feat(topic): match empty topic levels more loosely

So that the result of `emqx_topic:tokens/1` would be perfectly
matchable with the result of `emqx_topic:words/1` of a topic filter
with empty levels.

apps/emqx/src/emqx_topic.erl

@@ -91,13 +91,11 @@ match([H | T1], [H | T2]) ->
     match(T1, T2);
 match([_H | T1], ['+' | T2]) ->
     match(T1, T2);
+match([<<>> | T1], ['' | T2]) ->
+    match(T1, T2);
 match(_, ['#']) ->
     true;
-match([_H1 | _], [_H2 | _]) ->
-    false;
-match([_H1 | _], []) ->
-    false;
-match([], [_H | _T2]) ->
+match(_, _) ->
     false.
 
 -spec match_share(Name, Filter) -> boolean() when

apps/emqx/test/emqx_topic_SUITE.erl

@@ -115,6 +115,12 @@ t_sys_match(_) ->
     true = match(<<"a/b/$c">>, <<"a/b/#">>),
     true = match(<<"a/b/$c">>, <<"a/#">>).
 
+t_match_tokens(_) ->
+    true = match(emqx_topic:tokens(<<"a/b/c">>), words(<<"a/+/c">>)),
+    true = match(emqx_topic:tokens(<<"a//c">>), words(<<"a/+/c">>)),
+    false = match(emqx_topic:tokens(<<"a//c/">>), words(<<"a/+/c">>)),
+    true = match(emqx_topic:tokens(<<"a//c/">>), words(<<"a/+/c/#">>)).
+
 t_match_perf(_) ->
     true = match(<<"a/b/ccc">>, <<"a/#">>),
     Name = <<"/abkc/19383/192939/akakdkkdkak/xxxyyuya/akakak">>,