Python TCP socket 编程：recv 或 send 返回 ECONNRESET？

版权声明：本文为博主原创文章，转载请注明原文出处。 https://blog.csdn.net/woay2008/article/details/83189117

1. recv 返回 ECONNRESET

客户端代码：

import socket
import time 

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('127.0.0.1', 2222))

s.send('hello')
data = s.recv(1024)

s.close()

服务器代码：

import socket
import time

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind(('127.0.0.1', 2222))
s.listen(5)

c, addr = s.accept()
# 不读取数据，睡眠1秒后直接关闭连接
time.sleep(1)

c.close()

执行结果：

[root@localhost python]# python client.py 
Traceback (most recent call last):
  File "client.py", line 10, in <module>
    data = s.recv(1024)
socket.error: [Errno 104] Connection reset by peer

抓包结果：

17:14:28.718661 IP 127.0.0.1.44120 > 127.0.0.1.2222: Flags [S], seq 2427544330, win 32792, options [mss 16396,sackOK,TS val 250810717 ecr 0,nop,wscale 5], length 0
17:14:28.718722 IP 127.0.0.1.2222 > 127.0.0.1.44120: Flags [S.], seq 2412921910, ack 2427544331, win 32768, options [mss 16396,sackOK,TS val 250810718 ecr 250810717,nop,wscale 5], length 0
17:14:28.718734 IP 127.0.0.1.44120 > 127.0.0.1.2222: Flags [.], ack 1, win 1025, options [nop,nop,TS val 250810718 ecr 250810718], length 0
17:14:28.718831 IP 127.0.0.1.44120 > 127.0.0.1.2222: Flags [P.], seq 1:6, ack 1, win 1025, options [nop,nop,TS val 250810718 ecr 250810718], length 5
17:14:28.718839 IP 127.0.0.1.2222 > 127.0.0.1.44120: Flags [.], ack 6, win 1024, options [nop,nop,TS val 250810718 ecr 250810718], length 0
17:14:29.729482 IP 127.0.0.1.2222 > 127.0.0.1.44120: Flags [R.], seq 1, ack 6, win 1024, options [nop,nop,TS val 250811729 ecr 250810718], length 0

2. send 返回 ECONNRESET

客户端代码修改如下：

import socket
import time 

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('127.0.0.1', 2222))

s.send('hello')
time.sleep(2)
s.send('hello')

s.close()

执行结果：

[root@localhost python]# python client.py 
Traceback (most recent call last):
  File "client.py", line 9, in <module>
    s.send('hello')
socket.error: [Errno 104] Connection reset by peer

抓包结果：

17:16:47.555578 IP 127.0.0.1.44121 > 127.0.0.1.2222: Flags [S], seq 289819954, win 32792, options [mss 16396,sackOK,TS val 250949554 ecr 0,nop,wscale 5], length 0
17:16:47.555602 IP 127.0.0.1.2222 > 127.0.0.1.44121: Flags [S.], seq 289869249, ack 289819955, win 32768, options [mss 16396,sackOK,TS val 250949555 ecr 250949554,nop,wscale 5], length 0
17:16:47.555617 IP 127.0.0.1.44121 > 127.0.0.1.2222: Flags [.], ack 1, win 1025, options [nop,nop,TS val 250949555 ecr 250949555], length 0
17:16:47.555652 IP 127.0.0.1.44121 > 127.0.0.1.2222: Flags [P.], seq 1:6, ack 1, win 1025, options [nop,nop,TS val 250949555 ecr 250949555], length 5
17:16:47.555656 IP 127.0.0.1.2222 > 127.0.0.1.44121: Flags [.], ack 6, win 1024, options [nop,nop,TS val 250949555 ecr 250949555], length 0
17:16:48.561152 IP 127.0.0.1.2222 > 127.0.0.1.44121: Flags [R.], seq 1, ack 6, win 1024, options [nop,nop,TS val 250950560 ecr 250949555], length 0

3. 结论

在socket上执行recv或send时，如果该 socket 上接收到 RST 报文，则函数会返回ECONNRESET。
为什么这种情况下客户端socket上会收到RST报文？
因为 当服务端执行close函数时，socket 的接收缓冲区还有数据，这时候 TCP 会发送 RST 报文复位连接，而不会正常断开连接！。