[BUG][C#][Client: C-Sharp] Calling xHttpWithInfo methods do not return headers when 4xx responses are returned

Description

Calling a xHttpWithInfo method that returns a response in the 200 range returns an ApiResponse containing the domain model and the returned headers

However, if a response in the 400 range is received no headers are returned, only an ApiException.

This becomes an issue when a 429 response is received and Retry-After header is returned as there is no way to obtain this (see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After)

openapi-generator version

4.0.3

OpenAPI declaration file content or url

https://fbn-prd.lusid.com/api/swagger/v0/swagger.json

Command line used for generation

java -jar openapi-generator-cli.jar generate -g csharp -c config_file

{
  "packageName": "Lusid.Sdk",
  "sourceFolder": ".",
  "targetFramework": "v5.0",
  "useDateTimeOffset": true,
  "netCoreProjectFile": true,
  "returnICollection": true,
  "packageVersion": "0.10.841"
}

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/3473

Suggest a fix

1. Return an ApiResponse with the ApiException in the Data field

or

2. Return the headers in the ApiException

Start by tracing the generated C# xHttpWithInfo methods and ApiException handling, then inspect the C# generator templates used by the command in the issue. Verify how 4xx response headers, especially Retry-After, are exposed and confirm the chosen ApiResponse or ApiException behavior against the reported case.