[logger] Add handler callback filter_config/1

This function is called when a logger API function for fetching
handler configuration is called. The point is to allow the handler to
remove internal data fields that it might have stored in the
configuration database, before returning the handler configuration to
the caller.

An example of such internal data are the 'handler_pid' and 'mode_tab'
fields that logger_std_h and logger_disk_log_h store in their
configuration maps.

2 files changed, 30 insertions, 2 deletions

diff --git a/lib/kernel/doc/src/logger.xml b/lib/kernel/doc/src/logger.xml
index aa6e17f27b..2bcf137299 100644
--- a/lib/kernel/doc/src/logger.xml
+++ b/lib/kernel/doc/src/logger.xml
@@ -1123,6 +1123,26 @@ logger:set_process_metadata(maps:merge(logger:get_process_metadata(), Meta)).
     </func>
 
     <func>
+      <name>HModule:filter_config(Config) -> FilteredConfig</name>
+      <fsummary>Remove internal data from configuration.</fsummary>
+      <type>
+	<v>Config = FilteredConfig =
+	  <seealso marker="#type-handler_config">handler_config()</seealso></v>
+      </type>
+      <desc>
+	<p>This callback function is optional.</p>
+	<p>The function is called when one of the Logger API functions
+	  for fetching the handler configuration is called, for
+	  example
+	  <seealso marker="#get_handler_config-1">
+	    <c>logger:get_handler_config/1</c></seealso>.</p>
+	<p>It allows the handler to remove internal data fields from
+	  its configuration data before it is returned to the
+	  caller.</p>
+      </desc>
+    </func>
+
+    <func>
       <name>HModule:log(LogEvent, Config) -> void()</name>
       <fsummary>Log the given log event.</fsummary>
       <type>
diff --git a/lib/kernel/doc/src/logger_chapter.xml b/lib/kernel/doc/src/logger_chapter.xml
index 777c37058e..1870d2ab79 100644
--- a/lib/kernel/doc/src/logger_chapter.xml
+++ b/lib/kernel/doc/src/logger_chapter.xml
@@ -384,8 +384,8 @@ logger:debug(#{got => connection_request, id => Id, state => State},
 
     <p>In addition to the mandatory callback function <c>log/2</c>, a
       handler module can export the optional callback
-      functions <c>adding_handler/1</c>, <c>changing_config/3</c>
-      and <c>removing_handler/1</c>. See
+      functions <c>adding_handler/1</c>, <c>changing_config/3</c>,
+      <c>filter_config/1</c>, and <c>removing_handler/1</c>. See
       section <seealso marker="logger#handler_callback_functions">Handler
       Callback Functions</seealso> in the logger(3) manual page for
       more information about these function.</p>
@@ -1029,6 +1029,7 @@ ok</pre>
       <item><c>adding_handler(Config)</c></item>
       <item><c>removing_handler(Config)</c></item>
       <item><c>changing_config(SetOrUpdate, OldConfig, NewConfig)</c></item>
+      <item><c>filter_config(Config)</c></item>
     </list>
     <p>When a handler is added, by for example a call
       to <seealso marker="logger#add_handler-3">
@@ -1052,6 +1053,13 @@ ok</pre>
       calls <c>HModule:changing_config(SetOrUpdate, OldConfig, NewConfig)</c>. If
       this function returns <c>{ok,NewConfig1}</c>, Logger
       writes <c>NewConfig1</c> to the configuration database.</p>
+    <p>When <seealso marker="logger#get_config-0">
+	<c>logger:get_config/0</c></seealso> or
+      <seealso marker="logger#get_handler_config-0">
+	<c>logger:get_handler_config/0,1</c></seealso> is called,
+      Logger calls <c>HModule:filter_config(Config)</c>. This function
+      must return the handler configuration where internal data is
+      removed.</p>
 
     <p>A simple handler that prints to the terminal can be implemented
       as follows:</p>