feat(bridge): add is_template flag to bridge config fields

apps/emqx/src/emqx_schema.erl

@@ -61,6 +61,7 @@
 }.
 -type url() :: binary().
 -type json_binary() :: binary().
+-type template() :: binary().
 
 -typerefl_from_string({duration/0, emqx_schema, to_duration}).
 -typerefl_from_string({duration_s/0, emqx_schema, to_duration_s}).
@@ -78,6 +79,7 @@
 -typerefl_from_string({comma_separated_atoms/0, emqx_schema, to_comma_separated_atoms}).
 -typerefl_from_string({url/0, emqx_schema, to_url}).
 -typerefl_from_string({json_binary/0, emqx_schema, to_json_binary}).
+-typerefl_from_string({template/0, emqx_schema, to_template}).
 
 -type parsed_server() :: #{
     hostname := string(),
@@ -120,7 +122,8 @@
     to_erl_cipher_suite/1,
     to_comma_separated_atoms/1,
     to_url/1,
-    to_json_binary/1
+    to_json_binary/1,
+    to_template/1
 ]).
 
 -export([
@@ -160,7 +163,8 @@
     comma_separated_atoms/0,
     url/0,
     json_binary/0,
-    port_number/0
+    port_number/0,
+    template/0
 ]).
 
 -export([namespace/0, roots/0, roots/1, fields/1, desc/1, tags/0]).
@@ -2594,6 +2598,9 @@ to_json_binary(Str) ->
             Error
     end.
 
+to_template(Str) ->
+    {ok, iolist_to_binary(Str)}.
+
 %% @doc support the following format:
 %%  - 127.0.0.1:1883
 %%  - ::1:1883

apps/emqx_bridge_cassandra/src/emqx_bridge_cassandra.erl

@@ -181,7 +181,7 @@ fields("post", Type) ->
 cql_field() ->
     {cql,
         mk(
-            binary(),
+            emqx_schema:template(),
             #{desc => ?DESC("cql_template"), default => ?DEFAULT_CQL, format => <<"sql">>}
         )}.
 

apps/emqx_bridge_clickhouse/src/emqx_bridge_clickhouse.erl

@@ -184,8 +184,12 @@ fields("post", Type) ->
 sql_field() ->
     {sql,
         mk(
-            binary(),
+            emqx_schema:template(),
-            #{desc => ?DESC("sql_template"), default => ?DEFAULT_SQL, format => <<"sql">>}
+            #{
+                desc => ?DESC("sql_template"),
+                default => ?DEFAULT_SQL,
+                format => <<"sql">>
+            }
         )}.
 
 batch_value_separator_field() ->

apps/emqx_bridge_dynamo/src/emqx_bridge_dynamo.erl

@@ -160,13 +160,7 @@ fields(dynamo_action) ->
     );
 fields(action_parameters) ->
     Parameters =
-        [
+        [{template, template_field_schema()}] ++ emqx_bridge_dynamo_connector:fields(config),
-            {template,
-                mk(
-                    binary(),
-                    #{desc => ?DESC("template"), default => ?DEFAULT_TEMPLATE}
-                )}
-        ] ++ emqx_bridge_dynamo_connector:fields(config),
     lists:foldl(
         fun(Key, Acc) ->
             proplists:delete(Key, Acc)
@@ -199,11 +193,7 @@ fields(connector_resource_opts) ->
 fields("config") ->
     [
         {enable, mk(boolean(), #{desc => ?DESC("config_enable"), default => true})},
-        {template,
+        {template, template_field_schema()},
-            mk(
-                binary(),
-                #{desc => ?DESC("template"), default => ?DEFAULT_TEMPLATE}
-            )},
         {local_topic,
             mk(
                 binary(),
@@ -230,6 +220,15 @@ fields("put") ->
 fields("get") ->
     emqx_bridge_schema:status_fields() ++ fields("post").
 
+template_field_schema() ->
+    mk(
+        emqx_schema:template(),
+        #{
+            desc => ?DESC("template"),
+            default => ?DEFAULT_TEMPLATE
+        }
+    ).
+
 desc("config") ->
     ?DESC("desc_config");
 desc(Method) when Method =:= "get"; Method =:= "put"; Method =:= "post" ->

apps/emqx_bridge_es/src/emqx_bridge_es.erl

@@ -135,7 +135,7 @@ overwrite() ->
 index() ->
     {index,
         ?HOCON(
-            binary(),
+            emqx_schema:template(),
             #{
                 required => true,
                 example => <<"${payload.index}">>,
@@ -146,7 +146,7 @@ index() ->
 id(Required) ->
     {id,
         ?HOCON(
-            binary(),
+            emqx_schema:template(),
             #{
                 required => Required,
                 example => <<"${payload.id}">>,
@@ -157,7 +157,7 @@ id(Required) ->
 doc() ->
     {doc,
         ?HOCON(
-            binary(),
+            emqx_schema:template(),
             #{
                 required => false,
                 example => <<"${payload.doc}">>,
@@ -187,7 +187,7 @@ doc_as_upsert() ->
 routing() ->
     {routing,
         ?HOCON(
-            binary(),
+            emqx_schema:template(),
             #{
                 required => false,
                 example => <<"${payload.routing}">>,

apps/emqx_bridge_gcp_pubsub/src/emqx_bridge_gcp_pubsub.erl

@@ -122,7 +122,7 @@ fields(producer) ->
             )},
         {ordering_key_template,
             sc(
-                binary(),
+                emqx_schema:template(),
                 #{
                     default => <<>>,
                     desc => ?DESC("ordering_key_template")
@@ -130,7 +130,7 @@ fields(producer) ->
             )},
         {payload_template,
             sc(
-                binary(),
+                emqx_schema:template(),
                 #{
                     default => <<>>,
                     desc => ?DESC("payload_template")
@@ -201,8 +201,11 @@ fields(consumer_topic_mapping) ->
         {qos, mk(emqx_schema:qos(), #{default => 0, desc => ?DESC(consumer_mqtt_qos)})},
         {payload_template,
             mk(
-                string(),
+                emqx_schema:template(),
-                #{default => <<"${.}">>, desc => ?DESC(consumer_mqtt_payload)}
+                #{
+                    default => <<"${.}">>,
+                    desc => ?DESC(consumer_mqtt_payload)
+                }
             )}
     ];
 fields("consumer_resource_opts") ->
@@ -221,14 +224,18 @@ fields("consumer_resource_opts") ->
 fields(key_value_pair) ->
     [
         {key,
-            mk(binary(), #{
+            mk(emqx_schema:template(), #{
                 required => true,
                 validator => [
                     emqx_resource_validator:not_empty("Key templates must not be empty")
                 ],
                 desc => ?DESC(kv_pair_key)
             })},
-        {value, mk(binary(), #{required => true, desc => ?DESC(kv_pair_value)})}
+        {value,
+            mk(emqx_schema:template(), #{
+                required => true,
+                desc => ?DESC(kv_pair_value)
+            })}
     ];
 fields("get_producer") ->
     emqx_bridge_schema:status_fields() ++ fields("post_producer");

apps/emqx_bridge_hstreamdb/src/emqx_bridge_hstreamdb.erl

@@ -167,13 +167,13 @@ fields(action_parameters) ->
             })},
 
         {partition_key,
-            mk(binary(), #{
+            mk(emqx_schema:template(), #{
-                required => false, desc => ?DESC(emqx_bridge_hstreamdb_connector, "partition_key")
+                required => false,
+                desc => ?DESC(emqx_bridge_hstreamdb_connector, "partition_key")
             })},
 
         {grpc_flush_timeout, fun grpc_flush_timeout/1},
-        {record_template,
+        {record_template, record_template_schema()},
-            mk(binary(), #{default => <<"${payload}">>, desc => ?DESC("record_template")})},
         {aggregation_pool_size,
             mk(pos_integer(), #{
                 default => ?DEFAULT_AGG_POOL_SIZE, desc => ?DESC("aggregation_pool_size")
@@ -222,6 +222,12 @@ fields("put") ->
     hstream_bridge_common_fields() ++
         connector_fields().
 
+record_template_schema() ->
+    mk(emqx_schema:template(), #{
+        default => <<"${payload}">>,
+        desc => ?DESC("record_template")
+    }).
+
 grpc_timeout(type) -> emqx_schema:timeout_duration_ms();
 grpc_timeout(desc) -> ?DESC(emqx_bridge_hstreamdb_connector, "grpc_timeout");
 grpc_timeout(default) -> ?DEFAULT_GRPC_TIMEOUT_RAW;
@@ -239,8 +245,7 @@ hstream_bridge_common_fields() ->
         [
             {direction, mk(egress, #{desc => ?DESC("config_direction"), default => egress})},
             {local_topic, mk(binary(), #{desc => ?DESC("local_topic")})},
-            {record_template,
+            {record_template, record_template_schema()}
-                mk(binary(), #{default => <<"${payload}">>, desc => ?DESC("record_template")})}
         ] ++
         emqx_resource_schema:fields("resource_opts").
 

apps/emqx_bridge_http/src/emqx_bridge_http_schema.erl

@@ -287,7 +287,7 @@ method_field() ->
 body_field() ->
     {body,
         mk(
-            binary(),
+            emqx_schema:template(),
             #{
                 default => undefined,
                 desc => ?DESC("config_body")

apps/emqx_bridge_influxdb/src/emqx_bridge_influxdb.erl

@@ -42,7 +42,7 @@
 %% api
 
 write_syntax_type() ->
-    typerefl:alias("string", write_syntax()).
+    typerefl:alias("template", write_syntax()).
 
 %% Examples
 conn_bridge_examples(Method) ->

apps/emqx_bridge_iotdb/src/emqx_bridge_iotdb.erl

@@ -84,7 +84,7 @@ fields(action_parameters) ->
             )},
         {device_id,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     desc => ?DESC("config_device_id")
                 }
@@ -114,7 +114,7 @@ fields(action_parameters_data) ->
             )},
         {measurement,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     required => true,
                     desc => ?DESC("config_parameters_measurement")
@@ -122,7 +122,9 @@ fields(action_parameters_data) ->
             )},
         {data_type,
             mk(
-                hoconsc:union([enum([text, boolean, int32, int64, float, double]), binary()]),
+                hoconsc:union([
+                    enum([text, boolean, int32, int64, float, double]), emqx_schema:template()
+                ]),
                 #{
                     required => true,
                     desc => ?DESC("config_parameters_data_type")
@@ -130,7 +132,7 @@ fields(action_parameters_data) ->
             )},
         {value,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     required => true,
                     desc => ?DESC("config_parameters_value")

apps/emqx_bridge_kafka/src/emqx_bridge_kafka.erl

@@ -477,11 +477,20 @@ fields(producer_kafka_ext_headers) ->
     ];
 fields(kafka_message) ->
     [
-        {key, mk(string(), #{default => <<"${.clientid}">>, desc => ?DESC(kafka_message_key)})},
+        {key,
-        {value, mk(string(), #{default => <<"${.}">>, desc => ?DESC(kafka_message_value)})},
+            mk(emqx_schema:template(), #{
+                default => <<"${.clientid}">>,
+                desc => ?DESC(kafka_message_key)
+            })},
+        {value,
+            mk(emqx_schema:template(), #{
+                default => <<"${.}">>,
+                desc => ?DESC(kafka_message_value)
+            })},
         {timestamp,
-            mk(string(), #{
+            mk(emqx_schema:template(), #{
-                default => <<"${.timestamp}">>, desc => ?DESC(kafka_message_timestamp)
+                default => <<"${.timestamp}">>,
+                desc => ?DESC(kafka_message_timestamp)
             })}
     ];
 fields(producer_buffer) ->
@@ -536,8 +545,11 @@ fields(consumer_topic_mapping) ->
         {qos, mk(emqx_schema:qos(), #{default => 0, desc => ?DESC(consumer_mqtt_qos)})},
         {payload_template,
             mk(
-                string(),
+                emqx_schema:template(),
-                #{default => <<"${.}">>, desc => ?DESC(consumer_mqtt_payload)}
+                #{
+                    default => <<"${.}">>,
+                    desc => ?DESC(consumer_mqtt_payload)
+                }
             )}
     ];
 fields(consumer_kafka_opts) ->

apps/emqx_bridge_kinesis/src/emqx_bridge_kinesis.erl

@@ -150,7 +150,7 @@ fields(producer) ->
     [
         {payload_template,
             sc(
-                binary(),
+                emqx_schema:template(),
                 #{
                     default => <<"${.}">>,
                     desc => ?DESC("payload_template")

apps/emqx_bridge_mongodb/src/emqx_bridge_mongodb.erl

@@ -44,8 +44,10 @@ roots() -> [].
 fields("config") ->
     [
         {enable, mk(boolean(), #{desc => ?DESC("enable"), default => true})},
-        {collection, mk(binary(), #{desc => ?DESC("collection"), default => <<"mqtt">>})},
+        {collection,
-        {payload_template, mk(binary(), #{required => false, desc => ?DESC("payload_template")})},
+            mk(emqx_schema:template(), #{desc => ?DESC("collection"), default => <<"mqtt">>})},
+        {payload_template,
+            mk(emqx_schema:template(), #{required => false, desc => ?DESC("payload_template")})},
         {resource_opts,
             mk(
                 ref(?MODULE, "creation_opts"),

apps/emqx_bridge_mqtt/src/emqx_bridge_mqtt_connector_schema.erl

@@ -200,7 +200,7 @@ fields("ingress_local") ->
     [
         {topic,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     validator => fun emqx_schema:non_empty_string/1,
                     desc => ?DESC("ingress_local_topic"),
@@ -217,7 +217,7 @@ fields("ingress_local") ->
             )},
         {retain,
             mk(
-                hoconsc:union([boolean(), binary()]),
+                hoconsc:union([boolean(), emqx_schema:template()]),
                 #{
                     default => <<"${retain}">>,
                     desc => ?DESC("retain")
@@ -225,7 +225,7 @@ fields("ingress_local") ->
             )},
         {payload,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     default => undefined,
                     desc => ?DESC("payload")
@@ -268,7 +268,7 @@ fields("egress_remote") ->
     [
         {topic,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     required => true,
                     validator => fun emqx_schema:non_empty_string/1,
@@ -286,7 +286,7 @@ fields("egress_remote") ->
             )},
         {retain,
             mk(
-                hoconsc:union([boolean(), binary()]),
+                hoconsc:union([boolean(), emqx_schema:template()]),
                 #{
                     required => false,
                     default => false,
@@ -295,7 +295,7 @@ fields("egress_remote") ->
             )},
         {payload,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     default => undefined,
                     desc => ?DESC("payload")
@@ -344,7 +344,7 @@ desc(_) ->
     undefined.
 
 qos() ->
-    hoconsc:union([emqx_schema:qos(), binary()]).
+    hoconsc:union([emqx_schema:qos(), emqx_schema:template()]).
 
 parse_server(Str) ->
     #{hostname := Host, port := Port} = emqx_schema:parse_server(Str, ?MQTT_HOST_OPTS),

apps/emqx_bridge_mysql/src/emqx_bridge_mysql.erl

@@ -117,7 +117,7 @@ fields("config") ->
         {enable, mk(boolean(), #{desc => ?DESC("config_enable"), default => true})},
         {sql,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{desc => ?DESC("sql_template"), default => ?DEFAULT_SQL, format => <<"sql">>}
             )},
         {local_topic,

apps/emqx_bridge_opents/src/emqx_bridge_opents.erl

@@ -146,7 +146,7 @@ fields(action_parameters_data) ->
     [
         {timestamp,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     desc => ?DESC("config_parameters_timestamp"),
                     required => false
@@ -154,7 +154,7 @@ fields(action_parameters_data) ->
             )},
         {metric,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     required => true,
                     desc => ?DESC("config_parameters_metric")
@@ -162,7 +162,7 @@ fields(action_parameters_data) ->
             )},
         {tags,
             mk(
-                hoconsc:union([map(), binary()]),
+                hoconsc:union([map(), emqx_schema:template()]),
                 #{
                     required => true,
                     desc => ?DESC("config_parameters_tags"),
@@ -188,7 +188,7 @@ fields(action_parameters_data) ->
             )},
         {value,
             mk(
-                hoconsc:union([integer(), float(), binary()]),
+                hoconsc:union([integer(), float(), emqx_schema:template()]),
                 #{
                     required => true,
                     desc => ?DESC("config_parameters_value")

apps/emqx_bridge_oracle/src/emqx_bridge_oracle.erl

@@ -158,7 +158,7 @@ fields(action_parameters) ->
     [
         {sql,
             hoconsc:mk(
-                binary(),
+                emqx_schema:template(),
                 #{desc => ?DESC("sql_template"), default => ?DEFAULT_SQL, format => <<"sql">>}
             )}
     ];
@@ -177,7 +177,7 @@ fields("config") ->
             )},
         {sql,
             hoconsc:mk(
-                binary(),
+                emqx_schema:template(),
                 #{desc => ?DESC("sql_template"), default => ?DEFAULT_SQL, format => <<"sql">>}
             )},
         {local_topic,

apps/emqx_bridge_pgsql/src/emqx_bridge_pgsql.erl

@@ -61,7 +61,7 @@ fields(action_parameters) ->
     [
         {sql,
             hoconsc:mk(
-                binary(),
+                emqx_schema:template(),
                 #{desc => ?DESC("sql_template"), default => default_sql(), format => <<"sql">>}
             )}
     ];

apps/emqx_bridge_pulsar/src/emqx_bridge_pulsar_pubsub_schema.erl

@@ -51,12 +51,12 @@ fields(action_parameters) ->
 fields(producer_pulsar_message) ->
     [
         {key,
-            ?HOCON(string(), #{
+            ?HOCON(emqx_schema:template(), #{
                 default => <<"${.clientid}">>,
                 desc => ?DESC("producer_key_template")
             })},
         {value,
-            ?HOCON(string(), #{
+            ?HOCON(emqx_schema:template(), #{
                 default => <<"${.}">>,
                 desc => ?DESC("producer_value_template")
             })}

apps/emqx_bridge_rabbitmq/src/emqx_bridge_rabbitmq_pubsub_schema.erl

@@ -99,7 +99,7 @@ fields(action_parameters) ->
             )},
         {payload_template,
             hoconsc:mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     default => <<"">>,
                     desc => ?DESC(?CONNECTOR_SCHEMA, "payload_template")

apps/emqx_bridge_redis/src/emqx_bridge_redis.erl

@@ -211,7 +211,7 @@ desc(_) ->
     undefined.
 
 command_template(type) ->
-    list(binary());
+    hoconsc:array(emqx_schema:template());
 command_template(required) ->
     true;
 command_template(validator) ->

apps/emqx_bridge_rocketmq/src/emqx_bridge_rocketmq.erl

@@ -162,8 +162,11 @@ fields(action_parameters) ->
         [
             {template,
                 mk(
-                    binary(),
+                    emqx_schema:template(),
-                    #{desc => ?DESC("template"), default => ?DEFAULT_TEMPLATE}
+                    #{
+                        desc => ?DESC("template"),
+                        default => ?DEFAULT_TEMPLATE
+                    }
                 )}
         ] ++ emqx_bridge_rocketmq_connector:fields(config),
     lists:foldl(
@@ -205,7 +208,7 @@ fields("config") ->
         {enable, mk(boolean(), #{desc => ?DESC("config_enable"), default => true})},
         {template,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{desc => ?DESC("template"), default => ?DEFAULT_TEMPLATE}
             )},
         {local_topic,
@@ -214,8 +217,7 @@ fields("config") ->
                 #{desc => ?DESC("local_topic"), required => false}
             )}
     ] ++ emqx_resource_schema:fields("resource_opts") ++
-        (emqx_bridge_rocketmq_connector:fields(config) --
+        emqx_bridge_rocketmq_connector:fields(config);
-            emqx_connector_schema_lib:prepare_statement_fields());
 fields("post") ->
     [type_field(), name_field() | fields("config")];
 fields("put") ->

apps/emqx_bridge_rocketmq/src/emqx_bridge_rocketmq_connector.erl

@@ -47,7 +47,7 @@ fields(config) ->
         {servers, servers()},
         {topic,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{default => <<"TopicTest">>, desc => ?DESC(topic)}
             )},
         {access_key,

apps/emqx_bridge_s3/src/emqx_bridge_s3.erl

@@ -77,7 +77,7 @@ fields(s3_upload_parameters) ->
         [
             {content,
                 hoconsc:mk(
-                    string(),
+                    emqx_schema:template(),
                     #{
                         required => false,
                         default => <<"${.}">>,

apps/emqx_bridge_sqlserver/src/emqx_bridge_sqlserver.erl

@@ -192,7 +192,7 @@ fields(action_parameters) ->
     [
         {sql,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{desc => ?DESC("sql_template"), default => ?DEFAULT_SQL, format => <<"sql">>}
             )}
     ];

apps/emqx_bridge_syskeeper/src/emqx_bridge_syskeeper.erl

@@ -112,7 +112,7 @@ fields("parameters") ->
     [
         {target_topic,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{desc => ?DESC("target_topic"), default => <<"${topic}">>}
             )},
         {target_qos,
@@ -122,7 +122,7 @@ fields("parameters") ->
             )},
         {template,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{desc => ?DESC("template"), default => <<"${payload}">>}
             )}
     ];

apps/emqx_bridge_tdengine/src/emqx_bridge_tdengine.erl

@@ -83,7 +83,7 @@ fields("config") ->
         {enable, mk(boolean(), #{desc => ?DESC("config_enable"), default => true})},
         {sql,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     desc => ?DESC("sql_template"),
                     default => ?DEFAULT_SQL,
@@ -125,7 +125,7 @@ fields(action_parameters) ->
         {database, fun emqx_connector_schema_lib:database/1},
         {sql,
             mk(
-                binary(),
+                emqx_schema:template(),
                 #{
                     desc => ?DESC("sql_template"),
                     default => ?DEFAULT_SQL,

apps/emqx_conf/src/emqx_conf_schema_types.erl

@@ -65,6 +65,12 @@ readable("boolean()") ->
         dashboard => #{type => boolean},
         docgen => #{type => "Boolean"}
     };
+readable("template()") ->
+    #{
+        swagger => #{type => string},
+        dashboard => #{type => string, is_template => true},
+        docgen => #{type => "String", desc => ?DESC(template)}
+    };
 readable("binary()") ->
     #{
         swagger => #{type => string},

apps/emqx_s3/src/emqx_s3.app.src

@@ -1,6 +1,6 @@
 {application, emqx_s3, [
     {description, "EMQX S3"},
-    {vsn, "5.0.14"},
+    {vsn, "5.1.0"},
     {modules, []},
     {registered, [emqx_s3_sup]},
     {applications, [

apps/emqx_s3/src/emqx_s3_client.erl

@@ -103,7 +103,7 @@ put_object(Client, Key, Value) ->
 
 -spec put_object(client(), key(), upload_options(), iodata()) -> ok_or_error(term()).
 put_object(
-    #{bucket := Bucket, headers := BaseHeaders, aws_config := AwsConfig = #aws_config{}},
+    #{bucket := Bucket0, headers := BaseHeaders, aws_config := AwsConfig = #aws_config{}},
     Key,
     UploadOpts,
     Content
@@ -111,6 +111,7 @@ put_object(
     ECKey = erlcloud_key(Key),
     ECOpts = erlcloud_upload_options(UploadOpts),
     Headers = join_headers(BaseHeaders, maps:get(headers, UploadOpts, undefined)),
+    Bucket = to_list_string(Bucket0),
     try erlcloud_s3:put_object(Bucket, ECKey, Content, ECOpts, Headers, AwsConfig) of
         Props when is_list(Props) ->
             ok

apps/emqx_s3/src/emqx_s3_schema.erl

@@ -74,7 +74,7 @@ fields(s3_upload) ->
     [
         {bucket,
             mk(
-                string(),
+                emqx_schema:template(),
                 #{
                     desc => ?DESC("bucket"),
                     required => true
@@ -82,7 +82,7 @@ fields(s3_upload) ->
             )},
         {key,
             mk(
-                string(),
+                emqx_schema:template(),
                 #{
                     desc => ?DESC("key"),
                     required => true

rel/i18n/emqx_conf_schema_types.hocon

@@ -9,4 +9,7 @@ emqx_conf_schema_types {
     secret.desc:
     """A string holding some sensitive information, such as a password. When secret starts with <code>file://</code>, the rest of the string is interpreted as a path to a file containing the secret itself: whole content of the file except any trailing whitespace characters is considered a secret value. Note: when clustered, all EMQX nodes should have the same file present before using <code>file://</code> secrets."""
 
+    template.desc: """~
+        A string for `${.path.to.var}` style value interpolation,
+        where the leading dot is optional, and `${.}` represents all values as an object."""
 }