From 0aa4cdbaf355e6bce3fed48a975b1fe251c1af5d Mon Sep 17 00:00:00 2001
From: Andrew Mayorov <encube.ul@gmail.com>
Date: Tue, 30 Jul 2024 16:51:14 +0200
Subject: [PATCH] feat(ds): add generic preconditions implementation

---
 .../src/emqx_ds_precondition.erl              | 184 ++++++++++++++++++
 1 file changed, 184 insertions(+)
 create mode 100644 apps/emqx_durable_storage/src/emqx_ds_precondition.erl

diff --git a/apps/emqx_durable_storage/src/emqx_ds_precondition.erl b/apps/emqx_durable_storage/src/emqx_ds_precondition.erl
new file mode 100644
index 000000000..5f86d6c25
--- /dev/null
+++ b/apps/emqx_durable_storage/src/emqx_ds_precondition.erl
@@ -0,0 +1,184 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 20212024 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% 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.
+%%--------------------------------------------------------------------
+
+-module(emqx_ds_precondition).
+-include_lib("emqx_utils/include/emqx_message.hrl").
+-include_lib("emqx_durable_storage/include/emqx_ds.hrl").
+
+-export([verify/3]).
+-export([matches/2]).
+
+-export_type([matcher/0, mismatch/0]).
+
+-type matcher() :: #message_matcher{}.
+-type mismatch() :: emqx_types:message() | not_found.
+
+-callback lookup_message(_Ctx, matcher()) ->
+    emqx_types:message() | not_found | emqx_ds:error(_).
+
+%%
+
+-spec verify(module(), _Ctx, [emqx_ds:precondition()]) ->
+    ok | {precondition_failed, mismatch()} | emqx_ds:error(_).
+verify(Mod, Ctx, [_Precondition = {Cond, Msg} | Rest]) ->
+    case verify_precondition(Mod, Ctx, Cond, Msg) of
+        ok ->
+            verify(Mod, Ctx, Rest);
+        Failed ->
+            Failed
+    end;
+verify(_Mod, _Ctx, []) ->
+    ok.
+
+verify_precondition(Mod, Ctx, if_exists, Matcher) ->
+    case Mod:lookup_message(Ctx, Matcher) of
+        Msg = #message{} ->
+            verify_match(Msg, Matcher);
+        not_found ->
+            {precondition_failed, not_found};
+        Error = {error, _, _} ->
+            Error
+    end;
+verify_precondition(Mod, Ctx, unless_exists, Matcher) ->
+    case Mod:lookup_message(Ctx, Matcher) of
+        Msg = #message{} ->
+            verify_nomatch(Msg, Matcher);
+        not_found ->
+            ok;
+        Error = {error, _, _} ->
+            Error
+    end.
+
+verify_match(Msg, Matcher) ->
+    case matches(Msg, Matcher) of
+        true -> ok;
+        false -> {precondition_failed, Msg}
+    end.
+
+verify_nomatch(Msg, Matcher) ->
+    case matches(Msg, Matcher) of
+        false -> ok;
+        true -> {precondition_failed, Msg}
+    end.
+
+-spec matches(emqx_types:message(), matcher()) -> boolean().
+matches(
+    Message,
+    #message_matcher{from = From, topic = Topic, payload = Pat, headers = Headers}
+) ->
+    case Message of
+        #message{from = From, topic = Topic} when Pat =:= '_' ->
+            matches_headers(Message, Headers);
+        #message{from = From, topic = Topic, payload = Pat} ->
+            matches_headers(Message, Headers);
+        _ ->
+            false
+    end.
+
+matches_headers(_Message, MatchHeaders) when map_size(MatchHeaders) =:= 0 ->
+    true;
+matches_headers(#message{headers = Headers}, MatchHeaders) ->
+    maps:intersect(MatchHeaders, Headers) =:= MatchHeaders.
+
+%% Basic tests
+
+-ifdef(TEST).
+-include_lib("eunit/include/eunit.hrl").
+-compile(export_all).
+
+conjunction_test() ->
+    %% Contradictory preconditions, always false.
+    Preconditions = [
+        {if_exists, matcher(<<"c1">>, <<"t/1">>, 0, '_')},
+        {unless_exists, matcher(<<"c1">>, <<"t/1">>, 0, '_')}
+    ],
+    ?assertEqual(
+        {precondition_failed, not_found},
+        verify(?MODULE, [], Preconditions)
+    ),
+    %% Check that the order does not matter.
+    ?assertEqual(
+        {precondition_failed, not_found},
+        verify(?MODULE, [], lists:reverse(Preconditions))
+    ),
+    ?assertEqual(
+        {precondition_failed, message(<<"c1">>, <<"t/1">>, 0, <<>>)},
+        verify(
+            ?MODULE,
+            [message(<<"c1">>, <<"t/1">>, 0, <<>>)],
+            Preconditions
+        )
+    ).
+
+matches_test() ->
+    ?assert(
+        matches(
+            message(<<"mtest1">>, <<"t/same">>, 12345, <<?MODULE_STRING>>),
+            matcher(<<"mtest1">>, <<"t/same">>, 12345, '_')
+        )
+    ).
+
+matches_headers_test() ->
+    ?assert(
+        matches(
+            message(<<"mtest2">>, <<"t/same">>, 23456, <<?MODULE_STRING>>, #{h1 => 42, h2 => <<>>}),
+            matcher(<<"mtest2">>, <<"t/same">>, 23456, '_', #{h2 => <<>>})
+        )
+    ).
+
+mismatches_headers_test() ->
+    ?assertNot(
+        matches(
+            message(<<"mtest3">>, <<"t/same">>, 23456, <<?MODULE_STRING>>, #{h1 => 42, h2 => <<>>}),
+            matcher(<<"mtest3">>, <<"t/same">>, 23456, '_', #{h2 => <<>>, h3 => <<"required">>})
+        )
+    ).
+
+matcher(ClientID, Topic, TS, Payload) ->
+    matcher(ClientID, Topic, TS, Payload, #{}).
+
+matcher(ClientID, Topic, TS, Payload, Headers) ->
+    #message_matcher{
+        from = ClientID,
+        topic = Topic,
+        timestamp = TS,
+        payload = Payload,
+        headers = Headers
+    }.
+
+message(ClientID, Topic, TS, Payload) ->
+    message(ClientID, Topic, TS, Payload, #{}).
+
+message(ClientID, Topic, TS, Payload, Headers) ->
+    #message{
+        id = <<>>,
+        qos = 0,
+        from = ClientID,
+        topic = Topic,
+        timestamp = TS,
+        payload = Payload,
+        headers = Headers
+    }.
+
+lookup_message(Messages, Matcher) ->
+    case lists:search(fun(M) -> matches(M, Matcher) end, Messages) of
+        {value, Message} ->
+            Message;
+        false ->
+            not_found
+    end.
+
+-endif.