AspNetCoreServer: HTTP API v2 integration double escaped URL parameters

Description

AspNetCoreServer.APIGatewayHttpApiV2ProxyFunction URL-escapes the query string, but since it is receiving the raw, escaped query string from the API gateway this will result in a double escaping. MVC strips out one level of escaping, but that means that the web API controllers get escaped values rather than unescaped values.

This is done here in the code: https://github.com/aws/aws-lambda-dotnet/blob/master/Libraries/src/Amazon.Lambda.AspNetCoreServer/Internal/Utilities.cs#L121-L148

I have verified with a minimal Python lambda that just returns the 2.0 event as a JSON response that the query string in the event is already escaped.

Reproduction Steps

Test performed with a minimal controller based on serverless.AspNetCoreWebAPI but adapted to use HTTP API v2 instead.

Entry point:

public class LambdaEntryPoint : Amazon.Lambda.AspNetCoreServer.APIGatewayHttpApiV2ProxyFunction
{
    protected override void Init(IWebHostBuilder builder)
    {
        builder.UseStartup<Startup>();
    }
}

Controller:

[Route("api/[controller]")]
public class ValuesController : ControllerBase
{
    // GET api/values
    [HttpGet]
    public IActionResult Get([FromQuery] string a)
    {
        return Ok(new
        {
            A = a,
            RawQuery = Request.QueryString.ToString(),
        });
    }
}

Setting up a HTTP v2 integration and calling it with /api/values?a=b%3Dc produces the following output:

{ 
  "a": "b%3Dc", 
  "rawQuery" : "?a=b%253Dc"
}

The expected output is that a should have the unescaped value b=c.

Environment

Build Version:

<PackageReference Include="AWSSDK.Extensions.NETCore.Setup" Version="3.3.100.1" />
<PackageReference Include="Amazon.Lambda.AspNetCoreServer" Version="5.1.1" />

Targeted .NET Platform: Native .NET Core 3.1 runtime

Resolution

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

---

This is a 🐛 bug-report

[petli]

I’ve found a workaround for this by overriding the query string directly from the event after it has been converted by APIGatewayHttpApiV2ProxyFunction:

public class LambdaEntryPoint : Amazon.Lambda.AspNetCoreServer.APIGatewayHttpApiV2ProxyFunction
{
    // any other setup ...

    protected override void PostMarshallRequestFeature(IHttpRequestFeature aspNetCoreRequestFeature,
        APIGatewayHttpApiV2ProxyRequest lambdaRequest, ILambdaContext lambdaContext)
    {
        if (!string.IsNullOrWhiteSpace(lambdaRequest.RawQueryString))
        {
            aspNetCoreRequestFeature.QueryString = "?" + lambdaRequest.RawQueryString;
        }
    }
}

[normj]

PR has been released as part of version 6.0.0 of Amazon.Lambda.AspNetCoreServer.