Add a rate limiting filter for log messages

This should help cut down on the massive amount of emails I receive when
things go wrong on the production website.

Signed-off-by: Dan McGee <dan@archlinux.org>

1 files changed, 71 insertions, 0 deletions

diff --git a/main/log.py b/main/log.py
new file mode 100644
index 0000000..6363487
--- /dev/null
+++ b/main/log.py
@@ -0,0 +1,71 @@
+# Derived from Django snippets: http://djangosnippets.org/snippets/2242/
+from collections import OrderedDict
+from datetime import datetime, timedelta
+from hashlib import md5
+import traceback
+from pytz import utc
+
+
+class LimitedSizeDict(OrderedDict):
+    def __init__(self, *args, **kwargs):
+        self.size_limit = kwargs.pop('size', None)
+        if self.size_limit == 0:
+            self.size_limit = None
+        if self.size_limit and self.size_limit < 0:
+            raise Exception('Invalid size specified')
+        super(LimitedSizeDict, self).__init__(*args, **kwargs)
+        self.check_item_limits()
+
+    def __setitem__(self, key, value):
+        # delete and add to ensure it ends up at the end of the linked list
+        if key in self:
+            super(LimitedSizeDict, self).__delitem__(key)
+        super(LimitedSizeDict, self).__setitem__(key, value)
+        self.check_item_limits()
+
+    def check_item_limits(self):
+        if self.size_limit is None:
+            return
+        while len(self) > self.size_limit:
+            self.popitem(last=False)
+
+
+class RateLimitFilter(object):
+    def __init__(self, name='', rate=10, prefix='error_rate', max_keys=100):
+        # delayed import otherwise we have a circular dep when setting up
+        # the logging config: settings -> logging -> cache -> settings
+        self.cache_module = __import__('django.core.cache', fromlist=['cache'])
+        self.errors = LimitedSizeDict(size=max_keys)
+        self.rate = rate
+        self.prefix = prefix
+
+    def filter(self, record):
+        if self.rate == 0:
+            # rate == 0 means totally unfiltered
+            return True
+
+        trace = '\n'.join(traceback.format_exception(*record.exc_info))
+        key = md5(trace).hexdigest()
+        duplicate = False
+        cache = self.cache_module.cache
+
+        # Test if the cache works
+        try:
+            cache.set(self.prefix, 1, 300)
+            use_cache = (cache.get(self.prefix) == 1)
+        except:
+            use_cache = False
+
+        if use_cache:
+            cache_key = '%s_%s' % (self.prefix, key)
+            duplicate = (cache.get(cache_key) == 1)
+            cache.set(cache_key, 1, self.rate)
+        else:
+            now = datetime.utcnow().replace(tzinfo=utc)
+            min_date = now - timedelta(seconds=self.rate)
+            duplicate = (key in self.errors and self.errors[key] >= min_date)
+            self.errors[key] = now
+
+        return not duplicate
+
+# vim: set ts=4 sw=4 et: