Socket的正确关闭(改良版)

TIME_WAIT状态

如果服务端的Socket比客户端的Socket先关闭，会导致客户端出现TIME_WAIT状态，占用系统资源。

所以，必须等客户端先关闭Socket后，服务器端再关闭Socket才能避免TIME_WAIT状态的出现。

判断客户端Socket的关闭

最近试验发现，当客户端Socket关闭时，服务端的Socket会接收到0字节的通知。

private int Receive(StringBuilder sb)

{

int read = 0, total = 0;

if (_Client != null)

{

try

{

byte[] bytes = new byte[SIZE];

int available = _Client.Available;

do

{

read = _Client.Receive(bytes);//如果客户端Socket关闭，_Client会接受到read=0

total += read;

if (read > 0)

sb.Append(_Server.DefaultEncoding.GetString(bytes, 0, read));

} while (read > 0 && total < available);

}

catch (SocketException)

{

CloseSocket();

}

}

if (_Server.TraceInConsole && total > 0)

{

Console.WriteLine("Receive:" + total + "======================================");

Console.WriteLine(sb.ToString());

}

return total;

}

利用0字节接收条件判断客户端Socket的关闭，开始执行服务端Socket关闭代码。

private void ThreadHandler()

{

if (_Server.TraceInConsole)

Console.WriteLine("Begin HttpRequest...");

try

{

while (true)

{

StringBuilder sb = new StringBuilder();

int receive = Receive(sb);

if (receive > 0)

{

_Server.ReadRequest(this, sb.ToString());

_Server.Response(this);

_Server.ResponseFinished(this);

}

else

{

TryCloseSocket();

}

if (_Client == null)

break;

}

}

catch (Exception ex)

{

if (_Server.TraceInConsole)

Console.WriteLine(ex.Message);

}

if (_Server.TraceInConsole)

Console.WriteLine("End HttpRequest.");

}

服务端Socket的关闭

如果直接调用Socket的Close方法会关闭得太快，可能导致客户端TIME_WAIT现象；而Thead.Sleep延时再调用Socket的Close方法也不理想。应该采用尝试向客户端发送数据，然后利用异常来关闭Socket，方法如下。

private void TryCloseSocket()

{

try

{

while (true)

{

Thread.Sleep(1500);

Send(HttpServer.BYTES_CRLF); //发送自定义的字节，如果客户端关闭出现SocketException，然后关闭服务端Socket

if (_Client == null)

break;

}

}

catch (SocketException)

{

CloseSocket();

}

}

private void CloseSocket()

{

if (_Client != null)

{

_Client.Shutdown(SocketShutdown.Both);

_Client.Close();

_Client = null;

if (_Server.TraceInConsole)

{

Console.WriteLine("Close socket.");

}

}

}