"""
Implementing conceptual table
+++++++++++++++++++++++++++++

Listen and respond to SNMP GET/SET/GETNEXT/GETBULK queries with
the following options:

* SNMPv2c
* with SNMP community "public"
* define a simple SNMP Table within a newly created EXAMPLE-MIB
* pre-populate SNMP Table with a single row of values
* allow read access only to the subtree where example SNMP Table resides
* over IPv4/UDP, listening at 127.0.0.1:161
 
The following Net-SNMP commands will populate and walk a table:

| $ snmpset -v2c -c public 127.0.0.1 1.3.6.6.1.5.2.97.98.99 s 'my value'
| $ snmpset -v2c -c public 127.0.0.1 1.3.6.6.1.5.4.97.98.99 i 4
| $ snmpwalk -v2c -c public 127.0.0.1 1.3.6

...while the following command will destroy the same row

| $ snmpset -v2c -c public 127.0.0.1 1.3.6.6.1.5.4.97.98.99 i 6
| $ snmpwalk -v2c -c public 127.0.0.1 1.3.6

"""#
from pysnmp.entity import engine, config
from pysnmp.entity.rfc3413 import cmdrsp, context
from pysnmp.carrier.asyncore.dgram import udp
from pysnmp.proto.api import v2c

# Create SNMP engine
snmpEngine = engine.SnmpEngine()

# Transport setup

# UDP over IPv4
config.addTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTransport().openServerMode(('127.0.0.1', 161))
)

# SNMPv2c setup

# SecurityName <-> CommunityName mapping.
config.addV1System(snmpEngine, 'my-area', 'public')

# Allow read MIB access for this user / securityModels at VACM
config.addVacmUser(snmpEngine, 2, 'my-area', 'noAuthNoPriv', (1,3,6,6), (1,3,6,6))

# Create an SNMP context
snmpContext = context.SnmpContext(snmpEngine)

# --- define custom SNMP Table within a newly defined EXAMPLE-MIB ---

mibBuilder = snmpContext.getMibInstrum().getMibBuilder()

( MibTable,
  MibTableRow,
  MibTableColumn,
  MibScalarInstance ) = mibBuilder.importSymbols(
    'SNMPv2-SMI', 
    'MibTable',
    'MibTableRow',
    'MibTableColumn',
    'MibScalarInstance'
  )

RowStatus, = mibBuilder.importSymbols('SNMPv2-TC', 'RowStatus')

mibBuilder.exportSymbols(
  '__EXAMPLE-MIB',
  # table object
  exampleTable=MibTable((1,3,6,6,1)).setMaxAccess('readcreate'),
  # table row object, also carries references to table indices
  exampleTableEntry=MibTableRow((1,3,6,6,1,5)).setMaxAccess('readcreate').setIndexNames((0, '__EXAMPLE-MIB', 'exampleTableColumn1')),
  # table column: string index
  exampleTableColumn1=MibTableColumn((1,3,6,6,1,5,1), v2c.OctetString()).setMaxAccess('readcreate'),
  # table column: string value
  exampleTableColumn2=MibTableColumn((1,3,6,6,1,5,2), v2c.OctetString()).setMaxAccess('readcreate'),
  # table column: integer value with default
  exampleTableColumn3=MibTableColumn((1,3,6,6,1,5,3), v2c.Integer32(123)).setMaxAccess('readcreate'),
  # table column: row status
  exampleTableStatus=MibTableColumn((1,3,6,6,1,5,4), RowStatus('notExists')).setMaxAccess('readcreate')
)

# --- end of custom SNMP table definition, empty table now exists ---

# --- populate custom SNMP table with one row ---

( exampleTableEntry,
  exampleTableColumn2,
  exampleTableColumn3,
  exampleTableStatus ) = mibBuilder.importSymbols(
    '__EXAMPLE-MIB',
    'exampleTableEntry',
    'exampleTableColumn2',
    'exampleTableColumn3',
    'exampleTableStatus'
)
rowInstanceId = exampleTableEntry.getInstIdFromIndices('example record one')
mibInstrumentation = snmpContext.getMibInstrum()
mibInstrumentation.writeVars(
    (  (exampleTableColumn2.name+rowInstanceId, 'my string value'),
       (exampleTableColumn3.name+rowInstanceId, 123456),
       (exampleTableStatus.name+rowInstanceId, 'createAndGo') )
)

# --- end of SNMP table population ---

# 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.transportDispatcher.closeDispatcher()
    raise
