关闭TCP连接的面试问题三境界
- 描述下TCP连接关闭的过程？
- 描述下TCP连接关闭的步骤，以及每一步的状态？
- shutdwon与close的区别？
| step | packet | client state | server state | remark |
|---|---|---|---|---|
| 0 | ESTABLISHED | ESTABLISHED | ||
| 1 | client 向 server 发送FIN包(seq=x) server收到之前 | FIN_WAIT_1 | ESTABLISHED | client调用close |
| 2 | server收到FIN包，server向client发送ACK包(ack=x+1)，client收到之后 | FIN_WAIT_2 | CLOSE_WAIT | |
| 3 | server向client发送 FIN包(seq=y)，client收到之前 | FIN_WAIT_2 | LAST_ACK | server 调用close |
| 4 | client向server发送 ACK包(ack=y+1)，server收到确认之后 | TIME_WAIT | CLOSED |
shutdwon & close
man 2 shutdown
NAME shutdown - shut down part of a full-duplex connection SYNOPSIS #include <sys/socket.h> int shutdown(int sockfd, int how); DESCRIPTION The shutdown() call causes all or part of a full-duplex connection on the socket associated with sockfd to be shut down. If how is SHUT_RD, further receptions will be disallowed. If how is SHUT_WR, further transmissions will be disallowed. If how is SHUT_RDWR, further receptions and transmissions will be disallowed. shutdown 可以通过how参数选择关闭sockfd读端、写端或者读写端。
close 会关闭sockfd的读写两端，不能选择性关闭。
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