Execution Observer facility implemented to give app an inside view

of SNMP engine inner workings. This is thought to be a generic framework for viewing (and modifying) various internal states of pysnmp engine. Previously introduced non-RFC APIs (like getting peer's transport endpoint) will be gradually migrated to this new framework.
2013-11-09 22:01:33 +00:00 · 2013-11-09 22:01:33 +00:00 · ce56f1b40f
parent 7a821af6de
commit ce56f1b40f
15 changed files with 710 additions and 91 deletions
--- a/CHANGES.txt
+++ b/CHANGES.txt
@ -1,6 +1,12 @@
 Revision 4.2.6rc0
 -----------------

+- Execution Observer facility implemented to give app an inside view
+  of SNMP engine inner workings. This is thought to be a generic
+  framework for viewing (and modifying) various internal states
+  of pysnmp engine. Previously introduced non-RFC APIs (like
+  getting peer's transport endpoint) will be gradually migrated to
+  this new framework.
 - Memory leak fixed in CommandForwarder examples.
 - Fix to CommandGenerator to make sendRequestHandle persistent across
  multiple iterations of GETNEXT/GETBULK queries.
--- a/examples/hlapi/asyncore/sync/manager/cmdgen/specific-v3-engine-id.py
+++ b/examples/hlapi/asyncore/sync/manager/cmdgen/specific-v3-engine-id.py
@ -23,28 +23,38 @@ cmdGen = cmdgen.CommandGenerator(snmpEngine)
 transportTarget = cmdgen.UdpTransportTarget(('demo.snmplabs.com', 161))

 #
-# Discover remote SNMP EngineID
+# To discover remote SNMP EngineID we will tap on SNMP engine inner workings
+# by setting up execution point observer setup on INTERNAL class PDU processing
 #

+observerContext = {}
+
+# Register a callback to be invoked at specified execution point of 
+# SNMP Engine and passed local variables at execution point's local scope
+snmpEngine.observer.registerObserver(
+    lambda e,p,v,c: c.update(securityEngineId=v['securityEngineId']),
+    'rfc3412.prepareDataElements:internal',
+    cbCtx=observerContext
+)
+
+# Send probe SNMP request with invalid credentials
+
 authData = cmdgen.UsmUserData('non-existing-user')

 errorIndication, errorStatus, errorIndex, varBinds = cmdGen.getCmd(
    authData, transportTarget
 )

-# Check for errors and print out results
-if errorIndication == 'unknownUserName':
-    snmpV3MessageProcessor = snmpEngine.messageProcessingSubsystems[3]
-    securityEngineId, contextEngineId, contextName = snmpV3MessageProcessor.getPeerEngineInfo(*transportTarget.getTransportInfo())
-    if securityEngineId:
-        print('securityEngineId = %s' % securityEngineId.prettyPrint())
-    else:
-        print('Peer EngineID not available')
-        raise Exception()
-else:
-    print('Can\'t discover peer EngineID', errorIndication)
+# See if our SNMP engine received REPORT PDU containing securityEngineId
+
+if 'securityEngineId' not in observerContext:
+    print("Can't discover peer EngineID, errorIndication: %s" % errorIndication)
    raise Exception()

+securityEngineId = observerContext.pop('securityEngineId')
+
+print('Remote securityEngineId = %s' % securityEngineId.prettyPrint())
+
 #
 # Query remote SNMP Engine using usmUserTable entry configured for it
 #
--- a/examples/v3arch/asyncore/agent/cmdrsp/observe-request-processing.py
+++ b/examples/v3arch/asyncore/agent/cmdrsp/observe-request-processing.py
@ -0,0 +1,84 @@
+#
+# Command Responder
+#
+# Listen and respond to SNMP GET/SET/GETNEXT/GETBULK queries with
+# the following options:
+#
+# * SNMPv3
+# * with USM user 'usr-md5-des', auth: MD5, priv DES or
+# * allow access to SNMPv2-MIB objects (1.3.6.1.2.1)
+# * over IPv4/UDP, listening at 127.0.0.1:161
+# * registers its own execution observer to snmpEngine
+# 
+# Either of the following Net-SNMP's commands will walk this Agent:
+#
+# $ snmpwalk -v3 -u usr-md5-des -l authPriv -A authkey1 -X privkey1 localhost .1.3.6
+#
+from pysnmp.entity import engine, config
+from pysnmp.entity.rfc3413 import cmdrsp, context
+from pysnmp.carrier.asynsock.dgram import udp
+
+# Create SNMP engine
+snmpEngine = engine.SnmpEngine()
+
+# Execution point observer setup
+
+# Register a callback to be invoked at specified execution point of 
+# SNMP Engine and passed local variables at code point's local scope
+def requestObserver(snmpEngine, execpoint, variables, cbCtx):
+    print('Execution point: %s' % execpoint)
+    print('* transportDomain: %s' % '.'.join([str(x) for x in variables['transportDomain']]))
+    print('* transportAddress: %s' % '@'.join([str(x) for x in variables['transportAddress']]))
+    print('* securityModel: %s' % variables['securityModel'])
+    print('* securityName: %s' % variables['securityName'])
+    print('* securityLevel: %s' % variables['securityLevel'])
+    print('* contextEngineId: %s' % variables['contextEngineId'].prettyPrint())
+    print('* contextName: %s' % variables['contextName'].prettyPrint())
+    print('* PDU: %s' % variables['pdu'].prettyPrint())
+
+snmpEngine.observer.registerObserver(
+    requestObserver,
+    'rfc3412.receiveMessage:request',
+    'rfc3412.returnResponsePdu'
+)
+
+# Transport setup
+
+# UDP over IPv4
+config.addTransport(
+    snmpEngine,
+    udp.domainName,
+    udp.UdpTransport().openServerMode(('127.0.0.1', 161))
+)
+
+# SNMPv3/USM setup
+
+# user: usr-md5-des, auth: MD5, priv DES
+config.addV3User(
+    snmpEngine, 'usr-md5-des',
+    config.usmHMACMD5AuthProtocol, 'authkey1',
+    config.usmDESPrivProtocol, 'privkey1'
+)
+
+# Allow full MIB access for each user at VACM
+config.addVacmUser(snmpEngine, 3, 'usr-md5-des', 'authPriv', (1,3,6,1,2,1), (1,3,6,1,2,1)) 
+
+# Get default SNMP context this SNMP engine serves
+snmpContext = context.SnmpContext(snmpEngine)
+
+# Register SNMP Applications at the SNMP engine for particular SNMP context
+cmdrsp.GetCommandResponder(snmpEngine, snmpContext)
+cmdrsp.SetCommandResponder(snmpEngine, snmpContext)
+cmdrsp.NextCommandResponder(snmpEngine, snmpContext)
+cmdrsp.BulkCommandResponder(snmpEngine, snmpContext)
+
+# Register an imaginary never-ending job to keep I/O dispatcher running forever
+snmpEngine.transportDispatcher.jobStarted(1)
+
+# Run I/O dispatcher which would receive queries and send responses
+try:
+    snmpEngine.transportDispatcher.runDispatcher()
+except:
+    snmpEngine.observer.unregisterObserver()
+    snmpEngine.transportDispatcher.closeDispatcher()
+    raise
--- a/examples/v3arch/asyncore/manager/cmdgen/observe-request-processing.py
+++ b/examples/v3arch/asyncore/manager/cmdgen/observe-request-processing.py
@ -0,0 +1,99 @@
+#
+# GET Command Generator
+#
+# Send a SNMP GET request
+#     with SNMPv3 with user 'usr-sha-aes', SHA auth and AES128 privacy protocols
+#     over IPv4/UDP
+#     to an Agent at 195.218.195.228:161
+#     for an OID in tuple form
+#     also registers its own execution observer to snmpEngine
+#
+# This script performs similar to the following Net-SNMP command:
+#
+# $ snmpget -v3 -l authPriv -u usr-sha-aes -a SHA -A authkey1 -x AES -X privkey1 -ObentU 195.218.195.228:161  1.3.6.1.2.1.1.1.0
+#
+from pysnmp.entity import engine, config
+from pysnmp.carrier.asynsock.dgram import udp
+from pysnmp.entity.rfc3413 import cmdgen
+
+# Create SNMP engine instance
+snmpEngine = engine.SnmpEngine()
+
+# Execution point observer setup
+
+# Register a callback to be invoked at specified execution point of 
+# SNMP Engine and passed local variables at code point's local scope
+def requestObserver(snmpEngine, execpoint, variables, cbCtx):
+    print('Execution point: %s' % execpoint)
+    print('* transportDomain: %s' % '.'.join([str(x) for x in variables['transportDomain']]))
+    print('* transportAddress: %s' % '@'.join([str(x) for x in variables['transportAddress']]))
+    print('* securityModel: %s' % variables['securityModel'])
+    print('* securityName: %s' % variables['securityName'])
+    print('* securityLevel: %s' % variables['securityLevel'])
+    print('* contextEngineId: %s' % (variables['contextEngineId'] and variables['contextEngineId'].prettyPrint() or '<empty>',))
+    print('* contextName: %s' % variables['contextName'].prettyPrint())
+    print('* PDU: %s' % variables['pdu'].prettyPrint())
+
+snmpEngine.observer.registerObserver(
+    requestObserver, 
+    'rfc3412.sendPdu',
+    'rfc3412.receiveMessage:response'
+)
+
+#
+# SNMPv3/USM setup
+#
+
+# user: usr-sha-aes, auth: SHA, priv AES
+config.addV3User(
+    snmpEngine, 'usr-sha-aes',
+    config.usmHMACSHAAuthProtocol, 'authkey1',
+    config.usmAesCfb128Protocol, 'privkey1'
+)
+config.addTargetParams(snmpEngine, 'my-creds', 'usr-sha-aes', 'authPriv')
+
+#
+# Setup transport endpoint and bind it with security settings yielding
+# a target name
+#
+
+# UDP/IPv4
+config.addTransport(
+    snmpEngine,
+    udp.domainName,
+    udp.UdpSocketTransport().openClientMode()
+)
+config.addTargetAddr(
+    snmpEngine, 'my-router',
+    udp.domainName, ('195.218.195.228', 161),
+    'my-creds'
+)
+
+# Error/response receiver
+def cbFun(sendRequestHandle,
+          errorIndication, errorStatus, errorIndex,
+          varBinds, cbCtx):
+    if errorIndication:
+        print(errorIndication)
+    elif errorStatus:
+        print('%s at %s' % (
+            errorStatus.prettyPrint(),
+            errorIndex and varBinds[int(errorIndex)-1][0] or '?'
+            )
+        )
+    else:
+        for oid, val in varBinds:
+            print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))
+
+# Prepare and send a request message
+cmdgen.GetCommandGenerator().sendReq(
+    snmpEngine,
+    'my-router',
+    ( ((1,3,6,1,2,1,1,1,0), None), ),
+    cbFun
+)
+
+# Run I/O dispatcher which would send pending queries and process responses
+snmpEngine.transportDispatcher.runDispatcher()
+
+snmpEngine.observer.unregisterObserver()
--- a/examples/v3arch/asyncore/manager/ntfrcv/determine-peer-network-address.py
+++ b/examples/v3arch/asyncore/manager/ntfrcv/determine-peer-network-address.py
@ -0,0 +1,67 @@
+#
+# Notification Receiver
+#
+# Receive SNMP TRAP/INFORM messages with the following options:
+#
+# * SNMPv1/SNMPv2c
+# * with SNMP community "public"
+# * over IPv4/UDP, listening at 127.0.0.1:162
+# * use observer facility to pull lower-level request details from SNMP engine
+# * print received data on stdout
+# 
+# Either of the following Net-SNMP's commands will send notifications to this
+# receiver:
+#
+# $ snmptrap -v2c -c public 127.0.0.1:162 123 1.3.6.1.6.3.1.1.5.1 1.3.6.1.2.1.1.5.0 s test
+#
+from pysnmp.entity import engine, config
+from pysnmp.carrier.asynsock.dgram import udp
+from pysnmp.entity.rfc3413 import ntfrcv
+
+# Create SNMP engine with autogenernated engineID and pre-bound
+# to socket transport dispatcher
+snmpEngine = engine.SnmpEngine()
+
+# Transport setup
+
+# UDP over IPv4, first listening interface/port
+config.addTransport(
+    snmpEngine,
+    udp.domainName + (1,),
+    udp.UdpTransport().openServerMode(('127.0.0.1', 162))
+)
+
+# SNMPv1/2c setup
+
+# SecurityName <-> CommunityName mapping
+config.addV1System(snmpEngine, 'my-area', 'public')
+
+# Callback function for receiving notifications
+def cbFun(snmpEngine, stateReference, contextEngineId, contextName,
+          varBinds, cbCtx):
+    # Get an execution context...
+    execContext = snmpEngine.observer.getExecutionContext(
+        'rfc3412.receiveMessage:request'
+    )
+
+    # ... and use inner SNMP engine data to figure out peer address
+    print('Notification from %s, ContextEngineId "%s", ContextName "%s"' % (
+        '@'.join([str(x) for x in execContext['transportAddress']]),
+        contextEngineId.prettyPrint(),
+        contextName.prettyPrint()
+        )
+    )
+    for name, val in varBinds:
+        print('%s = %s' % (name.prettyPrint(), val.prettyPrint()))
+
+# Register SNMP Application at the SNMP engine
+ntfrcv.NotificationReceiver(snmpEngine, cbFun)
+
+snmpEngine.transportDispatcher.jobStarted(1) # this job would never finish
+
+# Run I/O dispatcher which would receive queries and send confirmations
+try:
+    snmpEngine.transportDispatcher.runDispatcher()
+except:
+    snmpEngine.transportDispatcher.closeDispatcher()
+    raise
--- a/examples/v3arch/asyncore/manager/ntfrcv/multiple-network-interfaces.py
+++ b/examples/v3arch/asyncore/manager/ntfrcv/multiple-network-interfaces.py
@ -45,14 +45,10 @@ config.addTransport(
 config.addV1System(snmpEngine, 'my-area', 'public')

 # Callback function for receiving notifications
-def cbFun(snmpEngine,
-          stateReference,
-          contextEngineId, contextName,
-          varBinds,
-          cbCtx):
-    transportDomain, transportAddress = snmpEngine.msgAndPduDsp.getTransportInfo(stateReference)
-    print('Notification from %s, ContextEngineId "%s", ContextName "%s"' % (
-        transportAddress, contextEngineId.prettyPrint(),
+def cbFun(snmpEngine, stateReference, contextEngineId, contextName,
+          varBinds, cbCtx):
+    print('Notification from ContextEngineId "%s", ContextName "%s"' % (
+        contextEngineId.prettyPrint(),
        contextName.prettyPrint()
        )
    )
--- a/examples/v3arch/asyncore/manager/ntfrcv/multiple-network-transports.py
+++ b/examples/v3arch/asyncore/manager/ntfrcv/multiple-network-transports.py
@ -46,14 +46,10 @@ config.addTransport(
 config.addV1System(snmpEngine, 'my-area', 'public')

 # Callback function for receiving notifications
-def cbFun(snmpEngine,
-          stateReference,
-          contextEngineId, contextName,
-          varBinds,
-          cbCtx):
-    transportDomain, transportAddress = snmpEngine.msgAndPduDsp.getTransportInfo(stateReference)
-    print('Notification from %s, ContextEngineId "%s", ContextName "%s"' % (
-        transportAddress, contextEngineId.prettyPrint(),
+def cbFun(snmpEngine, stateReference, contextEngineId, contextName,
+          varBinds, cbCtx):
+    print('Notification from ContextEngineId "%s", ContextName "%s"' % (
+        contextEngineId.prettyPrint(),
        contextName.prettyPrint()
        )
    )
--- a/examples/v3arch/asyncore/manager/ntfrcv/multiple-usm-users.py
+++ b/examples/v3arch/asyncore/manager/ntfrcv/multiple-usm-users.py
@ -84,13 +84,11 @@ config.addV3User(
 )

 # Callback function for receiving notifications
-def cbFun(snmpEngine,
-          stateReference,
-          contextEngineId, contextName,
-          varBinds,
-          cbCtx):
-    print('Notification received, ContextEngineId "%s", ContextName "%s"' % (
-        contextEngineId.prettyPrint(), contextName.prettyPrint()
+def cbFun(snmpEngine, stateReference, contextEngineId, contextName,
+          varBinds, cbCtx):
+    print('Notification from ContextEngineId "%s", ContextName "%s"' % (
+        contextEngineId.prettyPrint(),
+        contextName.prettyPrint()
        )
    )
    for name, val in varBinds:
--- a/examples/v3arch/asyncore/manager/ntfrcv/observe-request-processing.py
+++ b/examples/v3arch/asyncore/manager/ntfrcv/observe-request-processing.py
@ -0,0 +1,92 @@
+#
+# Notification Receiver
+#
+# Receive SNMP TRAP/INFORM messages with the following options:
+#
+# * SNMPv1/SNMPv2c
+# * with SNMP community "public"
+# * over IPv4/UDP, listening at 127.0.0.1:162
+#   over IPv6/UDP, listening at [::1]:162
+# * registers its own execution observer to snmpEngine
+# * print received data on stdout
+# 
+# Either of the following Net-SNMP's commands will send notifications to this
+# receiver:
+#
+# $ snmptrap -v1 -c public 127.0.0.1 1.3.6.1.4.1.20408.4.1.1.2 127.0.0.1 1 1 123 1.3.6.1.2.1.1.1.0 s test
+# $ snmptrap -v2c -c public udp6:[::1]:162 123 1.3.6.1.6.3.1.1.5.1 1.3.6.1.2.1.1.5.0 s test
+# $ snmpinform -v2c -c public 127.0.0.1 123 1.3.6.1.6.3.1.1.5.1
+#
+from pysnmp.entity import engine, config
+from pysnmp.carrier.asynsock.dgram import udp, udp6
+from pysnmp.entity.rfc3413 import ntfrcv
+
+# Create SNMP engine with autogenernated engineID and pre-bound
+# to socket transport dispatcher
+snmpEngine = engine.SnmpEngine()
+
+# Execution point observer setup
+
+# Register a callback to be invoked at specified execution point of 
+# SNMP Engine and passed local variables at code point's local scope
+def requestObserver(snmpEngine, execpoint, variables, cbCtx):
+    print('Execution point: %s' % execpoint)
+    print('* transportDomain: %s' % '.'.join([str(x) for x in variables['transportDomain']]))
+    print('* transportAddress: %s' % '@'.join([str(x) for x in variables['transportAddress']]))
+    print('* securityModel: %s' % variables['securityModel'])
+    print('* securityName: %s' % variables['securityName'])
+    print('* securityLevel: %s' % variables['securityLevel'])
+    print('* contextEngineId: %s' % variables['contextEngineId'].prettyPrint())
+    print('* contextName: %s' % variables['contextName'].prettyPrint())
+    print('* PDU: %s' % variables['pdu'].prettyPrint())
+
+snmpEngine.observer.registerObserver(
+    requestObserver,
+    'rfc3412.receiveMessage:request',
+    'rfc3412.returnResponsePdu'
+)
+
+# Transport setup
+
+# UDP over IPv4
+config.addTransport(
+    snmpEngine,
+    udp.domainName,
+    udp.UdpTransport().openServerMode(('127.0.0.1', 162))
+)
+
+# UDP over IPv6
+config.addTransport(
+    snmpEngine,
+    udp6.domainName,
+    udp6.Udp6Transport().openServerMode(('::1', 162))
+    )
+
+# SNMPv1/2c setup
+
+# SecurityName <-> CommunityName mapping
+config.addV1System(snmpEngine, 'my-area', 'public')
+
+# Callback function for receiving notifications
+def cbFun(snmpEngine, stateReference, contextEngineId, contextName,
+          varBinds, cbCtx):
+    print('Notification from ContextEngineId "%s", ContextName "%s"' % (
+        contextEngineId.prettyPrint(),
+        contextName.prettyPrint()
+        )
+    )
+    for name, val in varBinds:
+        print('%s = %s' % (name.prettyPrint(), val.prettyPrint()))
+
+# Register SNMP Application at the SNMP engine
+ntfrcv.NotificationReceiver(snmpEngine, cbFun)
+
+snmpEngine.transportDispatcher.jobStarted(1) # this job would never finish
+
+# Run I/O dispatcher which would receive queries and send confirmations
+try:
+    snmpEngine.transportDispatcher.runDispatcher()
+except:
+    snmpEngine.observer.unregisterObserver()
+    snmpEngine.transportDispatcher.closeDispatcher()
+    raise
--- a/examples/v3arch/twisted/manager/ntfrcv/multiple-interfaces.py
+++ b/examples/v3arch/twisted/manager/ntfrcv/multiple-interfaces.py
@ -47,15 +47,11 @@ config.addTransport(
 config.addV1System(snmpEngine, 'my-area', 'public')

 # Callback function for receiving notifications
-def cbFun(snmpEngine,
-          stateReference,
-          contextEngineId, contextName,
-          varBinds,
-          cbCtx):
-    transportDomain, transportAddress = snmpEngine.msgAndPduDsp.getTransportInfo(stateReference)
-    print('Notification from %s, SNMP Engine %s, Context %s' % (
-            transportAddress, contextEngineId.prettyPrint(),
-            contextName.prettyPrint()
+def cbFun(snmpEngine, stateReference, contextEngineId, contextName,
+          varBinds, cbCtx):
+    print('Notification from ContextEngineId "%s", Context "%s"' % (
+        contextEngineId.prettyPrint(),
+        contextName.prettyPrint()
        )
    )
    for name, val in varBinds:
--- a/examples/v3arch/twisted/manager/ntfrcv/multiple-usm-users.py
+++ b/examples/v3arch/twisted/manager/ntfrcv/multiple-usm-users.py
@ -89,12 +89,9 @@ config.addV3User(
 # -- end of SNMPv3/USM setup

 # Callback function for receiving notifications
-def cbFun(snmpEngine,
-          stateReference,
-          contextEngineId, contextName,
-          varBinds,
-          cbCtx):
-    print('Notification received, ContextEngineId "%s", ContextName "%s"' % (
+def cbFun(snmpEngine, stateReference, contextEngineId, contextName,
+          varBinds, cbCtx):
+    print('Notification from ContextEngineId "%s", ContextName "%s"' % (
            contextEngineId.prettyPrint(), contextName.prettyPrint()
        )
    )
--- a/pysnmp/entity/engine.py
+++ b/pysnmp/entity/engine.py
@ -7,12 +7,15 @@ from pysnmp.proto.secmod.rfc2576 import SnmpV1SecurityModel, \
     SnmpV2cSecurityModel
 from pysnmp.proto.secmod.rfc3414 import SnmpUSMSecurityModel
 from pysnmp.proto.acmod import rfc3415, void
+from pysnmp.entity import observer
 from pysnmp import error

 class SnmpEngine:
    def __init__(self, snmpEngineID=None, maxMessageSize=65507,
                 msgAndPduDsp=None):
        self.cache = {}
+        
+        self.observer = observer.MetaObserver()

        if msgAndPduDsp is None:
            self.msgAndPduDsp = MsgAndPduDispatcher()
@ -63,14 +66,14 @@ class SnmpEngine:
        self.msgAndPduDsp.receiveMessage(
            self, transportDomain, transportAddress, wholeMsg
        )
-                                         
+
    def __receiveTimerTickCbFun(self, timeNow):
        self.msgAndPduDsp.receiveTimerTick(self, timeNow)
        for mpHandler in self.messageProcessingSubsystems.values():
            mpHandler.receiveTimerTick(self, timeNow)
        for smHandler in self.securityModels.values():
            smHandler.receiveTimerTick(self, timeNow)
-        
+
    def registerTransportDispatcher(self, transportDispatcher, recvId=None):
        if self.transportDispatcher is not None and \
                self.transportDispatcher is not transportDispatcher:
--- a/pysnmp/proto/mpmod/rfc2576.py
+++ b/pysnmp/proto/mpmod/rfc2576.py
@ -33,8 +33,8 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
        expectResponse,
        sendPduHandle
        ):
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
-        snmpEngineID = snmpEngineID.syntax
+        snmpEngineId, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+        snmpEngineId = snmpEngineId.syntax
        
        # rfc3412: 7.1.1b
        if pdu.tagSet in rfc3411.confirmedClassPDUs:
@ -45,7 +45,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
        # Since there's no SNMP engine identification in v1/2c,
        # set destination contextEngineId to ours
        if not contextEngineId:
-            contextEngineId = snmpEngineID
+            contextEngineId = snmpEngineId

        # rfc3412: 7.1.5
        if not contextName:
@ -86,7 +86,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
            globalData,
            snmpEngineMaxMessageSize.syntax,
            securityModel,
-            snmpEngineID,
+            snmpEngineId,
            securityName,
            securityLevel,
            scopedPDU
@ -99,7 +99,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                int(msgID),
                sendPduHandle=sendPduHandle,
                msgID=msgID,
-                snmpEngineID=snmpEngineID,
+                snmpEngineId=snmpEngineId,
                securityModel=securityModel,
                securityName=securityName,
                securityLevel=securityLevel,
@ -109,6 +109,26 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                transportAddress=transportAddress
                )

+        communityName = msg.getComponentByPosition(1)  # for observer
+
+        snmpEngine.observer.storeExecutionContext(
+            snmpEngine,
+            'rfc2576.prepareOutgoingMessage',
+            dict(transportDomain=transportDomain,
+                 transportAddress=transportAddress,
+                 wholeMsg=wholeMsg,
+                 securityModel=securityModel,
+                 securityName=securityName,
+                 securityLevel=securityLevel,
+                 contextEngineId=contextEngineId,
+                 contextName=contextName,
+                 communityName=communityName,
+                 pdu=pdu)
+        )
+        snmpEngine.observer.clearExecutionContext(
+            snmpEngine, 'rfc2576.prepareOutgoingMessage'
+        )
+
        return ( transportDomain, transportAddress, wholeMsg )
            
    # rfc3412: 7.1
@ -127,8 +147,8 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
        stateReference,
        statusInformation
        ):
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
-        snmpEngineID = snmpEngineID.syntax
+        snmpEngineId, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+        snmpEngineId = snmpEngineId.syntax

        # rfc3412: 7.1.2.b
        if stateReference is None:
@ -162,7 +182,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
        # Since there's no SNMP engine identification in v1/2c,
        # set destination contextEngineId to ours
        if not contextEngineId:
-            contextEngineId = snmpEngineID
+            contextEngineId = snmpEngineId

        # rfc3412: 7.1.5
        if not contextName:
@ -193,8 +213,6 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                errorIndication = errind.unsupportedSecurityModel
                )

-        securityEngineId = snmpEngineID
-
        # rfc3412: 7.1.8.a
        ( securityParameters,
          wholeMsg ) = smHandler.generateResponseMsg(
@ -203,13 +221,31 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
            globalData,
            maxMessageSize,
            securityModel,
-            snmpEngineID,
+            snmpEngineId,
            securityName,
            securityLevel,
            scopedPDU,
            securityStateReference
            )

+        snmpEngine.observer.storeExecutionContext(
+            snmpEngine,
+            'rfc2576.prepareResponseMessage',
+            dict(transportDomain=transportDomain,
+                 transportAddress=transportAddress,
+                 securityModel=securityModel,
+                 securityName=securityName,
+                 securityLevel=securityLevel,
+                 contextEngineId=contextEngineId,
+                 contextName=contextName,
+                 securityEngineId=snmpEngineId,
+                 communityName=msg.getComponentByPosition(1),
+                 pdu=pdu)
+        )
+        snmpEngine.observer.clearExecutionContext(
+            snmpEngine, 'rfc2576.prepareResponseMessage'
+        )
+
        return ( transportDomain, transportAddress, wholeMsg )

    # rfc3412: 7.2.1
@ -241,8 +277,9 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):

        # rfc2576: 5.2.1
        snmpEngineMaxMessageSize, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
+        communityName = msg.getComponentByPosition(1)
        securityParameters = (
-            msg.getComponentByPosition(1),
+            communityName,
            # transportDomain identifies local enpoint
            (transportDomain, transportAddress)
        )
@ -261,7 +298,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                )

        # rfc3412: 7.2.6
-        ( securityEngineID,
+        ( securityEngineId,
          securityName,
          scopedPDU,
          maxSizeResponseScopedPDU,
@ -276,7 +313,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
            msg
            )

-        debug.logger & debug.flagMP and debug.logger('prepareDataElements: SM returned securityEngineID %r securityName %r' % (securityEngineID, securityName))
+        debug.logger & debug.flagMP and debug.logger('prepareDataElements: SM returned securityEngineId %r securityName %r' % (securityEngineId, securityName))

        # rfc3412: 7.2.6a --> noop

@ -329,6 +366,24 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
            
            stateReference = None

+            snmpEngine.observer.storeExecutionContext(
+                snmpEngine,
+                'rfc2576.prepareDataElements:response',
+                dict(transportDomain=transportDomain,
+                     transportAddress=transportAddress,
+                     securityModel=securityModel,
+                     securityName=securityName,
+                     securityLevel=securityLevel,
+                     contextEngineId=contextEngineId,
+                     contextName=contextName,
+                     securityEngineId=securityEngineId,
+                     communityName=communityName,
+                     pdu=pdu)
+            )
+            snmpEngine.observer.clearExecutionContext(
+                snmpEngine, 'rfc2576.prepareDataElements:response'
+            )
+
            # rfc3412: 7.2.12c
            smHandler.releaseStateInformation(securityStateReference)

@ -353,12 +408,12 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
            msgID = pdu.getComponentByPosition(0)

            # rfc3412: 7.2.13a
-            snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
-            if securityEngineID != snmpEngineID.syntax:
+            snmpEngineId, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+            if securityEngineId != snmpEngineId.syntax:
                smHandler.releaseStateInformation(securityStateReference)
                raise error.StatusInformation(
                    errorIndication = errind.engineIDMismatch
-                    )
+                )

            # rfc3412: 7.2.13b
            stateReference = self._cache.newStateReference()
@ -378,6 +433,24 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                transportAddress=transportAddress
                )

+            snmpEngine.observer.storeExecutionContext(
+                snmpEngine,
+                'rfc2576.prepareDataElements:confirmed',
+                dict(transportDomain=transportDomain,
+                     transportAddress=transportAddress,
+                     securityModel=securityModel,
+                     securityName=securityName,
+                     securityLevel=securityLevel,
+                     contextEngineId=contextEngineId,
+                     contextName=contextName,
+                     securityEngineId=securityEngineId,
+                     communityName=communityName,
+                     pdu=pdu)
+            )
+            snmpEngine.observer.clearExecutionContext(
+                snmpEngine, 'rfc2576.prepareDataElements:confirmed'
+            )
+
            debug.logger & debug.flagMP and debug.logger('prepareDataElements: cached by new stateReference %s' % stateReference)
                
            # rfc3412: 7.2.13c
@ -400,6 +473,24 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
            # Pass new stateReference to let app browse request details
            stateReference = self._cache.newStateReference()

+            snmpEngine.observer.storeExecutionContext(
+                snmpEngine,
+                'rfc2576.prepareDataElements:unconfirmed',
+                dict(transportDomain=transportDomain,
+                     transportAddress=transportAddress,
+                     securityModel=securityModel,
+                     securityName=securityName,
+                     securityLevel=securityLevel,
+                     contextEngineId=contextEngineId,
+                     contextName=contextName,
+                     securityEngineId=securityEngineId,
+                     communityName=communityName,
+                     pdu=pdu)
+            )
+            snmpEngine.observer.clearExecutionContext(
+                snmpEngine, 'rfc2576.prepareDataElements:unconfirmed'
+            )
+
            # This is not specified explicitly in RFC
            smHandler.releaseStateInformation(securityStateReference)

--- a/pysnmp/proto/mpmod/rfc3412.py
+++ b/pysnmp/proto/mpmod/rfc3412.py
@ -259,6 +259,23 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                transportAddress=transportAddress
                )

+        snmpEngine.observer.storeExecutionContext(
+            snmpEngine,
+            'rfc3412.prepareOutgoingMessage',
+            dict(transportDomain=transportDomain,
+                 transportAddress=transportAddress,
+                 wholeMsg=wholeMsg,
+                 securityModel=securityModel,
+                 securityName=securityName,
+                 securityLevel=securityLevel,
+                 contextEngineId=contextEngineId,
+                 contextName=contextName,
+                 pdu=pdu)
+        )
+        snmpEngine.observer.clearExecutionContext(
+            snmpEngine, 'rfc3412.prepareOutgoingMessage'
+        )
+
        return ( transportDomain,
                 transportAddress,
                 wholeMsg )
@ -296,7 +313,7 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
        transportAddress = cachedParams['transportAddress']

        debug.logger & debug.flagMP and debug.logger('prepareResponseMessage: stateReference %s' % (stateReference))
-        
+       
        # 7.1.3
        if statusInformation is not None and 'oid' in statusInformation:
            # 7.1.3a
@ -389,7 +406,7 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
        # XXX need to coerce MIB value as it has incompatible constraints set
        headerData.setComponentByPosition(
            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False
-            )
+        )

        # 7.1.7d
        msgFlags = 0
@ -452,6 +469,23 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
        if len(wholeMsg) > min(snmpEngineMaxMessageSize.syntax, maxMessageSize):
            raise error.StatusInformation(errorIndication=errind.tooBig)

+        snmpEngine.observer.storeExecutionContext(
+            snmpEngine,
+            'rfc3412.prepareResponseMessage',
+            dict(transportDomain=transportDomain,
+                 transportAddress=transportAddress,
+                 securityModel=securityModel,
+                 securityName=securityName,
+                 securityLevel=securityLevel,
+                 contextEngineId=contextEngineId,
+                 contextName=contextName,
+                 securityEngineId=snmpEngineID,
+                 pdu=pdu)
+        )
+        snmpEngine.observer.clearExecutionContext(
+            snmpEngine, 'rfc3412.prepareResponseMessage'
+        )
+
        return ( transportDomain, transportAddress, wholeMsg )

    # 7.2.1
@ -674,6 +708,23 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                
            # 7.2.11b (incomplete implementation)

+            snmpEngine.observer.storeExecutionContext(
+                snmpEngine,
+                'rfc3412.prepareDataElements:internal',
+                dict(transportDomain=transportDomain,
+                     transportAddress=transportAddress,
+                     securityModel=securityModel,
+                     securityName=securityName,
+                     securityLevel=securityLevel,
+                     contextEngineId=contextEngineId,
+                     contextName=contextName,
+                     securityEngineId=securityEngineId,
+                     pdu=pdu)
+            )
+            snmpEngine.observer.clearExecutionContext(
+                snmpEngine, 'rfc3412.prepareDataElements:internal'
+            )
+
            # 7.2.11c
            smHandler.releaseStateInformation(securityStateReference)

@ -700,6 +751,23 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                    errorIndication = errind.dataMismatch
                    )
                        
+            snmpEngine.observer.storeExecutionContext(
+                snmpEngine,
+                'rfc3412.prepareDataElements:response',
+                dict(transportDomain=transportDomain,
+                     transportAddress=transportAddress,
+                     securityModel=securityModel,
+                     securityName=securityName,
+                     securityLevel=securityLevel,
+                     contextEngineId=contextEngineId,
+                     contextName=contextName,
+                     securityEngineId=securityEngineId,
+                     pdu=pdu)
+            )
+            snmpEngine.observer.clearExecutionContext(
+                snmpEngine, 'rfc3412.prepareDataElements:response'
+            )
+
            # 7.2.12c
            smHandler.releaseStateInformation(securityStateReference)
            stateReference = None
@ -749,6 +817,23 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):

            debug.logger & debug.flagMP and debug.logger('prepareDataElements: new stateReference %s' % stateReference)

+            snmpEngine.observer.storeExecutionContext(
+                snmpEngine,
+                'rfc3412.prepareDataElements:confirmed',
+                dict(transportDomain=transportDomain,
+                     transportAddress=transportAddress,
+                     securityModel=securityModel,
+                     securityName=securityName,
+                     securityLevel=securityLevel,
+                     contextEngineId=contextEngineId,
+                     contextName=contextName,
+                     securityEngineId=securityEngineId,
+                     pdu=pdu)
+            )
+            snmpEngine.observer.clearExecutionContext(
+                snmpEngine, 'rfc3412.prepareDataElements:confirmed'
+            )
+
            # 7.2.13c
            return ( messageProcessingModel,
                     securityModel,
@ -768,7 +853,24 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
        if pduType in rfc3411.unconfirmedClassPDUs:
            # Pass new stateReference to let app browse request details
            stateReference = self._cache.newStateReference()
-            
+
+            snmpEngine.observer.storeExecutionContext(
+                snmpEngine,
+                'rfc3412.prepareDataElements:unconfirmed',
+                dict(transportDomain=transportDomain,
+                     transportAddress=transportAddress,
+                     securityModel=securityModel,
+                     securityName=securityName,
+                     securityLevel=securityLevel,
+                     contextEngineId=contextEngineId,
+                     contextName=contextName,
+                     securityEngineId=securityEngineId,
+                     pdu=pdu)
+            )
+            snmpEngine.observer.clearExecutionContext(
+                snmpEngine, 'rfc3412.prepareDataElements:unconfirmed'
+            )
+
            # This is not specified explicitly in RFC
            smHandler.releaseStateInformation(securityStateReference)
            
--- a/pysnmp/proto/rfc3412.py
+++ b/pysnmp/proto/rfc3412.py
@ -33,9 +33,10 @@ class MsgAndPduDispatcher:
        # Source of sendPduHandle and cache of requesting apps
        self.__sendPduHandle = nextid.Integer(0xffffff)

-        # To pass transport info to app
+        # To pass transport info to app (legacy)
        self.__transportInfo = {}

+    # legacy
    def getTransportInfo(self, stateReference):
        if stateReference in self.__transportInfo:
            return self.__transportInfo[stateReference]
@ -135,14 +136,17 @@ class MsgAndPduDispatcher:

        debug.logger & debug.flagDsp and debug.logger('sendPdu: new sendPduHandle %s, timeout %s ticks, cbFun %s' % (sendPduHandle, timeout, cbFun))

+        origTransportDomain = transportDomain
+        origTransportAddress = transportAddress
+
        # 4.1.1.4 & 4.1.1.5
        try:
-            ( destTransportDomain,
-              destTransportAddress,
+            ( transportDomain,
+              transportAddress,
              outgoingMessage ) = mpHandler.prepareOutgoingMessage(
                snmpEngine,
-                transportDomain,
-                transportAddress,
+                origTransportDomain,
+                origTransportAddress,
                messageProcessingModel,
                securityModel,
                securityName,
@ -168,21 +172,38 @@ class MsgAndPduDispatcher:
                self.__cache.pop(sendPduHandle)
            raise error.PySnmpError('Transport dispatcher not set')

+        snmpEngine.observer.storeExecutionContext(
+            snmpEngine,
+            'rfc3412.sendPdu',
+            dict(transportDomain=transportDomain,
+                 transportAddress=transportAddress,
+                 outgoingMessage=outgoingMessage,
+                 messageProcessingModel=messageProcessingModel,
+                 securityModel=securityModel,
+                 securityName=securityName,
+                 securityLevel=securityLevel,
+                 contextEngineId=contextEngineId,
+                 contextName=contextName,
+                 pdu=PDU)              
+        )
+
        try:
            snmpEngine.transportDispatcher.sendMessage(
-                outgoingMessage, destTransportDomain, destTransportAddress
+                outgoingMessage, transportDomain, transportAddress
            )
        except PySnmpError:
            if expectResponse:
                self.__cache.pop(sendPduHandle)
            raise
        
+        snmpEngine.observer.clearExecutionContext(snmpEngine, 'rfc3412.sendPdu')
+
        # Update cache with orignal req params (used for retrying)
        if expectResponse:
            self.__cache.update(
                sendPduHandle,
-                transportDomain=transportDomain,
-                transportAddress=transportAddress,
+                transportDomain=origTransportDomain,
+                transportAddress=origTransportAddress,
                securityModel=securityModel,
                securityName=securityName,
                securityLevel=securityLevel,
@ -210,7 +231,6 @@ class MsgAndPduDispatcher:
        stateReference,
        statusInformation
        ):
-        """PDU dispatcher -- prepare and serialize a response"""
        # Extract input values and initialize defaults
        k = int(messageProcessingModel)
        if k in snmpEngine.messageProcessingSubsystems:
@ -224,8 +244,8 @@ class MsgAndPduDispatcher:

        # 4.1.2.2
        try:
-            ( destTransportDomain,
-              destTransportAddress,
+            ( transportDomain,
+              transportAddress,
              outgoingMessage ) = mpHandler.prepareResponseMessage(
                snmpEngine,
                messageProcessingModel,
@ -239,7 +259,7 @@ class MsgAndPduDispatcher:
                maxSizeResponseScopedPDU,
                stateReference,
                statusInformation
-                )
+            )
            debug.logger & debug.flagDsp and debug.logger('returnResponsePdu: MP suceeded')
        except error.StatusInformation:
            # 4.1.2.3
@ -253,12 +273,31 @@ class MsgAndPduDispatcher:
            snmpSilentDrops.syntax = snmpSilentDrops.syntax + 1
            raise error.StatusInformation(errorIndication=errind.tooBig)

+        snmpEngine.observer.storeExecutionContext(
+            snmpEngine,
+            'rfc3412.returnResponsePdu',
+            dict(transportDomain=transportDomain,
+                 transportAddress=transportAddress,
+                 outgoingMessage=outgoingMessage,
+                 messageProcessingModel=messageProcessingModel,
+                 securityModel=securityModel,
+                 securityName=securityName,
+                 securityLevel=securityLevel,
+                 contextEngineId=contextEngineId,
+                 contextName=contextName,
+                 pdu=PDU)
+        )
+
        # 4.1.2.4
        snmpEngine.transportDispatcher.sendMessage(
            outgoingMessage,
-            destTransportDomain,
-            destTransportAddress
-            )
+            transportDomain,
+            transportAddress
+        )
+
+        snmpEngine.observer.clearExecutionContext(
+            snmpEngine, 'rfc3412.returnResponsePdu'
+        )

    # 4.2.1    
    def receiveMessage(
@ -396,11 +435,27 @@ class MsgAndPduDispatcher:
                # 4.2.2.1.2.d
                return restOfWholeMsg
            else:
-                # Pass transport info to app
+                snmpEngine.observer.storeExecutionContext(
+                    snmpEngine,
+                    'rfc3412.receiveMessage:request',
+                    dict(transportDomain=transportDomain,
+                         transportAddress=transportAddress,
+                         wholeMsg=wholeMsg,
+                         messageProcessingModel=messageProcessingModel,
+                         securityModel=securityModel,
+                         securityName=securityName,
+                         securityLevel=securityLevel,
+                         contextEngineId=contextEngineId,
+                         contextName=contextName,
+                         pdu=PDU)
+                )
+
+                # pass transport info to app (legacy)
                if stateReference is not None:
                    self.__transportInfo[stateReference] = (
                        transportDomain, transportAddress
-                        )
+                    )
+
                # 4.2.2.1.3
                processPdu(
                    snmpEngine,
@ -414,9 +469,16 @@ class MsgAndPduDispatcher:
                    PDU,
                    maxSizeResponseScopedPDU,
                    stateReference
-                    )
+                )
+        
+                snmpEngine.observer.clearExecutionContext(
+                    snmpEngine, 'rfc3412.receiveMessage:request'
+                )
+
+                # legacy
                if stateReference is not None:
                    del self.__transportInfo[stateReference]
+
                debug.logger & debug.flagDsp and debug.logger('receiveMessage: processPdu succeeded')
                return restOfWholeMsg
        else:
@ -436,6 +498,21 @@ class MsgAndPduDispatcher:
            # 4.2.2.2.3
            # no-op ? XXX

+            snmpEngine.observer.storeExecutionContext(
+                snmpEngine,
+                'rfc3412.receiveMessage:response',
+                dict(transportDomain=transportDomain,
+                     transportAddress=transportAddress,
+                     wholeMsg=wholeMsg,
+                     messageProcessingModel=messageProcessingModel,
+                     securityModel=securityModel,
+                     securityName=securityName,
+                     securityLevel=securityLevel,
+                     contextEngineId=contextEngineId,
+                     contextName=contextName,
+                     pdu=PDU)
+            )
+
            # 4.2.2.2.4
            processResponsePdu = cachedParams['cbFun']
            processResponsePdu(
@ -451,7 +528,12 @@ class MsgAndPduDispatcher:
                statusInformation,
                cachedParams['sendPduHandle'],
                cachedParams['cbCtx']
-                )
+            )
+
+            snmpEngine.observer.clearExecutionContext(
+                snmpEngine, 'rfc3412.receiveMessage:response'
+            )
+
            debug.logger & debug.flagDsp and debug.logger('receiveMessage: processResponsePdu succeeded')
            return restOfWholeMsg