Improve error/validation reporting by allowing for a strongly typed property, e.g. Result.Error<T>

[nhwilly]

When calling downstream API's there are times when the consuming program needs the details of an error so that domain specific actions can be taken.

Example:

MyBlazorApp calls MyBlazorAppApi to add a user to a downstream service using a DownstreamApi wrapper, which makes the actual REST calls to the downstream service.

MyBlazorAppApi endpoint:

public async Task<IActionResult<MyBlazorUser>> AddMyBlazorUser(string email)
{
  Result<DownstreamUser> downstreamUserResult = await AddDownstreamUser(email);
  if(downstreamUserResult.IsSuccess)
    {
      return downStreamUserResult.Value.Map<MyBlazorUser>();
    }
}

DownstreamAPI wrapper function:

public async Task<Result<DownstreamUser>> AddDownstreamUser(string email)
  {
    // make httpClient calls here...
    // return success with downstreamUser
    // or deserialize errors to errorData and return Result.Error<ErrorData>(errorData);
  }

For example, DownstreamApi reports that the user already exists and returns a 400 bad request with a specific error code in the errorData that's returned. Other 400 errors are show stoppers, but this one is not. If I know the actual error code that the downstream api is sending me, I can discriminate and take the proper action.

Using Result.Error<T> (or possibly Result.Invalid<T>) allows me to return the errorData up to the AddMyBlazorUser endpoint where a second call can be made to find the existing user via their email address and return the MyBlazorUser instance to the MyBlazorApp original caller.

As it stands, I am using some special delimiters to embed their error message in the standard collection of strings and then looking for it in the caller. Working but it could be improved.