Continuous nc data acquisition fails ocassionally


 
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# 22  
Old 06-28-2018
Quote:
Originally Posted by lanas1234
I know what is happening hopefully you can help me now:

-Two times a day the receiver from where I'm getting the data stops sending for a couple of seconds due to an internal cron job.
What exactly does this cron job do -- kill the sender, then restart it? nc doesn't like that. Even in UDP mode, it's not connectionless - it knows who it's talking to, knows when it dies, and won't take a second connection.

Last edited by Corona688; 06-28-2018 at 03:39 PM..
# 23  
Old 06-28-2018
GOT IT! If you want to send to nc more than once, you always have to do so from the same source port and IP. Otherwise nc will think you're a different sender and ignore it. And the source port is randomly chosen, unless you give the sender one with -p...

I have 192.168.0.126:19999 as the receiver here, and 192.168.0.150:20000 as the sender.

Receiving:

Code:
$ nc -u -l -p 20000 192.168.0.150 19999
asdf
asdf
...

Sending:

Code:
$ echo asdf | nc -p 19999 -u -w 1 192.168.0.126 20000
$ echo asdf | nc -p 19999 -u -w 1 192.168.0.126 20000
$

Note that the sender is not quitting at end-of-line, it's quitting at end-of-file, so should still be able to handle a long, slow stream.

Last edited by Corona688; 06-28-2018 at 06:09 PM..
These 2 Users Gave Thanks to Corona688 For This Post:
# 24  
Old 07-10-2018
Thanks a lot to Corona and everybody!

Corona I think your solution should work but the problem is that the sender is under a DHCP so the IP would change during time if a disconnection occurs for example.

I finally reach to this solution using ncat, but I think is portable to nc:

Code:
while true do
ncat -lu -p 56045 --recv-only -i 60s | ...
end

With this if a disconnection occurs or data sender stops, ncat will start a new connection and everything will continue.

All the best!
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