diff --git a/synapse/api/events/validator.py b/synapse/api/events/validator.py
new file mode 100644
index 0000000000..59b486d6d7
--- /dev/null
+++ b/synapse/api/events/validator.py
@@ -0,0 +1,81 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.api.errors import SynapseError, Codes
+
+
+class EventValidator(object):
+ def __init__(self, hs):
+ pass
+
+ def validate(self, event):
+ """Checks the given JSON content abides by the rules of the template.
+
+ Args:
+ content : A JSON object to check.
+ raises: True to raise a SynapseError if the check fails.
+ Returns:
+ True if the content passes the template. Returns False if the check
+ fails and raises=False.
+ Raises:
+ SynapseError if the check fails and raises=True.
+ """
+ # recursively call to inspect each layer
+ err_msg = self._check_json_template(
+ event.content,
+ event.get_content_template()
+ )
+ if err_msg:
+ raise SynapseError(400, err_msg, Codes.BAD_JSON)
+ else:
+ return True
+
+ def _check_json_template(self, content, template):
+ """Check content and template matches.
+
+ If the template is a dict, each key in the dict will be validated with
+ the content, else it will just compare the types of content and
+ template. This basic type check is required because this function will
+ be recursively called and could be called with just strs or ints.
+
+ Args:
+ content: The content to validate.
+ template: The validation template.
+ Returns:
+ str: An error message if the validation fails, else None.
+ """
+ if type(content) != type(template):
+ return "Mismatched types: %s" % template
+
+ if type(template) == dict:
+ for key in template:
+ if key not in content:
+ return "Missing %s key" % key
+
+ if type(content[key]) != type(template[key]):
+ return "Key %s is of the wrong type (got %s, want %s)" % (
+ key, type(content[key]), type(template[key]))
+
+ if type(content[key]) == dict:
+ # we must go deeper
+ msg = self._check_json(content[key], template[key])
+ if msg:
+ return msg
+ elif type(content[key]) == list:
+ # make sure each item type in content matches the template
+ for entry in content[key]:
+ msg = self._check_json(entry, template[key][0])
+ if msg:
+ return msg
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