1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
|
% 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").
-include_lib("mem3/include/mem3.hrl").
-include("couch_db_int.hrl").
-type subject()
:: #db{}
| #httpd{}
| #shard{}
| #ordered_shard{}
| 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, {couch_db:normalize_dbname(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{name = Name}) ->
subject_key(Name);
subject_key(#httpd{path_parts=[Name | _Rest]}) ->
subject_key(Name);
subject_key(#httpd{path_parts=[]}) ->
<<>>;
subject_key(#shard{name = Name}) ->
subject_key(Name);
subject_key(#ordered_shard{name = Name}) ->
subject_key(Name);
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.
|
