Data did not match any variant of untagged enum LambdaRequest with SAM local

[nmoutschen]

When running a Lambda function in Rust using the lambda-http crate with sam local start-api and an HttpApi event, the Lambda runtime is not able to deserialize the payload sent by SAM into a LambdaRequest.

I've created a minimum reproducible sample that just takes an event received by a Lambda function running locally in another language, and try to deserialize it into a lambda_http::request::LambdaRequest:

const PAYLOAD: &str = r#"{
    "version": "2.0",
    "routeKey": "GET /hello",
    "rawPath": "/hello",
    "rawQueryString": "",
    "cookies": [],
    "headers": {
      "Host": "127.0.0.1:3000",
      "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0",
      "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8",
      "Accept-Language": "en-US,en;q=0.5",
      "Accept-Encoding": "gzip, deflate",
      "Connection": "keep-alive",
      "Upgrade-Insecure-Requests": "1",
      "Sec-Fetch-Dest": "document",
      "Sec-Fetch-Mode": "navigate",
      "Sec-Fetch-Site": "none",
      "Sec-Fetch-User": "?1",
      "Cache-Control": "max-age=0",
      "X-Forwarded-Proto": "http",
      "X-Forwarded-Port": "3000"
    },
    "queryStringParameters": {},
    "requestContext": {
      "accountId": "123456789012",
      "apiId": "1234567890",
      "http": {
        "method": "GET",
        "path": "/hello",
        "protocol": "HTTP/1.1",
        "sourceIp": "127.0.0.1",
        "userAgent": "Custom User Agent String"
      },
      "requestId": "1ac06eee-f687-44ec-9036-dfd49d0be0a3",
      "routeKey": "GET /hello",
      "stage": "$default",
      "time": "16/Nov/2021:11:54:33 +0000",
      "timeEpoch": 1637063673,
      "domainName": "localhost",
      "domainPrefix": "localhost"
    },
    "body": "",
    "pathParameters": {},
    "stageVariables": null,
    "isBase64Encoded": false
  }"#;

fn main() {
    let val: lambda_http::request::LambdaRequest = serde_json::from_str(PAYLOAD).unwrap();
    println!("{:?}", val);
}

[nmoutschen]

If I change stageVariables from null into {}, the example above works.

[bnusunny]

This might be an issue with SAM local. API Gateway omits those null valued properties.

[nmoutschen]

Agree that this is probably an issue on SAM local, but that might be a possibility we need to deal with from a robustness principle perspective. lambda_http::request::LambdaRequest already supports fields with null values for Alb and ApiGateway variants. I've made a PR that would fix it for sam local in the meantime, and will create an issue for aws-sam-cli too.

[ionionascu]

I got a similar error when using the Test Method functionality of the API Gateway in the AWS Console, not related to SAM. I can see that the request sent to the lambda has:

    "headers": null,
    "multiValueHeaders": null,
    "queryStringParameters": null,
    "multiValueQueryStringParameters": null,
    "pathParameters": null,
    "stageVariables": null,

This happens for a deployment that used to work just fine until an unrelated lambda code change got deployed for testing.

[nmoutschen]

@ionionascu Could you retry by using the git version of the lambda_http crate to know if the latest changes fix the issue in that situation?

You can do that by replacing the dependency like this in your Cargo.toml:

lambda_http = { git = "https://github.com/awslabs/aws-lambda-rust-runtime/lambda-http" } 

[nmoutschen]

I'll close this issue since the PR is merged, but let me know if it doesn't work for you @ionionascu

[ionionascu]

I'll close this issue since the PR is merged, but let me know if it doesn't work for you @ionionascu

@nmoutschen , I have raised another issue, #367, as I think my problem has a different cause. I am testing with lambda_http = { git = "https://github.com/awslabs/aws-lambda-rust-runtime" } in Cargo.toml.