fix(ft): set more conservative filename length limit

Otherwise, local fs exporter will have a hard time preserving the
filemeta, because its filename is even 13 bytes longer.

apps/emqx_ft/src/emqx_ft_schema.erl

@@ -42,7 +42,9 @@
 %% on most filesystems. Even though, say, S3 does not have such limitations, it's
 %% still useful to have a limit on the filename length, to avoid having to deal with
 %% limits in the storage backends.
--define(MAX_FILENAME_BYTELEN, 255).
+%% Usual realistic limit is 255 bytes actually, but we leave some room for backends
+%% to spare.
+-define(MAX_FILENAME_BYTELEN, 240).
 
 -import(hoconsc, [ref/2, mk/2]).
 

apps/emqx_ft/src/emqx_ft_storage_exporter_fs.erl

@@ -128,7 +128,17 @@ complete(
     Filemeta = FilemetaIn#{checksum => Checksum},
     ok = file:close(Handle),
     _ = filelib:ensure_dir(ResultFilepath),
-    _ = file:write_file(mk_manifest_filename(ResultFilepath), encode_filemeta(Filemeta)),
+    ManifestFilepath = mk_manifest_filename(ResultFilepath),
+    case file:write_file(ManifestFilepath, encode_filemeta(Filemeta)) of
+        ok ->
+            ok;
+        {error, Reason} ->
+            ?SLOG(warning, "filemeta_write_failed", #{
+                path => ManifestFilepath,
+                meta => Filemeta,
+                reason => Reason
+            })
+    end,
     file:rename(Filepath, ResultFilepath).
 
 -spec discard(export_st()) ->

apps/emqx_ft/test/emqx_ft_SUITE.erl

@@ -261,6 +261,7 @@ t_nasty_clientids_fileids(_Config) ->
         fun({ClientId, FileId}) ->
             ok = emqx_ft_test_helpers:upload_file(ClientId, FileId, "justfile", ClientId),
             [Export] = list_files(ClientId),
+            ?assertMatch(#{meta := #{name := "justfile"}}, Export),
             ?assertEqual({ok, ClientId}, read_export(Export))
         end,
         Transfers
@@ -271,13 +272,14 @@ t_nasty_filenames(_Config) ->
         {<<"nasty1">>, "146%"},
         {<<"nasty2">>, "🌚"},
         {<<"nasty3">>, "中文.txt"},
-        {<<"nasty4">>, _254Bytes = string:join(lists:duplicate(255 div 5, "LONG"), ".")}
+        {<<"nasty4">>, _239Bytes = string:join(lists:duplicate(240 div 5, "LONG"), ".")}
     ],
     ok = lists:foreach(
         fun({ClientId, Filename}) ->
             FileId = unicode:characters_to_binary(Filename),
             ok = emqx_ft_test_helpers:upload_file(ClientId, FileId, Filename, FileId),
             [Export] = list_files(ClientId),
+            ?assertMatch(#{meta := #{name := Filename}}, Export),
             ?assertEqual({ok, FileId}, read_export(Export))
         end,
         Filenames