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#!/usr/bin/perl
# Perl Weekly Challenge - 098
# - https://perlweeklychallenge.org/blog/perl-weekly-challenge-098/
#
# Task 1 - Read N-characters
#
# Author: Niels 'PerlBoy' van Dijke
package readN;
use v5.16;
use strict;
use warnings;
use Fcntl qw(:DEFAULT);
use Time::HiRes qw(usleep);
require Exporter;
our @ISA = qw(Exporter);
our @EXPORT = qw(readN);
my %FH;
my %EOF;
sub readN ($$) {
my ($fileName, $length) = @_;
# Close the file when eof is reached
if (exists $EOF{$fileName}) {
delete $FH{$fileName};
delete $EOF{$fileName};
return;
}
if (!exists ($FH{$fileName})) {
sysopen($FH{$fileName}, $fileName, O_RDONLY) //
die "Can't open '$fileName' ($!)";
binmode($FH{$fileName});
}
my $return;
my $retry = 10;
do {
my $buf;
my $nread = sysread($FH{$fileName}, $buf, $length);
if (!defined $nread) {
$retry--; usleep 1_000;
} elsif ($nread == 0) {
$EOF{$fileName}++;
} elsif ($nread <= $length) {
$return .= $buf;
}
} while (!exists $EOF{$fileName} and length($return // '') != $length and $retry);
return $return;
}
1;
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