Ensure header names are handled in a case insensitive manner

To this end we are formatting the header names just like OTP does
except we do it for names of up to 32 characters, as there are
widely used header names of more than 20 characters, the limit that
OTP follows currently. An example of such header name would be
Sec-Websocket-Version.

The formatting itself is fairly simple: an uppercase character at
the start and after dashes, everything else lowercase.

src/cowboy_http_protocol.erl

@@ -35,6 +35,7 @@
 -export([init/4, parse_request/1]). %% FSM.
 
 -include("include/http.hrl").
+-include_lib("eunit/include/eunit.hrl").
 
 -record(state, {
 	listener :: pid(),
@@ -164,7 +165,8 @@ header({http_header, _I, 'Connection', _R, Connection}, Req, State) ->
 		headers=[{'Connection', Connection}|Req#http_req.headers]},
 		State#state{connection=ConnAtom});
 header({http_header, _I, Field, _R, Value}, Req, State) ->
-	parse_header(Req#http_req{headers=[{Field, Value}|Req#http_req.headers]},
+	Field2 = format_header(Field),
+	parse_header(Req#http_req{headers=[{Field2, Value}|Req#http_req.headers]},
 		State);
 %% The Host header is required.
 header(http_eoh, #http_req{host=undefined}, State) ->
@@ -297,6 +299,7 @@ terminate(#state{socket=Socket, transport=Transport}) ->
 version_to_connection({1, 1}) -> keepalive;
 version_to_connection(_Any) -> close.
 
+%% @todo Connection can take more than one value.
 -spec connection_to_atom(binary()) -> keepalive | close.
 connection_to_atom(<<"keep-alive">>) ->
 	keepalive;
@@ -312,6 +315,28 @@ connection_to_atom(Connection) ->
 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, $- >>);
+format_header(<< C, Rest/bits >>, true, Acc) ->
+	format_header(Rest, false, << Acc/binary, (char_to_upper(C)) >>);
+format_header(<< C, Rest/bits >>, false, Acc) ->
+	format_header(Rest, false, << Acc/binary, (char_to_lower(C)) >>).
+
 %% We are excluding a few characters on purpose.
 -spec binary_to_lower(binary()) -> binary().
 binary_to_lower(L) ->
@@ -346,3 +371,52 @@ char_to_lower($X) -> $x;
 char_to_lower($Y) -> $y;
 char_to_lower($Z) -> $z;
 char_to_lower(Ch) -> Ch.
+
+-spec char_to_upper(char()) -> char().
+char_to_upper($a) -> $A;
+char_to_upper($b) -> $B;
+char_to_upper($c) -> $C;
+char_to_upper($d) -> $D;
+char_to_upper($e) -> $E;
+char_to_upper($f) -> $F;
+char_to_upper($g) -> $G;
+char_to_upper($h) -> $H;
+char_to_upper($i) -> $I;
+char_to_upper($j) -> $J;
+char_to_upper($k) -> $K;
+char_to_upper($l) -> $L;
+char_to_upper($m) -> $M;
+char_to_upper($n) -> $N;
+char_to_upper($o) -> $O;
+char_to_upper($p) -> $P;
+char_to_upper($q) -> $Q;
+char_to_upper($r) -> $R;
+char_to_upper($s) -> $S;
+char_to_upper($t) -> $T;
+char_to_upper($u) -> $U;
+char_to_upper($v) -> $V;
+char_to_upper($w) -> $W;
+char_to_upper($x) -> $X;
+char_to_upper($y) -> $Y;
+char_to_upper($z) -> $Z;
+char_to_upper(Ch) -> Ch.
+
+%% 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.