1%% This Source Code Form is subject to the terms of the Mozilla Public
2%% License, v. 2.0. If a copy of the MPL was not distributed with this
3%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
4%%
5%% Copyright (c) 2007-2021 VMware, Inc. or its affiliates.  All rights reserved.
6%%
7
8-module(rabbit_exchange_decorator).
9
10-include_lib("rabbit_common/include/rabbit.hrl").
11
12-export([select/2, set/1]).
13
14-behaviour(rabbit_registry_class).
15
16-export([added_to_rabbit_registry/2, removed_from_rabbit_registry/1]).
17
18%% This is like an exchange type except that:
19%%
20%% 1) It applies to all exchanges as soon as it is installed, therefore
21%% 2) It is not allowed to affect validation, so no validate/1 or
22%%    assert_args_equivalence/2
23%%
24%% It's possible in the future we might make decorators
25%% able to manipulate messages as they are published.
26
27-type(tx() :: 'transaction' | 'none').
28-type(serial() :: pos_integer() | tx()).
29
30-callback description() -> [proplists:property()].
31
32%% Should Rabbit ensure that all binding events that are
33%% delivered to an individual exchange can be serialised? (they
34%% might still be delivered out of order, but there'll be a
35%% serial number).
36-callback serialise_events(rabbit_types:exchange()) -> boolean().
37
38%% called after declaration and recovery
39-callback create(tx(), rabbit_types:exchange()) -> 'ok'.
40
41%% called after exchange (auto)deletion.
42-callback delete(tx(), rabbit_types:exchange(), [rabbit_types:binding()]) ->
43    'ok'.
44
45%% called when the policy attached to this exchange changes.
46-callback policy_changed(rabbit_types:exchange(), rabbit_types:exchange()) ->
47    'ok'.
48
49%% called after a binding has been added or recovered
50-callback add_binding(serial(), rabbit_types:exchange(),
51                      rabbit_types:binding()) -> 'ok'.
52
53%% called after bindings have been deleted.
54-callback remove_bindings(serial(), rabbit_types:exchange(),
55                          [rabbit_types:binding()]) -> 'ok'.
56
57%% Allows additional destinations to be added to the routing decision.
58-callback route(rabbit_types:exchange(), rabbit_types:delivery()) ->
59    [rabbit_amqqueue:name() | rabbit_exchange:name()].
60
61%% Whether the decorator wishes to receive callbacks for the exchange
62%% none:no callbacks, noroute:all callbacks except route, all:all callbacks
63-callback active_for(rabbit_types:exchange()) -> 'none' | 'noroute' | 'all'.
64
65%%----------------------------------------------------------------------------
66
67added_to_rabbit_registry(_Type, _ModuleName) ->
68    [maybe_recover(X) || X <- rabbit_exchange:list()],
69    ok.
70removed_from_rabbit_registry(_Type) ->
71    [maybe_recover(X) || X <- rabbit_exchange:list()],
72    ok.
73
74%% select a subset of active decorators
75select(all,   {Route, NoRoute})  -> filter(Route ++ NoRoute);
76select(route, {Route, _NoRoute}) -> filter(Route);
77select(raw,   {Route, NoRoute})  -> Route ++ NoRoute.
78
79filter(Modules) ->
80    [M || M <- Modules, code:which(M) =/= non_existing].
81
82set(X) ->
83    Decs = lists:foldl(fun (D, {Route, NoRoute}) ->
84                               ActiveFor = D:active_for(X),
85                               {cons_if_eq(all,     ActiveFor, D, Route),
86                                cons_if_eq(noroute, ActiveFor, D, NoRoute)}
87                       end, {[], []}, list()),
88    X#exchange{decorators = Decs}.
89
90list() -> [M || {_, M} <- rabbit_registry:lookup_all(exchange_decorator)].
91
92cons_if_eq(Select,  Select, Item,  List) -> [Item | List];
93cons_if_eq(_Select, _Other, _Item, List) -> List.
94
95maybe_recover(X = #exchange{name       = Name,
96                            decorators = Decs}) ->
97    #exchange{decorators = Decs1} = set(X),
98    Old = lists:sort(select(all, Decs)),
99    New = lists:sort(select(all, Decs1)),
100    case New of
101        Old -> ok;
102        _   -> %% TODO create a tx here for non-federation decorators
103               [M:create(none, X) || M <- New -- Old],
104               rabbit_exchange:update_decorators(Name)
105    end.
106