refactor(topic_index): less special handling for leading $ words

apps/emqx/src/emqx_trie_search.erl

@@ -16,10 +16,10 @@
 
 %% @doc Topic index for matching topics to topic filters.
 %%
-%% Works on top of ETS ordered_set table. Keys are tuples constructed from
+%% Works on top of a ordered collection data set, such as ETS ordered_set table.
-%% parsed topic filters and record IDs, wrapped in a tuple to order them
+%% Keys are tuples constructed from parsed topic filters and record IDs,
-%% strictly greater than unit tuple (`{}`). Existing table may be used if
+%% wrapped in a tuple to order them strictly greater than unit tuple (`{}`).
-%% existing keys will not collide with index keys.
+%% Existing table may be used if existing keys will not collide with index keys.
 %%
 %% Designed to effectively answer questions like:
 %% 1. Does any topic filter match given topic?
@@ -110,15 +110,10 @@
 -type nextf() :: fun((key(_) | base_key()) -> ?END | key(_)).
 -type opts() :: [unique | return_first].
 
-
 %% Holds the constant values of each search.
 -record(ctx, {
     %% A function which can quickly find the immediate-next record of the given prefix
     nextf :: nextf(),
-    %% The initial prefix to start searching from
-    %% if the input topic starts with a dollar-word, it's the first word like [<<"$SYS">>]
-    %% otherwise it's a []
-    prefix0 :: [word()],
     %% The initial words of a topic
     words0 :: [word()],
     %% Return as soon as there is one match found
@@ -129,7 +124,7 @@
 -spec make_key(emqx_types:topic(), ID) -> key(ID).
 make_key(Topic, ID) when is_binary(Topic) ->
     Words = words(Topic),
-    case lists:any(fun erlang:is_atom/1, Words) of
+    case emqx_topic:wildcard(Words) of
         true ->
             %% it's a wildcard
             {Words, {ID}};
@@ -186,10 +181,9 @@ matches(Topic, NextF, Opts) ->
 
 %% @doc Entrypoint of the search for a given topic.
 search(Topic, NextF, Opts) ->
-    {Words, Prefix} = match_init(Topic),
+    Words = words(Topic),
     Context = #ctx{
         nextf = NextF,
-        prefix0 = Prefix,
         words0 = Words,
         return_first = proplists:get_bool(return_first, Opts)
     },
@@ -200,7 +194,15 @@ search(Topic, NextF, Opts) ->
             false ->
                 []
         end,
-    {MaybeEnd, Acc1} = search_new(Context, base(Prefix), Acc0),
+    Base =
+        case hd(Words) of
+            <<$$, _/binary>> ->
+                %% skip all filters starts with # or +
+                base([hd(Words)]);
+            _ ->
+                base([])
+        end,
+    {MaybeEnd, Acc1} = search_new(Context, Base, Acc0),
     Acc = match_topics(Context, Topic, MaybeEnd, Acc1),
     case is_map(Acc) of
         true ->
@@ -211,18 +213,30 @@ search(Topic, NextF, Opts) ->
 
 %% The recursive entrypoint of the trie-search algorithm.
 %% Always start from the initial prefix and words.
-search_new(C, NewBase, Acc) ->
+search_new(#ctx{words0 = Words} = C, NewBase, Acc) ->
-    search_moved(C, move_up(C, NewBase), Acc).
+    case move_up(C, NewBase) of
-
+        ?END ->
-search_moved(_, ?END, Acc) ->
             {?END, Acc};
-search_moved(#ctx{prefix0 = [], words0 = Words0} = C, {Filter, _} = T, Acc) ->
+        {Filter, _} = T ->
-    %% This is not a '$' topic, start from '+'
+            search_plus(C, Words, Filter, [], T, Acc)
-    search_plus(C, Words0, Filter, [], T, Acc);
+    end.
-search_moved(#ctx{prefix0 = Prefix, words0 = Words0} = C, {Filter, _} = T, Acc) ->
+
-    [DollarWord] = Prefix,
+%% Try to use '+' as the next word in the prefix.
-    %% Start from the '$' word
+search_plus(C, [W, X | Words], [W, X | Filter], RPrefix, T, Acc) ->
-    search_up(C, DollarWord, Words0, Filter, [], T, Acc).
+    %% Directly append the current word to the matching prefix (RPrefix).
+    %% Micro optimization: try not to call the next clause because
+    %% it is not a continuation.
+    search_plus(C, [X | Words], [X | Filter], [W | RPrefix], T, Acc);
+search_plus(C, [W | Words], ['+' | _] = Filter, RPrefix, T, Acc) ->
+    case search_up(C, '+', Words, Filter, RPrefix, T, Acc) of
+        {T, Acc1} ->
+            search_up(C, W, Words, Filter, RPrefix, T, Acc1);
+        TargetMoved ->
+            TargetMoved
+    end;
+search_plus(C, [W | Words], Filter, RPrefix, T, Acc) ->
+    %% not a plus
+    search_up(C, W, Words, Filter, RPrefix, T, Acc).
 
 %% Search to the bigger end of ordered collection of topics and topic-filters.
 search_up(C, Word, Words, Filter, RPrefix, T, Acc) ->
@@ -240,23 +254,6 @@ search_up(C, Word, Words, Filter, RPrefix, T, Acc) ->
             search_plus(C, Words, tl(Filter), [Word | RPrefix], T, Acc)
     end.
 
-%% Try to use '+' as the next word in the prefix.
-search_plus(C, [W, X | Words], [W, X | Filter], RPrefix, T, Acc) ->
-    %% Directly append the current word to the matching prefix (RPrefix).
-    %% Micro optimization: try not to call the next clause because
-    %% it is not a continuation.
-    search_plus(C, [X | Words], [X | Filter], [W | RPrefix], T, Acc);
-search_plus(C, [W | Words], ['+' | _] = Filter, RPrefix, T, Acc) ->
-    case search_up(C, '+', Words, Filter, RPrefix, T, Acc) of
-        {T, Acc} ->
-            search_up(C, W, Words, Filter, RPrefix, T, Acc);
-        TargetMoved ->
-            TargetMoved
-    end;
-search_plus(C, [W | Words], Filter, RPrefix, T, Acc) ->
-    %% not a plus
-    search_up(C, W, Words, Filter, RPrefix, T, Acc).
-
 %% Compare prefix word then the next words in suffix against the search-target
 %% topic or topic-filter.
 compare(_, NotFilter, _) when is_binary(NotFilter) ->
@@ -290,16 +287,6 @@ match_add(K = {_Filter, ID}, Acc = #{}) ->
 match_add(K, Acc) ->
     [K | Acc].
 
-match_init(Topic) ->
-    case words(Topic) of
-        [W = <<"$", _/bytes>> | Rest] ->
-            % NOTE
-            % This will effectively skip attempts to match special topics to `#` or `+/...`.
-            {Rest, [W]};
-        Words ->
-            {Words, []}
-    end.
-
 -spec words(emqx_types:topic()) -> [word()].
 words(Topic) when is_binary(Topic) ->
     % NOTE
@@ -320,9 +307,6 @@ match_topics(#ctx{nextf = NextF} = C, Topic, {Topic, _} = Key, Acc) ->
 match_topics(#ctx{nextf = NextF} = C, Topic, {F, _}, Acc) when F < Topic ->
     %% the last key is a filter, try jump to the topic
     match_topics(C, Topic, NextF(base(Topic)), Acc);
-match_topics(#ctx{nextf = NextF} = C, Topic, continue, Acc) ->
-    %% the last key is a '+/...' wildcard
-    match_topics(C, Topic, NextF(base(Topic)), Acc);
 match_topics(_C, _Topic, _Key, Acc) ->
     %% gone pass the topic
     Acc.

apps/emqx/test/emqx_topic_index_SUITE.erl

@@ -172,14 +172,25 @@ t_match8(Config) ->
     Filters = [<<"+">>, <<"dev/global/sensor">>, <<"dev/+/sensor/#">>],
     IDs = [1, 2, 3],
     Keys = [{F, ID} || F <- Filters, ID <- IDs],
-    lists:foreach(fun({F, ID}) ->
+    lists:foreach(
+        fun({F, ID}) ->
             M:insert(F, ID, <<>>, Tab)
-                  end, Keys),
+        end,
+        Keys
+    ),
     Topic = <<"dev/global/sensor">>,
     Matches = lists:sort(matches(M, Topic, Tab)),
-    ?assertEqual([<<"dev/+/sensor/#">>, <<"dev/+/sensor/#">>, <<"dev/+/sensor/#">>,
+    ?assertEqual(
-                  <<"dev/global/sensor">>, <<"dev/global/sensor">>, <<"dev/global/sensor">>],
+        [
-                 [emqx_topic_index:get_topic(Match) || Match <- Matches]).
+            <<"dev/+/sensor/#">>,
+            <<"dev/+/sensor/#">>,
+            <<"dev/+/sensor/#">>,
+            <<"dev/global/sensor">>,
+            <<"dev/global/sensor">>,
+            <<"dev/global/sensor">>
+        ],
+        [emqx_topic_index:get_topic(Match) || Match <- Matches]
+    ).
 
 t_match_fast_forward(Config) ->
     M = get_module(Config),