[feat] Allow users define custom log handlers and attach them to the framework

docs/howto.rst

@@ -1162,3 +1162,60 @@ If you use a Python-based configuration file, you can define your custom launche
 .. note::
 
    In versions prior to 4.0, launchers could only be implemented inside the source code tree of ReFrame.
+
+
+.. _custom-loggers:
+
+Implementing a custom log handler
+---------------------------------
+
+Here's an example implementation of a custom log handler defined in a Python-based configuration file.
+
+Define a custom log handler class based on :class:`~logging.Handler` which uses a custom logging API:
+
+.. code-block:: python
+
+   import logging
+   import mylogger
+
+   class MyLoggerHandler(logging.Handler):
+      def __init__(self, key):
+         super().__init__()
+         self.key = key
+
+      def emit(self, record):
+         myrecord = {
+            'value': record.check_perf_value,
+         }
+         mylogger.log(self.key, myrecord)
+
+Apply the :func:`~reframe.core.logging.register_log_handler` decorator to a function returns an instance of the custom log handler:
+
+.. code-block:: python
+
+   from reframe.core.logging import register_log_handler
+
+   @register_log_handler("mylogger")
+   def _create_mylogger_handler(site_config, config_prefix):
+      key = site_config.get(f'{config_prefix}/key')
+      return MyLoggerHandler(key)
+
+
+Finally, add a handler entry with type matching registered name for the custom log handler to the site config:
+
+.. code-block:: python
+
+   site_configuration = {
+      'logging': [
+         {
+            'handlers': [
+               {
+                  'type': 'mylogger',
+                  'key': 'abc',
+               },
+               ...
+            ]
+         }
+      ],
+      ...
+   }

reframe/core/logging.py

@@ -412,6 +412,19 @@ def stream_handler_kind(handler):
     return logger
 
 
+# Registry for log handler creation functions
+_create_handlers = {}
+
+
+def register_log_handler(name):
+    '''Register the decorated log handler creation function'''
+    def _create_handler_wrapper(fn):
+        _create_handlers[name] = fn
+        return fn
+    return _create_handler_wrapper
+
+
+@register_log_handler('file')
 def _create_file_handler(site_config, config_prefix):
     filename = os.path.expandvars(site_config.get(f'{config_prefix}/name'))
     if not filename:
@@ -431,6 +444,7 @@ def _create_file_handler(site_config, config_prefix):
                                                 mode='a+' if append else 'w+')
 
 
+@register_log_handler('filelog')
 def _create_filelog_handler(site_config, config_prefix):
     basedir = os.path.abspath(os.path.join(
         site_config.get('systems/0/prefix'),
@@ -447,6 +461,7 @@ def _create_filelog_handler(site_config, config_prefix):
                             ignore_keys=ignore_keys)
 
 
+@register_log_handler('syslog')
 def _create_syslog_handler(site_config, config_prefix):
     address = site_config.get(f'{config_prefix}/address')
 
@@ -485,6 +500,7 @@ def _create_syslog_handler(site_config, config_prefix):
     return logging.handlers.SysLogHandler(address, facility_type, socket_type)
 
 
+@register_log_handler('stream')
 def _create_stream_handler(site_config, config_prefix):
     stream = site_config.get(f'{config_prefix}/name')
     if stream == 'stdout':
@@ -496,6 +512,7 @@ def _create_stream_handler(site_config, config_prefix):
         raise AssertionError(f'unknown stream: {stream}')
 
 
+@register_log_handler('graylog')
 def _create_graylog_handler(site_config, config_prefix):
     try:
         import pygelf
@@ -528,6 +545,7 @@ def _create_graylog_handler(site_config, config_prefix):
                                   json_default=jsonext.encode)
 
 
+@register_log_handler('httpjson')
 def _create_httpjson_handler(site_config, config_prefix):
     url = site_config.get(f'{config_prefix}/url')
     extras = site_config.get(f'{config_prefix}/extras')
@@ -678,20 +696,6 @@ def emit(self, record):
             raise LoggingError('logging failed') from e
 
 
-_create_handler_registry = {
-    'file': _create_file_handler,
-    'filelog': _create_filelog_handler,
-    'syslog': _create_syslog_handler,
-    'stream': _create_stream_handler,
-    'graylog': _create_graylog_handler,
-    'httpjson': _create_httpjson_handler,
-}
-
-
-def register_plugin_handler(create_plugin_handler):
-    _create_handler_registry["plugin"] = create_plugin_handler
-
-
 def _extract_handlers(site_config, handlers_group):
     handler_prefix = f'logging/0/{handlers_group}'
     handlers_list = site_config.get(handler_prefix)
@@ -700,15 +704,15 @@ def _extract_handlers(site_config, handlers_group):
         handler_type = handler_config['type']
 
         try:
-            create_handler = _create_handler_registry[handler_type]
-            hdlr = create_handler(site_config, f'{handler_prefix}/{i}')
-            if hdlr is None:
-                getlogger().warning('could not initialize the '
-                                    f'{handler_type} handler; ignoring ...')
-                continue
+            create_handler = _create_handlers[handler_type]
         except KeyError:
-            # Should not enter here
-            raise AssertionError(f'unknown handler type: {handler_type}')
+            raise ConfigError(f'unknown handler type: {handler_type}') from None
+
+        hdlr = create_handler(site_config, f'{handler_prefix}/{i}')
+        if hdlr is None:
+            getlogger().warning('could not initialize the '
+                                f'{handler_type} handler; ignoring ...')
+            continue
 
         level = site_config.get(f'{handler_prefix}/{i}/level')
         fmt = site_config.get(f'{handler_prefix}/{i}/format')

reframe/schemas/config.json

@@ -49,10 +49,7 @@
         "handler_common": {
             "type": "object",
             "properties": {
-                "type": {
-                    "type": "string",
-                    "enum": ["file", "filelog", "graylog", "stream", "syslog", "httpjson", "plugin"]
-                },
+                "type": {"type": "string"},
                 "level": {"$ref": "#/defs/loglevel"},
                 "format": {"type": "string"},
                 "format_perfvars": {"type": "string"},