HttpWebRequest（跨域下载文件——网络流转换为内存流下载）

1.Stream 转换为 MemoryStream(Stream不支持查找)

MemoryStream StreamToMemoryStream(Stream instream)
        {
            MemoryStream outstream = new MemoryStream();
            const int bufferLen = 4096;
            byte[] buffer = new byte[bufferLen];
            int count = 0;
            while ((count = instream.Read(buffer, 0, bufferLen)) > 0)
            {
                outstream.Write(buffer, 0, count);
            }
            return outstream;
        }

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2.网络流转化为内存流并下载

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(filePath);
                        request.Method = "GET";
                        using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)
                        {
                            if (response.StatusCode == HttpStatusCode.OK)
                            {
                                Stream rs = response.GetResponseStream();
//网络流转换为内存流
                                var ms = StreamToMemoryStream(rs);
                                ms.Seek(0, SeekOrigin.Begin); int buffsize = (int)ms.Length; //rs.Length 此流不支持查找,先转为MemoryStream
                                byte[] bytes = new byte[buffsize];

                                ms.Read(bytes, 0, buffsize);
                                ms.Flush(); ms.Close();
                                rs.Flush(); rs.Close();
//以文件流的方式下载
                                Response.Charset = "utf-8";
                                Response.ContentEncoding = System.Text.Encoding.GetEncoding("utf-8");
                                Response.ContentType = "application/octet-stream";
                                if (HttpContext.Current.Request.UserAgent.ToUpper().Contains("MSIE") ||
                                    HttpContext.Current.Request.UserAgent.ToUpper().Contains("TRIDENT") ||
                                    HttpContext.Current.Request.UserAgent.ToUpper().Contains("EDGE"))
                                {
                                    name = HttpUtility.UrlEncode(name, System.Text.Encoding.UTF8);
                                }
                                else
                                {
                                    name = name.Replace(" ", "_");
                                }
                                //fileName = HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8);
                                Response.AddHeader("Content-Disposition", "attachment;   filename=" + name);
                                Response.BinaryWrite(bytes);
                                Response.Flush();
                                Response.End();
                            }
                        }

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3.网络路径

private string GetContractPathRules(string id, string name) {
            string url = ConfigurationManager.AppSettings["ContractUrl"];
            url = url.TrimEnd('/') + "/";
            return Path.Combine(url, Path.Combine(id + "/", name));
        }
//例如：http://x.x.x.x:8088/xxx/xxx.pdf

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