improve logger overide

- add Logger.atoms() that facilitates log format override.
- add Logger.atoms_wrapper_class that permits custom wrapping.

fix #510

gunicorn/glogging.py

@@ -202,6 +202,8 @@ class Logger(object):
     access_fmt = "%(message)s"
     syslog_fmt = "[%(process)d] %(message)s"
 
+    atoms_wrapper_class = SafeAtoms
+
     def __init__(self, cfg):
         self.error_log = logging.getLogger("gunicorn.error")
         self.access_log = logging.getLogger("gunicorn.access")
@@ -264,14 +266,9 @@ class Logger(object):
             lvl = self.LOG_LEVELS.get(lvl.lower(), logging.INFO)
         self.error_log.log(lvl, msg, *args, **kwargs)
 
-    def access(self, resp, req, environ, request_time):
-        """ Seee http://httpd.apache.org/docs/2.0/logs.html#combined
-        for format details
+    def atoms(self, resp, req, environ, request_time):
+        """ Gets atoms for log formating.
         """
-
-        if not self.cfg.accesslog and not self.cfg.logconfig:
-            return
-
         status = resp.status.split(None, 1)[0]
         atoms = {
             'h': environ.get('REMOTE_ADDR', '-'),
@@ -300,10 +297,21 @@ class Logger(object):
         # add response headers
         atoms.update(dict([("{%s}o" % k.lower(), v) for k, v in resp.headers]))
 
+        return atoms
+
+    def access(self, resp, req, environ, request_time):
+        """ See http://httpd.apache.org/docs/2.0/logs.html#combined
+        for format details
+        """
+
+        if not self.cfg.accesslog and not self.cfg.logconfig:
+            return
+
         # wrap atoms:
         # - make sure atoms will be test case insensitively
         # - if atom doesn't exist replace it by '-'
-        safe_atoms = SafeAtoms(atoms)
+        safe_atoms = self.atoms_wrapper_class(self.atoms(resp, req, environ,
+            request_time))
 
         try:
             self.access_log.info(self.cfg.access_log_format % safe_atoms)