Limit the size of HTTP requests.

Adds a new RequestBodySizeLimiter middleware to guard against
really large HTTP requests. The default max request size is 112k
although this limit is configurable via the 'max_request_body_size'
config parameter.

Fixes LP Bug #1099025.

Change-Id: Id51be3d9a0d829d63d55a92dca61a39a17629785

keystone/common/utils.py

@@ -311,3 +311,37 @@ def setup_remote_pydev_debug():
         except:
             LOG.exception(_(error_msg))
             raise
+
+
+class LimitingReader(object):
+    """Reader to limit the size of an incoming request."""
+    def __init__(self, data, limit):
+        """
+        :param data: Underlying data object
+        :param limit: maximum number of bytes the reader should allow
+        """
+        self.data = data
+        self.limit = limit
+        self.bytes_read = 0
+
+    def __iter__(self):
+        for chunk in self.data:
+            self.bytes_read += len(chunk)
+            if self.bytes_read > self.limit:
+                raise exception.RequestTooLarge()
+            else:
+                yield chunk
+
+    def read(self, i):
+        result = self.data.read(i)
+        self.bytes_read += len(result)
+        if self.bytes_read > self.limit:
+            raise exception.RequestTooLarge()
+        return result
+
+    def read(self):
+        result = self.data.read()
+        self.bytes_read += len(result)
+        if self.bytes_read > self.limit:
+            raise exception.RequestTooLarge()
+        return result