Stop accepting new TCP connections when the server is at maximum active connection capacity.

Add support for gracefully stopping the server.
Add primer on using ocserv with L3 load balancer.

Resolves: #345

Signed-off-by: Alan Jowett <alanjo@microsoft.com>

tests/test-drain-server

@@ -0,0 +1,61 @@
+#!/bin/sh
+#
+# Copyright (C) 2013 Nikos Mavrogiannopoulos
+#
+# This file is part of ocserv.
+#
+# ocserv is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the
+# Free Software Foundation; either version 2 of the License, or (at
+# your option) any later version.
+#
+# ocserv is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with GnuTLS; if not, write to the Free Software Foundation,
+# Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+SERV="${SERV:-../src/ocserv}"
+srcdir=${srcdir:-.}
+NO_NEED_ROOT=1
+PIDFILE=ocserv-pid.$$.tmp
+
+. `dirname $0`/common.sh
+
+eval "${GETPORT}"
+
+echo "Testing local backend with username-password... "
+
+update_config test1.config
+echo server-drain-ms=10000 >> ${CONFIG}
+
+launch_sr_server -d 1 -p ${PIDFILE} -f -c ${CONFIG} & PID=$!
+wait_server $PID
+
+echo "Connecting to obtain cookie... "
+( echo "test" | LD_PRELOAD=libsocket_wrapper.so $OPENCONNECT -q $ADDRESS:$PORT -u test --servercert=d66b507ae074d03b02eafca40d35f87dd81049d3 --cookieonly ) ||
+	fail $PID "Could not receive cookie from server"
+
+if ! test -f ${PIDFILE};then
+	fail $PID "Could not find pid file ${PIDFILE}"
+fi
+
+KILL_TIME=$(date +%s)
+kill -15 $(cat $PIDFILE)
+
+sleep 1
+
+echo "Connecting to obtain cookie... "
+( echo "test" | LD_PRELOAD=libsocket_wrapper.so $OPENCONNECT -q $ADDRESS:$PORT -u test --servercert=d66b507ae074d03b02eafca40d35f87dd81049d3 --cookieonly ) &&
+	fail $PID "Server is still listening"
+
+wait 
+END_TIME=$(date +%s)
+if [ $((END_TIME - KILL_TIME)) -lt 9 ]]; then
+	fail $PID "Server died too early - signalled at $KILL_TIME died at $END_TIME"
+fi
+cleanup
+
+exit 0