Sz command hanging and outputting ZNAK’s

[M1k3]

OS – Linux

I have a Perl script which exec’s the sz command to send files over modems (Z MODEM protocol). In some instances (for example when the power goes out on the receiving modem) the sz command hangs and ZNAK errors are written to a log file causing the process to hang and log file to rapidly grow. For example:

Retry 0: Bad CRC
Retry 0: Got ERROR
Retry 0: Bad CRC
Retry 0: Got ERROR
Retry 0: Got ZNAK
Retry 0: Got ZNAK
Retry 0: Got ZNAK
Retry 0: Got ZNAK

How can I trap for such errors/terminate the process as soon as there is a problem? Is there a parameter I can pass?

Sample code (exec $cmd is where it hangs):

my $gSendCommand = "sz -b -u"

 

my $ret = Run("$gSendCommand $gUploadFile", 1);

 

sub Run # ($cmd, $serial)

    {

    my ($cmd, $serial) = @_;

 

    my $ret = fork;

    ptUtil::fatal("Could not fork to run $cmd") if $ret < 0;

 

    if ($ret == 0)

       {

        if ($serial)

            {

            my $fileno = $gSerial->{FD};

            my $flags  = 0;

 

            # redirect STDIN and STDOUT to modem

            open(STDIN,  "<&=" . $fileno) or ptUtil::fatal("Could not 
+dup2 STDIN!");

            open(STDOUT, ">&=" . $fileno) or ptUtil::fatal("Could not 
+dup2 STDOUT!");

 

            # enable STDIN blocking

            if (fcntl(STDIN, F_GETFL, $flags))

                {

                $flags &= ~O_NONBLOCK;

                fcntl(STDIN, F_SETFL, $flags);

                }

 

            # enable STDOUT blocking

            if (fcntl(STDOUT, F_GETFL, $flags))

                {

                $flags &= ~O_NONBLOCK;

                fcntl(STDOUT, F_SETFL, $flags);

                }

            }

 

        # exec command

            ptUtil::log("Executing $cmd ($?)");

        exec($cmd) or ptUtil::fatal("Could not exec $cmd");

            ptUtil::log("Executed $cmd ($?)");

      }

 

    wait;

 

    return $?;

[anonymized user 468275]

You could use IPC::Open3 (saving the child pid it returns) to run the command and read its output from filehandles. Then if you don't like what it is doing on that basis, closing the filehandles will terminate the child and the parent can waitpid the pid of the child before iterating the next remote device cleanly.