Support subscribing to SNS ARNs

This updates `@app.on_sns_message` to accept either the topic name or
the topic ARN rather than just the name. While accepting the name can
be a simpler experience, it prevents users from subscribing to topics
that are in other regions or other accounts.

chalice/deploy/planner.py

@@ -439,31 +439,41 @@ def _plan_snslambdasubscription(self, resource):
         )
         topic_arn_varname = '%s_topic_arn' % resource.resource_name
         subscribe_varname = '%s_subscription_arn' % resource.resource_name
-        # To keep the user API simple, we only require the topic
-        # name and not the ARN.  However, the APIs require the topic
-        # ARN so we need to reconstruct it here in the planner.
-        instruction_for_topic_arn = [
-            models.BuiltinFunction(
-                'parse_arn',
-                [function_arn],
-                output_var='parsed_lambda_arn',
-            ),
-            models.JPSearch('account_id',
-                            input_var='parsed_lambda_arn',
-                            output_var='account_id'),
-            models.JPSearch('region',
-                            input_var='parsed_lambda_arn',
-                            output_var='region_name'),
-            models.StoreValue(
-                name=topic_arn_varname,
-                value=StringFormat(
-                    'arn:aws:sns:{region_name}:{account_id}:%s' % (
-                        resource.topic
+
+        instruction_for_topic_arn = []  # type: List[InstructionMsg]
+        if resource.topic.startswith('arn:aws:sns:'):
+            instruction_for_topic_arn += [
+                models.StoreValue(
+                    name=topic_arn_varname,
+                    value=resource.topic,
+                )
+            ]
+        else:
+            # To keep the user API simple, we only require the topic
+            # name and not the ARN.  However, the APIs require the topic
+            # ARN so we need to reconstruct it here in the planner.
+            instruction_for_topic_arn += [
+                models.BuiltinFunction(
+                    'parse_arn',
+                    [function_arn],
+                    output_var='parsed_lambda_arn',
+                ),
+                models.JPSearch('account_id',
+                                input_var='parsed_lambda_arn',
+                                output_var='account_id'),
+                models.JPSearch('region',
+                                input_var='parsed_lambda_arn',
+                                output_var='region_name'),
+                models.StoreValue(
+                    name=topic_arn_varname,
+                    value=StringFormat(
+                        'arn:aws:sns:{region_name}:{account_id}:%s' % (
+                            resource.topic
+                        ),
+                        ['region_name', 'account_id'],
                     ),
-                    ['region_name', 'account_id'],
                 ),
-            ),
-        ]  # type: List[InstructionMsg]
+            ]
         if self._remote_state.resource_exists(resource):
             # Given there's nothing about an SNS subscription you can
             # configure for now, if the resource exists, we don't do

docs/source/api.rst

@@ -235,8 +235,7 @@ Chalice
               app.log.info("SNS subject: %s", event.subject)
               app.log.info("SNS message: %s", event.message)
 
-      :param topic: The name of the SNS topic you want to subscribe to.
-        This is the name of the topic, not the topic ARN.
+      :param topic: The name or ARN of the SNS topic you want to subscribe to.
 
       :param name: The name of the function to use.  This name is combined
         with the chalice app name as well as the stage name to create the

docs/source/topics/events.rst

@@ -208,6 +208,10 @@ command::
     2018-06-28 17:49:30.513000 547e0f chalice-demo-sns - DEBUG - Received message with subject: TestSubject1, message: TestMessage1
     2018-06-28 17:49:40.391000 547e0f chalice-demo-sns - DEBUG - Received message with subject: TestSubject2, message: TestMessage2
 
+In this example we used the SNS topic name to register our handler, but you can
+also use the topic arn. This can be useful if your topic is in another region
+or account.
+
 
 .. _sqs-events:
 

tests/unit/deploy/test_planner.py

@@ -660,6 +660,63 @@ def test_can_plan_sns_subscription(self):
             ),
         ]
 
+    def test_can_plan_sns_arn_subscription(self):
+        function = create_function_resource('function_name')
+        topic_arn = 'arn:aws:sns:mars-west-2:123456789:mytopic'
+        sns_subscription = models.SNSLambdaSubscription(
+            resource_name='function_name-sns-subscription',
+            topic=topic_arn,
+            lambda_function=function
+        )
+        plan = self.determine_plan(sns_subscription)
+        plan_parse_arn = plan[0]
+        assert plan_parse_arn == models.StoreValue(
+            name='function_name-sns-subscription_topic_arn',
+            value=topic_arn,
+        )
+        topic_arn_var = Variable("function_name-sns-subscription_topic_arn")
+        assert plan[1:] == [
+            models.APICall(
+                method_name='add_permission_for_sns_topic',
+                params={
+                    'function_arn': Variable("function_name_lambda_arn"),
+                    'topic_arn': topic_arn_var,
+                },
+                output_var=None
+            ),
+            models.APICall(
+                method_name='subscribe_function_to_topic',
+                params={
+                    'function_arn': Variable("function_name_lambda_arn"),
+                    'topic_arn': topic_arn_var,
+                },
+                output_var='function_name-sns-subscription_subscription_arn'
+            ),
+            models.RecordResourceValue(
+                resource_type='sns_event',
+                resource_name='function_name-sns-subscription',
+                name='topic',
+                value=topic_arn),
+            models.RecordResourceVariable(
+                resource_type='sns_event',
+                resource_name='function_name-sns-subscription',
+                name='lambda_arn',
+                variable_name='function_name_lambda_arn'
+            ),
+            models.RecordResourceVariable(
+                resource_type='sns_event',
+                resource_name='function_name-sns-subscription',
+                name='subscription_arn',
+                variable_name='function_name-sns-subscription_subscription_arn'
+            ),
+            models.RecordResourceVariable(
+                resource_type='sns_event',
+                resource_name='function_name-sns-subscription',
+                name='topic_arn',
+                variable_name='function_name-sns-subscription_topic_arn',
+            ),
+        ]
+
     def test_sns_subscription_exists_is_noop_for_planner(self):
         function = create_function_resource('function_name')
         sns_subscription = models.SNSLambdaSubscription(