Several minor discrepancies between "cargo lambda watch" and actually running on aws

when there's no query, payload.rawQueryString on watch is Null, on aws it's String("").
payload.requestContext.http.protocol on watch is http, on aws it's HTTP/1.1.
there's an extra payload.httpMethod member on watch, which is identical to payload.requestContext.http.method, doesn't exist on aws.
payload.requestContext.http.userAgent on watch is cargo-lambda, on aws it mirrors payload.headers.user-agent
there's an extra payload.headers.lambda-runtime-aws-request-id header on watch, which mirrors payload.requestContext.requestId, doesn't exist on aws.

code is adapted from the streaming example
local testing is cargo lambda watch then curl http://127.0.0.1:9000
aws testing is deploying it as a function url, then curl

use lambda_runtime::{
	Error, LambdaEvent, service_fn,
	streaming::{Body, Response},
	tracing,
};
use serde_json::Value;

async fn func(event: LambdaEvent<Value>) -> Result<Response<Body>, Error> {
	let diag = format!("{:#?}", event.payload);

	let mut resp = Response::from(Body::from(diag));
	resp.metadata_prelude.headers.append("content-type", "text/plain".parse().unwrap());

	Ok(resp)
}

#[tokio::main]
async fn main() -> Result<(), Error> {
	// required to enable CloudWatch error logging by the runtime
	tracing::init_default_subscriber();

	lambda_runtime::run(service_fn(func)).await?;
	Ok(())
}

@Jimmy-Z

These all seem like great improvements to me, @Jimmy-Z ! Were you planning on cutting a PR for them?

This is probably because you're using Lambda Function URLs in production, while Cargo Lambda always sends ALB payloads. The easiest way to ignore these discrepancies is by using lambda-http instead of raw events. That will guarantee that the data is in the same places regardless of whether it's production or development.

Use this example as a starting point: https://github.com/awslabs/aws-lambda-rust-runtime/blob/main/examples/http-basic-lambda/src/main.rs

@jlizen

@jlizen Thanks for the hospitality, but I'm afraid I'm too new to this to make a PR.

@calavera I agree these are minor problems, and can be easily work around, but I think it's still worth noting, it might make newbie(me) wonder why their(my) program behaves differently, maybe something like "there are known minor differences in header handling when ..." somewhere in doc would be helpful enough.

I'm not sure if this is off-topic, as for why I'm using lambda-runtime instead of lambda-http, 1st I couldn't find a streaming example using lambda-http, 2nd is this: aws/aws-lambda-rust-runtime#632 (reply in thread)

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Several minor discrepancies between "cargo lambda watch" and actually running on aws #863

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Several minor discrepancies between "cargo lambda watch" and actually running on aws #863

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jlizen commented on Jun 30, 2025

calavera commented on Jun 30, 2025

Jimmy-Z commented on Jun 30, 2025

Jimmy-Z commented on Jun 30, 2025

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