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% 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.
% This module serves two functions
% - provides public API to use to get value for a given feature flag and subject
% - implements {feature_flags, couch_flags} service
% The module relies on couch_epi_data_gen which uses the data returned by
% `couch_flags_config:data()` to generate callback module `couch_epi_data_gen_flags_config`.
% The generated module shouldn't be used directly. We use following APIs
% - `couch_epi:get_handle({flags, config})` - to get handler (name of generated module)
% - `couch_epi:get_value(Handle, Key) - to do efficient matching
%
% The generated module implements clauses like the following
% - get(couch, {binary_match_rule()}) ->
% {matched_pattern(), size(matched_pattern()), [flag()]} | undefined
% For example
% - get(couch, {<<"/shards/test/exact">>}) ->
% {<<"/shards/test/exact">>,18,[baz,flag_bar,flag_foo]};
% - get(couch, {<<"/shards/test", _/binary>>}) ->
% {<<"/shards/test*">>,13,[baz,flag_bar,flag_foo]};
% - get(couch, {<<"/shards/exact">>}) ->
% {<<"/shards/exact">>,13,[flag_bar,flag_foo]};
% - get(couch, {<<"/shards/blacklist", _/binary>>}) ->
% {<<"/shards/blacklist*">>,18,[]};
% - get(couch, {<<"/", _/binary>>}) ->
% {<<"/*">>,2,[flag_foo]};
% - get(_, _) -> undefined.
%
% The `couch_epi:get/2` uses the Handler module to implement efficient matching.
% In order to distinguish between shards and clustered db the following
% convention is used.
% - it is a shard if pattern starts with `/`
-module(couch_flags).
%% Public API
-export([
enabled/1,
is_enabled/2
]).
%% For internal use
-export([
rules/0
]).
%% For use from plugin
-export([
subject_key/1
]).
-include_lib("couch/include/couch_db.hrl").
-type subject()
:: map()
| #httpd{}
| string()
| binary().
-define(SERVICE_ID, feature_flags).
-spec enabled(subject()) -> [atom()].
enabled(Subject) ->
Key = maybe_handle(subject_key, [Subject], fun subject_key/1),
Handle = couch_epi:get_handle({flags, config}),
lists:usort(enabled(Handle, {<<"/", Key/binary>>})
++ enabled(Handle, {Key})).
-spec is_enabled(FlagId :: atom(), subject()) -> boolean().
is_enabled(FlagId, Subject) ->
lists:member(FlagId, enabled(Subject)).
-spec rules() ->
[{Key :: string(), Value :: string()}].
rules() ->
Handle = couch_epi:get_handle(?SERVICE_ID),
lists:flatten(couch_epi:apply(Handle, ?SERVICE_ID, rules, [], [])).
-spec enabled(Handle :: couch_epi:handle(), Key :: {binary()}) -> [atom()].
enabled(Handle, Key) ->
case couch_epi:get_value(Handle, couch, Key) of
{_, _, Flags} -> Flags;
undefined -> []
end.
-spec subject_key(subject()) -> binary().
subject_key(#{} = Db) ->
subject_key(fabric2_db:name(Db));
subject_key(#httpd{path_parts=[Name | _Rest]}) ->
subject_key(Name);
subject_key(#httpd{path_parts=[]}) ->
<<>>;
subject_key(Name) when is_list(Name) ->
subject_key(list_to_binary(Name));
subject_key(Name) when is_binary(Name) ->
Name.
-spec maybe_handle(
Function :: atom(),
Args :: [term()],
Default :: fun((Args :: [term()]) -> term())) ->
term().
maybe_handle(Func, Args, Default) ->
Handle = couch_epi:get_handle(?SERVICE_ID),
case couch_epi:decide(Handle, ?SERVICE_ID, Func, Args, []) of
no_decision when is_function(Default) ->
apply(Default, Args);
{decided, Result} ->
Result
end.
|
