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Edit File: fixetchosts

#!/usr/local/cpanel/3rdparty/bin/perl

# cpanel - scripts/fixetchosts                     Copyright 2022 cPanel, L.L.C.
#                                                           All rights reserved.
# copyright@cpanel.net                                         http://cpanel.net
# This code is subject to the cPanel license. Unauthorized copying is prohibited

package scripts::fixetchosts;

use strict;
use Cpanel::SafeFile             ();
use Cpanel::Validate::Hostname   ();
use Cpanel::IP::Loopback         ();
use Cpanel::DIp::MainIP          ();
use Cpanel::Sys::Hostname::FQDN  ();
use Cpanel::FileUtils::TouchFile ();
use IO::Handle                   ();

exit script(@ARGV) unless caller;

sub script {
    return run('/etc/hosts');
}

sub run {
    my ($file)        = @_;
    my $mainip        = Cpanel::DIp::MainIP::getmainserverip();
    my $hostname      = Cpanel::Sys::Hostname::FQDN::get_fqdn_hostname();
    my $shorthostname = Cpanel::Sys::Hostname::FQDN::get_short_hostname();

# CPANEL-36014: If the returned hostname ends with a trailing dot, strip it.
    $hostname =~ s/\.$//;

Cpanel::FileUtils::TouchFile::touchfile($file);
    die "The hostname $hostname is not valid.\n" unless Cpanel::Validate::Hostname::is_valid($hostname);

update( $file, $mainip, $hostname, $shorthostname );
    return 0;
}

sub update {
    my ( $file, $mainip, $hostname, $shorthostname ) = @_;

my $hosts_fh   = IO::Handle->new();
    my $hosts_lock = Cpanel::SafeFile::safeopen( $hosts_fh, '+<', $file );
    if ($hosts_lock) {
        my %SEENIP;
        my @ETCHOSTS;

while ( my $line = readline $hosts_fh ) {
            chomp $line;
            if ( $line =~ m/^\s*#/ || $line =~ m/^\s*$/ ) {
                push @ETCHOSTS, { 'raw' => $line };
            }
            else {
                my ( $ip, $hosts ) = split( /\s+/, $line, 2 );
                my @line_hosts;
                foreach my $host ( split( /\s+/, $hosts ) ) {
                    next if ( $ip ne $mainip && $host eq $hostname );                                   # Drop mismatch hostnames for the main IP
                    next if ( $ip eq $mainip && ( $host eq $hostname || $host eq $shorthostname ) );    # These will be re-added
                    push @line_hosts, $host if ( !grep { $_ eq $host } @line_hosts );                   # Drop duplicates while preserving order
                }

if ( !@line_hosts ) {                                                                   ## Drop empty lines
                    next if $ip eq $mainip;                                                             # Prevent duplicate commented lines for the main IP
                    push @ETCHOSTS, { 'raw' => '# ' . $line };                                          # Preserve lines that were commented out in full
                }
                else {                                                                                  ## Save valid entries
                    push @ETCHOSTS, { 'ip' => $ip, 'hosts' => \@line_hosts };
                    $SEENIP{$ip} = 1;
                }
            }
        }
        seek( $hosts_fh, 0, 0 );

my $added_hostname = 0;
        foreach my $line_ref (@ETCHOSTS) {
            if ( exists $line_ref->{'raw'} ) {
                print {$hosts_fh} $line_ref->{'raw'} . "\n";
            }
            else {
                my $ip        = $line_ref->{'ip'};
                my $hosts_ref = $line_ref->{'hosts'};

if ( $ip eq $mainip && !$added_hostname ) {
                    $added_hostname = 1;
                    unshift @{$hosts_ref}, $hostname, $shorthostname;
                }
                elsif ( Cpanel::IP::Loopback::is_loopback($ip) ) {
                    if ( !grep { $_ eq 'localhost' } @{$hosts_ref} ) {
                        unshift @{$hosts_ref}, 'localhost';
                    }
                }
                print {$hosts_fh} $ip . "\t\t" . join( ' ', @{$hosts_ref} ) . "\n";
            }

}
        if ( !exists $SEENIP{'127.0.0.1'} ) {
            print {$hosts_fh} "127.0.0.1\t\tlocalhost\n";
        }
        if ( !exists $SEENIP{$mainip} ) {
            print {$hosts_fh} $mainip . "\t\t" . $hostname . ' ' . $shorthostname . "\n";
        }
        truncate( $hosts_fh, tell($hosts_fh) );
        Cpanel::SafeFile::safeclose( $hosts_fh, $hosts_lock );
    }
    return;
}