Parse 'Connection' headers as a list of tokens

Replaces the 'Connection' interpretation in cowboy_http_protocol
from raw value to the parsed value, looking for a single token
matching close/keep-alive instead of the whole raw value (which
could contain more than one token, for example with Firefox 6+
using websocket).

Introduce the functions cowboy_http_req:parse_header/2 and /3
to semantically parse the header values and return a proper
Erlang term.

src/cowboy_http.erl

@@ -0,0 +1,124 @@
+%% Copyright (c) 2011, Loïc Hoguin <essen@dev-extend.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_http).
+
+%% Parsing.
+-export([parse_tokens_list/1]).
+
+%% Interpretation.
+-export([connection_to_atom/1]).
+
+-include("include/http.hrl").
+-include_lib("eunit/include/eunit.hrl").
+
+%% Parsing.
+
+%% @doc Parse a list of tokens, as is often found in HTTP headers.
+%%
+%% From the RFC:
+%% <blockquote>Wherever this construct is used, null elements are allowed,
+%% but do not contribute to the count of elements present.
+%% That is, "(element), , (element) " is permitted, but counts
+%% as only two elements. Therefore, where at least one element is required,
+%% at least one non-null element MUST be present.</blockquote>
+-spec parse_tokens_list(binary()) -> [binary()] | {error, badarg}.
+parse_tokens_list(Value) ->
+	case parse_tokens_list(Value, ws_or_sep, <<>>, []) of
+		{error, badarg} ->
+			{error, badarg};
+		L when length(L) =:= 0 ->
+			{error, badarg};
+		L ->
+			lists:reverse(L)
+	end.
+
+-spec parse_tokens_list(binary(), token | ws | ws_or_sep, binary(),
+	[binary()]) -> [binary()] | {error, badarg}.
+parse_tokens_list(<<>>, token, Token, Acc) ->
+	[Token|Acc];
+parse_tokens_list(<< C, Rest/bits >>, token, Token, Acc)
+		when C =:= $\s; C =:= $\t ->
+	parse_tokens_list(Rest, ws, <<>>, [Token|Acc]);
+parse_tokens_list(<< $,, Rest/bits >>, token, Token, Acc) ->
+	parse_tokens_list(Rest, ws_or_sep, <<>>, [Token|Acc]);
+parse_tokens_list(<< C, Rest/bits >>, token, Token, Acc) ->
+	parse_tokens_list(Rest, token, << Token/binary, C >>, Acc);
+parse_tokens_list(<< C, Rest/bits >>, ws, <<>>, Acc)
+		when C =:= $\s; C =:= $\t ->
+	parse_tokens_list(Rest, ws, <<>>, Acc);
+parse_tokens_list(<< $,, Rest/bits >>, ws, <<>>, Acc) ->
+	parse_tokens_list(Rest, ws_or_sep, <<>>, Acc);
+parse_tokens_list(<<>>, ws_or_sep, <<>>, Acc) ->
+	Acc;
+parse_tokens_list(<< C, Rest/bits >>, ws_or_sep, <<>>, Acc)
+		when C =:= $\s; C =:= $\t ->
+	parse_tokens_list(Rest, ws_or_sep, <<>>, Acc);
+parse_tokens_list(<< $,, Rest/bits >>, ws_or_sep, <<>>, Acc) ->
+	parse_tokens_list(Rest, ws_or_sep, <<>>, Acc);
+parse_tokens_list(<< C, Rest/bits >>, ws_or_sep, <<>>, Acc) ->
+	parse_tokens_list(Rest, token, << C >>, Acc);
+parse_tokens_list(_Value, _State, _Token, _Acc) ->
+	{error, badarg}.
+
+%% Interpretation.
+
+%% @doc Walk through a tokens list and return whether
+%% the connection is keepalive or closed.
+-spec connection_to_atom([binary()]) -> keepalive | close.
+connection_to_atom([]) ->
+	keepalive;
+connection_to_atom([<<"keep-alive">>|_Tail]) ->
+	keepalive;
+connection_to_atom([<<"close">>|_Tail]) ->
+	close;
+connection_to_atom([Connection|Tail]) ->
+	case cowboy_bstr:to_lower(Connection) of
+		<<"close">> -> close;
+		<<"keep-alive">> -> keepalive;
+		_Any -> connection_to_atom(Tail)
+	end.
+
+%% Tests.
+
+-ifdef(TEST).
+
+parse_tokens_list_test_() ->
+	%% {Value, Result}
+	Tests = [
+		{<<>>, {error, badarg}},
+		{<<" ">>, {error, badarg}},
+		{<<" , ">>, {error, badarg}},
+		{<<",,,">>, {error, badarg}},
+		{<<"a b">>, {error, badarg}},
+		{<<"a , , , ">>, [<<"a">>]},
+		{<<" , , , a">>, [<<"a">>]},
+		{<<"a, , b">>, [<<"a">>, <<"b">>]},
+		{<<"close">>, [<<"close">>]},
+		{<<"keep-alive, upgrade">>, [<<"keep-alive">>, <<"upgrade">>]}
+	],
+	[{V, fun() -> R = parse_tokens_list(V) end} || {V, R} <- Tests].
+
+connection_to_atom_test_() ->
+	%% {Tokens, Result}
+	Tests = [
+		{[<<"close">>], close},
+		{[<<"ClOsE">>], close},
+		{[<<"Keep-Alive">>], keepalive},
+		{[<<"Keep-Alive">>, <<"Upgrade">>], keepalive}
+	],
+	[{lists:flatten(io_lib:format("~p", [T])),
+		fun() -> R = connection_to_atom(T) end} || {T, R} <- Tests].
+
+-endif.