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(); ???????????????} ???????????}.NET程序下载获得的ContentLength=-1
原文地址：https://www.cnblogs.com/peterYong/p/9756477.html