Bring back tuf/log.py from edec089965.

tuf/log.py

@@ -73,14 +73,16 @@
   '[%(funcName)s:%(lineno)s@%(filename)s] %(message)s'
 
 
+# Ask all Formatter instances to talk GMT.
+# http://docs.python.org/2/library/logging.html#logging.Formatter.formatException
 logging.Formatter.converter = time.gmtime
 formatter = logging.Formatter(_FORMAT_STRING)
 
-# Set the handlers for the logger.  The console handler is unset by default.  A
+# Set the handlers for the logger. The console handler is unset by default. A
 # module importing 'log.py' should explicitly set the console handler if
-# outputting log messages to the screen is needed.  Adding a console handler
-# can be done with tuf.log.add_console_handler().  Logging messages to a file
-# *is* set by default. 
+# outputting log messages to the screen is needed. Adding a console handler can
+# be done with tuf.log.add_console_handler(). Logging messages to a file *is*
+# set by default.
 console_handler = None
 
 # Set the built-in file handler.  Messages will be logged to
@@ -104,6 +106,51 @@
 
 
 
+class ConsoleFilter(logging.Filter):
+  def filter(self, record):
+    """
+    <Purpose>
+      Use Vinay Sajip's recommendation from Python issue #6435 to modify a
+      LogRecord object. This is meant to be used with our console handler.
+
+      http://stackoverflow.com/q/6177520
+      http://stackoverflow.com/q/5875225
+      http://bugs.python.org/issue6435
+      http://docs.python.org/2/howto/logging-cookbook.html#filters-contextual
+      http://docs.python.org/2/library/logging.html#logrecord-attributes
+
+    <Arguments>
+      record:
+        A logging.LogRecord object.
+
+    <Exceptions>
+      None.
+
+    <Side Effects>
+      Replaces the LogRecord exception text attribute.
+
+    <Returns>
+      True.
+
+    """
+
+    # If this LogRecord object has an exception, then we will replace its text.
+    if record.exc_info:
+      # We place the record's cached exception text (which usually contains the
+      # exception traceback) with much simpler exception information. This is
+      # most useful for the console handler, which we do not wish to deluge
+      # with too much data. Assuming that this filter is not applied to the
+      # file logging handler, the user may always consult the file log for the
+      # original exception traceback.
+      record.exc_text = str(record.exc_info)
+
+    # Always return True to signal that any given record must be formatted.
+    return True
+
+
+
+
+
 def set_log_level(log_level=_DEFAULT_LOG_LEVEL):
   """
   <Purpose>
@@ -200,7 +247,6 @@ def set_console_log_level(log_level=_DEFAULT_CONSOLE_LOG_LEVEL):
 
 
 
-
 def add_console_handler(log_level=_DEFAULT_CONSOLE_LOG_LEVEL):
   """
   <Purpose>
@@ -222,15 +268,46 @@ def add_console_handler(log_level=_DEFAULT_CONSOLE_LOG_LEVEL):
     None.
 
   """
-  
+  # Assign to the global console_handler object.
+  global console_handler
+
   # Does 'log_level' have the correct format?
   # Raise 'tuf.FormatError' if there is a mismatch.
   tuf.formats.LENGTH_SCHEMA.check_match(log_level)
 
-  # Set the console handler for the logger.  The built-in console handler will
-  # log messages to 'sys.stderr' and capture 'log_level' messages.
+  if not console_handler:
+    # Set the console handler for the logger. The built-in console handler will
+    # log messages to 'sys.stderr' and capture 'log_level' messages.
+    # NOTE: This is not thread-safe.
+    console_handler = logging.StreamHandler()
+    # Get our filter for the console handler.
+    console_filter = ConsoleFilter()
+
+    console_handler.setLevel(log_level)
+    console_handler.setFormatter(formatter)
+    console_handler.addFilter(console_filter)
+    logger.addHandler(console_handler)
+    logger.debug('Added a console handler.')
+  else:
+    logger.warn('We already have a console handler.')
+
+
+
+
+
+def remove_console_handler():
+  # Assign to the global console_handler object.
   global console_handler
-  console_handler = logging.StreamHandler()
-  console_handler.setLevel(log_level)
-  console_handler.setFormatter(formatter)
-  logger.addHandler(console_handler)
+
+  if console_handler:
+    logger.removeHandler(console_handler)
+    # NOTE: This is not thread-safe.
+    console_handler = None
+    logger.debug('Removed a console handler.')
+  else:
+    logger.warn('We do not have a console handler.')
+
+
+
+
+