System.Net.Http.WinHttpHandler.WinHttpHandler.AddRequestHeaders C# (CSharp) Method

        private static void AddRequestHeaders(
            SafeWinHttpHandle requestHandle,
            HttpRequestMessage requestMessage,
            CookieContainer cookies)
        {
            // Get a StringBuilder to use for creating the request headers.
            // We cache one in TLS to avoid creating a new one for each request.
            StringBuilder requestHeadersBuffer = t_requestHeadersBuilder;
            if (requestHeadersBuffer != null)
            {
                requestHeadersBuffer.Clear();
            }
            else
            {
                t_requestHeadersBuilder = requestHeadersBuffer = new StringBuilder();
            }

            // Manually add cookies.
            if (cookies != null && cookies.Count > 0)
            {
                string cookieHeader = WinHttpCookieContainerAdapter.GetCookieHeader(requestMessage.RequestUri, cookies);
                if (!string.IsNullOrEmpty(cookieHeader))
                {
                    requestHeadersBuffer.AppendLine(cookieHeader);
                }
            }

            // Serialize general request headers.
            requestHeadersBuffer.AppendLine(requestMessage.Headers.ToString());

            // Serialize entity-body (content) headers.
            if (requestMessage.Content != null)
            {
                // TODO (#5523): Content-Length header isn't getting correctly placed using ToString()
                // This is a bug in HttpContentHeaders that needs to be fixed.
                if (requestMessage.Content.Headers.ContentLength.HasValue)
                {
                    long contentLength = requestMessage.Content.Headers.ContentLength.Value;
                    requestMessage.Content.Headers.ContentLength = null;
                    requestMessage.Content.Headers.ContentLength = contentLength;
                }

                requestHeadersBuffer.AppendLine(requestMessage.Content.Headers.ToString());
            }

            // Add request headers to WinHTTP request handle.
            if (!Interop.WinHttp.WinHttpAddRequestHeaders(
                requestHandle,
                requestHeadersBuffer,
                (uint)requestHeadersBuffer.Length,
                Interop.WinHttp.WINHTTP_ADDREQ_FLAG_ADD))
            {
                WinHttpException.ThrowExceptionUsingLastError();
            }
        }