The following code snippet provides a crude timer mechanism for file read failures, somewhat along the lines of what Re: Redirecting stdout/stderr to pipe achieves for commands. The real code will run on many systems and I deem the timeout as necessary, although I know read failures are uncommon.

I eliminated the use of sysread+select due to the fact that I need @$outref populated line-by-line (whereas sysread uses buffers). I also do not have any real ideas on encoding. Can anyone make any improvement suggestions or is this ok?

Niel

UPDATE: fixed an endless loop in the example.

#!/usr/bin/perl -w
use strict;
use IO::Select;
use Symbol qw(gensym);

my $g_verbose = 1;
my $g_pid;
my $g_stop;
my $g_timeout = 2; #for test purposes
my $g_did_run;
my $g_max_cmd_size = 2_000_000;
my $g_max_file_size = 2_000_000;
my %g_pids;

sub read_stat($$$) {
   my ($file,$rcref,$statref) = @_;
   @$statref = stat($file);
   if ( $#$statref < 0 ) {
      print "Stat of file '$file' failed: $!\n";
      $$rcref = 1;
   } else {
      $$rcref = 0;
   }
   return $$rcref;
}
sub read_file($$$$$) {
   my ($file,$encoding,$rcref,$outref,$statref) = @_;
   @$outref = ();
   my $outbytes = 0; 
   $g_stop = 0;

# die if timeout occurs!
   local $SIG{ALRM} = sub {
      print "File \'$file\' collection reached deadline after $g_timeo
+ut secs.\n";
      die "Exiting - a read operation timed out!\n";
      $g_stop = 1;
   };
   alarm($g_timeout);

   if ( !defined($encoding) ) {
      $encoding = 'text/plain';
   }
   if ( $encoding ne 'text/plain' ) {
      print "Error: Can't collect file '$file' - '$encoding' encoding 
+is not supported.\n";
      $$rcref = -2;
      return $$rcref;
   }
   if ( $g_verbose ) {
      print "Collecting '$file'.\n";
   }

   read_stat($file,$rcref,$statref);
   if ( $$rcref != 0 ) {
      return undef;
   }
   if ( !open(IFILE,"<$file") ) {
      print "Open of file '$file' failed: $!\n";
      return undef;
   }

# read data into @$outref (line by line). alarm prevents timeout.
   while (!$g_stop) {
      last if (eof(IFILE));
      my $line = <IFILE>;
      chomp $line;
      push @$outref, $line;
# for test purposes - make it timeout!
      sleep 5;
      $outbytes += length($line);
      if ($outbytes >= $g_max_file_size) {
         print "Maximum file size reached after $outbytes bytes\n";
         last;
   alarm(0);
   close(IFILE);

   if (!$g_stop) {
      $$rcref = 0;
   } else {
      $$rcref = -1;
   }
   return $$rcref;
}
#MAIN
my $file = '/etc/hosts';
my $encoding = 'text/plain';
my $rc;
my (@cmdout,@stat);
$rc = read_file($file,$encoding,\$rc,\@cmdout,\@stat);
print "Collected $file (rc=$rc)\n";

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In reply to file read timeout by 0xbeef

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