fix(ft-gc): ensure GC of already complete transfers

apps/emqx_ft/src/emqx_ft_storage_fs.erl

@@ -267,8 +267,12 @@ lookup_assembler([Source | Sources]) ->
 
 check_if_already_exported(Storage, Transfer) ->
     case files(Storage, #{transfer => Transfer}) of
-        {ok, #{items := [_ | _]}} -> ok;
-        _ -> {error, not_found}
+        {ok, #{items := [_ | _]}} ->
+            % NOTE: we don't know coverage here, let's just clean up locally.
+            _ = emqx_ft_storage_fs_gc:collect(Storage, Transfer, [node()]),
+            ok;
+        _ ->
+            {error, not_found}
     end.
 
 lookup_local_assembler(Transfer) ->

apps/emqx_ft/test/emqx_ft_storage_fs_gc_SUITE.erl

@@ -266,6 +266,38 @@ t_gc_incomplete_transfers(_Config) ->
         0
     ).
 
+t_gc_repeated_transfer(_Config) ->
+    {local, Storage} = emqx_ft_storage:backend(),
+    Transfer = {
+        TID = {<<"clientclient">>, mk_file_id()},
+        #{name => "repeat.please", segments_ttl => 10},
+        emqx_ft_content_gen:new({?LINE, Size = 42}, 16)
+    },
+    Size = start_transfer(Storage, Transfer),
+    {ok, {ok, #{stats := Stats1}}} = ?wait_async_action(
+        ?assertEqual(ok, complete_transfer(Storage, TID, Size)),
+        #{?snk_kind := garbage_collection},
+        1000
+    ),
+    Size = start_transfer(Storage, Transfer),
+    {ok, {ok, #{stats := Stats2}}} = ?wait_async_action(
+        ?assertEqual(ok, complete_transfer(Storage, TID, Size)),
+        #{?snk_kind := garbage_collection},
+        1000
+    ),
+    ?assertMatch(
+        #gcstats{files = 4, directories = 2},
+        Stats1
+    ),
+    ?assertMatch(
+        #gcstats{files = 4, directories = 2},
+        Stats2
+    ),
+    ?assertEqual(
+        {ok, []},
+        emqx_ft_storage_fs:list(Storage, TID, fragment)
+    ).
+
 t_gc_handling_errors(_Config) ->
     ok = set_gc_config(minimum_segments_ttl, 0),
     ok = set_gc_config(maximum_segments_ttl, 0),
@@ -349,14 +381,18 @@ complete_transfer(Storage, Transfer, Size) ->
     complete_transfer(Storage, Transfer, Size, 100).
 
 complete_transfer(Storage, Transfer, Size, Timeout) ->
-    {async, Pid} = emqx_ft_storage_fs:assemble(Storage, Transfer, Size),
-    MRef = erlang:monitor(process, Pid),
-    Pid ! kickoff,
-    receive
-        {'DOWN', MRef, process, Pid, {shutdown, Result}} ->
-            Result
-    after Timeout ->
-        ct:fail("Assembler did not finish in time")
+    case emqx_ft_storage_fs:assemble(Storage, Transfer, Size) of
+        ok ->
+            ok;
+        {async, Pid} ->
+            MRef = erlang:monitor(process, Pid),
+            Pid ! kickoff,
+            receive
+                {'DOWN', MRef, process, Pid, {shutdown, Result}} ->
+                    Result
+            after Timeout ->
+                ct:fail("Assembler did not finish in time")
+            end
     end.
 
 mk_file_id() ->