Python 修改 TCP 窗口大小不生效

[holinhot]

from socket import socket, SOL_SOCKET, TCP_WINDOW_CLAMP, AF_INET, SOCK_STREAM, SOL_TCP
s = socket(AF_INET, SOCK_STREAM)
s.setsockopt(SOL_SOCKET, TCP_WINDOW_CLAMP, 500)

经过抓包测试还是用的系统自动计算出的窗口大小。

还是说现在系统内核不让自己改了吗

[lcdtyph]

这个 opt 的 level 是 IPPROTO_TCP，不是 SOL_SOCKET
setsockopt 是有返回值的，最好检查一下

[holinhot]

@lcdtyph
print(s.setsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP, 0))
None

返回是空

[holinhot]

@lcdtyph
返回是 0
Type "help", "copyright", "credits" or "license" for more information.
>>> from socket import socket, IPPROTO_TCP, TCP_WINDOW_CLAMP, AF_INET, SOCK_STREAM, SOL_TCP
>>>
>>> s = socket(AF_INET, SOCK_STREAM)
>>>
>>> s.setsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP, 0)
>>>
>>> s.getsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP)
0

23:15:01.484753 IP 127.0.0.1.http > 127.0.0.1.62668: Flags [S.], seq 2645892072, ack 98484869, win 29200, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0
23:15:01.521700 IP 127.0.0.1.http > 127.0.0.1.62668: Flags [.], ack 76, win 229, length 0

抓包还是不起作用

[holinhot]

@lcdtyph
不知道什么情况了
>>> s.setsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP, 1000)
>>> s.getsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP)
1152
>>>
>>> s.setsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP, 500)
>>> s.getsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP)
1152
>>> s.setsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP, 100)
>>> s.getsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP)
1152
>>> s.setsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP, 0)
>>> s.getsockopt(IPPROTO_TCP, TCP_WINDOW_CLAMP)
0

[lcdtyph]

@holinhot
kernel 会强行限制这个选项的最小值的，(SOCK_MIN_RCVBUF/2)
所以你不能设置的比这个值小

[lcdtyph]

https://elixir.bootlin.com/linux/v4.1/source/net/ipv4/tcp.c#L2502
而且 0 被特殊照顾了

[holinhot]

@lcdtyph 看了一下好像是关闭 tcp 连接时强制把 window_clamp 改为 0

[holinhot]

@holinhot if (!val) {
if (sk->sk_state != TCP_CLOSE) {
err = -EINVAL;
break;
}
tp->window_clamp = 0;
} else
tp->window_clamp = val < SOCK_MIN_RCVBUF / 2 ?
SOCK_MIN_RCVBUF / 2 : val;
break;
2.3
if (val==0) {
if (sk->state != TCP_CLOSE) {
err = -EINVAL;
break;
}
tp->window_clamp = 0;
} else {
tp->window_clamp = val<SOCK_MIN_RCVBUF/2 ?
SOCK_MIN_SNDBUF : val;
}
break;