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.

3 files changed, 314 insertions, 39 deletions

diff --git a/pysnmp/proto/mpmod/rfc2576.py b/pysnmp/proto/mpmod/rfc2576.py
index d988496..03ad11f 100644
--- 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)
 
diff --git a/pysnmp/proto/mpmod/rfc3412.py b/pysnmp/proto/mpmod/rfc3412.py
index f51033a..09779a4 100644
--- 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)
             
diff --git a/pysnmp/proto/rfc3412.py b/pysnmp/proto/rfc3412.py
index d18c74f..2aee1a6 100644
--- 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