$SIG{ALRM} = 'ALRMhandler';
my $line;
while ( alarm(30), $line=<$socket>, defined($line) )
{
   alarm(0);  #turn off alarm
   ... process data in $line ....
}
...here if $line is not defined....
...another possible "server went away" condition...

sub ALRMhandler
{
   ...see discussion...
}