Am 30.03.2015 um 09:51 schrieb John Denker via RT:
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Contrast the following two examples:
#1:
time : | openssl s_client -connect www.openssl.org:443 >& /dev/null
real 0m0.545s
user 0m0.000s
sys 0m0.000s
#2:
time : | openssl s_client -quiet -connect www.openssl.org:443 >& /dev/null
real 0m21.255s
user 0m9.500s
sys 0m11.180s
- -----------
Note the numerology: 21.225 - 9.5 - 11.18 = 0.545
That means that if you discount the half second it takes to actually
fetch the certificate, s_client was using 100% of the cpu the whole
time ... for more than 20 seconds.
I cannot imagine why it loops when "-quiet" is specified and not
otherwise. I cannot imagine why it loops for 20.5 seconds instead
of 20.5 minutes or 20.5 hours.
This is 100% reproducible chez moi, although the timings naturally
vary by a little bit.
(gdb) where
#0 0x00007ffff7903653 in __select_nocancel () at
../sysdeps/unix/syscall-template.S:81
#1 0x0000000000434d73 in s_client_main (argc=0, argv=0x7fffffffe680) at
s_client.c:1794
#2 0x00000000004039a8 in do_cmd (prog=0x990540, argc=4, argv=0x7fffffffe660)
at openssl.c:470
#3 0x00000000004035b8 in main (Argc=4, Argv=0x7fffffffe660) at openssl.c:366
That's maybe due to your chosen pipe shell construct. I can see the same
behavior, if I choose to let s_client read from /dev/null and set
"-quiet". It then loops trying to read from /dev/null, getting 0 bytes
but not EOF back. Without -quiet this does not happen. More precisely it
seems to happen with -ign_eof, which is set as a side effect of -quiet.
Reading from /dev/null without -ign_eof lets s_client end immediately
after the connect, with -ign_eof it hangs for 20 seconds (web server
timeout?) and eats 1 CPU during that time doing a lot of reads from
/dev/null.
The behavior is probably due to the following code snippet in s_client:
...
i = raw_read_stdin(cbuf, BUFSIZZ);
if ((!c_ign_eof) && ((i <= 0) || (cbuf[0] == 'Q'))) {
BIO_printf(bio_err, "DONE\n");
ret = 0;
goto shut;
}
Here I expect i==0, so without -ign_eof the code breaks the loop and
goes to "shut".
So this probably works as designed and when just running
openssl s_client -connect www.openssl.org:443
you shouldn't notice CPU hogging. Why -ign_eof is set as a side effect
of -quiet I do not know.
Regards,
Rainer
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