Implement basic SNS message filtering (#1521)

* Add support for FilterPolicy to sns subscription set_filter_attributes

* Add basic support for sns message filtering

This adds support for exact string value matching along with AND/OR
logic as described here:

https://docs.aws.amazon.com/sns/latest/dg/message-filtering.html

It does not provide support for:
- Anything-but string matching
- Prefix string matching
- Numeric Value Matching

The above filter policies (if configured) will not match messages.

moto/sns/models.py

@@ -42,11 +42,12 @@ class Topic(BaseModel):
         self.subscriptions_confimed = 0
         self.subscriptions_deleted = 0
 
-    def publish(self, message, subject=None):
+    def publish(self, message, subject=None, message_attributes=None):
         message_id = six.text_type(uuid.uuid4())
         subscriptions, _ = self.sns_backend.list_subscriptions(self.arn)
         for subscription in subscriptions:
-            subscription.publish(message, message_id, subject=subject)
+            subscription.publish(message, message_id, subject=subject,
+                                 message_attributes=message_attributes)
         return message_id
 
     def get_cfn_attribute(self, attribute_name):
@@ -81,9 +82,14 @@ class Subscription(BaseModel):
         self.protocol = protocol
         self.arn = make_arn_for_subscription(self.topic.arn)
         self.attributes = {}
+        self._filter_policy = None  # filter policy as a dict, not json.
         self.confirmed = False
 
-    def publish(self, message, message_id, subject=None):
+    def publish(self, message, message_id, subject=None,
+                message_attributes=None):
+        if not self._matches_filter_policy(message_attributes):
+            return
+
         if self.protocol == 'sqs':
             queue_name = self.endpoint.split(":")[-1]
             region = self.endpoint.split(":")[3]
@@ -98,6 +104,28 @@ class Subscription(BaseModel):
             region = self.arn.split(':')[3]
             lambda_backends[region].send_message(function_name, message, subject=subject)
 
+    def _matches_filter_policy(self, message_attributes):
+        # TODO: support Anything-but matching, prefix matching and
+        #       numeric value matching.
+        if not self._filter_policy:
+            return True
+
+        if message_attributes is None:
+            message_attributes = {}
+
+        def _field_match(field, rules, message_attributes):
+            if field not in message_attributes:
+                return False
+            for rule in rules:
+                if isinstance(rule, six.string_types):
+                    # only string value matching is supported
+                    if message_attributes[field] == rule:
+                        return True
+            return False
+
+        return all(_field_match(field, rules, message_attributes)
+                   for field, rules in six.iteritems(self._filter_policy))
+
     def get_post_data(self, message, message_id, subject):
         return {
             "Type": "Notification",
@@ -274,13 +302,14 @@ class SNSBackend(BaseBackend):
         else:
             return self._get_values_nexttoken(self.subscriptions, next_token)
 
-    def publish(self, arn, message, subject=None):
+    def publish(self, arn, message, subject=None, message_attributes=None):
         if subject is not None and len(subject) >= 100:
             raise ValueError('Subject must be less than 100 characters')
 
         try:
             topic = self.get_topic(arn)
-            message_id = topic.publish(message, subject=subject)
+            message_id = topic.publish(message, subject=subject,
+                                       message_attributes=message_attributes)
         except SNSNotFoundError:
             endpoint = self.get_endpoint(arn)
             message_id = endpoint.publish(message)
@@ -352,7 +381,7 @@ class SNSBackend(BaseBackend):
         return subscription.attributes
 
     def set_subscription_attributes(self, arn, name, value):
-        if name not in ['RawMessageDelivery', 'DeliveryPolicy']:
+        if name not in ['RawMessageDelivery', 'DeliveryPolicy', 'FilterPolicy']:
             raise SNSInvalidParameter('AttributeName')
 
         # TODO: should do validation
@@ -363,6 +392,9 @@ class SNSBackend(BaseBackend):
 
         subscription.attributes[name] = value
 
+        if name == 'FilterPolicy':
+            subscription._filter_policy = json.loads(value)
+
 
 sns_backends = {}
 for region in boto.sns.regions():

moto/sns/responses.py

@@ -241,6 +241,10 @@ class SNSResponse(BaseResponse):
         phone_number = self._get_param('PhoneNumber')
         subject = self._get_param('Subject')
 
+        message_attributes = self._get_map_prefix('MessageAttributes.entry',
+                                                  key_end='Name',
+                                                  value_end='Value')
+
         if phone_number is not None:
             # Check phone is correct syntax (e164)
             if not is_e164(phone_number):
@@ -265,7 +269,9 @@ class SNSResponse(BaseResponse):
         message = self._get_param('Message')
 
         try:
-            message_id = self.backend.publish(arn, message, subject=subject)
+            message_id = self.backend.publish(
+                arn, message, subject=subject,
+                message_attributes=message_attributes)
         except ValueError as err:
             error_response = self._error('InvalidParameter', str(err))
             return error_response, dict(status=400)

moto/sqs/responses.py

@@ -30,7 +30,7 @@ class SQSResponse(BaseResponse):
     @property
     def attribute(self):
         if not hasattr(self, '_attribute'):
-            self._attribute = self._get_map_prefix('Attribute', key_end='Name', value_end='Value')
+            self._attribute = self._get_map_prefix('Attribute', key_end='.Name', value_end='.Value')
         return self._attribute
 
     def _get_queue_name(self):