Read fails after tcpreplay with error: 0: Resource temporarily unavailabl

Question

I have a very simple script to run. It calls tcpreplay and then ask the user to type in something. Then the read will fail with read: read error: 0: Resource temporarily unavailable.

Here is the code

#!/bin/bash

tcpreplay -ieth4 SMTP.pcap

echo TEST
read HANDLE
echo $HANDLE

And the output is

[root@vse1 quick_test]# ./test.sh 
sending out eth4 
processing file: SMTP.pcap
Actual: 28 packets (4380 bytes) sent in 0.53 seconds.       Rated: 8264.2 bps, 0.06 Mbps, 52.83 pps
Statistics for network device: eth4
        Attempted packets:         28
        Successful packets:        28
        Failed packets:            0
        Retried packets (ENOBUFS): 0
        Retried packets (EAGAIN):  0
TEST
./test.sh: line 6: read: read error: 0: Resource temporarily unavailable

[root@vse1 quick_test]#

I am wondering if I need to close or clear up any handles or pipes after I run tcpreplay?

Answer 1

Apparently tcpreplay sets O_NONBLOCK on stdin and then doesn't remove it. I'd say it's a bug in tcpreplay. To work it around you can run tcpreplay with stdin redirected from /dev/null. Like this:

tcpreplay -i eth4 SMTP.pcap </dev/null

Addition: note that this tcpreplay behavior breaks non-interactive shells only.

Another addition: alternatively, if you really need tcpreplay to receive your input you can write a short program which resets O_NONBLOCK. Like this one (reset-nonblock.c):

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

int
main()
{
    if (fcntl(STDIN_FILENO, F_SETFL,
              fcntl(STDIN_FILENO, F_GETFL) & ~O_NONBLOCK) < 0) {
        perror(NULL);
        return 1;
    }
    return 0;
}

Make it with "make reset-nonblock", then put it in your PATH and use like this:

tcpreplay -i eth4 SMTP.pcap
reset-nonblock