Doubled response when using Amazon.Lambda.AspNetCoreServer.Hosting with .Net 6 Minimal API with custom endpoints extension

[heyjoey]

Description

When following the description to create a Minimal API with Amazon.Lambda.AspNetCoreServer.Hosting and added FastEndpoints, the response Dto is sent twice.

Reproduction Steps

Program.cs attached, created using serverless.AspNetCoreWebAPI project template and add a nuget package called FastEndpoints. Build and Publish to Lambda in Visual Studios 2022. Post payload as:

curl --location --request POST 'https://xxxxx.execute-api.ap-northeast-1.amazonaws.com/Prod/api/author' \
--header 'Content-Type: application/json' \
--data-raw '{
    "firstName": "John",
    "lastName": "Doe",
    "age": 16
}'

Response returned:

{
    "fullName": "John Doe",
    "isOver18": false
}{
    "fullName": "John Doe",
    "isOver18": false
}

Logs

screenshot attached.

Environment

• Build Version:
  • Amazon.Lambda.AspNetCoreServer.Hosting 1.0.0
  • FastEndpoints 3.9.1
• OS Info: Local Dev: Windows 10 | Lambda runtime: dotnet6 on AmazonLinux 2
• Build Environment: Visual Studio Community 2022
• Targeted .NET Platform: net6.0 (6.0.200)

Resolution

• 👋 I can/would-like-to implement a fix for this problem myself

It seems that Amazon.Lambda.AspNetCoreServer did not set the HasStarted property of the IHttpResponseFeature which the HttpContext reads from.

---

This is a 🐛 bug-report
Program.cs.txt

[dj-nitehawk]

the double response writing behavior is caused by the fact that FastEndpoints relies on the HttpContext.Response.HasStarted property. which works as expected when kestrel server is used and does not work when Amazon.Lambda.AspNetCoreServer is used. here's a minimal repro:

using Amazon.Lambda.Core;
using Amazon.Lambda.Serialization.SystemTextJson;

[assembly: LambdaSerializer(typeof(DefaultLambdaJsonSerializer))]
var builder = WebApplication.CreateBuilder();
builder.Services.AddAWSLambdaHosting(LambdaEventSource.RestApi);

var app = builder.Build();

app.MapGet("/test", async (HttpContext ctx) =>
{
    ctx.Response.StatusCode = 200;
    await ctx.Response.StartAsync();

    if (!ctx.Response.HasStarted)
        throw new InvalidOperationException("response has started but HasStarted says it's not, in aws lambda!");

    Console.WriteLine("this will only be printed with kestrel. won't print with aws lambda!");
});

app.Run();

i believe this is where the underlying value for this property is set by kestrel. so aws server should also do the same to keep in sync with the kestrel behavior i think.

[ashishdhingra]

@heyjoey Is it fine to mark this issue as feature-request instead of a bug since 3rd party dependency relies on some feature that is set by Kestrel server and it is desired to be set by Lambda runtime? Please advise.

[normj]

Thanks for reporting the issue @heyjoey and @dj-nitehawk. I agree this is a bug with how we are handling the response HasStarted bug. Looks like you have done a work around for 3.10.0 but we should still get this fixed in our library.