[core] allow LISTEN_PID to be ppid if TRACEME (fixes #3137)

allow LISTEN_PID to be ppid (parent pid) if TRACEME set in environment
(e.g. for strace, gdb on Linux; valgrind starts lighttpd as LISTEN_PID)

x-ref:
  "TRACEME environment option in tests broken with LISTEN_PID"
  https://redmine.lighttpd.net/issues/3137

src/network.c

@@ -581,7 +581,13 @@ static int network_socket_activation_from_env(server *srv, network_socket_config
     char *listen_fds = getenv("LISTEN_FDS");
     pid_t lpid = listen_pid ? (pid_t)strtoul(listen_pid,NULL,10) : 0;
     int nfds = listen_fds ? atoi(listen_fds) : 0;
-    int rc = (lpid == getpid() && nfds > 0 && nfds < 5000)
+    int rc = (nfds > 0 && nfds < 5000
+              && (lpid == getpid()
+                 #ifndef _WIN32
+                  || (0 == strncmp(listen_pid, "parent:", 7)
+                      && getppid() == (pid_t)strtoul(listen_pid+7,NULL,10))
+                 #endif
+                 ))
       ? network_socket_activation_nfds(srv, s, nfds)
       : 0;
     unsetenv("LISTEN_PID");

tests/LightyTest.pm

@@ -115,6 +115,7 @@ sub stop_proc {
 
 	my $pid = $self->{LIGHTTPD_PID};
 	if (defined $pid && $pid != -1) {
+		kill('USR1', $pid) if (($ENV{"TRACEME"}||'') eq 'strace');
 		kill('TERM', $pid) or return -1;
 		return -1 if ($pid != waitpid($pid, 0));
 	} else {
@@ -205,6 +206,9 @@ sub start_proc {
 		# set up systemd socket activation env vars
 		$ENV{LISTEN_FDS} = "1";
 		$ENV{LISTEN_PID} = $$;
+		if (defined($ENV{"TRACEME"}) && $ENV{"TRACEME"} ne "valgrind") {
+			$ENV{LISTEN_PID} = "parent:$$"; # lighttpd extension
+		}
 		listen($SOCK, 1024) || die "listen: $!";
 		if (fileno($SOCK) != 3) { # SD_LISTEN_FDS_START 3
 			require POSIX;