Function with 'Fn::Transform' as first events causes 'sam local start-api' to crash

Description:

If a template contains a Function, of which the top-most event is a Fn::Transform entry. Then sam local start-api fails to start with something like:

...
File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/lib/sam_api_provider.py", line 191, in extract_routes_from_events
    for _, event in serverless_function_events.items():
AttributeError: 'str' object has no attribute 'items'

This template does not cause any issues with other commands, including sam local invoke, sam package and sam deploy.

Steps to reproduce the issue:

1. Given the template:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Resources:
  Func1:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri:                      "./"
      Handler:                      "main"
      Runtime:                      "go1.x"
      Events:
        Api1:
          Type: Api
          Properties:
            Path:                   "/func1"
            Method:                 "GET"

  Func2:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri:                      "./"
      Handler:                      "main"
      Runtime:                      "go1.x"
      Events:
        Fn::Transform:
          Name: AWS::Include
          Parameters:
            Location:               "events.yaml"

1. Run sam local start-api

Observed result: sam local start-api fails to start:

Traceback (most recent call last):
  File "/usr/local/bin/sam", line 11, in <module>
    load_entry_point('aws-sam-cli==0.21.0', 'console_scripts', 'sam')()
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/decorators.py", line 64, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/telemetry/metrics.py", line 94, in wrapped
    raise exception  # pylint: disable=raising-bad-type
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/lib/telemetry/metrics.py", line 65, in wrapped
    return_value = func(*args, **kwargs)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/start_api/cli.py", line 60, in cli
    parameter_overrides)  # pragma: no cover
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/start_api/cli.py", line 95, in do_cli
    static_dir=static_dir)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/lib/local_api_service.py", line 43, in __init__
    cwd=self.cwd)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/lib/api_provider.py", line 42, in __init__
    self.api = self._extract_api(self.resources)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/lib/api_provider.py", line 71, in _extract_api
    provider.extract_resources(resources, collector, cwd=self.cwd)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/lib/sam_api_provider.py", line 52, in extract_resources
    self._extract_routes_from_function(logical_id, resource, collector)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/lib/sam_api_provider.py", line 172, in _extract_routes_from_function
    self.extract_routes_from_events(logical_id, serverless_function_events, collector)
  File "/usr/local/Cellar/aws-sam-cli/0.21.0/libexec/lib/python3.7/site-packages/samcli/commands/local/lib/sam_api_provider.py", line 191, in extract_routes_from_events
    for _, event in serverless_function_events.items():
AttributeError: 'str' object has no attribute 'items'

Expected result: sam local start-api should process the Fn::Transform entry and run properly.

Or (also acceptable for my use case) sam local start-api should ignore the Fn::Transform entry completely and not crash.

Workarounds: If you add any other event above the Fn::Transform entry, sam local start-api will work. But the included events (events.yaml in this case) do not get picked up by sam local start-api.

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Resources:

  Func1:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri:                      "./"
      Handler:                      "main"
      Runtime:                      "go1.x"
      Events:
        Api1:
          Type: Api
          Properties:
            Path:                   "/func1"
            Method:                 "GET"

  Func2:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri:                      "./"
      Handler:                      "main"
      Runtime:                      "go1.x"
      Events:
        Schedule2:
          Type: Schedule
          Properties:
            Schedule:               "rate(5 minutes)"
        Fn::Transform:
          Name: AWS::Include
          Parameters:
            Location:               "events.yaml"

Versions:

SAM CLI, version 0.21.0
aws-cli/1.16.210 Python/3.7.4 Darwin/18.7.0 botocore/1.12.200

[sgates]

I’m having a similar issue with transform used to process a swagger template for an Api Gateway declaration. This works fine in v0.19.0 but breaks after. Little bit of debugging - it seems the parsing of the swagger file doesn’t happen, and it tries to get the resources out of a dict, but it’s a string not a dict so I get a similar error as OP: AttributeError: ‘str’ object has no attribute ‘get’. I can provide more details if needed, but it looks very similar and is also related to a change in the transform.

Edit: For anyone else having this issue that wants to revert and you’re using home-brew try this:

$ brew uninstall was-sam-cli
$ brew install https://raw.githubusercontent.com/aws/homebrew-tap/2160475c2a6d86cb9d5ceea25d4ad791ee908908/Formula/aws-sam-cli.rb

[joskark]

I am also having the same issue as @sgates with AWS::Serverless::Api. I tried to debug and I found that the error is somewhere in the intrinsic_property_resolver.py. This is the Cloudformation part:

Api:
    Type: AWS::Serverless::Api
    Properties:
      StageName: !Ref Variable
      Cors: "'*'"
      DefinitionBody:
        Fn::Transform:
          Name: AWS::Include
          Parameters:
            Location: !Ref Swagger

Then i am getting the sanitized version that gives: 'DefinitionBody': 'Swagger' 'StageName': 'Variable'

I found that the change happens here: https://github.com/awslabs/aws-sam-cli/blob/704c1ea94a72d7db9438a61d64da64156d4cbe53/samcli/lib/intrinsic_resolver/intrinsic_property_resolver.py#L217

Below is the output from before and after the sanitation.

original: 'StageName' -> '{'Ref': 'Variable'}'
sanitized: 'StageName' -> 'Variable'

original: 'DefinitionBody' -> 'OrderedDict([('Fn::Transform', OrderedDict([('Name', 'AWS::Include'), ('Parameters', OrderedDict([('Location', {'Ref': 'Swagger'})]))]))])'
sanitized: 'DefinitionBody' -> 'Swagger'

sanitized: 'Properties' -> '{'MethodSettings': [{'LoggingLevel': 'INFO', 'MetricsEnabled': True, 'DataTraceEnabled': True, 'ResourcePath': '/*', 'HttpMethod': '*'}], 'StageName': 'Variable', 'Cors': "'*'", 'DefinitionBody': 'Swagger'}'

SAM version: 0.22.0 Python: 3.7.4

Hope that helps and I will try to continue debugging when I will have some time in case it’s not solved.