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Let's keep these notes as references for later use. Polling on connect() can sometimes return a few unexpected state combinations that such tests illustrate. They can serve as reminders for special error handling.
94 lines
3.5 KiB
Plaintext
94 lines
3.5 KiB
Plaintext
2022-11-17 - Tests involving poll() return states upon a pending connect().
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- connect() to a closed port returns OUT and HUP:
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$ dev/poll/poll -v -l clo -c pol
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#### BEGIN ####
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cmd #1 stp #1: clo(l=3): ret=0
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cmd #2 stp #0: con(c=4): ret=-1 (Connection refused)
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cmd #2 stp #1: pol(c=4): ret=1 ev=0x14 (OUT HUP)
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#### END ####
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=> with HUP we *know* the connection failed, since we never asked for a
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SHUTW before connecting. It is indeed an error as can be seen with
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connect() returning -1 ECONNREFUSED.
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- connect() to a port that does close(accept()) does return IN and RDHUP:
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$ dev/poll/poll -v -s clo -c pol
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#### BEGIN ####
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cmd #1 stp #0: con(c=4): ret=0
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cmd #1 stp #0: acc(l=3): ret=5
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cmd #1 stp #1: clo(s=5): ret=0
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cmd #2 stp #1: pol(c=4): ret=1 ev=0x2005 (IN OUT RDHUP)
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#### END ####
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=> here there's no HUP, only RDHUP because the FIN is pending in the
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socket buffers, waiting to be read.
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- for a HUP to happen after a connect() to a valid port, one would have to
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perform a shutw() on the client, which is normally not the case, indicating
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that HUP is reliable here:
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$ dev/poll/poll -v -s clo -c shw,pol
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#### BEGIN ####
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cmd #1 stp #0: con(c=4): ret=0
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cmd #1 stp #0: acc(l=3): ret=5
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cmd #1 stp #1: clo(s=5): ret=0
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cmd #2 stp #1: shw(c=4): ret=0
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cmd #2 stp #2: pol(c=4): ret=1 ev=0x2015 (IN OUT HUP RDHUP)
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#### END ####
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- one case that may happen is when sending a request and immediately shutw()
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(which leaves a TIME_WAIT so not recommended):
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$ dev/poll/poll -v -c snd,shw -s clo -c pol,rcv,pol
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#### BEGIN ####
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cmd #1 stp #0: con(c=4): ret=0
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cmd #1 stp #1: snd(c=4): ret=3
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cmd #1 stp #2: shw(c=4): ret=0
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cmd #2 stp #0: acc(l=3): ret=5
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cmd #2 stp #1: clo(s=5): ret=0
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cmd #3 stp #1: pol(c=4): ret=1 ev=0x201d (IN OUT ERR HUP RDHUP)
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cmd #3 stp #2: rcv(c=4): ret=-1 (Connection reset by peer)
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cmd #3 stp #3: pol(c=4): ret=1 ev=0x2015 (IN OUT HUP RDHUP)
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#### END ####
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=> here it's impossible to know from the client whether the server consumed the
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data or not, which is normal since a close on the server causes an RST to be
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emitted for the data in flight, hence the ERR here. It's also worth noting
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that once POLL_ERR is consumed by recv() it disappears.
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- for the server, sending a shutw() before closing here delivers an ACK in time
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that prevents the RST from being sent, thus connect() is not notified (but if
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the server has too much to send, it will truncate and emit an RST):
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$ dev/poll/poll -v -c snd,shw -s shw,clo -c pol,rcv,pol
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#### BEGIN ####
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cmd #1 stp #0: con(c=4): ret=0
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cmd #1 stp #1: snd(c=4): ret=3
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cmd #1 stp #2: shw(c=4): ret=0
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cmd #2 stp #0: acc(l=3): ret=5
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cmd #2 stp #1: shw(s=5): ret=0
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cmd #2 stp #2: clo(s=5): ret=0
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cmd #3 stp #1: pol(c=4): ret=1 ev=0x2015 (IN OUT HUP RDHUP)
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cmd #3 stp #2: rcv(c=4): ret=0
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cmd #3 stp #3: pol(c=4): ret=1 ev=0x2015 (IN OUT HUP RDHUP)
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#### END ####
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- if the server sends a response, disables lingering and closes with RST, it is
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possible to get HUP and ERR at the same time during the connect() phase, and
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recv() can still receive the pending response:
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$ dev/poll/poll -v -s snd,lin,clo -c pol,rcv,pol
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#### BEGIN ####
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cmd #1 stp #0: con(c=4): ret=0
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cmd #1 stp #0: acc(l=3): ret=5
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cmd #1 stp #1: snd(s=5): ret=3
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cmd #1 stp #2: lin(s=5): ret=0
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cmd #1 stp #3: clo(s=5): ret=0
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cmd #2 stp #1: pol(c=4): ret=1 ev=0x201d (IN OUT ERR HUP RDHUP)
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cmd #2 stp #2: rcv(c=4): ret=3
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cmd #2 stp #3: pol(c=4): ret=1 ev=0x201d (IN OUT ERR HUP RDHUP)
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#### END ####
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