For some reason, this website has been having trouble staying up. But it is working at the moment. I will attach a client/server pair that I wrote some time ago. This shows one way of using the alarm signal to timeout read requests to the server. The big problem with this approach is that once you get a signal, there is not much you can do about it other than clean up some stuff and die. But often that is enough. See if this approach will work for you.

There are other ways where it is possible to check if data is available on the pipe before attempting to read so that you don't hang. I have another project competing for my time right now. So can't provide an example of that right away.

#!/usr/bin/perl

# Simple client for testing 
# https://www.perlmonks.org/?node_id=11151665

use strict;
use warnings;
$!=1;
use IO::Socket;

my $socket = IO::Socket::INET -> new 
          (PeerAddr  => 'localhost',
           PeerPort  => 8081,
           Proto     => 'tcp',
           Type      => SOCK_STREAM)
      or
die "Cannot open socket!";  

print "$socket";

my $cmd = <<'END_MESSAGE';
GET /DATA_String/{300 continuous characters of sensor data}HTTP/1.1
Some host line
Some Connection line
Some user-agent line, next line is blank

END_MESSAGE

$SIG{PIPE} = 'handler';
$SIG{INT}  = 'handler';
$SIG{QUIT} = 'handler';
$SIG{ALRM} = 'handler';

server_request($cmd);  #single request

close $socket;     #hang up
exit();


sub server_request
{
    my $cmd = shift;
    print "sending CMD to server\n";
    alarm(2);
    print $socket "$cmd";
    $socket->flush();
    alarm(0);
    

    print "client debug: back from server: \n";
    while (alarm(2),my $sResponse = <$socket>)
    { 
       alarm(0);
       print "from Server: $sResponse";
    }
    alarm(0);
}

sub handler
{
   my ($signo) = shift;
   if ($signo eq "INT" or $signo eq "QUIT")
   {
       print $socket "QUIT\n";
       close ($socket);
       exit (1);
   }
   elsif ($signo eq "ALRM")
   {
       print "server too slow - request timed out!\n";
       exit (2);
   }
   else  #SIGPIPE (probably!)
   {
       print "Server died with signal $signo\n";
       exit (3);
   }
}
[download]

#!/usr/bin/perl

# Perl SOPW 
# https://www.perlmonks.org/?node_id=11151665

use strict;
use warnings;
$|=1; #Turn stdio buffering off

use IO::Socket;
use POSIX qw(sys_wait_h);
use constant LISTEN_PORT => 8081;

my $socket = IO::Socket::INET->new
              ( LocalPort => 8081,
                Proto     => 'tcp',
                Type      => SOCK_STREAM,
                Reuse     => 1,
                Listen    => 10,
               )
           or
die "Could not open port 8081!";

my $client;

while (1)
{
   $client = $socket->accept() || next; #accept() is not re-entrant
                                        #loop if error
   
   my $pid = fork();
   die "Bad Fork!" unless defined $pid;
   
   if ($pid == 0 )  # child
   {
       close ($socket); # children don't listen for new connections
       
       my $line;
       my @buff;
       
       while (defined ($line=<$client>) and $line !~ /^\s*$/)
       {
          push @buff, $line;
       }
             
       my $time = time();
       print "INCOMING from a Client Connection at $time\n";
       
       do_command(\@buff);
       
       exit(0);
   }
   else              # parent
   {
       close ($client); #wait for next client request
   }
}

sub do_command  
{
    my $buff = shift;
    
    print $client "START\n";
    print $client "$_" for @$buff;  #just loopback lines to client
    print $client "END\n";
    $client->flush();
}
[download]

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