WebApi 下载文件流?

后端：

        /// <summary>
        /// 下载文件
        /// </summary>
        /// <param name="docGuid">影像资料guid</param>
        /// <returns></returns>
        [AcceptVerbs("GET", "POST")]
        [HttpPost, Route("Download2")]
        public HttpResponseMessage Download2(string docGuid, string docName)
        {
            MediaTypeHeaderValue _mediaType = MediaTypeHeaderValue.Parse("application/octet-stream");//指定文件类型
            ContentDispositionHeaderValue _disposition = ContentDispositionHeaderValue.Parse("attachment;filename=" + System.Web.HttpUtility.UrlEncode(docName));//指定文件名称（编码中文）
            try
            {
                string tmpName = Util.BaseDirectory.TrimEnd('\\') + "\\tmp\\" + docGuid + Util.GetFileExt(docName);
                if (!File.Exists(tmpName))
                    throw new HttpResponseException(HttpStatusCode.NotFound);

                FileStream fileStream = new FileStream(tmpName, FileMode.Open);
                HttpResponseMessage fullResponse = Request.CreateResponse(HttpStatusCode.OK);
                fullResponse.Content = new StreamContent(fileStream);

                fullResponse.Content.Headers.ContentType = _mediaType;
                fullResponse.Content.Headers.ContentDisposition = _disposition;
                return fullResponse;
            }
            catch (Exception ex)
            {
                Logger.Error(ex);
                throw new HttpResponseException(HttpStatusCode.NotFound);
            }
        }

前端：

                   var url = UrlList.BaseUrl + UrlList.AfterLoanUrl + "CustLoanDoc/Download2?docGuid=" + cur.movedoc.DocGuid + "&docName=" + cur.movedoc.DocName;//指向webApi方法路径
                    var link = document.createElement('a');
                    link.href = url;
                    link.click();
                    window.URL.revokeObjectURL(link.href);