%% Copyright (c) 2019, Loïc Hoguin <[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.
-module(cow_link).
-compile({no_auto_import, [link/1]}).
-export([parse_link/1]).
-export([resolve_link/2]).
-export([resolve_link/3]).
-export([link/1]).
-include("cow_inline.hrl").
-include("cow_parse.hrl").
-type link() :: #{
target := binary(),
rel := binary(),
attributes := [{binary(), binary()}]
}.
-export_type([link/0]).
-type resolve_opts() :: #{
allow_anchor => boolean()
}.
-type uri() :: uri_string:uri_map() | uri_string:uri_string() | undefined.
%% Parse a link header.
%% This function returns the URI target from the header directly.
%% Relative URIs must then be resolved as per RFC3986 5. In some
%% cases it might not be possible to resolve URIs, for example when
%% the link header is returned with a 404 status code.
-spec parse_link(binary()) -> [link()].
parse_link(Link) ->
before_target(Link, []).
before_target(<<>>, Acc) -> lists:reverse(Acc);
before_target(<<$<,R/bits>>, Acc) -> target(R, Acc, <<>>);
before_target(<<C,R/bits>>, Acc) when ?IS_WS(C) -> before_target(R, Acc).
target(<<$>,R/bits>>, Acc, T) -> param_sep(R, Acc, T, []);
target(<<C,R/bits>>, Acc, T) -> target(R, Acc, <<T/binary, C>>).
param_sep(<<>>, Acc, T, P) -> lists:reverse(acc_link(Acc, T, P));
param_sep(<<$,,R/bits>>, Acc, T, P) -> before_target(R, acc_link(Acc, T, P));
param_sep(<<$;,R/bits>>, Acc, T, P) -> before_param(R, Acc, T, P);
param_sep(<<C,R/bits>>, Acc, T, P) when ?IS_WS(C) -> param_sep(R, Acc, T, P).
before_param(<<C,R/bits>>, Acc, T, P) when ?IS_WS(C) -> before_param(R, Acc, T, P);
before_param(<<C,R/bits>>, Acc, T, P) when ?IS_TOKEN(C) -> ?LOWER(param, R, Acc, T, P, <<>>).
param(<<$=,$",R/bits>>, Acc, T, P, K) -> quoted(R, Acc, T, P, K, <<>>);
param(<<$=,C,R/bits>>, Acc, T, P, K) when ?IS_TOKEN(C) -> value(R, Acc, T, P, K, <<C>>);
param(<<C,R/bits>>, Acc, T, P, K) when ?IS_TOKEN(C) -> ?LOWER(param, R, Acc, T, P, K).
quoted(<<$",R/bits>>, Acc, T, P, K, V) -> param_sep(R, Acc, T, [{K, V}|P]);
quoted(<<$\\,C,R/bits>>, Acc, T, P, K, V) when ?IS_VCHAR_OBS(C) -> quoted(R, Acc, T, P, K, <<V/binary,C>>);
quoted(<<C,R/bits>>, Acc, T, P, K, V) when ?IS_VCHAR_OBS(C) -> quoted(R, Acc, T, P, K, <<V/binary,C>>).
value(<<C,R/bits>>, Acc, T, P, K, V) when ?IS_TOKEN(C) -> value(R, Acc, T, P, K, <<V/binary,C>>);
value(R, Acc, T, P, K, V) -> param_sep(R, Acc, T, [{K, V}|P]).
acc_link(Acc, Target, Params0) ->
Params1 = lists:reverse(Params0),
%% The rel parameter MUST be present. (RFC8288 3.3)
{value, {_, Rel}, Params2} = lists:keytake(<<"rel">>, 1, Params1),
%% Occurrences after the first MUST be ignored by parsers.
Params = filter_out_duplicates(Params2, #{}),
[#{
target => Target,
rel => ?LOWER(Rel),
attributes => Params
}|Acc].
%% This function removes duplicates for attributes that don't allow them.
filter_out_duplicates([], _) ->
[];
%% The "rel" is mandatory and was already removed from params.
filter_out_duplicates([{<<"rel">>, _}|Tail], State) ->
filter_out_duplicates(Tail, State);
filter_out_duplicates([{<<"anchor">>, _}|Tail], State=#{anchor := true}) ->
filter_out_duplicates(Tail, State);
filter_out_duplicates([{<<"media">>, _}|Tail], State=#{media := true}) ->
filter_out_duplicates(Tail, State);
filter_out_duplicates([{<<"title">>, _}|Tail], State=#{title := true}) ->
filter_out_duplicates(Tail, State);
filter_out_duplicates([{<<"title*">>, _}|Tail], State=#{title_star := true}) ->
filter_out_duplicates(Tail, State);
filter_out_duplicates([{<<"type">>, _}|Tail], State=#{type := true}) ->
filter_out_duplicates(Tail, State);
filter_out_duplicates([Tuple={<<"anchor">>, _}|Tail], State) ->
[Tuple|filter_out_duplicates(Tail, State#{anchor => true})];
filter_out_duplicates([Tuple={<<"media">>, _}|Tail], State) ->
[Tuple|filter_out_duplicates(Tail, State#{media => true})];
filter_out_duplicates([Tuple={<<"title">>, _}|Tail], State) ->
[Tuple|filter_out_duplicates(Tail, State#{title => true})];
filter_out_duplicates([Tuple={<<"title*">>, _}|Tail], State) ->
[Tuple|filter_out_duplicates(Tail, State#{title_star => true})];
filter_out_duplicates([Tuple={<<"type">>, _}|Tail], State) ->
[Tuple|filter_out_duplicates(Tail, State#{type => true})];
filter_out_duplicates([Tuple|Tail], State) ->
[Tuple|filter_out_duplicates(Tail, State)].
-ifdef(TEST).
parse_link_test_() ->
Tests = [
{<<>>, []},
{<<" ">>, []},
%% Examples from the RFC.
{<<"<http://example.com/TheBook/chapter2>; rel=\"previous\"; title=\"previous chapter\"">>, [
#{
target => <<"http://example.com/TheBook/chapter2">>,
rel => <<"previous">>,
attributes => [
{<<"title">>, <<"previous chapter">>}
]
}
]},
{<<"</>; rel=\"http://example.net/foo\"">>, [
#{
target => <<"/">>,
rel => <<"http://example.net/foo">>,
attributes => []
}
]},
{<<"</terms>; rel=\"copyright\"; anchor=\"#foo\"">>, [
#{
target => <<"/terms">>,
rel => <<"copyright">>,
attributes => [
{<<"anchor">>, <<"#foo">>}
]
}
]},
% {<<"</TheBook/chapter2>; rel=\"previous\"; title*=UTF-8'de'letztes%20Kapitel, "
% "</TheBook/chapter4>; rel=\"next\"; title*=UTF-8'de'n%c3%a4chstes%20Kapitel">>, [
% %% @todo
% ]}
{<<"<http://example.org/>; rel=\"start http://example.net/relation/other\"">>, [
#{
target => <<"http://example.org/">>,
rel => <<"start http://example.net/relation/other">>,
attributes => []
}
]},
{<<"<https://example.org/>; rel=\"start\", "
"<https://example.org/index>; rel=\"index\"">>, [
#{
target => <<"https://example.org/">>,
rel => <<"start">>,
attributes => []
},
#{
target => <<"https://example.org/index">>,
rel => <<"index">>,
attributes => []
}
]},
%% Relation types are case insensitive.
{<<"</>; rel=\"SELF\"">>, [
#{
target => <<"/">>,
rel => <<"self">>,
attributes => []
}
]},
{<<"</>; rel=\"HTTP://EXAMPLE.NET/FOO\"">>, [
#{
target => <<"/">>,
rel => <<"http://example.net/foo">>,
attributes => []
}
]},
%% Attribute names are case insensitive.
{<<"</terms>; REL=\"copyright\"; ANCHOR=\"#foo\"">>, [
#{
target => <<"/terms">>,
rel => <<"copyright">>,
attributes => [
{<<"anchor">>, <<"#foo">>}
]
}
]}
],
[{V, fun() -> R = parse_link(V) end} || {V, R} <- Tests].
-endif.
%% Resolve a link based on the context URI and options.
-spec resolve_link(Link, uri()) -> Link | false when Link::link().
resolve_link(Link, ContextURI) ->
resolve_link(Link, ContextURI, #{}).
-spec resolve_link(Link, uri(), resolve_opts()) -> Link | false when Link::link().
%% When we do not have a context URI we only succeed when the target URI is absolute.
%% The target URI will only be normalized in that case.
resolve_link(Link=#{target := TargetURI}, undefined, _) ->
case uri_string:parse(TargetURI) of
URIMap = #{scheme := _} ->
Link#{target => uri_string:normalize(URIMap)};
_ ->
false
end;
resolve_link(Link=#{attributes := Params}, ContextURI, Opts) ->
AllowAnchor = maps:get(allow_anchor, Opts, true),
case lists:keyfind(<<"anchor">>, 1, Params) of
false ->
do_resolve_link(Link, ContextURI);
{_, Anchor} when AllowAnchor ->
do_resolve_link(Link, resolve(Anchor, ContextURI));
_ ->
false
end.
do_resolve_link(Link=#{target := TargetURI}, ContextURI) ->
Link#{target => uri_string:recompose(resolve(TargetURI, ContextURI))}.
-ifdef(TEST).
resolve_link_test_() ->
Tests = [
%% No context URI available.
{#{target => <<"http://a/b/./c">>}, undefined, #{},
#{target => <<"http://a/b/c">>}},
{#{target => <<"a/b/./c">>}, undefined, #{},
false},
%% Context URI available, allow_anchor => true.
{#{target => <<"http://a/b">>, attributes => []}, <<"http://a/c">>, #{},
#{target => <<"http://a/b">>, attributes => []}},
{#{target => <<"b">>, attributes => []}, <<"http://a/c">>, #{},
#{target => <<"http://a/b">>, attributes => []}},
{#{target => <<"b">>, attributes => [{<<"anchor">>, <<"#frag">>}]}, <<"http://a/c">>, #{},
#{target => <<"http://a/b">>, attributes => [{<<"anchor">>, <<"#frag">>}]}},
{#{target => <<"b">>, attributes => [{<<"anchor">>, <<"d/e">>}]}, <<"http://a/c">>, #{},
#{target => <<"http://a/d/b">>, attributes => [{<<"anchor">>, <<"d/e">>}]}},
%% Context URI available, allow_anchor => false.
{#{target => <<"http://a/b">>, attributes => []}, <<"http://a/c">>, #{allow_anchor => false},
#{target => <<"http://a/b">>, attributes => []}},
{#{target => <<"b">>, attributes => []}, <<"http://a/c">>, #{allow_anchor => false},
#{target => <<"http://a/b">>, attributes => []}},
{#{target => <<"b">>, attributes => [{<<"anchor">>, <<"#frag">>}]},
<<"http://a/c">>, #{allow_anchor => false}, false},
{#{target => <<"b">>, attributes => [{<<"anchor">>, <<"d/e">>}]},
<<"http://a/c">>, #{allow_anchor => false}, false}
],
[{iolist_to_binary(io_lib:format("~0p", [L])),
fun() -> R = resolve_link(L, C, O) end} || {L, C, O, R} <- Tests].
-endif.
%% @todo This function should ideally be part of Erlang/OTP's uri_string module.
resolve(URI, BaseURI) ->
case resolve1(ensure_map_uri(URI), BaseURI) of
TargetURI = #{path := Path0} ->
%% We remove dot segments. Normalizing the entire URI
%% will sometimes add an extra slash we don't want.
#{path := Path} = uri_string:normalize(#{path => Path0}, [return_map]),
TargetURI#{path => Path};
TargetURI ->
TargetURI
end.
resolve1(URI=#{scheme := _}, _) ->
URI;
resolve1(URI=#{host := _}, BaseURI) ->
#{scheme := Scheme} = ensure_map_uri(BaseURI),
URI#{scheme => Scheme};
resolve1(URI=#{path := <<>>}, BaseURI0) ->
BaseURI = ensure_map_uri(BaseURI0),
Keys = case maps:is_key(query, URI) of
true -> [scheme, host, port, path];
false -> [scheme, host, port, path, query]
end,
maps:merge(URI, maps:with(Keys, BaseURI));
resolve1(URI=#{path := <<"/",_/bits>>}, BaseURI0) ->
BaseURI = ensure_map_uri(BaseURI0),
maps:merge(URI, maps:with([scheme, host, port], BaseURI));
resolve1(URI=#{path := Path}, BaseURI0) ->
BaseURI = ensure_map_uri(BaseURI0),
maps:merge(
URI#{path := merge_paths(Path, BaseURI)},
maps:with([scheme, host, port], BaseURI)).
merge_paths(Path, #{host := _, path := <<>>}) ->
<<$/, Path/binary>>;
merge_paths(Path, #{path := BasePath0}) ->
case string:split(BasePath0, <<$/>>, trailing) of
[BasePath, _] -> <<BasePath/binary, $/, Path/binary>>;
[_] -> <<$/, Path/binary>>
end.
ensure_map_uri(URI) when is_map(URI) -> URI;
ensure_map_uri(URI) -> uri_string:parse(iolist_to_binary(URI)).
-ifdef(TEST).
resolve_test_() ->
Tests = [
%% 5.4.1. Normal Examples
{<<"g:h">>, <<"g:h">>},
{<<"g">>, <<"http://a/b/c/g">>},
{<<"./g">>, <<"http://a/b/c/g">>},
{<<"g/">>, <<"http://a/b/c/g/">>},
{<<"/g">>, <<"http://a/g">>},
{<<"//g">>, <<"http://g">>},
{<<"?y">>, <<"http://a/b/c/d;p?y">>},
{<<"g?y">>, <<"http://a/b/c/g?y">>},
{<<"#s">>, <<"http://a/b/c/d;p?q#s">>},
{<<"g#s">>, <<"http://a/b/c/g#s">>},
{<<"g?y#s">>, <<"http://a/b/c/g?y#s">>},
{<<";x">>, <<"http://a/b/c/;x">>},
{<<"g;x">>, <<"http://a/b/c/g;x">>},
{<<"g;x?y#s">>, <<"http://a/b/c/g;x?y#s">>},
{<<"">>, <<"http://a/b/c/d;p?q">>},
{<<".">>, <<"http://a/b/c/">>},
{<<"./">>, <<"http://a/b/c/">>},
{<<"..">>, <<"http://a/b/">>},
{<<"../">>, <<"http://a/b/">>},
{<<"../g">>, <<"http://a/b/g">>},
{<<"../..">>, <<"http://a/">>},
{<<"../../">>, <<"http://a/">>},
{<<"../../g">>, <<"http://a/g">>},
%% 5.4.2. Abnormal Examples
{<<"../../../g">>, <<"http://a/g">>},
{<<"../../../../g">>, <<"http://a/g">>},
{<<"/./g">>, <<"http://a/g">>},
{<<"/../g">>, <<"http://a/g">>},
{<<"g.">>, <<"http://a/b/c/g.">>},
{<<".g">>, <<"http://a/b/c/.g">>},
{<<"g..">>, <<"http://a/b/c/g..">>},
{<<"..g">>, <<"http://a/b/c/..g">>},
{<<"./../g">>, <<"http://a/b/g">>},
{<<"./g/.">>, <<"http://a/b/c/g/">>},
{<<"g/./h">>, <<"http://a/b/c/g/h">>},
{<<"g/../h">>, <<"http://a/b/c/h">>},
{<<"g;x=1/./y">>, <<"http://a/b/c/g;x=1/y">>},
{<<"g;x=1/../y">>, <<"http://a/b/c/y">>},
{<<"g?y/./x">>, <<"http://a/b/c/g?y/./x">>},
{<<"g?y/../x">>, <<"http://a/b/c/g?y/../x">>},
{<<"g#s/./x">>, <<"http://a/b/c/g#s/./x">>},
{<<"g#s/../x">>, <<"http://a/b/c/g#s/../x">>},
{<<"http:g">>, <<"http:g">>} %% for strict parsers
],
[{V, fun() -> R = uri_string:recompose(resolve(V, <<"http://a/b/c/d;p?q">>)) end} || {V, R} <- Tests].
-endif.
%% Build a link header.
-spec link([#{
target := binary(),
rel := binary(),
attributes := [{binary(), binary()}]
}]) -> iodata().
link(Links) ->
lists:join(<<", ">>, [do_link(Link) || Link <- Links]).
do_link(#{target := TargetURI, rel := Rel, attributes := Params}) ->
[
$<, TargetURI, <<">"
"; rel=\"">>, Rel, $",
[[<<"; ">>, Key, <<"=\"">>, escape(iolist_to_binary(Value), <<>>), $"]
|| {Key, Value} <- Params]
].
escape(<<>>, Acc) -> Acc;
escape(<<$\\,R/bits>>, Acc) -> escape(R, <<Acc/binary,$\\,$\\>>);
escape(<<$\",R/bits>>, Acc) -> escape(R, <<Acc/binary,$\\,$\">>);
escape(<<C,R/bits>>, Acc) -> escape(R, <<Acc/binary,C>>).
-ifdef(TEST).
link_test_() ->
Tests = [
{<<>>, []},
%% Examples from the RFC.
{<<"<http://example.com/TheBook/chapter2>; rel=\"previous\"; title=\"previous chapter\"">>, [
#{
target => <<"http://example.com/TheBook/chapter2">>,
rel => <<"previous">>,
attributes => [
{<<"title">>, <<"previous chapter">>}
]
}
]},
{<<"</>; rel=\"http://example.net/foo\"">>, [
#{
target => <<"/">>,
rel => <<"http://example.net/foo">>,
attributes => []
}
]},
{<<"</terms>; rel=\"copyright\"; anchor=\"#foo\"">>, [
#{
target => <<"/terms">>,
rel => <<"copyright">>,
attributes => [
{<<"anchor">>, <<"#foo">>}
]
}
]},
% {<<"</TheBook/chapter2>; rel=\"previous\"; title*=UTF-8'de'letztes%20Kapitel, "
% "</TheBook/chapter4>; rel=\"next\"; title*=UTF-8'de'n%c3%a4chstes%20Kapitel">>, [
% %% @todo
% ]}
{<<"<http://example.org/>; rel=\"start http://example.net/relation/other\"">>, [
#{
target => <<"http://example.org/">>,
rel => <<"start http://example.net/relation/other">>,
attributes => []
}
]},
{<<"<https://example.org/>; rel=\"start\", "
"<https://example.org/index>; rel=\"index\"">>, [
#{
target => <<"https://example.org/">>,
rel => <<"start">>,
attributes => []
},
#{
target => <<"https://example.org/index">>,
rel => <<"index">>,
attributes => []
}
]},
{<<"</>; rel=\"previous\"; quoted=\"name=\\\"value\\\"\"">>, [
#{
target => <<"/">>,
rel => <<"previous">>,
attributes => [
{<<"quoted">>, <<"name=\"value\"">>}
]
}
]}
],
[{iolist_to_binary(io_lib:format("~0p", [V])),
fun() -> R = iolist_to_binary(link(V)) end} || {R, V} <- Tests].
-endif.
