Client3 needs to verify client1 and client2. client 4 needs to verify all client1,2 and 3s..

How many clients are there?

Say there were 10. The tenth client has to check 9 md5s and produce one. But who'd check that one?

And why, if two clients have already checked the MD5 of a file and concurred, do you expect that a third client would suddenly produce a different result?

And, presumably the server can also access these files--else how does it randomly pick from them for the clients to operate upon? In which case, why not have the server pick a dozen of so files at random--calculate and store the MD5s--and then supply the entire list of files & md5s to each connecting client for verification. The only response required then is yes or no. Ie:

• Client connects:
• Server sends single packet of filename MD5 filename md5....
• Client reads list.
• Reads file and calculates md5.
• If different send "failed" to server; else sends "passed".
• Done.

clients are on different machines, how could the code fit in 20 lines

Well, that was for the server; the client would be about the same again. Eg.

Server:

#! perl -sw
use strict;
use threads;
use threads::shared;
use IO::Socket;
use Digest::MD5 qw[ md5_hex ];
use List::Util qw[ shuffle ];

use constant CRLF => chr( 13 ) . chr( 10 );
$/ = $\ = CRLF;

my %files :shared = map{
    open my $fh, '<:raw', $_ or warn "$_: $!";
    $_ => md5_hex( do{ local $/; <$fh> } );
} (shuffle glob '*.pl' )[ 0 .. 9 ];

my $server = IO::Socket::INET->new(
    LocalHost => 'localhost', LocalPort => 1234, Listen => SOMAXCONN, 
+Reuse =>1,
) or die "Couldn't create listening socket";

while( 1 ) {
    my $client = $server->accept;
    async {
        my $peerhost = $client->peerhost .':'. $client->peerport;
        print $client join ' ', %files;
        my $reply = <$client>;
        print $client 'DONE';
        warn "$peerhost : $reply\n";
    }->detach;
}

close $server;
__END__
c:\test>850473-s.pl
127.0.0.1:59137 : PASSED
127.0.0.1:59138 : PASSED
127.0.0.1:59139 : PASSED
127.0.0.1:59140 : PASSED
127.0.0.1:59141 : PASSED
127.0.0.1:59142 : PASSED
127.0.0.1:59143 : PASSED
127.0.0.1:59144 : PASSED
127.0.0.1:59145 : PASSED
127.0.0.1:59146 : PASSED
127.0.0.1:59147 : PASSED
127.0.0.1:59148 : PASSED
127.0.0.1:59149 : PASSED
127.0.0.1:59150 : PASSED
127.0.0.1:59151 : PASSED
[download]

Client:

#! perl -sw
use strict;
use Digest::MD5 qw[ md5_hex ];
use IO::Socket;

$/ = $\ = chr( 13 ) . chr( 10 );

my $server = IO::Socket::INET->new(
    'localhost:1234'
) or die $^E;

my %files= split ' ', <$server>;
my $result = 'PASSED';

for my $file ( keys %files ) {
    open my $fh, '<:raw', $file or warn "$_ : $!";
    my $md5 = md5_hex( do{ local $/; <$fh> } );
    warn "$file: $md5 eq $files{ $file }\n";
    next if $md5 eq $files{ $file };
    $result = 'FAILED';
    last;
}

printf $server "$result\cM\cJ";
print scalar <$server>;
close $server;

__END__
junk67.pl: c9c8f25e0d4263a253f45d63b18fb062 eq c9c8f25e0d4263a253f45d6
+3b18fb062
CPtest.pl: 103017b3f98578db15060a31316087e7 eq 103017b3f98578db15060a3
+1316087e7
junk2.pl: 5367ddba375163542c7197bfa355be88 eq 5367ddba375163542c7197bf
+a355be88
789655-2.pl: c6b1a7367b57bba6ae0e4556aeb1053c eq c6b1a7367b57bba6ae0e4
+556aeb1053c
burnCPU.pl: 0e8afcf32f03fa9382b1bce9b8a5646b eq 0e8afcf32f03fa9382b1bc
+e9b8a5646b
815861.pl: cb37349c218e9cd6d4017dc32e436d72 eq cb37349c218e9cd6d4017dc
+32e436d72
junk33.pl: c298090e1bc7f8ec599c3b9bff08598e eq c298090e1bc7f8ec599c3b9
+bff08598e
MovingAves.pl: 98f1b81b1d9ee099b937982320a1f347 eq 98f1b81b1d9ee099b93
+7982320a1f347
797136-b.pl: 02152b03bb0766e141da67739161f192 eq 02152b03bb0766e141da6
+7739161f192
junk67.pl: c9c8f25e0d4263a253f45d63b18fb062 eq c9c8f25e0d4263a253f45d6
+3b18fb062
817762verify.pl: f0a6b204112d7d8aa7df99e307890705 eq f0a6b204112d7d8aa
+7df99e307890705
CPtest.pl: 103017b3f98578db15060a31316087e7 eq 103017b3f98578db15060a3
+1316087e7
DONE
[download]