System.Net.Http.WinHttpRequestCallback.RequestCallback C# (CSharp) Method

        private static void RequestCallback(
            IntPtr handle,
            WinHttpRequestState state,
            uint internetStatus,
            IntPtr statusInformation,
            uint statusInformationLength)
        {
            try
            {
                switch (internetStatus)
                {
                    case Interop.WinHttp.WINHTTP_CALLBACK_STATUS_HANDLE_CLOSING:
                        OnRequestHandleClosing(state);
                        return;

                    case Interop.WinHttp.WINHTTP_CALLBACK_STATUS_SENDREQUEST_COMPLETE:
                        OnRequestSendRequestComplete(state);
                        return;

                    case Interop.WinHttp.WINHTTP_CALLBACK_STATUS_DATA_AVAILABLE:
                        Debug.Assert(statusInformationLength == Marshal.SizeOf<int>());
                        int bytesAvailable = Marshal.ReadInt32(statusInformation);
                        OnRequestDataAvailable(state, bytesAvailable);
                        return;

                    case Interop.WinHttp.WINHTTP_CALLBACK_STATUS_READ_COMPLETE:
                        OnRequestReadComplete(state, statusInformationLength);
                        return;

                    case Interop.WinHttp.WINHTTP_CALLBACK_STATUS_WRITE_COMPLETE:
                        OnRequestWriteComplete(state);
                        return;

                    case Interop.WinHttp.WINHTTP_CALLBACK_STATUS_HEADERS_AVAILABLE:
                        OnRequestReceiveResponseHeadersComplete(state);
                        return;

                    case Interop.WinHttp.WINHTTP_CALLBACK_STATUS_REDIRECT:
                        string redirectUriString = Marshal.PtrToStringUni(statusInformation);
                        var redirectUri = new Uri(redirectUriString);
                        OnRequestRedirect(state, redirectUri);
                        return;

                    case Interop.WinHttp.WINHTTP_CALLBACK_STATUS_SENDING_REQUEST:
                        OnRequestSendingRequest(state);
                        return;

                    case Interop.WinHttp.WINHTTP_CALLBACK_STATUS_REQUEST_ERROR:
                        Debug.Assert(
                            statusInformationLength == Marshal.SizeOf<Interop.WinHttp.WINHTTP_ASYNC_RESULT>(),
                            "RequestCallback: statusInformationLength=" + statusInformationLength +
                            " must be sizeof(WINHTTP_ASYNC_RESULT)=" + Marshal.SizeOf<Interop.WinHttp.WINHTTP_ASYNC_RESULT>());

                        var asyncResult = Marshal.PtrToStructure<Interop.WinHttp.WINHTTP_ASYNC_RESULT>(statusInformation);
                        OnRequestError(state, asyncResult);
                        return;

                    default:
                        return;
                }
            }
            catch (Exception ex)
            {
                Interop.WinHttp.WinHttpCloseHandle(handle);
                state.SavedException = ex;
            }
        }