snmp: don't let CommandGenerator be a singleton

With SNMPv3, it seems to keep some state. Add some test to highlight the bug.

Closes #35.

snimpy/snmp.py

@@ -74,8 +74,6 @@ class Session(object):
     session. From such an instance, one can get information from the
     associated agent."""
 
-    _cmdgen = cmdgen.CommandGenerator()
-
     def __init__(self, host,
                  community="public", version=2,
                  secname=None,
@@ -116,6 +114,7 @@ def __init__(self, host,
         """
         self._host = host
         self._version = version
+        self._cmdgen = cmdgen.CommandGenerator()
 
         # Put authentication stuff in self._auth
         if version in [1, 2]:

tests/agent.py

@@ -11,9 +11,12 @@ class TestAgent(object):
 
     """Agent for testing purpose"""
 
-    def __init__(self, ipv6=False):
+    def __init__(self, ipv6=False, community='public', authpass='authpass', privpass='privpass'):
         q = Queue()
         self.ipv6 = ipv6
+        self.community = community
+        self.authpass = authpass
+        self.privpass = privpass
         self._process = Process(target=self._setup, args=(q,))
         self._process.start()
         self.port = q.get()
@@ -40,16 +43,15 @@ def _setup(self, q):
                 udp.domainName,
                 udp.UdpTransport().openServerMode(('127.0.0.1', port)))
         # Community is public and MIB is writable
-        config.addV1System(snmpEngine, 'read-write', 'public')
+        config.addV1System(snmpEngine, 'read-write', self.community)
         config.addVacmUser(snmpEngine, 1, 'read-write', 'noAuthNoPriv',
                            (1, 3, 6), (1, 3, 6))
         config.addVacmUser(snmpEngine, 2, 'read-write', 'noAuthNoPriv',
                            (1, 3, 6), (1, 3, 6))
         config.addV3User(
             snmpEngine, 'read-write',
-            config.usmHMACMD5AuthProtocol, 'authpass',
-            config.usmAesCfb128Protocol, 'privpass'
-        )
+            config.usmHMACMD5AuthProtocol, self.authpass,
+            config.usmAesCfb128Protocol, self.privpass)
         config.addVacmUser(snmpEngine, 3, 'read-write', 'authPriv',
                            (1, 3, 6), (1, 3, 6))
 

tests/test_snmp.py

@@ -312,6 +312,26 @@ def setUp(self):
             authprotocol="MD5", authpassword="authpass",
             privprotocol="AES", privpassword="privpass")
 
+    def testSeveralSessions(self):
+        agent2 = agent.TestAgent(authpass='authpass2', privpass='privpass2')
+        try:
+            session1 = self.session
+            session2 = snmp.Session(
+                host="127.0.0.1:{0}".format(agent2.port),
+                version=3,
+                secname="read-write",
+                authprotocol="MD5", authpassword="authpass2",
+                privprotocol="AES", privpassword="privpass2")
+            ooid = mib.get('SNMPv2-MIB', 'sysDescr').oid + (0,)
+            oid1, a1 = session1.get(ooid)[0]
+            oid2, a2 = session2.get(ooid)[0]
+            self.assertEqual(oid1, ooid)
+            self.assertEqual(oid2, ooid)
+            self.assertEqual(a1, b"Snimpy Test Agent")
+            self.assertEqual(a2, b"Snimpy Test Agent")
+        finally:
+            agent2.terminate()
+
 
 class TestSnmpTransports(unittest.TestCase):