implement nop sending every 5s if idle using alarm

diff --git a/terminal-server.pl b/terminal-server.pl
index 4b964ed..6d86992 100755 (executable)
--- a/terminal-server.pl
+++ b/terminal-server.pl
@@ -5,6 +5,7 @@ use strict;
 use Data::Dump qw(dump);
 
 use IO::Socket::INET;
+use Time::HiRes;
 
 $| = 1;
 
@@ -25,6 +26,9 @@ my $prices = {
        DUPLEX => -0.05,
 };
 
+
+my $next_nop_t = time() + 5;
+
 while(1) {
        our $client_socket = $socket->accept();
 
@@ -35,11 +39,30 @@ while(1) {
        }
 
        sub client_line {
-               my $line = <$client_socket>;
-               if ( defined $line ) {
-                       $line =~ s/[\r\n]+$//;
-                       warn "<< $line\n";
+               #my $line = <$client_socket>;
+
+               my $line;
+               my $timeout = $next_nop_t - time();
+               if ( $timeout > 0 ) {
+                       eval {
+                               local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
+                               alarm $timeout;
+                               warn "# NOP alarm $timeout";
+                               $line = <$client_socket>;
+                               alarm 0;
+                       };
+                       if ($@) {
+                               # timed out
+                               client_send ".NOP";
+                               $line = <$client_socket>;
+                       }
+               } else {
+                       $line = <$client_socket>;
                }
+
+               $line =~ s/[\r\n]+$//;
+               warn "<< $line\n";
+
                return $line;
        }
 
@@ -109,8 +132,7 @@ while(1) {
                } elsif ( $line =~ m/^\.NOP/ ) {
                        # XXX it's important to sleep, before sending response or
                        # interface on terminal device will be unresponsive
-                       sleep 1;
-                       client_send  ".NOP";
+                       $next_nop_t = time() + 5; # NOP every 5s?
                } elsif ( $line =~ m/^\.END/ ) {
                        client_send  ".DONE BLK WAIT";
                        client_send  ".NOP";