Monday, February 5, 2024

[SOLVED] Skip a get request in perl if it takes more than a specified time

Issue

I am writing a perl script to extract certain data using curl commands. EG:

my $raw_json = `curl -X GET <some website url> -H <some parameters>`;

The issue is sometimes this website crashes and my code gets stuck at the same place for a long time. I want the code to skip this line and go to the next line if the request is taking more than a specified time, say 30 seconds.

I tried using $SIG{ALRM} in my script as follows:

my $timeout = 30;
eval {
   local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
   alarm $timeout;
   my $raw_json = `curl -X GET <some website url> -H <some parameters>`;
   alarm 0;
};
if ($@) {
 print "\nERROR!\n";
   die;   # propagate unexpected errors
      # timed out
} 
else {
   # didn't
}

I expected the run to stop after 30 seconds, but what is happening is I do get the "ERROR" statement printed after 30 seconds but get request keeps on running even after that.


Solution

The curl is happening in a subprocess, so you need to stop that subprocess. Perl isn't going to stop that for you.

Use the --connect-timeout or --max-time to curl so you don't need the alarm and curl cleans itself up.

As @ikegami suggested, the next simplest thing is IPC::Run, which can handle the details of a timeout for an external process.

Or, if you want to handle the alarm yourself, you need to work at a lower level so you have the PID of the subprocess and can kill it yourself. See perlipc.



Answered By - brian d foy
Answer Checked By - Mildred Charles (WPSolving Admin)
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