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Authored by CDanis on Aug 1 2025, 7:45 PM.

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	F65701305: raw-paste-data.txt
	Aug 1 2025, 7:45 PM

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	#!/usr/bin/bpftrace
	#
	# Hook TCP listener connection completion and print the client's reported initial window size.
	#
	# You can see that rcv_wnd for the server socket is greatly decreased
	# if a Linux client sets a small SO_RCVBUF:
	# ```py
	# sock.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, int(sys.argv[1]) if len(sys.argv) > 1 else 512)
	# ```


	#include <linux/tcp.h>

	BEGIN
	{
	printf("%-16s %-24s %-8s %-8s\n", "", "Elapsed(us)", "snd_cwnd", "rcv_wnd", "snd_wnd");
	}

	kprobe:tcp_finish_connect
	{
	$tcps = (struct tcp_sock*)arg0;
	printf("rcv\t\t0x%llx\t%lld\t%d\t\t%d\t\t%d\n", arg0, elapsed/1000, $tcps->snd_cwnd, $tcps->rcv_wnd, $tcps->snd_wnd);
	}

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