.NET程序下载获得的ContentLength=-1

你写的.NET（C#）下载程序是否会遇到过这样的问题？－－ContentLength=-1．

例如，有如下代码：

HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);

HttpWebResponse webResponse = null;

webRequest.Timeout = 100000;
webResponse = (HttpWebResponse)webRequest.GetResponse();
Stream resStream = webResponse.GetResponseStream();

StreamReader xtReader = new StreamReader(resStream);
int DataSize = webResponse.ContentLength;//ContentLength 等于-1

会发现ContentLength=-1，这是为什么呢？！

用http分析工具会发现，原因原来是很简单的，这是因为某些网站服务器在发送响应内容时，会用gzip或 deflate等压缩算法压缩网页的内容，这样能使网页内容的数据包体积大大减小，从而加快了网络传输，这样客户端的浏览器显示网页也加快了。就是因为这 个gzip或 deflate功能，使得网页数据在进行http传输时不会在header里加上ContentLength属性，所以程序取回 来的ContentLength 的数值就默认为-1了（而 没有gzip或 deflate功能的网页肯定会ContentLength具体数值）

改进：

byte[] arraryByte = new byte[1024];
            try
            {
                HttpWebRequest req = (HttpWebRequest)WebRequest.Create(filePath);
                req.Method = "Get";
                ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Ssl3;
                ServicePointManager.ServerCertificateValidationCallback += (object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors) => true;
                using (HttpWebResponse wr = (HttpWebResponse)req.GetResponse())
                {
                    Stream stream = wr.GetResponseStream();
                    //读取到内存
                    MemoryStream stmMemory = new MemoryStream();
                    byte[] buffer1 = new byte[1024 * 100];  //每次从文件读取1024个字节。
                    int i;
                    //将字节逐个放入到Byte 中
                    while ((i = stream.Read(buffer1, 0, buffer1.Length)) > 0)
                    {
                        stmMemory.Write(buffer1, 0, i);
                    }
                    arraryByte = stmMemory.ToArray();
                    stmMemory.Close();
                    stream.Close();
                }
            }