stageVariables with value null for sam local start-api

[nmoutschen]

Description:

When using an HttpApi event type for a Lambda function in a SAM template and running it locally, sam local uses a stageVariables key with a null value, which breaks deserialization for the Rust Lambda runtime and does not map to what API Gateway actually sends.

See awslabs/aws-lambda-rust-runtime#365 for more information on the Rust runtime side.

Steps to reproduce:

• Use sam init to create a new project
• Select Zip, Python3.9, and Hello World example
• Modify the template.yaml file to use HttpApi instead of Api
• Modify the function code to display the event payload
• Run sam local start-api
• Invoke the local API
• Notice the stageVariables field with a value of null

Observed result:

Here is a sample payload sent to the Lambda function from sam local start-api:

{
    "headers": {
      "accept": "*/*",
      "content-length": "0",
      "host": "xxx.execute-api.us-east-1.amazonaws.com",
      "user-agent": "curl/7.64.1",
      "x-amzn-trace-id": "Root=1-5eb33c07-de25b420912dee103a5db434",
      "x-forwarded-for": "65.78.31.245",
      "x-forwarded-port": "443",
      "x-forwarded-proto": "https"
    },
    "isBase64Encoded": false,
    "rawPath": "/",
    "rawQueryString": "",
    "requestContext": {
      "accountId": "123456789012",
      "apiId": "xxx",
      "domainName": "xxx.execute-api.us-east-1.amazonaws.com",
      "domainPrefix": "xxx",
      "http": {
        "method": "GET",
        "path": "/",
        "protocol": "HTTP/1.1",
        "sourceIp": "65.78.31.245",
        "userAgent": "curl/7.64.1"
      },
      "requestId": "MIZRNhJtIAMEMDw=",
      "routeKey": "$default",
      "stage": "$default",
      "time": "06/May/2020:22:36:55 +0000",
      "timeEpoch": 1588804615616
    },
    "routeKey": "$default",
    "version": "2.0"
  }

Expected result:

stageVariables would either be missing or contain an empty object.

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. OS: Ubuntu 20.04
2. sam --version: 1.34.1
3. AWS region: eu-north-1

[wchengru]

Hi, I can reproduce this issue and confirm that the stageVariables is None instead of an empty object.