From 8ff9a03df3b93076d9c0b477569540cef241bc05 Mon Sep 17 00:00:00 2001
From: ieQu1 <99872536+ieQu1@users.noreply.github.com>
Date: Thu, 9 Jun 2022 13:46:56 +0200
Subject: [PATCH] fix(retainer): Handle zero-length topic levels

---
 apps/emqx_retainer/src/emqx_retainer_index.erl        | 4 ++--
 apps/emqx_retainer/test/emqx_retainer_index_SUITE.erl | 8 ++++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/apps/emqx_retainer/src/emqx_retainer_index.erl b/apps/emqx_retainer/src/emqx_retainer_index.erl
index 0d739e2b0..3f5b87b90 100644
--- a/apps/emqx_retainer/src/emqx_retainer_index.erl
+++ b/apps/emqx_retainer/src/emqx_retainer_index.erl
@@ -176,11 +176,11 @@ condition([NIndex | OtherIndex], ['+' | OtherTokens], N, IndexMatch, OtherMatch)
 condition(Index, ['+' | OtherTokens], N, IndexMatch, OtherMatch) ->
     condition(Index, OtherTokens, N + 1, IndexMatch, ['_' | OtherMatch]);
 condition([NIndex | OtherIndex], [Token | OtherTokens], N, IndexMatch, OtherMatch) when
-    NIndex =:= N, is_binary(Token)
+    NIndex =:= N, is_binary(Token) orelse Token =:= ''
 ->
     condition(OtherIndex, OtherTokens, N + 1, [Token | IndexMatch], OtherMatch);
 condition(Index, [Token | OtherTokens], N, IndexMatch, OtherMatch) when
-    is_binary(Token)
+    is_binary(Token) orelse Token =:= ''
 ->
     condition(Index, OtherTokens, N + 1, IndexMatch, [Token | OtherMatch]).
 
diff --git a/apps/emqx_retainer/test/emqx_retainer_index_SUITE.erl b/apps/emqx_retainer/test/emqx_retainer_index_SUITE.erl
index ce37f2788..793df0410 100644
--- a/apps/emqx_retainer/test/emqx_retainer_index_SUITE.erl
+++ b/apps/emqx_retainer/test/emqx_retainer_index_SUITE.erl
@@ -193,6 +193,14 @@ t_condition_index(_Config) ->
             [1],
             [<<"a">>, '#']
         )
+    ),
+
+    ?assertEqual(
+        {[1, 2, 3], {['', <<"saya">>, '_'], []}},
+        emqx_retainer_index:condition(
+            [1, 2, 3],
+            ['', <<"saya">>, '+']
+        )
     ).
 
 t_restore_topic(_Config) ->