Using perl module Log::Syslog::Fast - Unable to catch exception

Question

I am using Log::Syslog::Fast to forward logs to a syslog server. I was testing the script to see how it would react if the syslog server suddenly crashed.

To test I created a file with test messages, started the script & then shutdown the syslog server after 2 messages were received at the syslog server.

The script sent the third message & then dies. The termination is not being caught by eval & 'use warnings 'FATAL' => 'all';' does not help.

Could someone please help me catch the exception & close down the script more gracefully?

What needs to happen here is - After the Command2 is sent, the script should catch the exception & display:

Fail: Command3

Code extract:

$logger = Log::Syslog::Fast->new(LOG_TCP,$server, 514, 13, 6, "test_machine", "Syslog");
$logger->set_pid(0);

foreach $line(<SPOOL>)
{
        ($machine,$time,$message)=(split '\|',$line);
        eval{
                $logger->set_sender($machine);
                $logger->send($message,$time);
        };
        if($@)
        {
                print "\nFail: $message\n";
                exit;
        }
        else
        {
                print "\nSuccess: $message\n";
        }
        sleep 5;
}

Input File:

test_machine1|1461201306|Command1
test_machine1|1461201311|Command2
test_machine1|1461203214|Command3
test_machine1|1461203219|Command4
test_machine2|1461204005|Command5
test_machine2|1461204006|Command6
test_machine2|1461204149|Command7
test_machine3|1461204154|Command8
test_machine3|1461206936|Command9
test_machine3|1461206942|Command10

Output:

Success: Command1

Success: Command2

Success: Command3

Strace Output:

read(4, "test_machine1|1461201306|Command"..., 4096) = 341
read(4, "", 4096)                       = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
sendto(3, "<110>Apr 20 21:15:06 test_machin"..., 59, 0, NULL, 0) = 59
write(1, "Success Command1\n\n\n", 19Success Command1


)  = 19
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
nanosleep({5, 0}, 0x7ffc707478f0)       = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
sendto(3, "<110>Apr 20 21:15:11 test_machin"..., 59, 0, NULL, 0) = 59
write(1, "Success Command2\n\n\n", 19Success Command2


)  = 19
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
nanosleep({5, 0}, 0x7ffc707478f0)       = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
sendto(3, "<110>Apr 20 21:46:54 test_machin"..., 59, 0, NULL, 0) = 59

I want the script to fail here when it tries to send the third message but it does not.

write(1, "Success Command3\n\n\n", 19Success Command3


)  = 19
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
nanosleep({5, 0}, 0x7ffc707478f0)       = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=3519, ...}) = 0
sendto(3, "<110>Apr 20 21:46:59 test_machin"..., 59, 0, NULL, 0) = -1 EPIPE (Broken pipe)
--- SIGPIPE {si_signo=SIGPIPE, si_code=SI_USER, si_pid=26037, si_uid=3179} ---
+++ killed by SIGPIPE +++

The script finally dies while trying to send the fourth message. Unfortunately the eval is not catching the exception.

Answer 1

Try adding a line

$SIG{PIPE} = sub {
die "SIGPIPE";
};

before anything is being sent.

You might also want to try "print" instead of die.

Answer 2

You might want to trap SIGPIPE like this:

$SIG{PIPE} = "IGNORE";

From the perlipc:

If you're writing to a pipe, you should also trap SIGPIPE. Otherwise, think of what happens when you start up a pipe to a command that doesn't exist: the open() will in all likelihood succeed (it only reflects the fork()'s success), but then your output will fail--spectacularly. Perl can't know whether the command worked, because your command is actually running in a separate process whose exec() might have failed. Therefore, while readers of bogus commands return just a quick EOF, writers to bogus commands will get hit with a signal, which they'd best be prepared to handle.

Also, have a look at this behavior in a C program when writing to a broken socket.