Merge pull request #7461 from ieQu1/doc-schema-6

docs(schema): Document fields and records

apps/emqx/etc/emqx.conf

@@ -894,7 +894,7 @@ conn_congestion {
   ## Whether to alarm the congested connections.
   ##
   ## Sometimes the mqtt connection (usually an MQTT subscriber) may
-  ## get "congested", because there're too many packets to be sent.
+  ## get "congested", because there's too many packets to sent.
   ## The socket tries to buffer the packets until the buffer is
   ## full. If more packets come after that, the packets will be
   ## "pending" in a queue and we consider the connection is
@@ -914,7 +914,7 @@ conn_congestion {
   enable_alarm = true
 
   ## Won't clear the congested alarm in how long time.
-  ## The alarm is cleared only when there're no pending bytes in
+  ## The alarm is cleared only when there's no pending bytes in
   ## the queue, and also it has been `min_alarm_sustain_duration`
   ## time since the last time we considered the connection is "congested".
   ##

apps/emqx/src/emqx_limiter/src/emqx_limiter_schema.erl

@@ -20,7 +20,7 @@
 
 -export([ roots/0, fields/1, to_rate/1, to_capacity/1
         , minimum_period/0, to_burst_rate/1, to_initial/1
-        , namespace/0, get_bucket_cfg_path/2
+        , namespace/0, get_bucket_cfg_path/2, desc/1
         ]).
 
 -define(KILOBYTE, 1024).
@@ -149,6 +149,17 @@ the check/consume will succeed, but it will be forced to wait for a short period
                              , default => force})}
     ].
 
+desc(limiter) ->
+    "Settings for the rate limiter.";
+desc(limiter_opts) ->
+    "Settings for the limiter.";
+desc(bucket_opts) ->
+    "Settings for the bucket.";
+desc(client_bucket) ->
+    "Settings for the client bucket.";
+desc(_) ->
+    undefined.
+
 %% minimum period is 100ms
 minimum_period() ->
     100.

apps/emqx/src/emqx_schema.erl

@@ -304,7 +304,7 @@ fields("stats") ->
                 boolean(),
                 #{
                     default => true,
-                    desc => "Enable/disable statistic data collection"
+                    desc => "Enable/disable statistic data collection."
                 }
             )}
     ];
@@ -339,17 +339,26 @@ fields("cache") ->
         {"enable",
             sc(
                 boolean(),
-                #{default => true}
+                #{
+                    default => true,
+                    desc => "Enable or disable the authorization cache."
+                }
             )},
         {"max_size",
             sc(
                 range(1, 1048576),
-                #{default => 32}
+                #{
+                    default => 32,
+                    desc => "Maximum number of cached items."
+                }
             )},
         {"ttl",
             sc(
                 duration(),
-                #{default => "1m"}
+                #{
+                    default => "1m",
+                    desc => "Time to live for the cached data."
+                }
             )}
     ];
 fields("mqtt") ->
@@ -762,12 +771,23 @@ fields("conn_congestion") ->
         {"enable_alarm",
             sc(
                 boolean(),
-                #{default => false}
+                #{
+                    default => false,
+                    desc => "Enable or disable connection congestion alarm."
+                }
             )},
         {"min_alarm_sustain_duration",
             sc(
                 duration(),
-                #{default => "1m"}
+                #{
+                    default => "1m",
+                    desc =>
+                        "Minimal time before clearing the alarm.\n\n"
+                        "The alarm is cleared only when there's no pending data in\n"
+                        "the queue, and at least `min_alarm_sustain_duration`\n"
+                        "milliseconds passed since the last time we considered the connection \"congested\".\n\n"
+                        "This is to avoid clearing and raising the alarm again too often."
+                }
             )}
     ];
 fields("force_gc") ->
@@ -1357,7 +1377,7 @@ fields("sysmon_vm") ->
                     desc =>
                         "The threshold, as percentage of processes, for how many\n"
                         " processes can simultaneously exist at the local node before the corresponding\n"
-                        " alarm is set."
+                        " alarm is raised."
                 }
             )},
         {"process_low_watermark",
@@ -1431,7 +1451,7 @@ fields("sysmon_os") ->
                     default => "80%",
                     desc =>
                         "The threshold, as percentage of system CPU load,\n"
-                        " for how much system cpu can be used before the corresponding alarm is set."
+                        " for how much system cpu can be used before the corresponding alarm is raised."
                 }
             )},
         {"cpu_low_watermark",
@@ -1459,7 +1479,7 @@ fields("sysmon_os") ->
                     default => "70%",
                     desc =>
                         "The threshold, as percentage of system memory,\n"
-                        " for how much system memory can be allocated before the corresponding alarm is set."
+                        " for how much system memory can be allocated before the corresponding alarm is raised."
                 }
             )},
         {"procmem_high_watermark",
@@ -1470,7 +1490,7 @@ fields("sysmon_os") ->
                     desc =>
                         "The threshold, as percentage of system memory,\n"
                         " for how much system memory can be allocated by one Erlang process before\n"
-                        " the corresponding alarm is set."
+                        " the corresponding alarm is raised."
                 }
             )}
     ];
@@ -1704,7 +1724,13 @@ base_listener() ->
                 }
             )},
         {"limiter",
-            sc(map("ratelimit's type", emqx_limiter_schema:bucket_name()), #{default => #{}})}
+            sc(
+                map("ratelimit's type", emqx_limiter_schema:bucket_name()),
+                #{
+                    default => #{},
+                    desc => "Type of the rate limit."
+                }
+            )}
     ].
 
 desc("persistent_session_store") ->

apps/emqx_authn/src/emqx_authn_password_hashing.erl

@@ -73,14 +73,17 @@ fields(other_algorithms) ->
      {salt_position, fun salt_position/1}].
 
 salt_position(type) -> {enum, [prefix, suffix]};
+salt_position(desc) -> "Specifies whether the password salt is stored as a prefix or the suffix.";
 salt_position(default) -> prefix;
 salt_position(_) -> undefined.
 
 salt_rounds(type) -> integer();
+salt_rounds(desc) -> "Cost factor for the bcrypt hash.";
 salt_rounds(default) -> 10;
 salt_rounds(_) -> undefined.
 
 dk_length(type) -> integer();
+dk_length(desc) -> "Length of the derived key.";
 dk_length(required) -> false;
 dk_length(_) -> undefined.
 

apps/emqx_authn/src/emqx_authn_schema.erl

@@ -55,11 +55,15 @@ root_type() ->
 
 mechanism(Name) ->
     hoconsc:mk(hoconsc:enum([Name]),
-               #{required => true}).
+               #{ required => true
+                , desc => "Authentication mechanism."
+                }).
 
 backend(Name) ->
     hoconsc:mk(hoconsc:enum([Name]),
-               #{required => true}).
+               #{ required => true
+                , desc => "Backend type."
+                }).
 
 fields("metrics_status_fields") ->
     [ {"metrics", mk(ref(?MODULE, "metrics"), #{desc => "The metrics of the resource"})}
@@ -89,7 +93,7 @@ fields("node_metrics") ->
 
 fields("node_status") ->
     [ node_name()
-    , {"status", mk(status(), #{})}
+    , {"status", mk(status(), #{desc => "Status of the node."})}
     ].
 
 status() ->

apps/emqx_authn/src/simple_authn/emqx_authn_mongodb.erl

@@ -26,6 +26,7 @@
 -export([ namespace/0
         , roots/0
         , fields/1
+        , desc/1
         ]).
 
 -export([ refs/0
@@ -55,6 +56,15 @@ fields('replica-set') ->
 fields('sharded-cluster') ->
     common_fields() ++ emqx_connector_mongo:fields(sharded).
 
+desc(standalone) ->
+    "Configuration for a standalone MongoDB instance.";
+desc('replica-set') ->
+    "Configuration for a replica set.";
+desc('sharded-cluster') ->
+    "Configuration for a sharded cluster.";
+desc(_) ->
+    undefined.
+
 common_fields() ->
     [ {mechanism, emqx_authn_schema:mechanism('password_based')}
     , {backend, emqx_authn_schema:backend(mongodb)}
@@ -67,19 +77,27 @@ common_fields() ->
     ] ++ emqx_authn_schema:common_fields().
 
 collection(type) -> binary();
+collection(desc) -> "Collection used to store authentication data.";
 collection(_) -> undefined.
 
 selector(type) -> map();
+selector(desc) -> "Statement that is executed during the authentication process. "
+                  "Commands can support following wildcards:\n"
+                  " - `${username}`: substituted with client's username\n"
+                  " - `${clientid}`: substituted with the clientid";
 selector(_) -> undefined.
 
 password_hash_field(type) -> binary();
+password_hash_field(desc) -> "Document field that contains password hash.";
 password_hash_field(_) -> undefined.
 
 salt_field(type) -> binary();
+salt_field(desc) -> "Document field that contains the password salt.";
 salt_field(required) -> false;
 salt_field(_) -> undefined.
 
 is_superuser_field(type) -> binary();
+is_superuser_field(desc) -> "Document field that defines if the user has superuser privileges.";
 is_superuser_field(required) -> false;
 is_superuser_field(_) -> undefined.
 

apps/emqx_authz/src/emqx_authz_schema.erl

@@ -66,7 +66,7 @@ fields("authorization") ->
                     ]),
                   default => [],
                   desc =>
-"""
+"
 Authorization data sources.<br>
 An array of authorization (ACL) data providers.
 It is designed as an array, not a hash-map, so the sources can be
@@ -84,7 +84,7 @@ the default action configured in 'authorization.no_match' is applied.<br>
 NOTE:
 The source elements are identified by their 'type'.
 It is NOT allowed to configure two or more sources of the same type.
-"""
+"
                  }
       }
     ];
@@ -94,7 +94,7 @@ fields(file) ->
                  default => true}}
     , {path, #{type => string(),
                required => true,
-               desc => """
+               desc => "
 Path to the file which contains the ACL rules.<br>
 If the file provisioned before starting EMQX node,
 it can be placed anywhere as long as EMQX has read access to it.
@@ -102,7 +102,7 @@ it can be placed anywhere as long as EMQX has read access to it.
 In case the rule-set is created from EMQX dashboard or management API,
 the file will be placed in `authz` subdirectory inside EMQX's `data_dir`,
 and the new rules will override all rules from the old config file.
-"""
+"
               }}
     ];
 fields(http_get) ->
@@ -145,18 +145,19 @@ fields(redis_cluster) ->
 
 http_common_fields() ->
     [ {url, fun url/1}
-    , {request_timeout, mk_duration("Request timeout", #{default => "30s"})}
-    , {body, #{type => map(), required => false}}
+    , {request_timeout, mk_duration("Request timeout", #{default => "30s", desc => "Request timeout."})}
+    , {body, #{type => map(), required => false, desc => "HTTP request body."}}
     ] ++ maps:to_list(maps:without([ base_url
                                    , pool_type],
                                    maps:from_list(connector_fields(http)))).
 
 mongo_common_fields() ->
-    [ {collection, #{type => atom()}}
-    , {selector, #{type => map()}}
-    , {type, #{type => mongodb}}
+    [ {collection, #{type => atom(), desc => "`MongoDB` collection containing the authorization data."}}
+    , {selector, #{type => map(), desc => "MQL query used to select the authorization record."}}
+    , {type, #{type => mongodb, desc => "Database backend."}}
     , {enable, #{type => boolean(),
-                 default => true}}
+                 default => true,
+                 desc => "Enable or disable the backend."}}
     ].
 
 validations() ->
@@ -165,6 +166,7 @@ validations() ->
     ].
 
 headers(type) -> list({binary(), binary()});
+headers(desc) -> "List of HTTP headers.";
 headers(converter) ->
     fun(Headers) ->
         maps:to_list(maps:merge(default_headers(), transform_header_name(Headers)))
@@ -173,6 +175,7 @@ headers(default) -> default_headers();
 headers(_) -> undefined.
 
 headers_no_content_type(type) -> list({binary(), binary()});
+headers_no_content_type(desc) -> "List of HTTP headers.";
 headers_no_content_type(converter) ->
     fun(Headers) ->
        maps:to_list(maps:merge(default_headers_no_content_type(), transform_header_name(Headers)))
@@ -181,6 +184,7 @@ headers_no_content_type(default) -> default_headers_no_content_type();
 headers_no_content_type(_) -> undefined.
 
 url(type) -> binary();
+url(desc) -> "URL of the auth server.";
 url(validator) -> [?NOT_EMPTY("the value of the field 'url' cannot be empty")];
 url(required) -> true;
 url(_) -> undefined.
@@ -244,6 +248,7 @@ union_array(Item) when is_list(Item) ->
 
 query() ->
     #{type => binary(),
+      desc => "",
       validator => fun(S) ->
                          case size(S) > 0 of
                              true -> ok;
@@ -264,9 +269,10 @@ connector_fields(DB, Fields) ->
               error:Reason ->
                   erlang:error(Reason)
           end,
-    [ {type, #{type => DB}}
+    [ {type, #{type => DB, desc => "Database backend."}}
     , {enable, #{type => boolean(),
-                 default => true}}
+                 default => true,
+                 desc => "Enable or disable the backend."}}
     ] ++ erlang:apply(Mod, fields, [Fields]).
 
 to_list(A) when is_atom(A) ->

apps/emqx_conf/src/emqx_conf_schema.erl

@@ -421,7 +421,7 @@ fields("db") ->
            , 'readOnly' => true
            , desc => """
 Select the backend for the embedded database.<br/>
-<code>rlog</code> is the default backend, a new experimental backend
+<code>rlog</code> is the default backend,
 that is suitable for very large clusters.<br/>
 <code>mnesia</code> is a backend that offers decent performance in small clusters.
 """

apps/emqx_connector/include/emqx_connector.hrl

@@ -24,12 +24,13 @@
 -define(REDIS_DEFAULT_PORT, 6379).
 -define(PGSQL_DEFAULT_PORT, 5432).
 
--define(SERVERS_DESC, "A Node list for Cluster to connect to. The nodes should be split with ',', such as: 'Node[,Node]'<br>\nFor each Node should be:<br>").
+-define(SERVERS_DESC, "A Node list for Cluster to connect to. The nodes should be separated with commas, such as: `Node[,Node].<br/>`
+For each Node should be: ").
 
--define(SERVER_DESC(TYPE, DEFAULT_PORT), """
-The IPv4 or IPv6 address or host name to connect to.<br>
-A host entry has the following form: 'Host[:Port]'<br>
-The """ ++ TYPE ++ " default port " ++ DEFAULT_PORT ++ " is used if '[:Port]' isn't present"
+-define(SERVER_DESC(TYPE, DEFAULT_PORT), "
+The IPv4 or IPv6 address or the hostname to connect to.<br/>
+A host entry has the following form: `Host[:Port]`.<br/>
+The " ++ TYPE ++ " default port " ++ DEFAULT_PORT ++ " is used if `[:Port]` is not specified."
 ).
 
 -define(THROW_ERROR(Str), erlang:throw({error, Str})).

apps/emqx_connector/src/emqx_connector_mongo.erl

@@ -54,13 +54,15 @@ roots() ->
 
 fields(single) ->
     [ {mongo_type, #{type => single,
-                     default => single}}
+                     default => single,
+                     desc => "Standalone instance."}}
     , {server, fun server/1}
     , {w_mode, fun w_mode/1}
     ] ++ mongo_fields();
 fields(rs) ->
     [ {mongo_type, #{type => rs,
-                     default => rs}}
+                     default => rs,
+                     desc => "Replica set."}}
     , {servers, fun servers/1}
     , {w_mode, fun w_mode/1}
     , {r_mode, fun r_mode/1}
@@ -68,7 +70,8 @@ fields(rs) ->
     ] ++ mongo_fields();
 fields(sharded) ->
     [ {mongo_type, #{type => sharded,
-                     default => sharded}}
+                     default => sharded,
+                     desc => "Sharded cluster."}}
     , {servers, fun servers/1}
     , {w_mode, fun w_mode/1}
     ] ++ mongo_fields();
@@ -306,22 +309,27 @@ servers(desc) -> ?SERVERS_DESC ++ server(desc);
 servers(_) -> undefined.
 
 w_mode(type) -> hoconsc:enum([unsafe, safe]);
+w_mode(desc) -> "Write mode.";
 w_mode(default) -> unsafe;
 w_mode(_) -> undefined.
 
 r_mode(type) -> hoconsc:enum([master, slave_ok]);
+r_mode(desc) -> "Read mode.";
 r_mode(default) -> master;
 r_mode(_) -> undefined.
 
 duration(type) -> emqx_schema:duration_ms();
+duration(desc) -> "Time interval, such as timeout or TTL.";
 duration(required) -> false;
 duration(_) -> undefined.
 
 replica_set_name(type) -> binary();
+replica_set_name(desc) -> "Name of the replica set.";
 replica_set_name(required) -> false;
 replica_set_name(_) -> undefined.
 
 srv_record(type) -> boolean();
+srv_record(desc) -> "Use DNS SRV record.";
 srv_record(default) -> false;
 srv_record(_) -> undefined.
 

apps/emqx_connector/src/emqx_connector_schema_lib.erl

@@ -52,7 +52,8 @@ fields(_) -> [].
 
 ssl_fields() ->
     [ {ssl, #{type => hoconsc:ref(emqx_schema, ssl_client_opts),
-              default => #{<<"enable">> => false}
+              default => #{<<"enable">> => false},
+              desc => "SSL connection settings."
              }
       }
     ].
@@ -66,24 +67,29 @@ relational_db_fields() ->
     ].
 
 database(type) -> binary();
+database(desc) -> "Database name.";
 database(required) -> true;
 database(validator) -> [?NOT_EMPTY("the value of the field 'database' cannot be empty")];
 database(_) -> undefined.
 
 pool_size(type) -> integer();
+pool_size(desc) -> "Size of the connection pool.";
 pool_size(default) -> 8;
 pool_size(validator) -> [?MIN(1)];
 pool_size(_) -> undefined.
 
 username(type) -> binary();
+username(desc) -> "EMQX's username in the external database.";
 username(required) -> false;
 username(_) -> undefined.
 
 password(type) -> binary();
+password(desc) -> "EMQX's password in the external database.";
 password(required) -> false;
 password(_) -> undefined.
 
 auto_reconnect(type) -> boolean();
+auto_reconnect(desc) -> "Enable automatic reconnect to the database.";
 auto_reconnect(default) -> true;
 auto_reconnect(_) -> undefined.
 

apps/emqx_connector/src/mqtt/emqx_connector_mqtt_schema.erl

@@ -22,6 +22,7 @@
 
 -export([ roots/0
         , fields/1
+        , desc/1
         ]).
 
 -export([ ingress_desc/0
@@ -43,19 +44,19 @@ fields("connector") ->
     [ {mode,
         sc(hoconsc:enum([cluster_shareload]),
            #{ default => cluster_shareload
-            , desc => """
-The mode of the MQTT Bridge. Can be one of 'cluster_singleton' or 'cluster_shareload'<br>
+            , desc => "
+The mode of the MQTT Bridge. Can be one of 'cluster_singleton' or 'cluster_shareload'<br/>
 
-- cluster_singleton: create a unique MQTT connection within the emqx cluster.<br>
+- cluster_singleton: create a unique MQTT connection within the emqx cluster.<br/>
 In 'cluster_singleton' node, all messages toward the remote broker go through the same
-MQTT connection.<br>
-- cluster_shareload: create an MQTT connection on each node in the emqx cluster.<br>
+MQTT connection.<br/>
+- cluster_shareload: create an MQTT connection on each node in the emqx cluster.<br/>
 In 'cluster_shareload' mode, the incoming load from the remote broker is shared by
-using shared subscription.<br>
+using shared subscription.<br/>
 Note that the 'clientid' is suffixed by the node name, this is to avoid
 clientid conflicts between different nodes. And we can only use shared subscription
 topic filters for 'remote_topic' of ingress connections.
-"""
+"
             })}
     , {server,
         sc(emqx_schema:ip_port(),
@@ -97,11 +98,7 @@ topic filters for 'remote_topic' of ingress connections.
             , desc => "Max inflight (sent, but un-acked) messages of the MQTT protocol"
             })}
     , {replayq,
-        sc(ref("replayq"),
-           #{ desc => """
-Queue messages in disk files.
-"""
-            })}
+        sc(ref("replayq"), #{})}
     ] ++ emqx_connector_schema_lib:ssl_fields();
 
 fields("ingress") ->
@@ -120,23 +117,23 @@ fields("ingress") ->
     , {local_topic,
         sc(binary(),
            #{ validator => fun ?MODULE:non_empty_string/1
-            , desc => """
-Send messages to which topic of the local broker.<br>
+            , desc => "
+Send messages to which topic of the local broker.<br/>
 Template with variables is allowed.
-"""
+"
             })}
     , {local_qos,
         sc(qos(),
            #{ default => <<"${qos}">>
-            , desc => """
-The QoS of the MQTT message to be sent.<br>
-Template with variables is allowed."""
+            , desc => "
+The QoS of the MQTT message to be sent.<br/>
+Template with variables is allowed."
             })}
     , {hookpoint,
         sc(binary(),
-           #{ desc => """
+           #{ desc => "
 The hook point will be triggered when there's any message received from the remote broker.
-"""
+"
             })}
     ] ++ common_inout_confs();
 
@@ -151,94 +148,101 @@ fields("egress") ->
         sc(binary(),
            #{ default => <<"${topic}">>
             , validator => fun ?MODULE:non_empty_string/1
-            , desc => """
-Forward to which topic of the remote broker.<br>
+            , desc => "
+Forward to which topic of the remote broker.<br/>
 Template with variables is allowed.
-"""
+"
             })}
     , {remote_qos,
         sc(qos(),
            #{ default => <<"${qos}">>
-            , desc => """
-The QoS of the MQTT message to be sent.<br>
-Template with variables is allowed."""
+            , desc => "
+The QoS of the MQTT message to be sent.<br/>
+Template with variables is allowed."
             })}
     ] ++ common_inout_confs();
 
 fields("replayq") ->
     [ {dir,
         sc(hoconsc:union([boolean(), string()]),
-           #{ desc => """
-The dir where the replayq file saved.<br>
+           #{ desc => "
+The dir where the replayq file saved.<br/>
 Set to 'false' disables the replayq feature.
-"""
+"
             })}
     , {seg_bytes,
         sc(emqx_schema:bytesize(),
            #{ default => "100MB"
-            , desc => """
-The size in bytes of a single segment.<br>
+            , desc => "
+The size in bytes of a single segment.<br/>
 A segment is mapping to a file in the replayq dir. If the current segment is full, a new segment
 (file) will be opened to write.
-"""
+"
             })}
     , {offload,
         sc(boolean(),
            #{ default => false
-            , desc => """
-In offload mode, the disk queue is only used to offload queue tail segments.<br>
+            , desc => "
+In offload mode, the disk queue is only used to offload queue tail segments.<br/>
 The messages are cached in the memory first, then it writes to the replayq files after the size of
 the memory cache reaches 'seg_bytes'.
-"""
+"
             })}
     ].
 
+desc("ingress") ->
+    ingress_desc();
+desc("egress") ->
+    egress_desc();
+desc("replayq") ->
+    "Queue messages in disk files.";
+desc(_) ->
+    undefined.
+
 topic_mappings() ->
     [ {ingress,
         sc(ref("ingress"),
            #{ default => #{}
-            , desc => ingress_desc()
             })}
     , {egress,
         sc(ref("egress"),
            #{ default => #{}
-            , desc => egress_desc()
             })}
     ].
 
-ingress_desc() -> """
+ingress_desc() -> "
 The ingress config defines how this bridge receive messages from the remote MQTT broker, and then
-send them to the local broker.<br>
+send them to the local broker.<br/>
 Template with variables is allowed in 'local_topic', 'remote_qos', 'qos', 'retain',
-'payload'.<br>
+'payload'.<br/>
 NOTE: if this bridge is used as the input of a rule (emqx rule engine), and also local_topic is
 configured, then messages got from the remote broker will be sent to both the 'local_topic' and
 the rule.
-""".
+".
 
-egress_desc() -> """
+egress_desc() -> "
 The egress config defines how this bridge forwards messages from the local broker to the remote
-broker.<br>
-Template with variables is allowed in 'remote_topic', 'qos', 'retain', 'payload'.<br>
+broker.<br/>
+Template with variables is allowed in 'remote_topic', 'qos', 'retain', 'payload'.<br/>
 NOTE: if this bridge is used as the output of a rule (emqx rule engine), and also local_topic
 is configured, then both the data got from the rule and the MQTT messages that matches
 local_topic will be forwarded.
-""".
+".
 
 common_inout_confs() ->
     [ {retain,
         sc(hoconsc:union([boolean(), binary()]),
            #{ default => <<"${retain}">>
-            , desc => """
-The 'retain' flag of the MQTT message to be sent.<br>
-Template with variables is allowed."""
+            , desc => "
+The 'retain' flag of the MQTT message to be sent.<br/>
+Template with variables is allowed."
             })}
     , {payload,
         sc(binary(),
            #{ default => <<"${payload}">>
-            , desc => """
-The payload of the MQTT message to be sent.<br>
-Template with variables is allowed."""
+            , desc => "
+The payload of the MQTT message to be sent.<br/>
+Template with variables is allowed."
             })}
     ].
 

apps/emqx_exhook/src/emqx_exhook_schema.erl

@@ -32,7 +32,7 @@
 
 -reflect_type([duration/0]).
 
--export([namespace/0, roots/0, fields/1, server_config/0]).
+-export([namespace/0, roots/0, fields/1, desc/1, server_config/0]).
 
 namespace() -> exhook.
 
@@ -41,7 +41,9 @@ roots() -> [exhook].
 fields(exhook) ->
     [{servers,
       sc(hoconsc:array(ref(server)),
-          #{default => []})}
+          #{ default => []
+           , desc => "List of exhook servers."
+           })}
     ];
 
 fields(server) ->
@@ -61,7 +63,7 @@ fields(server) ->
                             })}
     , {failed_action, failed_action()}
     , {ssl,
-       sc(ref(ssl_conf), #{desc => "SSL client config"})}
+       sc(ref(ssl_conf), #{})}
     , {auto_reconnect,
        sc(hoconsc:union([false, duration()]),
           #{ default => "60s"
@@ -81,6 +83,15 @@ fields(ssl_conf) ->
     Schema = emqx_schema:client_ssl_opts_schema(#{}),
     lists:keydelete(user_lookup_fun, 1, Schema).
 
+desc(exhook) ->
+    "External hook (exhook) configuration.";
+desc(server) ->
+    "gRPC server configuration.";
+desc(ssl_conf) ->
+    "SSL client configuration.";
+desc(_) ->
+    undefined.
+
 %% types
 sc(Type, Meta) -> Meta#{type => Type}.
 

apps/emqx_gateway/src/emqx_gateway_schema.erl

@@ -294,18 +294,22 @@ fields(exproto) ->
 fields(exproto_grpc_server) ->
     [ {bind,
        sc(hoconsc:union([ip_port(), integer()]),
-          #{required => true})}
+          #{ required => true
+           , desc => "Listening address and port for the gRPC server."
+           })}
     , {ssl,
        sc(ref(ssl_server_opts),
           #{ required => {false, recursively}
+           , desc => "SSL configuration for the gRPC server."
            })}
     ];
 
 fields(exproto_grpc_handler) ->
-    [ {address, sc(binary(), #{required => true})}
+    [ {address, sc(binary(), #{required => true, desc => "gRPC server address."})}
     , {ssl,
        sc(ref(emqx_schema, ssl_client_opts),
           #{ required => {false, recursively}
+           , desc => "SSL configuration for the gRPC client."
            })}
     ];
 
@@ -318,9 +322,9 @@ fields(ssl_server_opts) ->
        }, true);
 
 fields(clientinfo_override) ->
-    [ {username, sc(binary())}
-    , {password, sc(binary())}
-    , {clientid, sc(binary())}
+    [ {username, sc(binary(), #{desc => "Template for overriding username."})}
+    , {password, sc(binary(), #{desc => "Template for overriding password."})}
+    , {clientid, sc(binary(), #{desc => "Template for overriding clientid."})}
     ];
 
 fields(lwm2m_translators) ->
@@ -362,25 +366,31 @@ the LwM2M client"
     ];
 
 fields(translator) ->
-    [ {topic, sc(binary(), #{required => true})}
-    , {qos, sc(emqx_schema:qos(), #{default => 0})}
+    [ {topic, sc(binary(),
+                 #{ required => true
+                  , desc => "Which topic the device's upstream message is published to."
+                  })}
+    , {qos, sc(emqx_schema:qos(),
+               #{ default => 0
+                , desc => "QoS of the published messages."
+                })}
     ];
 
 fields(udp_listeners) ->
-    [ {udp, sc(map(name, ref(udp_listener)))}
-    , {dtls, sc(map(name, ref(dtls_listener)))}
+    [ {udp, sc(map(name, ref(udp_listener)), #{desc => "UDP configuration."})}
+    , {dtls, sc(map(name, ref(dtls_listener)), #{desc => "DTLS configuration."})}
     ];
 
 fields(tcp_listeners) ->
-    [ {tcp, sc(map(name, ref(tcp_listener)))}
-    , {ssl, sc(map(name, ref(ssl_listener)))}
+    [ {tcp, sc(map(name, ref(tcp_listener)), #{desc => "TCP configuration."})}
+    , {ssl, sc(map(name, ref(ssl_listener)), #{desc => "SSL configuration."})}
     ];
 
 fields(udp_tcp_listeners) ->
-    [ {udp, sc(map(name, ref(udp_listener)))}
-    , {dtls, sc(map(name, ref(dtls_listener)))}
-    , {tcp, sc(map(name, ref(tcp_listener)))}
-    , {ssl, sc(map(name, ref(ssl_listener)))}
+    [ {udp, sc(map(name, ref(udp_listener)), #{desc => "UDP configuration."})}
+    , {dtls, sc(map(name, ref(dtls_listener)), #{desc => "DTLS configuration."})}
+    , {tcp, sc(map(name, ref(tcp_listener)), #{desc => "TCP configuration."})}
+    , {ssl, sc(map(name, ref(ssl_listener)), #{desc => "SSL configuration."})}
     ];
 
 fields(tcp_listener) ->
@@ -524,9 +534,7 @@ It has two purposes:
            , desc => ""
            })}
     , {clientinfo_override,
-       sc(ref(clientinfo_override),
-          #{ desc => "ClientInfo override"
-           })}
+       sc(ref(clientinfo_override), #{})}
     , {?EMQX_AUTHENTICATION_CONFIG_ROOT_NAME_ATOM, authentication_schema()}
     ].
 

apps/emqx_modules/src/emqx_modules_schema.erl

@@ -23,7 +23,8 @@
 -export([
     namespace/0,
     roots/0,
-    fields/1
+    fields/1,
+    desc/1
 ]).
 
 namespace() -> modules.
@@ -65,6 +66,17 @@ fields("rewrite") ->
 fields("topic_metrics") ->
     [{topic, sc(binary(), #{})}].
 
+desc("telemetry") ->
+    "Settings for the telemetry module.";
+desc("delayed") ->
+    "Settings for the delayed module.";
+desc("rewrite") ->
+    "Settings for the rewrite module.";
+desc("topic_metrics") ->
+    "Settings for the topic metrics module.";
+desc(_) ->
+    undefined.
+
 regular_expression(type) -> binary();
 regular_expression(desc) -> "Regular expressions";
 regular_expression(example) -> "^x/y/(.+)$";

apps/emqx_rule_engine/src/emqx_rule_engine_schema.erl

@@ -22,7 +22,9 @@
 
 -export([ namespace/0
         , roots/0
-        , fields/1]).
+        , fields/1
+        , desc/1
+        ]).
 
 -export([ validate_sql/1
         ]).
@@ -82,30 +84,7 @@ counter of the function output or the bridge channel will increase.
 
 fields("builtin_output_republish") ->
     [ {function, sc(republish, #{desc => "Republish the message as a new MQTT message"})}
-    , {args, sc(ref("republish_args"),
-        #{ desc => """
-The arguments of the built-in 'republish' output.<br>
-We can use variables in the args.<br>
-
-The variables are selected by the rule. For example, if the rule SQL is defined as following:
-<code>
-    SELECT clientid, qos, payload FROM \"t/1\"
-</code>
-Then there are 3 variables available: <code>clientid</code>, <code>qos</code> and
-<code>payload</code>. And if we've set the args to:
-<code>
-    {
-        topic = \"t/${clientid}\"
-        qos = \"${qos}\"
-        payload = \"msg: ${payload}\"
-    }
-</code>
-When the rule is triggered by an MQTT message with payload = \"hello\", qos = 1,
-clientid = \"Steve\", the rule will republish a new MQTT message to topic \"t/Steve\",
-payload = \"msg: hello\", and qos = 1.
-"""
-         , default => #{}
-         })}
+    , {args, sc(ref("republish_args"), #{default => #{}})}
     ];
 
 fields("builtin_output_console") ->
@@ -178,6 +157,38 @@ of the rule, then the string \"undefined\" is used.
          })}
     ].
 
+desc("rule_engine") ->
+    "Configuration for the EMQX Rule Engine.";
+desc("rules") ->
+    "Configuration for a rule.";
+desc("builtin_output_republish") ->
+    "Configuration for a built-in output.";
+desc("builtin_output_console") ->
+    "Configuration for a built-in output.";
+desc("user_provided_function") ->
+    "Configuration for a built-in output.";
+desc("republish_args") ->
+    "The arguments of the built-in 'republish' output.<br>"
+    "One can use variables in the args.<br>\n"
+    "The variables are selected by the rule. For example, if the rule SQL is defined as following:\n"
+    "<code>\n"
+    "    SELECT clientid, qos, payload FROM \"t/1\"\n"
+    "</code>\n"
+    "Then there are 3 variables available: <code>clientid</code>, <code>qos</code> and\n"
+    "<code>payload</code>. And if we've set the args to:\n"
+    "<code>\n"
+    "    {\n"
+    "        topic = \"t/${clientid}\"\n"
+    "        qos = \"${qos}\"\n"
+    "        payload = \"msg: ${payload}\"\n"
+    "    }\n"
+    "</code>\n"
+    "When the rule is triggered by an MQTT message with payload = `hello`, qos = 1,\n"
+    "clientid = `Steve`, the rule will republish a new MQTT message to topic `t/Steve`,\n"
+    "payload = `msg: hello`, and `qos = 1`.";
+desc(_) ->
+    undefined.
+
 rule_name() ->
     {"name", sc(binary(),
         #{ desc => "The name of the rule"