support for URL _rewrites

3 files changed, 421 insertions, 1 deletions

diff --git a/ebin/chttpd.app b/ebin/chttpd.app
index c33b3112..c85e58e8 100644
--- a/ebin/chttpd.app
+++ b/ebin/chttpd.app
@@ -9,6 +9,7 @@
         chttpd_external,
         chttpd_misc,
         chttpd_oauth,
+        chttpd_rewrite,
         chttpd_show,
         chttpd_stats,
         chttpd_sup,
diff --git a/src/chttpd.erl b/src/chttpd.erl
index a4bb1293..93047b80 100644
--- a/src/chttpd.erl
+++ b/src/chttpd.erl
@@ -212,7 +212,8 @@ design_url_handlers() ->
         {<<"_show">>,           fun chttpd_show:handle_doc_show_req/3},
         {<<"_list">>,           fun chttpd_show:handle_view_list_req/3},
         {<<"_update">>,         fun chttpd_show:handle_doc_update_req/3},
-        {<<"_info">>,           fun chttpd_db:handle_design_info_req/3}
+        {<<"_info">>,           fun chttpd_db:handle_design_info_req/3},
+        {<<"_rewrite">>,        fun chttpd_rewrite:handle_rewrite_req/3}
     ].
 
 % Utilities
diff --git a/src/chttpd_rewrite.erl b/src/chttpd_rewrite.erl
new file mode 100644
index 00000000..4aeaf31c
--- /dev/null
+++ b/src/chttpd_rewrite.erl
@@ -0,0 +1,418 @@
+% Licensed under the Apache License, Version 2.0 (the "License"); you may not
+% use this file except in compliance with the License. You may obtain a copy of
+% the License at
+%
+% http://www.apache.org/licenses/LICENSE-2.0
+%
+% Unless required by applicable law or agreed to in writing, software
+% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+% License for the specific language governing permissions and limitations under
+% the License.
+%
+% bind_path is based on bind method from Webmachine
+
+
+%% @doc Module for URL rewriting by pattern matching.
+
+-module(chttpd_rewrite).
+-export([handle_rewrite_req/3]).
+-include("chttpd.hrl").
+
+-define(SEPARATOR, $\/).
+-define(MATCH_ALL, '*').
+
+
+%% doc The http rewrite handler. All rewriting is done from
+%% /dbname/_design/ddocname/_rewrite by default.
+%%
+%% each rules should be in rewrites member of the design doc.
+%% Ex of a complete rule :
+%%
+%%  {
+%%      ....
+%%      "rewrites": [
+%%      {
+%%          "from": "",
+%%          "to": "index.html",
+%%          "method": "GET",
+%%          "query": {}
+%%      }
+%%      ]
+%%  }
+%%
+%%  from: is the path rule used to bind current uri to the rule. It
+%% use pattern matching for that.
+%%
+%%  to: rule to rewrite an url. It can contain variables depending on binding
+%% variables discovered during pattern matching and query args (url args and from
+%% the query member.)
+%%
+%%  method: method to bind the request method to the rule. by default "*"
+%%  query: query args you want to define they can contain dynamic variable
+%% by binding the key to the bindings
+%%
+%%
+%% to and from are path with  patterns. pattern can be string starting with ":" or
+%% "*". ex:
+%% /somepath/:var/*
+%%
+%% This path is converted in erlang list by splitting "/". Each var are
+%% converted in atom. "*" is converted to '*' atom. The pattern matching is done
+%% by splitting "/" in request url in a list of token. A string pattern will
+%% match equal token. The star atom ('*' in single quotes) will match any number
+%% of tokens, but may only be present as the last pathtern in a pathspec. If all
+%% tokens are matched and all pathterms are used, then the pathspec matches. It works
+%% like webmachine. Each identified token will be reused in to rule and in query
+%%
+%% The pattern matching is done by first matching the request method to a rule. by
+%% default all methods match a rule. (method is equal to "*" by default). Then
+%% It will try to match the path to one rule. If no rule match, then a 404 error
+%% is displayed.
+%%
+%% Once a rule is found we rewrite the request url using the "to" and
+%% "query" members. The identified token are matched to the rule and
+%% will replace var. if '*' is found in the rule it will contain the remaining
+%% part if it exists.
+%%
+%% Examples:
+%%
+%% Dispatch rule            URL             TO                  Tokens
+%%
+%% {"from": "/a/b",         /a/b?k=v        /some/b?k=v         var =:= b
+%% "to": "/some/"}                                              k = v
+%%
+%% {"from": "/a/b",         /a/b            /some/b?var=b       var =:= b
+%% "to": "/some/:var"}
+%%
+%% {"from": "/a",           /a              /some
+%% "to": "/some/*"}
+%%
+%% {"from": "/a/*",         /a/b/c          /some/b/c
+%% "to": "/some/*"}
+%%
+%% {"from": "/a",           /a              /some
+%% "to": "/some/*"}
+%%
+%% {"from": "/a/:foo/*",    /a/b/c          /some/b/c?foo=b     foo =:= b
+%% "to": "/some/:foo/*"}
+%%
+%% {"from": "/a/:foo",     /a/b             /some/?k=b&foo=b    foo =:= b
+%% "to": "/some",
+%%  "query": {
+%%      "k": ":foo"
+%%  }}
+%%
+%% {"from": "/a",           /a?foo=b        /some/b             foo =:= b
+%% "to": "/some/:foo",
+%%  }}
+
+
+
+handle_rewrite_req(#httpd{
+        path_parts=[DbName, <<"_design">>, DesignName, _Rewrite|PathParts],
+        method=Method,
+        mochi_req=MochiReq}=Req, _Db, DDoc) ->
+
+    % we are in a design handler
+    DesignId = <<"_design/", DesignName/binary>>,
+    Prefix = <<"/", DbName/binary, "/", DesignId/binary>>,
+    QueryList = couch_httpd:qs(Req),
+    QueryList1 = [{to_atom(K), V} || {K, V} <- QueryList],
+
+    #doc{body={Props}} = DDoc,
+
+    % get rules from ddoc
+    case couch_util:get_value(<<"rewrites">>, Props) of
+        undefined ->
+            couch_httpd:send_error(Req, 404, <<"rewrite_error">>,
+                            <<"Invalid path.">>);
+        Rules ->
+            % create dispatch list from rules
+            DispatchList =  [make_rule(Rule) || {Rule} <- Rules],
+
+            %% get raw path by matching url to a rule.
+            RawPath = case try_bind_path(DispatchList, Method, PathParts,
+                                    QueryList1) of
+                no_dispatch_path ->
+                    throw(not_found);
+                {NewPathParts, Bindings} ->
+                    Parts = [mochiweb_util:quote_plus(X) || X <- NewPathParts],
+
+                    % build new path, reencode query args, eventually convert
+                    % them to json
+                    Path = lists:append(
+                        string:join(Parts, [?SEPARATOR]),
+                        case Bindings of
+                            [] -> [];
+                            _ -> [$?, encode_query(Bindings)]
+                        end),
+                    
+                    % if path is relative detect it and rewrite path
+                    case mochiweb_util:safe_relative_path(Path) of
+                        undefined ->
+                            ?b2l(Prefix) ++ "/" ++ Path;
+                        P1 ->
+                            ?b2l(Prefix) ++ "/" ++ P1
+                    end
+
+                end,
+
+            % normalize final path (fix levels "." and "..")
+            RawPath1 = ?b2l(iolist_to_binary(normalize_path(RawPath))),
+
+            ?LOG_DEBUG("rewrite to ~p ~n", [RawPath1]),
+
+            % build a new mochiweb request
+            MochiReq1 = mochiweb_request:new(MochiReq:get(socket),
+                                             MochiReq:get(method),
+                                             RawPath1,
+                                             MochiReq:get(version),
+                                             MochiReq:get(headers)),
+
+            % cleanup, It force mochiweb to reparse raw uri.
+            MochiReq1:cleanup(),
+
+            chttpd:handle_request(MochiReq1)
+        end.
+
+
+
+%% @doc Try to find a rule matching current url. If none is found
+%% 404 error not_found is raised
+try_bind_path([], _Method, _PathParts, _QueryList) ->
+    no_dispatch_path;
+try_bind_path([Dispatch|Rest], Method, PathParts, QueryList) ->
+    [{PathParts1, Method1}, RedirectPath, QueryArgs] = Dispatch,
+    case bind_method(Method1, Method) of
+        true ->
+            case bind_path(PathParts1, PathParts, []) of
+                {ok, Remaining, Bindings} ->
+                    Bindings1 = Bindings ++ QueryList,
+
+                    % we parse query args from the rule and fill
+                    % it eventually with bindings vars
+                    QueryArgs1 = make_query_list(QueryArgs, Bindings1, []),
+                    
+                    % remove params in QueryLists1 that are already in
+                    % QueryArgs1
+                    Bindings2 = lists:foldl(fun({K, V}, Acc) ->
+                        K1 = to_atom(K),
+                        KV = case couch_util:get_value(K1, QueryArgs1) of
+                            undefined -> [{K1, V}];
+                            _V1 -> []
+                        end,
+                        Acc ++ KV
+                    end, [], Bindings1),
+
+                    FinalBindings = Bindings2 ++ QueryArgs1,
+                    NewPathParts = make_new_path(RedirectPath, FinalBindings,
+                                    Remaining, []),
+                    {NewPathParts, FinalBindings};
+                fail ->
+                    try_bind_path(Rest, Method, PathParts, QueryList)
+            end;
+        false ->
+            try_bind_path(Rest, Method, PathParts, QueryList)
+    end.
+
+%% rewriting dynamically the quey list given as query member in
+%% rewrites. Each value is replaced by one binding or an argument
+%% passed in url.
+make_query_list([], _Bindings, Acc) ->
+    Acc;
+make_query_list([{Key, {Value}}|Rest], Bindings, Acc) ->
+    Value1 = to_json({Value}),
+    make_query_list(Rest, Bindings, [{to_atom(Key), Value1}|Acc]);
+make_query_list([{Key, Value}|Rest], Bindings, Acc) when is_binary(Value) ->
+    Value1 = replace_var(Key, Value, Bindings),
+    make_query_list(Rest, Bindings, [{to_atom(Key), Value1}|Acc]);
+make_query_list([{Key, Value}|Rest], Bindings, Acc) when is_list(Value) ->
+    Value1 = replace_var(Key, Value, Bindings),
+    make_query_list(Rest, Bindings, [{to_atom(Key), Value1}|Acc]);
+make_query_list([{Key, Value}|Rest], Bindings, Acc) ->
+    make_query_list(Rest, Bindings, [{to_atom(Key), Value}|Acc]).
+
+replace_var(Key, Value, Bindings) ->
+    case Value of
+        <<":", Var/binary>> ->
+            get_var(Var, Bindings, Value);
+        _ when is_list(Value) ->
+            Value1 = lists:foldr(fun(V, Acc) ->
+                V1 = case V of
+                    <<":", VName/binary>> ->
+                        case get_var(VName, Bindings, V) of
+                            V2 when is_list(V2) ->
+                                iolist_to_binary(V2);
+                            V2 -> V2
+                        end;
+                    _ ->
+                        
+                        V
+                end,
+                [V1|Acc]
+            end, [], Value),
+            to_json(Value1);
+        _ when is_binary(Value) ->
+            Value;
+        _ ->
+            case Key of
+                <<"key">> -> to_json(Value);
+                <<"startkey">> -> to_json(Value);
+                <<"endkey">> -> to_json(Value);
+                _ ->
+                    lists:flatten(?JSON_ENCODE(Value))
+            end
+    end.
+
+
+get_var(VarName, Props, Default) ->
+    VarName1 = list_to_atom(binary_to_list(VarName)),
+    couch_util:get_value(VarName1, Props, Default).
+
+%% doc: build new patch from bindings. bindings are query args
+%% (+ dynamic query rewritten if needed) and bindings found in
+%% bind_path step.
+make_new_path([], _Bindings, _Remaining, Acc) ->
+    lists:reverse(Acc);
+make_new_path([?MATCH_ALL], _Bindings, Remaining, Acc) ->
+    Acc1 = lists:reverse(Acc) ++ Remaining,
+    Acc1;
+make_new_path([?MATCH_ALL|_Rest], _Bindings, Remaining, Acc) ->
+    Acc1 = lists:reverse(Acc) ++ Remaining,
+    Acc1;
+make_new_path([P|Rest], Bindings, Remaining, Acc) when is_atom(P) ->
+    P2 = case couch_util:get_value(P, Bindings) of
+        undefined -> << "undefined">>;
+        P1 -> P1
+    end,
+    make_new_path(Rest, Bindings, Remaining, [P2|Acc]);
+make_new_path([P|Rest], Bindings, Remaining, Acc) ->
+    make_new_path(Rest, Bindings, Remaining, [P|Acc]).
+
+
+%% @doc If method of the query fith the rule method. If the
+%% method rule is '*', which is the default, all
+%% request method will bind. It allows us to make rules
+%% depending on HTTP method.
+bind_method(?MATCH_ALL, _Method) ->
+    true;
+bind_method(Method, Method) ->
+    true;
+bind_method(_, _) ->
+    false.
+
+
+%% @doc bind path. Using the rule from we try to bind variables given
+%% to the current url by pattern matching
+bind_path([], [], Bindings) ->
+    {ok, [], Bindings};
+bind_path([?MATCH_ALL], Rest, Bindings) when is_list(Rest) ->
+    {ok, Rest, Bindings};
+bind_path(_, [], _) ->
+    fail;
+bind_path([Token|RestToken],[Match|RestMatch],Bindings) when is_atom(Token) ->
+    bind_path(RestToken, RestMatch, [{Token, Match}|Bindings]);
+bind_path([Token|RestToken], [Token|RestMatch], Bindings) ->
+    bind_path(RestToken, RestMatch, Bindings);
+bind_path(_, _, _) ->
+    fail.
+
+
+%% normalize path.
+normalize_path(Path)  ->
+    "/" ++ string:join(normalize_path1(string:tokens(Path,
+                "/"), []), [?SEPARATOR]).
+
+
+normalize_path1([], Acc) ->
+    lists:reverse(Acc);
+normalize_path1([".."|Rest], Acc) ->
+    Acc1 = case Acc of
+        [] -> [".."|Acc];
+        [T|_] when T =:= ".." -> [".."|Acc];
+        [_|R] -> R
+    end,
+    normalize_path1(Rest, Acc1);
+normalize_path1(["."|Rest], Acc) ->
+    normalize_path1(Rest, Acc);
+normalize_path1([Path|Rest], Acc) ->
+    normalize_path1(Rest, [Path|Acc]).
+
+
+%% @doc transform json rule in erlang for pattern matching
+make_rule(Rule) ->
+    Method = case couch_util:get_value(<<"method">>, Rule) of
+        undefined -> '*';
+        M -> list_to_atom(?b2l(M))
+    end,
+    QueryArgs = case couch_util:get_value(<<"query">>, Rule) of
+        undefined -> [];
+        {Args} -> Args
+        end,
+    FromParts  = case couch_util:get_value(<<"from">>, Rule) of
+        undefined -> ['*'];
+        From ->
+            parse_path(From)
+        end,
+    ToParts  = case couch_util:get_value(<<"to">>, Rule) of
+        undefined ->
+            throw({error, invalid_rewrite_target});
+        To ->
+            parse_path(To)
+        end,
+    [{FromParts, Method}, ToParts, QueryArgs].
+
+parse_path(Path) ->
+    {ok, SlashRE} = re:compile(<<"\\/">>),
+    path_to_list(re:split(Path, SlashRE), [], 0).
+
+%% @doc convert a path rule (from or to) to an erlang list
+%% * and path variable starting by ":" are converted
+%% in erlang atom.
+path_to_list([], Acc, _DotDotCount) ->
+    lists:reverse(Acc);
+path_to_list([<<>>|R], Acc, DotDotCount) ->
+    path_to_list(R, Acc, DotDotCount);
+path_to_list([<<"*">>|R], Acc, DotDotCount) ->
+    path_to_list(R, [?MATCH_ALL|Acc], DotDotCount);
+path_to_list([<<"..">>|R], Acc, DotDotCount) when DotDotCount == 2 ->
+    case couch_config:get("httpd", "secure_rewrites", "true") of
+    "false" ->
+        path_to_list(R, [<<"..">>|Acc], DotDotCount+1);
+    _Else ->
+        ?LOG_INFO("insecure_rewrite_rule ~p blocked", [lists:reverse(Acc) ++ [<<"..">>] ++ R]),
+        throw({insecure_rewrite_rule, "too many ../.. segments"})
+    end;
+path_to_list([<<"..">>|R], Acc, DotDotCount) ->
+    path_to_list(R, [<<"..">>|Acc], DotDotCount+1);
+path_to_list([P|R], Acc, DotDotCount) ->
+    P1 = case P of
+        <<":", Var/binary>> ->
+            list_to_atom(binary_to_list(Var));
+        _ -> P
+    end,
+    path_to_list(R, [P1|Acc], DotDotCount).
+
+encode_query(Props) ->
+    Props1 = lists:foldl(fun ({K, V}, Acc) ->
+        V1 = case is_list(V) of
+            true -> V;
+            false when is_binary(V) ->
+                V;
+            false ->
+                mochiweb_util:quote_plus(V)
+        end,
+        [{K, V1} | Acc]
+    end, [], Props),
+    lists:flatten(mochiweb_util:urlencode(Props1)).
+
+to_atom(V) when is_atom(V) ->
+    V;
+to_atom(V) when is_binary(V) ->
+    to_atom(?b2l(V));
+to_atom(V) ->
+    list_to_atom(V).
+
+to_json(V) ->
+    iolist_to_binary(?JSON_ENCODE(V)).