How to return multipart content with html and xml - asp.net-core

Question

I have to re-write a web service in .NET Core 2.2, and the service must return a multipart response with XML and base-64 encoded HTML. The current service is a really old java program with no documentation.
The request comes from an old service that can't change and must receive HTML 4.01 as the response. An actual sample is shown below.
What kind of response object do I return?
How do I combine the XML and encoded HTML together into one response object?
I don't expect anyone to write my code for me but I would appreciate some help getting started.
Sample response
--75df5969-8400-11d5-c000-0021ffffff97
Content-type: text/xml; charset="UTF-8"
Content-id: XMLROOT
<?xml version="1.0" encoding="UTF-8"?><XMLROOT><Service><StatusCd>0</StatusCd></Service></XMLROOT>
--75df5969-8400-11d5-c000-0021ffffff97
Content-type: application/html
Content-id: Inquiry.html
Content-description: Response to View Inquiry
PCFET0NUWVBFIEhUTUwgUFVCTElDICItLy9XM0MvL0RURCBIVE1MIDQuMDEgVHJhbnNpdGlvbmFsLy9FTiI+Cgo8SFRNTD4KPEhFQUQ+CjxNRVRBIGh0dHAtZXF1aXY9IkNvbnRlbnQtVHlwZSIgY29udGVudD0idGV4dC9odG1sOyBjaGFyc2V0PUlTTy04ODU5LTEiPgo8TUVUQSBodHRwLWVxdWl2PSJDb250ZW50LVN0eWxlLVR5cGUiIGNvbnRlbnQ9InRleHQvY3NzIj4KCgk8U1RZTEUgVFlQRT0idGV4dC9jc3MiPgoJCVRSIHsgYmFja2dyb3VuZC1jb2xvcjogbGlnaHRncmV5IH0KCQkudGREYXRhIHsKCSAJCWZvbnQtc2l6ZTo4cHQ7CgkJCWNvbG9yOiMwMDAwOUM7CgkJCWZvbnQtZmFtaWx5OlZlcmRhbmEsIEFyaWFsLCBIZWx2ZXRpY2EsIHNhbnMtc2VyaWY7IH0KCQkudGRMYWJlbCB7CgkgCQlmb250LXNpemU6OHB0OwoJCQlmb250LXdlaWdodDpib2xkZXI7CgkJCWZvbnQtZmFtaWx5OlZlcmRhbmEsIEFyaWFsLCBIZWx2ZXRpY2EsIHNhbnMtc2VyaWY7IH0KCQkudGRIZWFkIHsKCQkJYmFja2dyb3VuZC1jb2xvcjojODA4MDgwOwoJCQl0ZXh0LWFsaWduOmNlbnRlcjsKCSAJCWZvbnQtc2l6ZTo4cHQ7CgkJCWZvbnQtd2VpZ2h0OmJvbGRlcjsKCQkJZm9udC1mYW1pbHk6VmVyZGFuYSwgQXJpYWwsIEhlbHZldGljYSwgc2Fucy1zZXJpZjsgfQoJPC9TVFlMRT4KCjxUSVRMRT5JbnF1aXJ5PC9USVRMRT4KPC9IRUFEPgo8Qk9EWT4KPHRhYmxlIEJPUkRFUj0iMCIgQ0VMTFBBRERJTkc9IjAiIENFTExTUEFDSU5HPSIwIiBXSURUSD0iNzAwIj4KCTx0cj4gCgkJPHRkIEJHQ09MT1I9IiNmZmZmZmYiPgoJCQk8VEFCTEUgQk9SREVSPSIxIiBDRUxMUEFERElORz0iMiIgQ0VMTFNQQUNJTkc9IjEiIFdJRFRIPSI3MDAiPgoJCQkJPFRSPjxURCBDT0xTUEFOPSI0IiBBTElHTj0iY2VudGVyIiBCR0NPTE9SPSIjZmZmZmZmIj4KCQkJCQlUZXN0IG1lc3NhZ2UgCgkJCQk8L1REPjwvVFI+CgkJCTwvVEFCTEU+CQoJCTx0ZD48L3RkPgoJPHRyPjwvdHI+CjwvdGFibGU+Cgo8L0JPRFk+CjwvSFRNTD4=
--75df5969-8400-11d5-c000-0021ffffff97--

Answer 1

What kind of response object do I return? How do I combine the XML and encoded HTML together into one response object?
There's no such a built-in result type. However, it would be easy to create a custom MultipartResult that will contains the XML + HTML (encoded). For example:
public class XmlAndEncodedHtmlMultipartResult : IActionResult
{
private StringContent _xmlContent;
private StringContent _htmlContent;
private MultipartContent _multipartContent=new MultipartContent(Subtype); // the final content
public static string Subtype = "my-xml+html" ; // `content-type: multipart/{Subtype}`
public XmlAndEncodedHtmlMultipartResult SetXmlContent(string xml, string contentId = "XMLROOT")
{
var xmlContent = new StringContent(xml, Encoding.UTF8, "text/xml");
xmlContent.Headers.Add("Content-id", contentId);
this._xmlContent = xmlContent;
return this;
}
public XmlAndEncodedHtmlMultipartResult SetEncodedHtmlContent(string rawHtml,string contentId="Inquiry.html", string description="Response to View Inquiry")
{
var bytes= Encoding.UTF8.GetBytes(rawHtml);
var encodedHtml = Convert.ToBase64String(bytes);
var htmlContent = new StringContent(encodedHtml, Encoding.UTF8, "application/html");
htmlContent.Headers.Add("Content-id", contentId);
htmlContent.Headers.Add("Content-description",description);
this._htmlContent = htmlContent;
return this;
}
public async Task ExecuteResultAsync(ActionContext context)
{
if(this._htmlContent ==null || this._xmlContent ==null){ throw new Exception("html content & xml must be null");}
this._multipartContent.Add(this._xmlContent);
this._multipartContent.Add(this._htmlContent);
var response = context.HttpContext.Response;
response.ContentType = this._multipartContent.Headers.ContentType.ToString();
// ... custom other headers as you like
await _multipartContent.CopyToAsync(response.Body);
}
}
In your action, just invoke it as below :
public IActionResult Privacy()
{
var xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><XMLROOT><Service><StatusCd>0</StatusCd></Service></XMLROOT>";
var html = "<html><head></head><body>hello,world</body></html>";
return new XmlAndEncodedHtmlMultipartResult().SetEncodedHtmlContent(html).SetXmlContent(xml);
}