server: service discovery over UDP.

implement RFC-005
- server broadcasts once on startup and answers to broadcasts
- small tool for listening on the port and sending broadcasts

Change-Id: I02d1184d6be62bef6f964eb9d238220aef062e94
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/34851
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Georg Brandl <g.brandl@fz-juelich.de>

test/test_discovery.py

@@ -0,0 +1,62 @@
+# *****************************************************************************
+#
+# This program 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.
+#
+# This program 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
+# this program; if not, write to the Free Software Foundation, Inc.,
+# 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+#
+# Module authors:
+#   Alexander Zaft <a.zaft@fz-juelich.de>
+#
+# *****************************************************************************
+"""Test discovery messages"""
+
+from test.test_modules import LoggerStub
+from frappy.protocol.discovery import UDPListener, MAX_MESSAGE_LEN
+from frappy.version import get_version
+
+
+def test_empty():
+    logger = LoggerStub()
+    udp = UDPListener('', '', ['tcp://0'], logger)
+    udp.firmware = ''
+    # 78 is the maximum overhead
+    assert 78 == len(udp._getMessage(2**16-1))
+
+
+def test_basic():
+    logger = LoggerStub()
+    udp = UDPListener('eq', 'desc', ['tcp://1234'], logger)
+    assert udp.description == 'desc'
+    assert udp.equipment_id == 'eq'
+    assert udp.ports == [1234]
+    assert udp.firmware == 'FRAPPY ' + get_version()
+
+
+def test_ascii_truncation():
+    logger = LoggerStub()
+    desc = 'a' * MAX_MESSAGE_LEN
+    udp = UDPListener('eq', desc, ['tcp://1234'], logger)
+    assert MAX_MESSAGE_LEN == len(udp._getMessage(65535))
+    fw = len(('FRAPPY ' + get_version()).encode('utf-8'))
+    expected_length = 430 - fw - 2
+    assert expected_length == len(udp.description)
+
+
+def test_unicode_truncation():
+    logger = LoggerStub()
+    desc = '\U0001f604' * 400
+    udp = UDPListener('eq', desc, ['tcp://1234'], logger)
+    fw = len(('FRAPPY ' + get_version()).encode('utf-8'))
+    # 4 bytes per symbol, rounded down for the potential cut
+    expected_length = (430 - fw - 2) // 4
+    assert expected_length == len(udp.description)