header(Req#http_req{headers=[{Field2, Value}|Req#http_req.headers]},
		State);
%% The Host header is required in HTTP/1.1.
header(http_eoh, #http_req{version={1, 1}, host=undefined}, State) ->
	error_terminate(400, State);
%% It is however optional in HTTP/1.0.
header(http_eoh, Req=#http_req{version={1, 0}, transport=Transport,
		host=undefined}, State=#state{buffer=Buffer}) ->
	Port = default_port(Transport:name()),
	onrequest(Req#http_req{host=[], raw_host= <<>>,
		port=Port, buffer=Buffer}, State#state{buffer= <<>>});
header(http_eoh, Req, State=#state{buffer=Buffer}) ->
	onrequest(Req#http_req{buffer=Buffer}, State#state{buffer= <<>>});
header(_Any, _Req, State) ->
	error_terminate(400, State).

%% Call the global onrequest callback. The callback can send a reply,
%% in which case we consider the request handled and move on to the next
%% one. Note that since we haven't dispatched yet, we don't know the
%% handler, host_info, path_info or bindings yet.
-spec onrequest(#http_req{}, #state{}) -> ok.
onrequest(Req, State=#state{onrequest=undefined}) ->
	dispatch(Req, State);
onrequest(Req, State=#state{onrequest=OnRequest}) ->
	Req2 = OnRequest(Req),
	case Req2#http_req.resp_state of
		waiting -> dispatch(Req2, State);
		_ -> next_request(Req2, State, ok)
	end.

-spec dispatch(#http_req{}, #state{}) -> ok.
dispatch(Req=#http_req{host=Host, path=Path},
		State=#state{dispatch=Dispatch}) ->
	case cowboy_dispatcher:match(Host, Path, Dispatch) of
		{ok, Handler, Opts, Binds, HostInfo, PathInfo} ->
			handler_init(Req#http_req{host_info=HostInfo, path_info=PathInfo,
				bindings=Binds}, State#state{handler={Handler, Opts}});
		{error, notfound, host} ->
			error_terminate(400, State);
		{error, notfound, path} ->
			error_terminate(404, State)
	end.

-spec handler_init(#http_req{}, #state{}) -> ok.
handler_init(Req, State=#state{transport=Transport,
		handler={Handler, Opts}}) ->
	try Handler:init({Transport:name(), http}, Req, Opts) of
		{ok, Req2, HandlerState} ->
			handler_handle(HandlerState, Req2, State);
		{loop, Req2, HandlerState} ->
			handler_before_loop(HandlerState, Req2, State);
		{loop, Req2, HandlerState, hibernate} ->
			handler_before_loop(HandlerState, Req2,
				State#state{hibernate=true});
		{loop, Req2, HandlerState, Timeout} ->
			handler_before_loop(HandlerState, Req2,
				State#state{loop_timeout=Timeout});
		{loop, Req2, HandlerState, Timeout, hibernate} ->
			handler_before_loop(HandlerState, Req2,
				State#state{hibernate=true, loop_timeout=Timeout});
		{shutdown, Req2, HandlerState} ->
			handler_terminate(HandlerState, Req2, State);
		%% @todo {upgrade, transport, Module}
		{upgrade, protocol, Module} ->
			upgrade_protocol(Req, State, Module)
	catch Class:Reason ->
		error_terminate(500, State),
		error_logger:error_msg(
			"** Handler ~p terminating in init/3~n"
			"   for the reason ~p:~p~n"
			"** Options were ~p~n"
			"** Request was ~p~n** Stacktrace: ~p~n~n",
			[Handler, Class, Reason, Opts, Req, erlang:get_stacktrace()])
	end.

-spec upgrade_protocol(#http_req{}, #state{}, atom()) -> ok.
upgrade_protocol(Req, State=#state{listener=ListenerPid,
		handler={Handler, Opts}}, Module) ->
	case Module:upgrade(ListenerPid, Handler, Opts, Req) of
		{UpgradeRes, Req2} -> next_request(Req2, State, UpgradeRes);
		_Any -> terminate(State)
	end.

-spec handler_handle(any(), #http_req{}, #state{}) -> ok.
handler_handle(HandlerState, Req, State=#state{handler={Handler, Opts}}) ->
	try Handler:handle(Req, HandlerState) of
		{ok, Req2, HandlerState2} ->
			terminate_request(HandlerState2, Req2, State)
	catch Class:Reason ->
		error_logger:error_msg(
			"** Handler ~p terminating in handle/2~n"
			"   for the reason ~p:~p~n"
			"** Options were ~p~n** Handler state was ~p~n"
			"** Request was ~p~n** Stacktrace: ~p~n~n",
			[Handler, Class, Reason, Opts,
			 HandlerState, Req, erlang:get_stacktrace()]),
		handler_terminate(HandlerState, Req, State),
		error_terminate(500, State)
	end.

%% We don't listen for Transport closes because that would force us
%% to receive data and buffer it indefinitely.
-spec handler_before_loop(any(), #http_req{}, #state{}) -> ok.
handler_before_loop(HandlerState, Req, State=#state{hibernate=true}) ->
	State2 = handler_loop_timeout(State),
	catch erlang:hibernate(?MODULE, handler_loop,
		[HandlerState, Req, State2#state{hibernate=false}]),
	ok;
handler_before_loop(HandlerState, Req, State) ->
	State2 = handler_loop_timeout(State),
	handler_loop(HandlerState, Req, State2).

%% Almost the same code can be found in cowboy_http_websocket.
-spec handler_loop_timeout(#state{}) -> #state{}.
handler_loop_timeout(State=#state{loop_timeout=infinity}) ->
	State#state{loop_timeout_ref=undefined};
handler_loop_timeout(State=#state{loop_timeout=Timeout,
		loop_timeout_ref=PrevRef}) ->
	_ = case PrevRef of undefined -> ignore; PrevRef ->
		erlang:cancel_timer(PrevRef) end,
	TRef = make_ref(),
	erlang:send_after(Timeout, self(), {?MODULE, timeout, TRef}),
	State#state{loop_timeout_ref=TRef}.

-spec handler_loop(any(), #http_req{}, #state{}) -> ok.
handler_loop(HandlerState, Req, State=#state{loop_timeout_ref=TRef}) ->
	receive
		{?MODULE, timeout, TRef} ->
			terminate_request(HandlerState, Req, State);
		{?MODULE, timeout, OlderTRef} when is_reference(OlderTRef) ->
			handler_loop(HandlerState, Req, State);
		Message ->
			handler_call(HandlerState, Req, State, Message)
	end.

-spec handler_call(any(), #http_req{}, #state{}, any()) -> ok.
handler_call(HandlerState, Req, State=#state{handler={Handler, Opts}},
		Message) ->
	try Handler:info(Message, Req, HandlerState) of
		{ok, Req2, HandlerState2} ->
			terminate_request(HandlerState2, Req2, State);
		{loop, Req2, HandlerState2} ->
			handler_before_loop(HandlerState2, Req2, State);
		{loop, Req2, HandlerState2, hibernate} ->
			handler_before_loop(HandlerState2, Req2,
				State#state{hibernate=true})
	catch Class:Reason ->
		error_logger:error_msg(
			"** Handler ~p terminating in info/3~n"
			"   for the reason ~p:~p~n"
			"** Options were ~p~n** Handler state was ~p~n"
			"** Request was ~p~n** Stacktrace: ~p~n~n",
			[Handler, Class, Reason, Opts,
			 HandlerState, Req, erlang:get_stacktrace()]),
		handler_terminate(HandlerState, Req, State),
		error_terminate(500, State)
	end.

-spec handler_terminate(any(), #http_req{}, #state{}) -> ok.
handler_terminate(HandlerState, Req, #state{handler={Handler, Opts}}) ->
	try
		Handler:terminate(Req#http_req{resp_state=locked}, HandlerState)
	catch Class:Reason ->
		error_logger:error_msg(
			"** Handler ~p terminating in terminate/2~n"
			"   for the reason ~p:~p~n"
			"** Options were ~p~n** Handler state was ~p~n"
			"** Request was ~p~n** Stacktrace: ~p~n~n",
			[Handler, Class, Reason, Opts,
			 HandlerState, Req, erlang:get_stacktrace()])
	end.

-spec terminate_request(any(), #http_req{}, #state{}) -> ok.
terminate_request(HandlerState, Req, State) ->
	HandlerRes = handler_terminate(HandlerState, Req, State),
	next_request(Req, State, HandlerRes).

-spec next_request(#http_req{}, #state{}, any()) -> ok.
next_request(Req=#http_req{connection=Conn},
		State=#state{req_keepalive=Keepalive, max_keepalive=MaxKeepalive},
		HandlerRes) ->
	RespRes = ensure_response(Req),
	{BodyRes, Buffer} = ensure_body_processed(Req),
	%% Flush the resp_sent message before moving on.
	receive {cowboy_http_req, resp_sent} -> ok after 0 -> ok end,
	case {HandlerRes, BodyRes, RespRes, Conn} of
		{ok, ok, ok, keepalive} when Keepalive < MaxKeepalive ->
			?MODULE:parse_request(State#state{
				buffer=Buffer, req_empty_lines=0,
				req_keepalive=Keepalive + 1});
		_Closed ->
			terminate(State)
	end.

-spec ensure_body_processed(#http_req{}) -> {ok | close, binary()}.
ensure_body_processed(#http_req{body_state=done, buffer=Buffer}) ->
	{ok, Buffer};
ensure_body_processed(Req=#http_req{body_state=waiting}) ->
	case cowboy_http_req:body(Req) of
		{error, badarg} -> {ok, Req#http_req.buffer}; %% No body.
		{error, _Reason} -> {close, <<>>};
		{ok, _, Req2} -> {ok, Req2#http_req.buffer}
	end;
ensure_body_processed(Req=#http_req{body_state={multipart, _, _}}) ->
	{ok, Req2} = cowboy_http_req:multipart_skip(Req),
	ensure_body_processed(Req2).

-spec ensure_response(#http_req{}) -> ok.
%% The handler has already fully replied to the client.
ensure_response(#http_req{resp_state=done}) ->
	ok;
%% No response has been sent but everything apparently went fine.
%% Reply with 204 No Content to indicate this.
ensure_response(Req=#http_req{resp_state=waiting}) ->
	_ = cowboy_http_req:reply(204, [], [], Req),
	ok;
%% Close the chunked reply.
ensure_response(#http_req{method='HEAD', resp_state=chunks}) ->
	close;
ensure_response(#http_req{version={1, 0}, resp_state=chunks}) ->
	close;
ensure_response(#http_req{socket=Socket, transport=Transport,
		resp_state=chunks}) ->
	Transport:send(Socket, <<"0\r\n\r\n">>),
	close.

%% Only send an error reply if there is no resp_sent message.
-spec error_terminate(cowboy_http:status(), #state{}) -> ok.
error_terminate(Code, State=#state{socket=Socket, transport=Transport}) ->
	receive
		{cowboy_http_req, resp_sent} -> ok
	after 0 ->
		_ = cowboy_http_req:reply(Code, #http_req{
			socket=Socket, transport=Transport,
			connection=close, pid=self(), resp_state=waiting}),
		ok
	end,
	terminate(State).

-spec terminate(#state{}) -> ok.
terminate(#state{socket=Socket, transport=Transport}) ->
	Transport:close(Socket),
	ok.

%% Internal.

-spec version_to_connection(cowboy_http:version()) -> keepalive | close.
version_to_connection({1, 1}) -> keepalive;
version_to_connection(_Any) -> close.

-spec default_port(atom()) -> 80 | 443.
default_port(ssl) -> 443;
default_port(_) -> 80.

%% @todo While 32 should be enough for everybody, we should probably make
%%       this configurable or something.
-spec format_header(atom()) -> atom(); (binary()) -> binary().
format_header(Field) when is_atom(Field) ->
	Field;
format_header(Field) when byte_size(Field) =< 20; byte_size(Field) > 32 ->
	Field;
format_header(Field) ->
	format_header(Field, true, <<>>).

-spec format_header(binary(), boolean(), binary()) -> binary().
format_header(<<>>, _Any, Acc) ->
	Acc;
%% Replicate a bug in OTP for compatibility reasons when there's a - right
%% after another. Proper use should always be 'true' instead of 'not Bool'.
format_header(<< $-, Rest/bits >>, Bool, Acc) ->
	format_header(Rest, not Bool, << Acc/binary, $- >>);
format_header(<< C, Rest/bits >>, true, Acc) ->
	format_header(Rest, false, << Acc/binary, (cowboy_bstr:char_to_upper(C)) >>);
format_header(<< C, Rest/bits >>, false, Acc) ->
	format_header(Rest, false, << Acc/binary, (cowboy_bstr:char_to_lower(C)) >>).

%% Tests.

-ifdef(TEST).

format_header_test_() ->
	%% {Header, Result}
	Tests = [
		{<<"Sec-Websocket-Version">>, <<"Sec-Websocket-Version">>},
		{<<"Sec-WebSocket-Version">>, <<"Sec-Websocket-Version">>},
		{<<"sec-websocket-version">>, <<"Sec-Websocket-Version">>},
		{<<"SEC-WEBSOCKET-VERSION">>, <<"Sec-Websocket-Version">>},
		%% These last tests ensures we're formatting headers exactly like OTP.
		%% Even though it's dumb, it's better for compatibility reasons.
		{<<"Sec-WebSocket--Version">>, <<"Sec-Websocket--version">>},
		{<<"Sec-WebSocket---Version">>, <<"Sec-Websocket---Version">>}
	],
	[{H, fun() -> R = format_header(H) end} || {H, R} <- Tests].

-endif.