c# 网络

http://www.cnblogs.com/fuchongjundream/p/4079128.html

http://stackoverflow.com/questions/21728773/the-underlying-connection-was-closed-an-unexpected-error-occurred-on-a-receiv

http://www.cnblogs.com/wzd24/archive/2007/05/22/755050.html

http://www.cnblogs.com/a311300/archive/2008/07/15/1243612.html

https://msdn.microsoft.com/zh-cn/library/system.net.httpwebrequest.keepalive(VS.80).aspx

http://www.cnblogs.com/x4646/archive/2013/04/11/3014634.html