Ensure TRAP PDU consistency in v1arch

Also, consistency ensuring code unified with v3arch piece what
has the side effect of *requiring* snmpTrapOID to be always
present anywhere among user-supplied variable-bindings.

pysnmp/hlapi/v1arch/asyncio/ntforg.py

@@ -7,6 +7,7 @@
 from pysnmp.hlapi.v1arch.auth import *
 from pysnmp.hlapi.varbinds import *
 from pysnmp.hlapi.v1arch.asyncio.transport import *
+from pysnmp.proto.api import v2c
 from pysnmp.proto.proxy import rfc2576
 from pysnmp.smi.rfc1902 import *
 from pysnmp.proto import api
@@ -51,24 +52,27 @@ async def sendNotification(
         or :py:class:`~pysnmp.smi.rfc1902.ObjectType` class instances
         of :py:class:`~pysnmp.smi.rfc1902.NotificationType` objects.
 
-        SNMP Notification PDU places rigid requirement on the ordering of
-        the variable-bindings.
-
-        Mandatory variable-bindings:
+        Besides user variable-bindings, SNMP Notification PDU requires at
+        least two variable-bindings to be present:
 
         0. SNMPv2-MIB::sysUpTime.0 = <agent uptime>
-        1. SNMPv2-SMI::snmpTrapOID.0 = {SNMPv2-MIB::coldStart, ...}
+        1. SNMPv2-SMI::snmpTrapOID.0 = <notification ID>
 
-        Optional variable-bindings (applicable to SNMP v1 TRAP):
+        When sending SNMPv1 TRAP, more variable-bindings could be present:
 
         2. SNMP-COMMUNITY-MIB::snmpTrapAddress.0 = <agent-IP>
         3. SNMP-COMMUNITY-MIB::snmpTrapCommunity.0 = <snmp-community-name>
         4. SNMP-COMMUNITY-MIB::snmpTrapEnterprise.0 = <enterprise-OID>
 
-        Informational variable-bindings:
+        If user does not supply some or any of the above variable-bindings or
+        if they are at the wrong positions, the system will add/reorder the
+        missing ones automatically.
 
-        * SNMPv2-SMI::NOTIFICATION-TYPE
-        * SNMPv2-SMI::OBJECT-TYPE
+        On top of that, some notification types imply including some additional
+        variable-bindings providing additional details on the event being
+        reported. Therefore it is generally easier to use
+        :py:class:`~pysnmp.smi.rfc1902.NotificationType` object which will
+        help adding relevant variable-bindings.
 
     Other Parameters
     ----------------
@@ -121,14 +125,54 @@ class instances (if `lookupMib` is `True`) representing MIB variables
     >>>
     """
 
+    sysUpTime = v2c.apiTrapPDU.sysUpTime
+    snmpTrapOID = v2c.apiTrapPDU.snmpTrapOID
+
+    def _ensureVarBinds(varBinds):
+        # Add sysUpTime if not present already
+        if not varBinds or varBinds[0][0] != sysUpTime:
+            varBinds.insert(0, (v2c.ObjectIdentifier(sysUpTime), v2c.TimeTicks(0)))
+
+        # Search for and reposition sysUpTime if it's elsewhere
+        for idx, varBind in enumerate(varBinds[1:]):
+            if varBind[0] == sysUpTime:
+                varBinds[0] = varBind
+                del varBinds[idx]
+                break
+
+        if len(varBinds) < 2:
+            raise error.PySnmpError(
+                "SNMP notification PDU requires "
+                "SNMPv2-MIB::snmpTrapOID.0 to be present"
+            )
+
+        # Search for and reposition snmpTrapOID if it's elsewhere
+        for idx, varBind in enumerate(varBinds[2:]):
+            if varBind[0] == snmpTrapOID:
+                del varBinds[idx]
+                if varBinds[1][0] == snmpTrapOID:
+                    varBinds[1] = varBind
+                else:
+                    varBinds.insert(1, varBind)
+                break
+
+        # Fail on missing snmpTrapOID
+        if varBinds[1][0] != snmpTrapOID:
+            raise error.PySnmpError(
+                "SNMP notification PDU requires "
+                "SNMPv2-MIB::snmpTrapOID.0 to be present"
+            )
+
+        return varBinds
+
     def _cbFun(snmpDispatcher, stateHandle, errorIndication, rspPdu, _cbCtx):
         if future.cancelled():
             return
 
-        errorStatus = pMod.apiTrapPDU.getErrorStatus(rspPdu)
-        errorIndex = pMod.apiTrapPDU.getErrorIndex(rspPdu)
+        errorStatus = v2c.apiTrapPDU.getErrorStatus(rspPdu)
+        errorIndex = v2c.apiTrapPDU.getErrorIndex(rspPdu)
 
-        varBinds = pMod.apiTrapPDU.getVarBinds(rspPdu)
+        varBinds = v2c.apiTrapPDU.getVarBinds(rspPdu)
 
         try:
             varBindsUnmade = VB_PROCESSOR.unmakeVarBinds(
@@ -173,10 +217,14 @@ def _cbFun(snmpDispatcher, stateHandle, errorIndication, rspPdu, _cbCtx):
     if notifyType == "trap":
         reqPdu = pMod.TrapPDU()
     else:
-        reqPdu = pMod.InformRequestPDU()
+        reqPdu = v2c.InformRequestPDU()
+
+    v2c.apiTrapPDU.setDefaults(reqPdu)
+    v2c.apiTrapPDU.setVarBinds(reqPdu, varBinds)
+
+    varBinds = v2c.apiTrapPDU.getVarBinds(reqPdu)
 
-    pMod.apiTrapPDU.setDefaults(reqPdu)
-    pMod.apiTrapPDU.setVarBinds(reqPdu, varBinds)
+    v2c.apiTrapPDU.setVarBinds(reqPdu, _ensureVarBinds(varBinds))
 
     if authData.mpModel == 0:
         reqPdu = rfc2576.v2ToV1(reqPdu)