chore(psk): improve configuration file

apps/emqx_psk/etc/emqx_psk.conf

@@ -1,7 +1,19 @@
+##--------------------------------------------------------------------
+## EMQ X PSK
+##--------------------------------------------------------------------
+
 psk {
+    ## Whether to enable the PSK feature.
     enable = true
 
-    # boot_file = {{ platform_data_dir }}/boot.psk
+    ## If boot file is specified, emqx will import PSKs from the file 
+    ## into the built-in database at startup for use by the runtime.
+    ##
+    ## The file has to be structured line-by-line, each line must be in
+    ## the format: <PSKIdentity>:<SharedSecret>
+    ## boot_file = {{ platform_data_dir }}/boot.psk
 
-    # delimiter = ":"
+    ## Specifies the separator for PSKIdentity and SharedSecret in the boot file.
+    ## The default is colon (:)
+    ## separator = ":"
 }

apps/emqx_psk/src/emqx_psk.erl

@@ -148,15 +148,15 @@ is_enable() ->
 boot_file() ->
     emqx_config:get([psk, boot_file], undefined).
 
-delimiter() ->
-    emqx_config:get([psk, delimiter], ?DEFAULT_DELIMITER).
+separator() ->
+    emqx_config:get([psk, separator], ?DEFAULT_DELIMITER).
 
 import_psks(SrcFile) ->
     case file:open(SrcFile, [read, raw, binary, read_ahead]) of
         {error, Reason} ->
             {error, Reason};
         {ok, Io} ->
-            case Result = import_psks(Io, delimiter()) of
+            case Result = import_psks(Io, separator()) of
                 ok -> ignore;
                 {error, Reason} ->
                     ?LOG("Failed to import psk from ~s due to ~p", [SrcFile, Reason])

apps/emqx_psk/src/emqx_psk_schema.erl

@@ -29,7 +29,7 @@ roots() -> [].
 fields("psk") ->
     [ {enable,    fun enable/1}
     , {boot_file, fun boot_file/1}
-    , {delimiter, fun delimiter/1}
+    , {separator, fun separator/1}
     ].
 
 enable(type) -> boolean();
@@ -40,6 +40,6 @@ boot_file(type) -> binary();
 boot_file(nullable) -> true;
 boot_file(_) -> undefined.
 
-delimiter(type) -> binary();
-delimiter(default) -> <<":">>;
-delimiter(_) -> undefined.
+separator(type) -> binary();
+separator(default) -> <<":">>;
+separator(_) -> undefined.