fix(ft): add `enable` flag to every backend

And tolerate multiple configured backends, as long as only one of
them is enabled.

apps/emqx_ft/README.md

@@ -29,6 +29,7 @@ file_transfer {
   enable = true
   storage {
     local {
+      enable = true
       exporter {
         local { root = "/var/lib/emqx/transfers" }
       }
@@ -50,7 +51,9 @@ file_transfer {
   enable = true
   storage {
     local {
+      enable = true
       exporter {
+        enable = true
         s3 {
           host = "s3.us-east-1.amazonaws.com"
           port = "443"

apps/emqx_ft/src/emqx_ft_schema.erl

@@ -26,6 +26,7 @@
 -export([schema/1]).
 
 -export([translate/1]).
+-export([backend/1]).
 
 -type json_value() ::
     null
@@ -142,7 +143,7 @@ fields(local_storage) ->
                     }
                 }
             )}
-    ];
+    ] ++ common_backend_fields();
 fields(local_storage_segments) ->
     [
         {root,
@@ -190,9 +191,9 @@ fields(local_storage_exporter) ->
                     required => false
                 }
             )}
-    ];
+    ] ++ common_backend_fields();
 fields(s3_exporter) ->
-    emqx_s3_schema:fields(s3);
+    emqx_s3_schema:fields(s3) ++ common_backend_fields();
 fields(local_storage_segments_gc) ->
     [
         {interval,
@@ -229,6 +230,18 @@ fields(local_storage_segments_gc) ->
             )}
     ].
 
+common_backend_fields() ->
+    [
+        {enable,
+            mk(
+                boolean(), #{
+                    desc => ?DESC("backend_enable"),
+                    required => false,
+                    default => true
+                }
+            )}
+    ].
+
 desc(file_transfer) ->
     "File transfer settings";
 desc(local_storage) ->
@@ -275,11 +288,19 @@ validator(filename) ->
     ];
 validator(backend) ->
     fun(Config) ->
-        case maps:keys(Config) of
-            [_Type] ->
+        Enabled = maps:filter(
+            fun(_, Backend) ->
+                maps:get(enable, Backend, false) or maps:get(<<"enable">>, Backend, false)
+            end,
+            Config
+        ),
+        case maps:to_list(Enabled) of
+            [{_Type, _BackendConfig}] ->
                 ok;
             _Conflicts = [_ | _] ->
-                {error, multiple_conflicting_backends}
+                {error, multiple_enabled_backends};
+            _None = [] ->
+                {error, no_enabled_backend}
         end
     end.
 
@@ -319,3 +340,13 @@ translate(Conf) ->
             ?MODULE, #{atom_to_binary(Root) => Conf}, #{atom_key => true}, [Root]
         )
     ).
+
+-spec backend(emqx_config:config()) ->
+    {_Type :: atom(), emqx_config:config()}.
+backend(Config) ->
+    catch maps:foreach(fun emit_enabled/2, Config).
+
+-spec emit_enabled(atom(), emqx_config:config()) ->
+    no_return().
+emit_enabled(Type, BConf = #{enable := Enabled}) ->
+    Enabled andalso throw({Type, BConf}).

apps/emqx_ft/src/emqx_ft_storage.erl

@@ -182,8 +182,8 @@ on_backend_update(BackendOld, BackendNew) when
 %%--------------------------------------------------------------------
 
 -spec backend(config()) -> backend().
-backend(#{local := Storage}) ->
-    {local, Storage}.
+backend(Config) ->
+    emqx_ft_schema:backend(Config).
 
 on_storage_start({Type, Storage}) ->
     (mod(Type)):start(Storage).

apps/emqx_ft/src/emqx_ft_storage_exporter.erl

@@ -175,10 +175,10 @@ stop({ExporterMod, ExporterOpts}) ->
 %%------------------------------------------------------------------------------
 
 exporter(Storage) ->
-    case maps:get(exporter, Storage) of
-        #{local := Options} ->
+    case emqx_ft_schema:backend(maps:get(exporter, Storage)) of
+        {local, Options} ->
             {emqx_ft_storage_exporter_fs, Options};
-        #{s3 := Options} ->
+        {s3, Options} ->
             {emqx_ft_storage_exporter_s3, Options}
     end.
 

apps/emqx_ft/src/emqx_ft_storage_exporter_fs.erl

@@ -46,6 +46,7 @@
 -export_type([options/0]).
 
 -type options() :: #{
+    enable := true,
     root => file:name(),
     _ => _
 }.

apps/emqx_ft/src/emqx_ft_storage_fs.erl

@@ -102,6 +102,7 @@
 
 -type storage() :: #{
     type := 'local',
+    enable := true,
     segments := segments(),
     exporter := emqx_ft_storage_exporter:exporter()
 }.

apps/emqx_ft/test/emqx_ft_assembler_SUITE.erl

@@ -256,6 +256,7 @@ storage(Config) ->
                     },
                     <<"exporter">> => #{
                         <<"local">> => #{
+                            <<"enable">> => true,
                             <<"root">> => ?config(exports_root, Config)
                         }
                     }

apps/emqx_ft/test/emqx_ft_conf_SUITE.erl

@@ -77,6 +77,7 @@ t_update_config(_Config) ->
                         },
                         <<"exporter">> => #{
                             <<"local">> => #{
+                                <<"enable">> => true,
                                 <<"root">> => <<"/tmp/exports">>
                             }
                         }
@@ -104,7 +105,10 @@ t_disable_restore_config(Config) ->
         {ok, _},
         emqx_conf:update(
             [file_transfer],
-            #{<<"enable">> => true, <<"storage">> => #{<<"local">> => #{}}},
+            #{
+                <<"enable">> => true,
+                <<"storage">> => #{<<"local">> => #{}}
+            },
             #{}
         )
     ),
@@ -207,6 +211,7 @@ t_switch_exporter(_Config) ->
             [file_transfer, storage, local, exporter],
             #{
                 <<"s3">> => #{
+                    <<"enable">> => true,
                     <<"bucket">> => <<"emqx">>,
                     <<"host">> => <<"https://localhost">>,
                     <<"port">> => 9000,
@@ -234,7 +239,7 @@ t_switch_exporter(_Config) ->
         {ok, _},
         emqx_conf:update(
             [file_transfer, storage, local, exporter],
-            #{<<"local">> => #{}},
+            #{<<"local">> => #{<<"enable">> => true}},
             #{}
         )
     ),

apps/emqx_ft/test/emqx_ft_storage_fs_gc_SUITE.erl

@@ -45,9 +45,10 @@ init_per_testcase(TC, Config) ->
                 <<"enable">> => true,
                 <<"storage">> => #{
                     <<"local">> => #{
+                        <<"enable">> => true,
                         <<"segments">> => #{<<"root">> => SegmentsRoot},
                         <<"exporter">> => #{
-                            <<"local">> => #{<<"root">> => ExportsRoot}
+                            <<"local">> => #{<<"enable">> => true, <<"root">> => ExportsRoot}
                         }
                     }
                 }

apps/emqx_ft/test/emqx_ft_test_helpers.erl

@@ -55,17 +55,24 @@ local_storage(Config) ->
 local_storage(Config, Opts) ->
     #{
         <<"local">> => #{
+            <<"enable">> => true,
             <<"segments">> => #{<<"root">> => root(Config, node(), [segments])},
             <<"exporter">> => exporter(Config, Opts)
         }
     }.
 
 exporter(Config, #{exporter := local}) ->
-    #{<<"local">> => #{<<"root">> => root(Config, node(), [exports])}};
+    #{
+        <<"local">> => #{
+            <<"enable">> => true,
+            <<"root">> => root(Config, node(), [exports])
+        }
+    };
 exporter(_Config, #{exporter := s3, bucket_name := BucketName}) ->
     BaseConfig = emqx_s3_test_helpers:base_raw_config(tcp),
     #{
         <<"s3">> => BaseConfig#{
+            <<"enable">> => true,
             <<"bucket">> => list_to_binary(BucketName),
             <<"host">> => ?S3_HOST,
             <<"port">> => ?S3_PORT

rel/i18n/emqx_ft_schema.hocon

@@ -18,6 +18,9 @@ store_segment_timeout.desc:
 """Timeout for storing a file segment.<br/>
 After reaching the timeout, message with the segment will be acked with an error"""
 
+backend_enable.desc:
+"""Whether to enable this backend."""
+
 storage_backend.desc:
 """Storage settings for file transfer."""