socket 之RST

 SO_LINGER是用来设置函数close()关闭TCP连接时的行为。缺省close()的行为是，如果有数据残留在socket发送缓冲区中则系统将继续发送这些数据给对方，等待被确认，然后返回。

设置此选项并把超时时间设置为零，调用close()会立即关闭该连接，通过发送RST分组(而不是用正常的FIN|ACK|FIN|ACK四个分组)来关闭该连接。至于发送缓冲区中如果有未发送完的数据，则丢弃。
import socket
import struct
import time
s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, struct.pack('ii', 1, 0))
s.connect(("192.168.137.2",8080))
time.sleep(30)
s.close()


22:04:37.803432 IP 192.168.137.1.57348 > node1.webcache: Flags [S], seq 3840842057, win 8192, options [mss 1460,nop,wscale 2,nop,nop,sackOK], length 0
22:04:37.803479 IP node1.webcache > 192.168.137.1.57348: Flags [S.], seq 770814913, ack 3840842058, win 1536, options [mss 256,nop,nop,sackOK,nop,wscale 6], length 0
22:04:37.803622 IP 192.168.137.1.57348 > node1.webcache: Flags [.], ack 770814914, win 16482, length 0



22:05:07.763150 IP 192.168.137.1.57348 > node1.webcache: Flags [R.], seq 3840842058, ack 770814914, win 0, length 0